- Email: [email protected]
Deep-burial dissolution in an Oligocene-Miocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development
Journal Pre-proof Deep-burial dissolution in an Oligocene-Miocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development Fernando L. Valencia, Juan C. Laya PII:
S0264-8172(19)30596-3
DOI:
https://doi.org/10.1016/j.marpetgeo.2019.104144
Reference:
JMPG 104144
To appear in:
Marine and Petroleum Geology
Received Date: 18 September 2019 Revised Date:
15 November 2019
Accepted Date: 18 November 2019
Please cite this article as: Valencia, F.L., Laya, J.C., Deep-burial dissolution in an OligoceneMiocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development, Marine and Petroleum Geology (2019), doi: https://doi.org/10.1016/ j.marpetgeo.2019.104144. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
1 1 2 3 4 5 6 7 8 9
Deep-burial dissolution in an Oligocene-Miocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development. FERNANDO L. VALENCIAa and JUAN C. LAYAb a Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada (e-mail: [email protected]) b Department of Geology and Geophysics, Texas A&M University, College Station, U.S.A.
10
ABSTRACT
11
Sedimentary rocks tend to progressively lose porosity with depth due to mechanical and
12
chemical compaction. In carbonates, this trend is hard to predict since many factors can create
13
porosity in the burial setting. The Oligocene-Miocene Perla Limestone, a giant gas reservoir
14
located in the Gulf of Venezuela Basin, shows a complex porosity system marked by a strong
15
diagenetic control. Despite exhaustive depositional facies modelling carried out in the carbonate
16
reservoir, inconsistencies remained when distributing petrophysical properties with depositional
17
facies. These inconsistencies become more important in areas strongly affected by intense
18
diagenetic processes. After the initial investigation, burial dissolution was identified as the main
19
diagenetic process affecting porosity in this succession. To understand the origin of the burial
20
dissolution process and its distribution along the reservoir, detailed petrographic, mineralogical
21
and isotopic studies were carried out on recovered cores from different exploration wells. Results
22
show a series of diagenetic features which were associated with the evolution of the strata
23
including burial dissolution, dolomitization and compaction as the main processes. After testing
24
several hypotheses, the results support an inorganic-CO2 model as responsible for the burial
25
dissolution process in the Perla Limestone. According to this model, deep-burial dissolution
26
created pervasive microporosity, with subordinated moldic and vuggy pores that enhanced the
27
reservoir quality in localized areas of the carbonate succession. These features are located where
2 28
the ascent of hydrothermal CO2-rich fluids funneled by discontinuity surfaces (faults, fractures,
29
stylolites, etc.) reached the Perla Limestone.
30
Keywords: Inorganic-CO2; Deep-burial dissolution; Microporosity; Diagenetic model;
31
Carbonate reservoir; Perla Limestone.
32
1. INTRODUCTION
33
The petrophysical behaviour of carbonate reservoirs is controlled by depositional and diagenetic
34
processes and their spatial interrelationship and trends (Skalinski and Kenter, 2014).
35
Depositional processes determine the initial pore-size distribution and the permeability of the
36
individual depositional facies (Choquette and Pray 1970; Lucia, 1995). Diagenetic processes are
37
responsible for most of the primary porosity and permeability modifications of the evolving
38
limestones (Moore and Wade, 2013).
39
Modern carbonate sediments are characterized by porosities of around 40 to 80 % (Enos and
40
Sawatzky, 1981), while ancient carbonate rocks usually have 3 to 35 % of porosity (Saller,
41
2013). This porosity reduction is often associated to compactional processes that occur in
42
response to the progressive increase of overburden thickness (e.g. Hamilton, 1976; Schmoker
43
and Halley, 1982; Shinn and Robbin, 1983; Croizet et al., 2013; Worden et al. 2018).
44
Nevertheless, in carbonate rocks, the expected compactional porosity loss can be substantially
45
affected by diagenetic processes creating significant volumes of porosity in the burial realm
46
(Moore, 2001).
47
Among the diagenetic processes, carbonate dissolution is considered a major controlling factor
48
of the reservoir quality in carbonate successions (Moore, 2001). It may occur at any point on the
49
diagenetic evolution of a carbonate deposit as a response to important changes in the pore-fluid
3 50
chemistry, such as variations in salinity, pCO2, pH, temperature and many other factors (Moore
51
and Wade, 2013). Carbonate dissolution is considered particularly significant in the meteoric
52
setting since meteoric waters are usually undersaturated with respect to most carbonate mineral
53
species, stimulating dissolution of metastable minerals and creating porosity (Bathurst, 1975;
54
Longman, 1980; Moore, 2001). In contrast, in the burial setting where pore water is commonly
55
in equilibrium with the host rock, processes such as acidification, fluid mixing, changes in
56
temperature or pressure are required to generate dissolution of already-stabilized minerals
57
(Moore, 2001; Esteban and Taberner, 2003; Ali et al., 2010).
58
The importance of burial dissolution creating significant porosity is a matter of a long-standing
59
debate in the literature. Several studies have reported enhanced porosity and permeability in
60
carbonate reservoirs due to burial dissolution (e.g. Pöppelreiter et al., 2005; Corbella et al., 2004;
61
Beavington-Penney et al., 2008; etc.). In contrast, Ehrenberg et al. (2012) conclude that burial
62
dissolution models are unsupported by empirical data and violate important chemical constraints
63
on mass transport. Nevertheless, recent studies on the Tarim Basin in China, reflect an
64
unquestionable impact of burial dissolution processes in the development of good reservoir zones
65
(e.g. Jiang et al., 2015; Liu et al., 2017; Wei et al., 2017).
66
The aim of this research is to understand the controls on dissolution of the Oligocene-Miocene
67
Perla Limestone reservoir, the largest gas reservoir in Latin America (Castillo et al., 2017), since
68
it shows some clear evidence of a dissolution process creating significant secondary porosity in
69
the burial realm (Borromeo et al., 2011; Castillo et al., 2017). The origin of this process is still
70
under discussion, however, several elements support the hypothesis of a burial dissolution
71
process induced by the rising of hydrothermal acidic-fluids from the basement. This research
72
included a detailed petrographic, mineralogical and geochemical study of cores recovered from
4 73
the Perla Limestone, aimed at understanding the impact of burial dissolution on the reservoir
74
quality. The results of this study will represent a novel and well-documented example of the
75
importance of burial dissolution in producing carbonate reservoirs, as well as, promote further
76
integration of diagenetic models with reservoir characterization studies in general.
77
2. GEOLOGICAL CONTEXT
78
2.1.
79
The Gulf of Venezuela Basin is characterized by a wide continental shelf limited to the north by
80
the Caribbean Sea; to the south, by the Falcón and Maracaibo basins; to the west, by the Guajira
81
Peninsula and the east, by the Paraguaná Peninsula (Fig. 1). The tectonic history of the Gulf of
82
Venezuela Basin is intrinsically connected to the evolution of the interaction between the
83
Caribbean and South American plates (Macellari, 1995). Its history shows evidence of six main
84
tectonic phases: (1) Cretaceous passive margin development, (2) late Paleocene–early Eocene
85
foredeep and consequent forebulge erosion, (3) late Eocene tectonic flexure and faulting phase,
86
(4) Oligocene–early Miocene transtensional faulting phase, (5) middle-late Miocene
87
transpressional regime and (6) Pliocene to Present Andean uplift (Audemard, 1993; Macellari,
88
1995; Escalona and Mann, 2011; Castillo et al., 2017). Because of this complex tectonic
89
evolution, two distinct structural provinces were established: the Dabajuro-Guajira and the
90
Urumaco provinces, which are separated by the Urumaco Trough (Malave and Contreras, 2013;
91
see Fig. 1).
92
The Urumaco Province comprises a thick Paleogene-Neogene sedimentary succession resting
93
directly on a Meso-Neoproterozoic granodioritic basement, with a structural style dominated by
94
NW-SE high-angle normal faults, in which the basement is involved (Baquero, 2015; Baquero et
Tectonic evolution
5 95
al., 2015; Castillo et al., 2017). During Oligocene-Miocene times, the tectonic evolution of the
96
Urumaco Province favored the deposition of the Perla Limestone atop of a Paleogene siliciclastic
97
succession; on a basement-high defined by an NW-SE trending faulted-anticline-like structure
98
(Castillo et al., 2017).
99 100 101 102
Figure 1. Structural map showing the Perla field location and the structural provinces of the Gulf of Venezuela Basin (yellow area) (modified from Malave and Contreras, 2013).
103
2.2.
104
The Gulf of Venezuela Basin is a relatively unexplored area compared with the rest of the
105
Venezuelan hydrocarbon basins and consequently lacks formal lithostratigraphy. Nevertheless,
106
some authors (e.g. Díaz de Gamero et al., 1993; Macellari, 1995; Castillo et al., 2017) have
107
integrated seismic and well data from exploration wells and correlated the stratigraphy with the
108
adjacent Falcón Basin (Fig. 2).
109
Locally in the Perla field area, the Gulf of Venezuela-strata consists of three major units
110
deposited atop of the Meso-Neoproterozoic basement (Fig. 3): (1) a Paleogene, mostly Oligocene
Stratigraphy
6 111
siliciclastic succession; (2) an upper Oligocene to lower Miocene carbonate deposit (Perla
112
Limestone); and (3) a siliciclastic-dominated succession deposited from the lower Miocene to the
113
Present (Rojas et al., 2015).
114 115 116 117 118
119
Figure 2. Chronostratigraphic chart showing the correlation between the Falcón Basin and the Gulf of Venezuela Basin in the Perla field area (compiled from Díaz de Gamero et al., 1993; Macellari, 1995; Castillo et al., 2017).
7 120 121 122
Figure 3. Seismic section showing the stratigraphic succession of the Perla field area, with the exploration wells drilled by Cardon IV, S.A. (modified from Rojas et al., 2015). An inset map in the lower-right corner indicates the orientation of the seismic section.
123
The Perla Limestone is an ca 250 m-thick carbonate succession composed by branching red-
124
algae, rhodoliths (nodular coralline red-algae) and large benthic foraminifera (LBF), with a
125
minor contribution of corals, mollusks, echinoderms, barnacles, green algae, bryozoans and
126
planktonic foraminifera (Pinto et al., 2011; Borromeo et al., 2011, 2013; Pomar et al., 2015).
127
Internally, the Perla Limestone can be subdivided into two main chronostratigraphic units, the
128
Oligocene and the lower Miocene successions (Pinto et al., 2011; Moscariello et al., 2018). The
129
Oligocene unit (upper Rupelian to Chattian) comprises inner to middle-ramp deposits, with
130
occasional interbeds of siliciclastic sediments at the bottom. In contrast, the lower Miocene unit
131
(Aquitanian-Burdigalian) is formed by middle to outer-ramp carbonates, stacked and cyclically
132
organized, that pass upward to outer-ramp facies dominated by rhodoliths with abundant
133
nannofossils and planktonic foraminifera (Borromeo et al., 2013). Based on core analysis, Pomar
134
et al. (2015) identified twelve different depositional facies in the Perla Limestone (Table 1).
135
These facies conform a distally-steepened carbonate ramp, developed in an isolated bank,
136
vertically marked by an overall deepening-upward trend, with the characteristic transgressive
137
backstepping-pattern (Pinto et al., 2011; Borromeo et al., 2013; Pomar et al., 2015).
138 139
Table 1. Depositional facies of the Perla Limestone described by Pomar et al. (2015).
SS MS PS CF SPG FG GSG CBRA FBRA RF RR
Depositional Facies Siliciclastic sandstones Mixed sandstone-carbonates Packstones-wackestones with siliciclastics Coral floatstone-rudstone Skeletal packstones and grainstones Fine skeletal grainstones Gray skeletal grainstones Coarse branching red algae floatstone-rudstone Fine branching red algae floatstone-rudstone Rhodolith floatstones Rhodolith rudstones
8 LBFR
Larger benthic foraminifer rudstones
140 141
Based on the integration of well-logs, sedimentological data, chronostratigraphic and seismic-
142
stratigraphic interpretations, Rojas et al. (2015) subdivided the Perla Limestone into seven
143
reservoir-units. From the base to top, these are the Oligocene units “O-3”, “O-4” and “O-5”;
144
overlain by the lower Miocene units “M-1”, “M-2”, “M-3” and “M-4”. O-4 is the only unit not
145
cored yet despite recognition on seismic. The reservoir units of the Perla Limestone comprise
146
different lithofacies associations and have variable thickness and geometry (see Fig. 4).
147 148 149 150
Figure 4. Reservoir units and exploration wells of the Perla Limestone. A: Oligocene and lower Miocene reservoir units of the Perla Limestone from Rojas et al. (2015). B: Structural map of the Perla Limestone showing the location of the exploration wells.
151
3. SAMPLING AND METHODS
152
Since the exploration campaign up to the present, a total of nine wells have been drilled in the
153
Perla field, by the operating company Cardon IV, S.A. Four exploration wells (P-AX, P-BX, P-
154
CX and P-DX) and five development wells. After the discovery well, P-AX, three cores were
9 155
recovered from P-BX, P-CX and P-DX wells. P-CX is placed in the crest of the structure, while
156
P-BX and P-DX are positioned in the transition to the flanks-area (Fig. 4).
157
A total of 277 samples were collected from cores and prepared for petrographic analysis (Table
158
2). The sampling was determined by the thickness of the carbonate succession in each well,
159
ensuring the coverage of the different reservoir units, as well as, a high sedimentological
160
resolution (see Table 2 for more detail). In specific cases, the sampling was incremented in zones
161
with microporosity patches (see Dissolution porosity section on the results).
162
Thin sections were impregnated with blue-epoxy and examined by conventional petrography.
163
Porosity types were identified and estimated using a comparison chart for visual percentage
164
estimation (Tarduno et al., 2002). Specific samples in areas with a higher density of
165
microporosity patches were analyzed by backscatter-electron microscopy (SEM) and
166
cathodoluminescence (CL). Additionally, core-plug helium porosity and horizontal permeability
167
data reported by Valencia (2016) were collected for later comparison and interpretations.
168
A representative subset (193 powdered samples) was selected for bulk rock stable isotope
169
analysis carbon (δ13C) and oxygen (δ18O), using isotope-ratio mass spectrometry (IRMS). The
170
isotope ratio measurement precision is ± 0.08 ‰ for δ13C and ± 0.1 ‰ for δ18O. Sub-samplings
171
via acid digestion and micro-drilling were performed, to analyze dolomites and calcite cements,
172
respectively (Table 2). All these analyses were carried out in the laboratory facilities of Eni
173
S.p.A., Repsol Technology Center and the Intevep at Petróleos de Venezuela, S.A.
174 175 176 177 178 179 180
10 181 182 183 184 185 186 187
Table 2. Sampling detail in the different cores and reservoir units. BC=blocky spar calcite cement and DOL=dolomite cement.
Analysis
Reservoir unit
M-4 M-3 M-2 Petrography M-1 O-5 O-3 M-4 M-3 M-2 Stable isotopes (C and O)
P-BX # samples [unit thickness] (sub-samples) 3 [26 m] 14 [36 m] 13 [39 m] 25 [106 m] 17 [56 m] 10 [37 m] 3 14 10 (+ 2 BC)
M-1
13
O-5
8
O-3
3 (+ 2 BC)
Core P-CX # samples [unit thickness] (sub-samples) 2 [10 m] 12 [26 m] 14 [41 m] 40 [94 m] 16 [37 m] 6 [5 m] 2 12 14 (+ 5 DOL) 39 (+ 15 DOL + 7 BC) 16 (+ 5 DOL + 1 BC) 2 (+ 2 BC)
P-DX # samples [unit thickness] (sub-samples) Not present 4 [21 m] Not present 2 [6 m] 28 [72 m] 21 [44 m] Not present 4 Not present 2 (+ 1 DOL) 28 (+ 12 DOL) 23 (+ 5 DOL)
188 189
4. RESULTS
190
4.1.
191
4.1.1. Main components (particles/grains and cements)
192
The samples analyzed contain bioclasts and carbonate cements, with minor amounts of a micritic
193
matrix, non-carbonate cements, non-carbonate grains, peloids and intraclasts. Bioclasts are
194
mostly composed by rhodoliths, branching red-algae (Corallinaceae and Sporalithaceae) and
Petrography and mineralogy
11 195
LBF (Miogypsina, Amphistegina, Heterostegina, etc.); subordinated by echinoids, planktonic
196
foraminifera, mollusks, bryozoans, barnacles, green algae and corals (Fig. 5).
197 198 199 200 201 202 203
Figure 5. Main components of the Perla Limestone. A: Ellipsoidal rhodolith (arrowed) with encrusting foraminifera. B: Red algae fragments in a bioclastic matrix (arrowed). C: LBF bioclasts (arrowed). D: Bryozoan bioclast (arrowed). E: Re-worked barnacle fragments (arrowed). F: Coral fragment almost completely replaced by calcite cement (arrowed). Scale bar is 2.5 millimeters-size.
204
Five main types of calcite cement were identified: blocky spar, microspar, syntaxial, bladed and
205
dogtooth spar calcite.
206
Blocky: Blocky calcite is the dominant cement in the Perla Limestone. It is usually not
207
luminescent under CL, with dull to bright red luminescence in very few samples of the
4.1.1.1.
Calcite cements
12 208
Oligocene units (Fig. 6b). This cement is mainly distributed in O-3, O-5 and M-1, where it can
209
reach up to 40 % volume of some samples. Blocky cement can be subdivided in blocky-1 and
210
blocky-2, based on crystal-size and occurrence. Blocky-1 consists of subhedral to anhedral
211
limpid-crystals, with diameters ranging from 50 to 250 µm (Fig. 6, 7a). It is found void-filling
212
primary inter- and intraparticle porosity, as well as, moldic-pores and post-compactional
213
features. Alternatively, blocky-2 corresponds to a scarcer version of this cement, which is
214
characterized by larger crystal-sizes (up to 2 mm in diameter) exclusively observed void-filling
215
large secondary pores and post-compactional features, such as tension gashes (Fig. 7b, d).
216 217 218 219 220 221
Figure 6. Blocky-1 under transmitted-light and CL petrography. A: Transmitted-light petrography showing blocky-1 precipitated in moldic-pore (green arrow), as well as, filling post-compactional feature (blue arrow). B: CL petrography showing blocky-1 with dull red luminescence (green arrow) and bright red luminescence (blue arrow). Scale bar is 500 micrometers-size.
222
Microspar: Microspar occurs as subhedral to anhedral microcrystals, with crystal-sizes from 5 to
223
20 µm. It is not luminescent under CL. Microspar is found either as aggregates of micropeloidal
224
matrix (microspar-1) or void-filling secondary pores (microspar-2); see Fig. 7c, 7d and 8b. Both
225
microspars are scarce but microspar-1 can be locally abundant in O-3 and O-5.
226
Syntaxial: Syntaxial rim cement appears as overgrown-crystals on echinoid spines and plates,
227
with diameters up to 250 µm-size (Fig. 7f). It is usually not luminescent under CL, except for
13 228
few samples with bright red luminescence. This cement is scarce, and its abundance is controlled
229
by the presence of echinoderms, which are more abundant in O-3 and O-5.
230
Bladed and dogtooth spar: They consists of non-isopachous crystal rims growing around the
231
external and internal walls of determined bioclasts, such as of foraminifera tests and echinoids
232
spines (Fig. 7f). Also, they are occasionally preserved like internal rims within macroborings
233
(Fig. 8). Bladed cement has individual crystal-sizes under 10 µm in diameter, while, dogtooth
234
consists of larger crystals (up to 20 µm), with a more prismatic habit that locally develops
235
scalenohedral geometry (Fig. 7e). Under CL, these cements are non-luminescent. Bladed and
236
dogtooth cement are rare but scattered along the Perla Limestone.
237 238 239
Figure 7. Calcite cements identified in the Perla Limestone samples. A: Blocky-1 filling mollusk mold (arrowed). B: Blocky-2 precipitated in tension gashes (arrowed). C: Microspar-1 replacing the micritic-
14 240 241 242 243
matrix (arrowed). D: Blocky-2 and microspar-2 void-filling secondary porosity in red-algal fragment. E: Bladed calcite cement well-preserved in a benthic foraminifera bioclast (internally and externally). F: Syntaxial and dogtooth cement developed in echinoderm fragments. Scale bar is 200 micrometers-size.
244 245 246 247 248
Figure 8. Bladed and microspar cements. A: Bladed cement (green arrow) as internal rim in Gastrochaenolites ichnotaxon (red arrow) that preserves its producer (bivalve; blue arrow). B: Microspar1 (green arrow) associated with a rounded pellet (blue arrow), engulfed by Blocky-1 (red arrow). Scale bar is 500 micrometers-size.
249 250
4.1.1.2.
Dolomite
251
Petrography and SEM analysis allowed the recognition of three types of dolomite based on
252
crystal-size and textural features: DOL-1, DOL-2 and DOL-3.
253
DOL-1: DOL-1 consists of replacive microcrystalline dolomite, with anhedral to subhedral
254
crystals less than 5 µm in size. It is precipitated as internal rims within the red-algae cell-walls
255
(Fig. 9a). Under CL, DOL-1 shows bright red luminescence (Fig. 10). DOL-1 is scarce (< 5 % of
256
rock volume) but scattered throughout the carbonate succession.
257
DOL-2: DOL-2 refers to a microcrystalline to finely crystalline dolomite cement, with euhedral
258
to subhedral crystals up to 30 µm-size. It is both void-filling red-algae moldic-pores and partially
259
replacing the micritic-matrix nearby pressure-dissolution seams (Fig. 9b, c, d). Under CL, DOL-
260
2 crystals show a non-luminescent to dull red luminescent core, with a bright red luminescent
261
rim of variable size (Fig. 10). DOL-2 is visibly the dominant type of dolomite in the Perla
15 262
Limestone. In general, it accounts for less than 5 % of the rock volume in M-4 and M-3, 5 to 10
263
% in M-2 and 10 to 30 % in the underlying units. It can be locally abundant (≈ 30 % of rock
264
volume) in specific zones of the Oligocene units with high-concentration of pressure-dissolution
265
seams.
266
DOL-3: DOL-3 consists of a medium to coarse-crystalline dolomite cement, with individual
267
crystals in size from 30 to 100 µm (Fig. 9d). It is typically found void-filling moldic-pores
268
adjacent to pressure-dissolution seams, in association with DOL-2. Under CL, DOL-3 shows
269
zoned rhombs with four zones, a non-luminescent to bright red luminescent core, a bright red
270
luminescent middle zone and a dull red outer zone, with a lighter red luminescent overgrowth
271
rim (Fig. 10). DOL-3 is volumetrically minor and usually accounts for less than 5 % of the total
272
rock volume. Rare samples have warped crystal wedges than can suggest a saddle dolomite
273
variety (e.g. Radke and Mathis, 1980).
274 275 276
Figure 9. SEM images showing the dolomites recognized in the Perla Limestone samples. A: DOL-1 precipitated as rims within the red algae cell-walls. B: DOL-2 void-filling enlarged intraparticle pores in
16 277 278 279
280 281 282 283 284 285 286 287
red algae fragment. C: DOL-2 and DOL-3 void-filling intraparticle pore in red algae fragment. D: DOL-2 filling a stylolite-surface, accompanied by framboidal pyrite. Scale bar is 30 micrometers-size.
Figure 10. Dolomites of the Perla Limestone under CL. A: Enlarged-intraparticle pore within a red algae fragment, void-filled by DOL-2 crystals engulfed by blocky-1. The DOL-2 crystals show a nonluminescent to dull red luminescent core, with bright red luminescent rim. B: Fracture filled by DOL-3 crystals showing rhombs with four zones, a non-luminescent to bright red luminescent core, a bright red luminescent middle zone and a dull red outer zone, with a lighter red luminescent overgrowth rim. C: Red algae bioclast partially replaced by bright red luminescent DOL-1 crystals, associated with DOL-2. Scale bar is 50 micrometers-size.
288 289
4.1.1.3.
Other cements
290
Non-carbonate cements in the Perla Limestone include pyrite, fluorite, sphalerite, galena, barite,
291
clays, iron-oxyhydroxides, apatite and quartz. Pyrite cements occur in framboidal and finely
292
crystalline forms. The framboidal pyrite occurs along pressure-dissolution surfaces and void-
293
filling primary/secondary micropores. In contrast, the finely crystalline pyrite is strictly
17 294
precipitated in the vicinity of pressure-dissolution seams (Fig. 11a, b, d, e). Pyrite is scattered but
295
relatively more abundant in M-3 and M-4.
296
Fluorite cement occurs as traces in O-3, O-5, M-1 and M-2. It consists of fine crystals and
297
aggregates up to 50 µm-size, which are usually filling secondary pores (Fig. 11f). Likewise,
298
microcrystalline traces of sphalerite, galena and barite cement occur within secondary pores (Fig.
299
11b and e). In general, sphalerite, galena, barite and pyrite occur as ephemeral mineralization
300
halos. These halos show parallel to sub-vertical spatial disposition respect the main pressure-
301
dissolution surfaces. Also, they are usually found in association with DOL-2 (Fig. 11c).
302
Traces of kaolinite, illite, smectite and rare organic matter are frequently accumulated along
303
pressure-dissolution surfaces. On the other hand, a kaolinite-polytype recognized as dickite is
304
found filling intraparticle pores and stylolite-related microfractures (Fig. 11c, d). Dickite differs
305
from other kaolinite-polytypes due to its blockier and more euhedral crystals (Ehrenberg et al.,
306
1993).
307 308 309 310
18
311 312 313 314 315 316 317 318 319 320 321
Figure 11. SEM photomicrographs showing different non-carbonate cements present in the Perla Limestone. A: framboidal pyrite cement precipitated along stylolite-surface filled with blocky-2. B: Finely crystalline pyrite with galena inclusions precipitated along a vein, in the vicinity of a stylolite filled with DOL-2. C: Dickite crystals with a blocky-booklet habit, precipitated in interparticle pore filled with blocky-2. D: Framboidal pyrite, DOL-2 and dickite precipitated in dissolution-enlarged interparticle pore. E: Sphalerite, DOL-2 and pyrite precipitated in vuggy pore. F: Vein filled with DOL-2 and fluorite cement. Scale bar is 100 micrometers-size.
19 322
4.1.2. Porosity types
323
Petrographic analyses allowed the identification and quantitative estimation of nine main pore-
324
types (Table 4). They were classified using the carbonate porosity classifications of Choquette
325
and Pray (1970), Kaczmarek et al. (2015) and Hashim and Kaczmarek (2019), as guides. From a
326
total of nine pore types, two represent primary depositional porosity (interparticle and
327
intraparticle), while the rest corresponds to secondary porosity.
328 329 330 331 332 333
Table 3. Pore-type distribution in the Perla Limestone. A (abundant) = 20–30 %, C (common) = 10-20 %, F (frequent) = 5-10 %, O (occasional) = 1-5 %; n/p = traces or not present. IP: interparticle porosity; WP: intraparticle porosity; MO-A: moldic porosity associated with former aragonitic bioclasts; MO-HMC: moldic porosity associated with former high-Mg calcite bioclasts; VUG: vuggy porosity; IX: intercrystalline porosity (dolomites); mFr: microfracture porosity; BO: boring porosity. Porosity types
P-BX
Unit M-4 M-3 M-2 M-1 O-5 O-3
P-CX
Unit M-4 M-3 M-2 M-1 O-5 O-3
P-DX
Unit M-3 M-1 O-5 O-3
IP
WP
MO-A
Microporosity
C C O O O n/p
C C O O O n/p
O O O O n/p n/p
F F C F F O
IP
WP
MO-A
Microporosity
C C O O n/p n/p
C C O O O n/p
n/p O O n/p n/p n/p
F C A C F O
IP
WP
MO-A
Microporosity
n/p n/p n/p n/p
n/p n/p n/p n/p
O O n/p n/p
O O F F
MO-HMC
VUG
IX
mFR
BO
n/p n/p O O n/p n/p
n/p O O O O F
O O n/p O O n/p
O n/p n/p n/p n/p n/p
VUG
IX
mFR
BO
n/p n/p F O n/p O
n/p O O F O F
O O n/p n/p O O
O O O n/p n/p n/p
MO-HMC
VUG
IX
mFR
BO
O O O O
n/p n/p n/p n/p
n/p O O O
O O O O
n/p n/p n/p n/p
F O C F O O Porosity types MO-HMC
O F C F O O Porosity types
Total porosity (%, by visual estimation) 30 - 40 20 - 30 20 - 30 15 - 25 10 - 20 5 - 10 Total porosity (%, by visual estimation) 30 - 40 30 - 40 40 - 50 20 - 30 10 - 20 5 - 10 Total porosity (%, by visual estimation) 5 - 10 5 - 10 10 - 15 10 - 15
20
334 335 336 337 338 339 340 341 342 343
Figure 12. Thin-section photomicrographs of porosities in the Perla Limestone. A: Interparticle porosity (IP) between bioclasts and intraparticle porosity (WP) within LBF bioclasts, barnacles, among others. B: Vuggy porosity (VUG), moldic porosity associated with former HMC-bioclasts (MO-HMC) and intercrystalline porosity (IX) in partially dolomitized red-algal rich sample; the opaque mineral was identified as pyrite. C: Moldic porosity related to aragonitic bioclasts (MO-A) developed from former gastropods. D: Pervasive microporosity indistinctly affecting bioclasts, matrix and cement and forming dissolution vugs. E: Microporosity and vuggy porosity (VUG) developed from the dissolution of blocky-1 cement. Scale bar is 500 micrometers-size.
4.1.2.1.
Primary porosity
344
The interparticle porosity is abundant in the uppermost lower Miocene units (Table 3). It consists
345
of pore-space with diameters ranging from 10 to 500 µm; depending on both the associated type
346
of bioclasts and the degree of mechanical compaction (Fig. 12a). Likewise, the intraparticle
21 347
porosity shows different sizes depending on the type of bioclast. It usually ranges from 10 to 30
348
µm in diameter in red algae, 50 to 100 µm in LBF and 100 to 250 µm in larger bioclasts such as
349
bryozoans (Fig. 12a). The intraparticle pores show a similar distribution pattern than the
350
interparticle pores (Table 3). Both pore-types remain very well preserved in P-BX and P-CX but
351
obliterated in P-DX.
352
4.1.2.2.
Dissolution porosity
353
The porosity associated with dissolution processes is the focus of this article. Petrographic
354
observations on the Perla Limestone recognized four main types of dissolution porosity:
355
(1) a fabric-selective dissolution porosity characterized by molds up to 600 µm-size, created by
356
dissolution and collapse of aragonitic fossils (Fig. 12c).
357
(2) a fabric-selective dissolution porosity characterized by molds ranging from less than 10 to
358
200 µm-size, formed by dissolution-enlarged intraparticle pores within former high-Mg calcite
359
(HMC) bioclasts such as red-algae fragments and LBF (Fig. 12b, 13a, 13b).
360
(3) a non-fabric selective microporosity, with pore-sizes under 10 µm, associated with granular-
361
subhedral textures, which is indistinctly affecting bioclasts, matrix and cements (Fig. 12d, 12e,
362
13a, 14, 21c, 21d).
363
(4) a non-fabric selective vuggy porosity, with pores ranging from 5 to 250 µm in diameter,
364
derived by dissolution-enlarged interparticle and intercrystalline pores (Fig. 12b, 12d, 12e, 13b,
365
13c, 14).
366
Microporosity is the dominant secondary pore type in the Perla Limestone (Table 3). This
367
microporosity could be classified as granular microporosity, due to its textural similarities with
368
the petrophysical pore type (granular microporosity - Type I) defined by Kaczmarek et al.
22 369
(2015). The microporosity is mainly distributed in the lower Miocene units of the P-CX and P-
370
BX; specifically, in the section between the topmost part of M-1 and the basal area of M-3. In
371
contrast, in the P-DX it is scarce but present in the Oligocene units (Table 3). Moreover,
372
microporosity is frequently observed in association with vuggy porosity, intercrystalline porosity
373
and moldic porosity in former HMC bioclasts (Fig. 12d, 12e and 13a). These porosities form
374
microporous to finely porous assemblages that can be macroscopically recognizable in cores, by
375
the presence of light beige to whitish patches, characterized by chalky-like texture (Fig. 14, 15a,
376
15b). These microporous patches are commonly associated with major stylolitic surfaces (Fig.
377
15b). However, in the P-CX core, they do not show any preferential distribution but instead, are
378
rather broad and diffuse (Fig. 15a).
379
On the other hand, the moldic porosity created by dissolution and collapse of aragonitic fossils is
380
poorly preserved. It tends to be scarce in the lower Miocene units and very rare in the Oligocene
381
units of the Perla Limestone (Table 3).
382
4.1.2.3.
Dolomite-related porosity
383
This porosity corresponds to a fabric-selective intercrystalline microporosity, with less than 10
384
µm pore-size, developed between dolomite crystals that partially replaced the micritic-matrix
385
(Fig. 12b). It is mainly distributed in O-3, O-5, M-1 and M-2, specifically in areas dominated by
386
pressure-dissolution surfaces.
387
4.1.2.4.
Other types of porosity
388
In addition to the pore-types described above, two other minor secondary pore-types were
389
identified (Table 3). These are boring porosity and microfracture porosity. The boring porosity is
390
characterized by a rounded shape, with pore sizes from 30 to 500 µm and is locally present in red
391
algae fragments (Fig. 8a, 13c). The microfracture porosity is formed by 5 to 50 µm-size pores,
23 392
typically in elongated bioclasts, as well as, cross-cutting blocky-1 cement and stylolites (Fig.13a,
393
c, d).
394 395 396 397 398 399
Figure 13. Thin-section photomicrographs of porosities in the Perla Limestone. A: Coeval microporosity, moldic (MO-HMC) and microfracture porosity (mFR). B: Vuggy porosity (VUG) postdating blocky-1 and a preceding syntaxial cement associated with an echinoderm. C: Boring (BO), microfracture (mFR) and vuggy (VUG) porosities associated with red-algal fragment. D: Late generation of microfractures cross-cutting bioclasts, stylolites and blocky-1 (red-arrow). Scale bar is 500 micrometers-size.
24
400 401 402 403 404
Figure 14. Macrograph and photomicrograph (magnification = 1000x) of the P-CX core affected by the dissolution porosity (chalky-like texture), with occurrences of microporosity and vuggy porosity. Corroded non-sutured dissolution seam with clayey infilling is arrowed. The core is 10 centimeters wide.
405 406 407 408 409
Figure 15. Macrographs of the P-CX (left) and P-BX (right) cores. A: Area in the M-2 unit of the P-CX affected by dissolution porosity (delimited by dashed lines). B: Area in the M-2 unit of the P-BX affected by dissolution porosity (delimited by dashed lines) linked to pressure-dissolution surfaces (red arrow). Individual bottom-cores are 10 centimeters-wide.
25 410
4.1.3. Porosity and permeability data from core-plugs
411
Helium porosity and horizontal permeability data from core-plugs analysis were collected and
412
plotted to compare values and trends along with the different units of the carbonate succession
413
(see Fig. 16 and Table 4). The P-CX well has the highest reservoir quality of the analyzed wells,
414
followed by the P-BX and the P-DX, respectively. Also, in general, the lower Miocene units
415
show the highest porosities and permeabilities of the carbonate succession. However, in the P-
416
DX the higher porosity and permeability values belong to the Oligocene reservoir units.
417
Moreover, it is also interesting to notice that highly microporous zones (chalky-like texture) tend
418
to have higher porosity and permeability values (Fig. 16).
26
419 420 421 422 423 424 425 426 427 428 429 430 431 432
Figure 16. Helium porosity and horizontal permeability data from core analysis performed on the Perla Limestone (compiled from Valencia, 2016). Superimposed zones with higher abundance of microporosity (chalky-like patches) were visually recognized in the present study.
27 433 434 435 436 437
Table 4. Range of distribution, median and average of helium porosity and horizontal permeability by reservoir unit in the Perla Limestone (reported by Valencia, 2016). Core
P-BX
P-CX
P-DX
Unit
Thickness (m)
M-4 M-3 M-2 M-1 O-5 O-3 M-4 M-3 M-2 M-1 O-5 O-3 M-3 M-1 O-5 O-3
26 36 39 106 56 37 10 26 41 94 37 5 4 2 28 21
Helium Porosity (%) Range Median Average 14 - 28 24.1 22.4 8 - 29 15.6 16.1 7 - 38 17.6 19.6 8 - 37 18.0 18.7 5 - 35 19.3 19.3 4 - 28 16.0 15.7 19 - 31 28.7 27.7 10 - 31 22.0 21.4 13 - 42 29.3 27.3 8 - 38 21.4 21.4 7 - 34 17.3 18.5 4 - 20 11.2 11.0 2 - 12 6.8 6.9 5 - 12 7.3 8.3 6 - 32 20 20.4 3 - 36 15 14.4
Horizontal permeability (mD) Range Median Average 3 - 57 17.8 24.5 0 - 484 2.9 27.8 0 - 96 0.8 4.5 0 - 23 0.7 1.4 0 - 11 0.8 1.6 0-6 0.4 0.4 6 - 322 14.4 40.5 1 - 671 15.0 50.8 0 - 278 12.1 28.4 0 - 37 0.8 2.4 0-3 0.5 0.8 0 - 21 0.3 2.4 0 - 25 0.0 2.0 0-4 0.0 0.5 0 - 122 0.8 2.0 0-4 0.2 0.5
438
4.1.4. Other diagenetic features
439
In addition to the diagenetic cements and neomorphic textures described above, several other
440
diagenetic features such as borings, fractures, pressure-dissolution surfaces and overgrowth pores
441
were recognized in the Perla Limestone.
442
4.1.4.1.
Borings
443
Petrographic analyses allowed the identification of macroborings, microborings and micritic
444
envelopes caused by microbial micritization. Based on morphological analysis, macroborings
445
ichnotypes such as Entobia isp., Trypanites isp. and Gastrochaenolites isp. occur in the Perla
446
Limestone. The Entobia traces seem to be most abundant. They show single and multiple
447
chambers, with an irregular-rounded to sub-angular shape. Diameter ranges from 0.5 to 2 mm-
448
size (Fig. 17a). The Trypanites is represented by a singular elongated and straight boring tube,
449
with an approximately constant diameter (0.5 to 1 mm) and rounded termination (Fig. 17a). The
28 450
Gastrochaenolites traces are characterized by a sub-ellipsoidal chamber that can reach up to 2
451
mm in diameter (Fig. 8a, 17b).
452 453 454 455 456 457 458
Figure 17. Thin-section photomicrographs showing the different macroboring ichnotypes in red algae bioclasts from the Perla Limestone. A: Trypanites and Entobia ichnotypes in red algae fragment. B: Gastrochaenolites ichnotaxon containing valves of its producer (bivalve shells). Scale bar is 2.5 millimeters-size.
459
The deformation features observed in the Perla Limestone have been classified into two major
460
groups: fractures and pressure-dissolution surfaces. Fractures with variable length were
461
recognized (Fig. 13a, c, d). Most of them correspond to microfractures (grain breakages)
462
affecting elongated or flat grains, such as branching red-algae, mollusks and barnacles. They are
463
usually infilled by blocky-1, however, in the uppermost units, they are frequently open and
464
connecting previously isolated pores. A later generation of microfractures is found cross-cutting
465
stylolites and blocky-1 cement (Fig. 13d).
466
Pressure-dissolution surfaces comprise sets of non-sutured seams and stylolites. The non-sutured
467
seams are dominant. They are laterally continuous on core-scale (cm-size), with wispy-surfaces
468
parallel to sub-parallel to the bedding plane (Fig. 18a, c). Also, they are sporadically associated
4.1.4.2.
Deformation features
29 469
with secondary networks of micro-stylolites. In contrast, the stylolite surfaces are characterized
470
by horizontal to pseudo-horizontal sets of low to high-amplitude jagged-surfaces, which are
471
laterally continuous at the core-scale (Fig. 18b, d). Tension gashes and microfractures are often
472
associated with the stylolite-surfaces. Likewise, rare vertical stylolites are also present. Variable
473
amounts of non-carbonate cements and rare organic matter were preferentially accumulated in
474
both non-sutured seams and stylolites (Fig. 18a, b, c).
475 476 477 478 479 480 481
Figure 18. Thin-section photomicrographs and photo-macrographs showing pressure-dissolution features in the Perla Limestone. A (photomicrograph) and C (phot-macrograph): Non-sutured dissolution seams (arrowed), with parallel to sub-parallel surfaces infilled by insoluble material. B: Saturated contact between LBF bioclasts. D: High-amplitude sub-parallel to sub-perpendicular stylolites: Yellow-scale bar is 500 micrometers-size.
482
4.2.
483
δ13C and δ18O isotope analysis were performed on bulk samples (Fig. 19). Therefore, these
484
isotopic values only represent a mixture of original values (unaltered grains), variably altered
Stable carbon and oxygen isotopes
30 485
grains and cements. However, in some instances, it was possible to separate and analyze
486
dolomites (undifferentiated) and blocky-2 cement.
487
δ13C ratios in the bulk samples vary from -8.89 to +1.10 ‰ (V-PDB), with an average of slightly
488
positive values (+0.12 ‰), and a few strongly depleted values in the Oligocene units. The δ18O
489
composition varies from -7.48 to -0.72 ‰ (V-PDB), with most of the samples ranging from -3.00
490
to -1.5 ‰.
491 492 493 494
Figure 19. δ18O vs. δ13C ratios in calcite (bulk), dolomites and blocky-2 cement from the Perla Limestone. Group A, B and C denote possible dolomite families. Green dashed-line include strongly depleted 13C values from the O-3 unit in the P-DX.
495
Blocky-2 samples show δ13C ratios from -1.62 to +0.69 ‰ (V-PDB). While the δ18O values
496
range from -8.15 to -4.51 ‰ (V-PDB). The 18O values are strongly depleted compared with the
497
host rock (Fig. 19). The average δ18O ratio of blocky-2 cement is -6.2 ‰ (V-PDB), while the
498
average of the bulk samples analyzed is -3.1 ‰ (V-PDB). On the other hand, δ13C ratios are
499
comparatively similar to their analogue bulk samples.
31 500
Dolomite samples show δ13C ratios from -8.51 to +1.33 ‰ (V-PDB). While the δ18O values
501
range from -12.51 to -0.02 ‰ (V-PDB). When these values are plotted in a δ18O vs. δ13C cross-
502
plot graph, they show a positive correlation and seem to be clustered into three main groups:
503
Group-A, Group-B and Group-C (Fig. 19). Group-A (δ13C: -0.10 to +1.33 ‰; δ18O: -1.65 to -
504
0.02 ‰) is characterized by slightly positive δ13C ratios and less negative δ18O values, compared
505
with the host rock. Group-B (δ13C: -2.97 to -0.13 ‰; δ18O: -6.34 to -2.49 ‰) consists of
506
dolomites with more depleted 13C and slightly depleted 18O than the bulk samples. On the other
507
hand, Group-C (δ13C: -8.51 to -4.22 ‰; δ18O: -12.51 to -8.82 ‰) is characterized by dolomites
508
strongly depleted in 13C and 18O, when compared with the host rock. The dolomites from Group-
509
A are distributed along the entire carbonate column, while dolomites from Group-B and Group-C
510
are mainly distributed from O-3 to M-2.
511 512 513 514 515 516
32 517
5. DISCUSSION
518
5.1.
519
The Perla Limestone has experienced a complex sequence of diagenetic modifications associated
520
with four main diagenetic environments: marine, meteoric, shallow-burial and deep-burial
521
environment (Fig. 20).
Paragenesis of the Perla Limestone
522 523 524
Figure 20. Paragenetic scheme of the diagenetic processes occurred in the near-surface, shallow-burial and deep-burial environments that modified the petrophysical properties of the Perla Limestone.
525
5.1.1. Early diagenetic stages (marine and ephemeral meteoric environment)
526
Diagenetic processes started early in the depositional setting. The first diagenetic modifications
527
in the marine environment were bioerosion and microbial micritization, evidenced by the
33 528
presence of different boring ichnotypes in red-algae fragments (Fig. 17). The boring activity
529
predates most of the early marine cementation, as per the presence of bladed and dogtooth
530
cements precipitated within macroborings (Fig. 8a). The bioerosion process was dominated by
531
the activity of sponges (Entobia), while the microbial micritization process was probably
532
induced by the activity of fungus/bacteria (e.g. Checconi et al., 2010). These diagenetic events
533
enhanced the primary porosity in the red algae-rich facies of the Perla Limestone. In contrast,
534
early marine cementation reduced porosity. However, considering the scarcity of early marine
535
cements, their impact on the pore network is considered minor.
536
An early, fabric-selective dissolution process was also documented. This process was responsible
537
for creating moldic pores as the result of mineral stabilizations in the early diagenetic
538
environment. However, during the mineral stabilization process, the aragonite and HMC
539
bioclasts did not follow the same alteration pathway. The dissolution of aragonite skeletal
540
fragments created complete molds of the former bioclasts, resulting in no preservation of the
541
original texture (Fig. 12c). In contrast, the stabilization of HMC bioclasts (red-algae and LBF)
542
resulted in excellent preservation of the primary texture (Fig. 12b, 13a, 13d). The textural
543
preservation of HMC bioclasts during diagenesis is commonly explained by an incongruent
544
dissolution process, which considers that the dissolution of HMC grains and subsequent
545
precipitation of calcite with lower concentration of Mg, occur across thin reaction films, with the
546
two reactions barely separated in time (Bathurst, 1975; Budd, 1992; Bischoff et al., 1993).
547
Although the mineral stabilization process is typical of the meteoric environment (Bathurst,
548
1975; Longman, 1980; Moore, 2001), the absence of substantial meteoric alteration, only locally
549
identified in the Oligocene units, suggests a dissolution process that occurred in marine or
34 550
slightly modified marine waters at or near the sea-floor (e.g. Melim et al., 1995; Knoerich and
551
Mutti, 2003; Swart, 2015).
552
Scarce to rare meteoric alterations are present at some levels in the Oligocene units O-3 and O-5
553
in the P-CX well, and the O-3 unit in the P-Bx and P-DX. The main evidence of these shallowing
554
episodes includes: (1) rare dissolution macro-cavities infilled either by mixed carbonate-
555
siliciclastic deposits in the P-BX and P-CX cores; and (2) strongly depleted
556
lowermost section (O-3) of the P-DX (Fig. 17). Depleted
557
occurrence of greenish siliciclastic sandstones lithofacies (SS), associated with ephemeral
558
subaerial exposures episodes during the Oligocene, according to Pomar et al. (2015). However,
559
given the scarcity of the meteoric alterations in the Perla Limestone, their impact on the reservoir
560
quality seems to be limited.
561
Petrographic and SEM analysis also allowed the recognition of an early dolomitization process
562
(DOL-1). This dolomitization pre-dates the precipitation of blocky-1, in accordance with spatial
563
relationships (Fig. 8a). Presumably, this dolomitization process has occurred by redistribution of
564
available magnesium coming from red-algal mineralogical stabilization (e.g. Land and Epstein,
565
1970). However, a primary origin, biologically mediated by the red algae is not discarded (e.g.
566
Nash et al., 2011).
567
Unfortunately, it was not possible to physically separate the three different types of dolomite
568
recognized by petrography and SEM, for geochemical purposes (δ18O and δ13C). Interestingly,
569
however, three groups of dolomites can be defined based on their isotopic print: Group-A,
570
Group-B and Group-C (Fig. 17). On the basis that the δ18O ratio in carbonates is considered
571
inversely proportional to the temperature of crystallization (Hudson, 1977; Swart, 2015), it
572
would be reasonable to assume that the earliest stage of dolomitization (DOL-1) corresponds to
13
13
C values in the
C values are consistent with the
35 18
573
the Group-A. Whereas, more
O-depleted groups, would correspond to later diagenetic
574
dolomites (DOL-2 and DOl-3).
575
Assuming that DOL-1 precipitated from the same waters than the host-rock, the “average DOL-
576
1” would have precipitated at similar but slightly higher precipitation temperature than the
577
“average bulk calcite” in the Perla Limestone (36
578
O’Neil, 1997 and Craig, 1965).
579
5.1.2. Shallow-burial environment
580
The dissolution process of unstable minerals eventually leads to supersaturation of the fluid with
581
respect to low-Mg calcite (LMC) and to the subsequent precipitation of LMC-cement (Moore,
582
2001). As a result, significant precipitation of calcite cement should occur in the transition
583
between the near-surface to the shallow-burial environment. This process is documented in the
584
Perla Limestone by the precipitation of blocky-1 within pre-existent interparticle, intraparticle,
585
moldic (aragonitic grains), boring pores, as well as, filling post-compactional features (Fig. 6,
586
7a). Blocky-1 destroyed most of the primary and early-secondary porosity in the lowermost
587
units. In contrast, in the uppermost units (M-3 and M-4), the primary and early-secondary
588
porosity remained well preserved.
589
Microspar formation is believed to have occurred in two different diagenetic stages. Petrographic
590
evidence suggests an early version of microspar (microspar-1), which is the product of
591
replacement process, with the partial dissolution of a precursor micritic-matrix and subsequent
592
microspar precipitation (e.g. Folk, 1965; Longman, 1977; Lucia and Loucks, 2013). The
593
presence of microspar-1 engulfed by blocky-1 reveals its early diagenetic nature (Fig. 8b). In
594
contrast, a later version of microspar (microspar-2), considered a primary microspar cement (e.g.
C vs. 30
C; using the equations in Kim and
36 595
Munnecke et al., 1997; Melim et al., 2002), is found precipitated in dissolution-enlarged
596
intraparticle pores in association with DOL-2 (Fig. 7d).
597
The progressive and increased incidence of mechanical compaction generated an expected
598
porosity-reduction in the Perla Limestone (e.g. Hamilton, 1976; Croizet et al., 2013). However,
599
this process affected the reservoir in different ways. Early-cemented units (e.g. O-3 and O-5)
600
were generally less compacted than the poorly/non-cement units (e.g. M-3 and M-4). Also, in
601
these poorly/non-cemented units, the microfractures were usually found connecting previously
602
isolated interparticle and intraparticle pores; thus, increasing permeability (Fig. 13c).
603
Microfractures and fractures occurred at different diagenetic stages in the Perla Limestone. Some
604
early microfractures predate the blocky-1 precipitation. While others are found orthogonally
605
cross-cutting pressure-dissolution features (Fig. 13d); thus, representing a later diagenetic event.
606
5.1.3. Deep-burial environment
607
Postdating the first stages of mechanical compaction, the Perla Limestone started to experience
608
an intense chemical compaction process that created numerous pressure-dissolution features,
609
such as non-sutured seams and stylolites, at both microscopic and macroscopic level (Fig. 14,
610
15b, 18). This process reduced the porosity volume in the Perla Limestone (e.g. Croizet et al.,
611
2013). However, it could also have created discontinuity surfaces that served as conduits for
612
diagenetic fluids responsible for later dissolution processes (e.g. Paganoni et al., 2015; Barnett et
613
al., 2015). This can be supported by the presence of some corroded pressure-dissolution seams
614
constraining the dissolution timing to be post-stylolitization (Fig. 13a, 14, 15b).
615
The presence of DOL-2 and DOL-3 associated with ephemeral base-metal sulphide
616
mineralization in the vicinity of pressure-dissolution surfaces, as well as, in dissolution pores
37 617
created during the first stages of pressure-dissolution deformation, suggests a dolomitization and
618
sulphide mineralization either coeval or post-dating the chemical compaction process. This
619
interpretation can be supported by dolomite samples with depleted 18O values (Group-B and C in
620
Fig. 19), which reveals their late diagenetic origin (e.g. Lavoie et al., 2005; Lonnee and Machel,
621
2006).
622
CL analysis revealed that DOL-3 crystals are composed by zoned rhombs that seem to be DOL-2
623
crystals with an overgrown dull red middle-outer zone and lighter red luminescent rim (Fig.
624
10b). Based on this assumption, DOL-3 would be a late diagenetic overgrown phase of DOL-2.
625
This interpretation can be also supported by the fact that the DOL-3 crystals are not affected by
626
the late burial dissolution process compared to the DOL-2 crystals (21a, b); thus, representing a
627
later diagenetic phase. The dolomites with strongly depleted
628
could represent the DOL-3 observed in thin sections. However, more analyses are required.
629
Interestingly, the occurrence of high-temperature dolomites (DOL-2 and DOL-3), seems to be
630
genetically controlled not only by the presence of pressure-dissolution features but the red-algae
631
content. Moreover, it can be noticed that dolomite-replaced matrix is only present in the
632
surrounding areas of red-algae bioclasts when these are affected by the pressure-dissolution
633
process. Base on that, a compactional dolomitization model, where the increment of temperature
634
with depth, favors dolomitization by removing the kinetic barriers that inhibit dolomitization is
635
considered. A common weakness of the burial compaction model is the supply and transport of
636
magnesium ions (Lonne, 1999). However, in the case of the Perla Limestone, remobilized
637
magnesium ions from red-algal rich facies and/or Mg-rich compactional brines from the
638
underlying Paleogene-siliciclastic succession, funneled by pressure-dissolution features and/or
18
O values (Group-C in Fig. 19)
38 639
fault and fractures are considered to have induced the burial dolomitization process (e.g. Ronchi
640
et al., 2011).
641
An alternative structurally controlled hydrothermal dolomitization model (e.g. Davies and Smith,
642
2006) is not discarded. However, the absence of saddle dolomite (only present as traces in some
643
dolomitized samples) seems not to be compatible with this model. The authors consider that
644
further investigation regarding fluid inclusions, isotopes and epifluorescence in the Perla
645
Limestone dolomites is required.
646
The burial dolomitization process was responsible for the creation of intercrystalline porosity,
647
which is an important type of porosity in the Perla Limestone. It is mainly distributed in units O-
648
3, O-5, M-1 and M-2 (see Table 3). The burial environment was also the site of a significant
649
dissolution process that created pervasive microporosity. This topic will be discussed later in
650
detail in the burial dissolution section.
651
The arrival of organic gases from the source rock to the reservoir seems not to have a major
652
impact in the diagenetic evolution of the carbonate succession. Physical evidence of bitumen was
653
not recorded in the Perla Limestone samples. However, epifluorescence imaging analysis would
654
be required to confirm its absence. According to Pirela (2017), the source rock of the
655
hydrocarbons present in the Perla field is a geochronologic equivalent of the Agua Clara Fm.
656
(Falcón Basin) that reached the hydrocarbon generative window in the deepest zone of the
657
Urumaco Trough, located at the south-eastern area of the structure (see Fig. 1 and 2 for spatial
658
and stratigraphic reference). In addition, Castillo et al. (2017) based on geochemical data
659
indicated that the gas present in the Perla field was generated from the latest late Miocene to the
660
Holocene. This suggests that the timing of hydrocarbon charge would have occurred somewhere
661
between ca 5.3 m.y.a. to the Present. During this period, the Perla Limestone was buried by at
39 662
least 1.3 km of a lower to late Miocene succession, according to the stratigraphic markers from
663
Rojas et al. (2015). Based on this information, it would be reasonable to assume that the
664
hydrocarbon migration occurred after most of the diagenetic events observed in the Perla
665
Limestone.
666
5.2.
667
Deep-burial dissolution creating microporosity: Petrographic, mineralogical
and geochemical evidence
668
A line of evidence confirmed the presence of an important dissolution process that created a
669
pervasive non-fabric selective microporosity, with subordinate moldic and vuggy porosities in
670
the lower Miocene units of the P-CX and P-BX cores (Table 3). This dissolution process is
671
interpreted to have occurred in the deep-burial setting based on genetic relationships with post-
672
compactional features and late diagenetic cements. Post-compactional features such as fractures,
673
stylolites and non-sutured seams, are usually micro-corroded. Likewise, late diagenetic cements
674
such as blocky-1, blocky-2, DOL-2, pyrite, fluorite, among others are partial to totally micro-
675
corroded (Fig. 21a, b, c, 14).
676
Moreover, LMC bioclasts such as echinoderms, which are usually stable in the diagenetic
677
environment (de Boer, 1977), are also micro-corroded (Fig. 21d), thus implying the inflow of
678
corrosive diagenetic fluids. In addition, the presence of non-carbonate cements such as dickite,
679
pyrite, sphalerite, barite and fluorite, is also a potential indication of high-temperature exotic
680
fluids (e.g. Palinkas et al., 2009; Liu et al., 2017). The fact that these non-carbonate minerals are
681
coeval with DOL-2 (Fig. 11), as well as, precipitated within secondary porosity and post-
682
compactional features, reveal their late diagenetic origin.
40 683
The origin of microporosity in limestones is subject of a long-standing debate in the literature.
684
However, most authors agree with a mineral stabilization process as the main driver for
685
microporosity development (e.g. Saller and Moore, 1989; Richard et al., 2007; Volery et al.,
686
2010; Morad et al., 2018; Hashim and Kaczmareck, 2019). In contrast, in the Perla Limestone,
687
our study suggests microporosity development as a result of an acid-driven dissolution
688
mechanism associated with external corrosive-fluids. Similar cases of microporosity related to
689
burial diagenetic fluids have been reported (e.g. Lambert et al., 2006).
690 691 692 693 694
Figure 21. SEM and thin-section photomicrographs showing the evidence of the late nature of the burial dissolution process. A: Corroded DOL-2, pyrite and blocky-2 cement. B: Corroded DOL-2, pyrite and quartz cement. C: Corroded Fluorite and blocky-1 cement. D: Highly corroded LMC-echinoderm (echinoid spine). Scale bar is 50 micrometers-size.
695
In addition to the evidence collected in this study, Valencia and d’Alterio (2014) performed a
696
geochemical analysis of gas samples from the Perla Limestone reservoir. They reported δ13CCO2
697
ratios from -2.7 to -6.9 ‰ (PDB), with an average of -4.2 ‰ (PDB), and the less depleted 13CCO2
698
values in the P-CX well. These isotopic values are considered typical of inorganic origin
41 699
(δ13CCO2 from 0 to -10 ‰ PDB, sensu Wycherley et al., 1999). Within the inorganic sources of
700
CO2, Valencia and d’Alterio (2014) considered that the CO2 from the Perla field was originated
701
from magmatic/mantle degassing and carbonate dissolution sources (-4 to -7 ‰ PDB and -2 to
702
+3 ‰ PDB, sensu Clayton et al., 1990 and Baines and Worden, 2004; respectively). According
703
to these authors, the burial dissolution of the Perla Limestone would have shifted the normal
704
mantle-derived CO2 print to relatively heavy-values in some areas of the reservoir. Moreover,
705
they also reported a
706
concentration. This is characteristic of magmatic/mantle-derived gases (e.g. Truesdell et al.,
707
1994; Ballentine and Holland, 2008). The presence of both mantle-derived fluids and CO2
708
product of carbonate dissolution is considered a clear indication of the interaction between the
709
Perla Limestone and CO2-charged basement-related fluids.
710
5.3.
711
Aggressive fluids unconnected to active hydrologic systems could create burial dissolution
712
(Machel and Lonnee, 2002; Wright and Harris, 2013). These fluids are commonly introduced
713
into the carbonate system through discontinuity surfaces such as faults, fractures, bedding planes
714
and stylolites (Esteban and Taberner, 2003; Salas et al., 2007). From a reservoir perspective, it is
715
important to understand the nature of these fluids capable of carbonate dissolution in the burial
716
realm, to predict the possible geometry of diagenetic geobodies. Several models have been
717
proposed in the literature, where the most common are: (1) the kerogen-related fluids model (e.g.
718
Mazzullo and Harris, 1992; Schulz et al., 2016), (2) the thermochemical sulfate reduction model
719
(e.g. Orr, 1977; Machel, 2001), (3) the mixing-corrosion (e.g. Plummer, 1975; Esteban and
720
Taberner, 2003), (4) the inorganic-CO2 model (e.g. Corbella et al., 2004; Beavington-Penney et
721
al., 2008), (5) the retrograde solubility model (e.g. Heydari, 2000), (6) the pressure-change
3
He-enrichment in the Perla Limestone respect the standard air
Deep-burial dissolution model
42 722
model (e.g. Collins et al., 2013) and (7) the clay-mineral decomposition model (Tosca and
723
Wright, 2015). In the case of the Perla Limestone, petrographic, mineralogical and geochemical
724
evidence supports an inorganic-CO2 model.
725
5.3.1. Inorganic-CO2 model for the Perla Limestone
726
Burial pervasive microporosity (corrosion) in bioclasts, matrix, cements, as well as, in late
727
diagenetic features, was documented in the Perla Limestone. The origin of this secondary
728
porosity is considered the result of an acid-driven dissolution mechanism, associated with the
729
upward migration of hydrothermal CO2-charged fluids from the basement to the reservoir. The
730
mobilization of these fluids was mediated by basement-root faults, fractures and stylolites
731
corridors that allowed the development of pervasive secondary porosity in the vicinity of the
732
major discontinuity surfaces (Fig. 22).
733 734 735
Figure 22. Mechanism of the inorganic-CO2 model proposed for the burial dissolution porosity observed in the Perla Limestone.
43 736
In the following section, a simplified hypothetical sequence of events producing the burial
737
dissolution of the Perla Limestone is proposed:
738
(1) During the middle Miocene to late Miocene, a major tectonic reactivation of the Gulf of
739
Venezuela Basin occurred (Albert-Villanueva et al., 2017; Audemard 2009). At that time,
740
the Perla Limestone was buried by at least 500 m (up to 1300 m) of a siliciclastic-
741
dominated succession, based on stratigraphic markers from Rojas et al. (2015).
742
(2) Because of the active tectonic regime, some antecedent faults and fractures were
743
reactivated favouring the entrance of diagenetic fluids from the crystalline basement up
744
to the reservoir. Pressure-dissolution surfaces also helped to enhance the invasion of
745
these diagenetic fluids (e.g. Paganoni et al., 2015; Barnett et al., 2015). At that depth (≥
746
300 m), assuming a normal geothermal and geobaric gradient (25
747
MPa/km, respectively), the CO2 could have been in the supercritical phase; which is a
748
superfluid phase theoretically reached by the CO2 at 31 C and 7.4 MPa (André et al.,
749
2007). This phase has a low resistance to flow, 6 % lower density than liquid water
750
(Spycher et al., 2003); allowing an easy displacement from the parent magma to the
751
reservoir rock (Domingo et al., 2004).
C/km and 25
752
(3) During the migration towards the Perla Limestone, the supercritical CO2 could also have
753
encountered basinal brines in the underlying Paleogene-siliciclastic unit and mixed with
754
it, creating even more aggressive fluids (e.g. Decker et al., 2015), or reducing its
755
dissolution potential due to high-sulfate content in the basinal brines (e.g. Rosenbauer et
756
al. 2005).
757
(4) Once in contact with the carbonate succession, the acidic fluids were responsible for the
758
creation of extensive dissolution and microporosity development in the Perla Limestone.
44 759
This process was favored by the presence of basement-root faults, fractures and other
760
discontinuity surfaces that funneled the ascending fluids into the carbonate succession.
761
5.3.2. Key considerations for the inorganic-CO2 model
762
Even though it was noticed that the burial dissolution process was not directly related to any
763
specific depositional facies, the fact that it is more frequent in the lower Miocene units (M-2 >
764
M-3 > M-1 > M-4), suggests a connection between the burial dissolution process and these
765
geological units. The more frequent mud-lean or poorly cemented lithofacies in the lower
766
Miocene units might favor the fluid migration on these strata compared to the Oligocene units
767
(Borromeo et al., 2013; Pomar et al., 2015). On the other hand, the diminishing of micro-
768
corrosion from the middle M-3 unit to the top-reservoir (M-4), can be explained by a chemical
769
reaction shut-down due to the limited acidic-fluid input, followed by a rapid chemical-
770
equilibrium with the carbonate formation.
771
The impact of burial dissolution is higher in P-CX well compared with P-BX and P-DX wells.
772
This could be explained by the fact that the P-CX is located in a paleo-topographic basement
773
high, close to a major fault system, with the carbonate succession directly in contact with the
774
basement-rock since the Paleogene-siliciclastic succession (present in P-BX and P-DX) is
775
missing (Fig. 3). The relatively shallower position of the P-CX (paleo-topographic high) with
776
respect to the other wells, might have contributed to a greater flow of diagenetic fluids, due to
777
the naturally expected fluid-flow migration towards lower-pressure zones. Moreover, the
778
stratigraphic omission of the underlying Paleogene-siliciclastic sequence provided a direct
779
contact between the basement and reservoir, and a more efficient pathway for the entrance of
780
diagenetic fluids from the basement-root faults and fractures. A relationship between high-
781
porosity zones and major faults system is evidenced in pseudo-porosity maps created by Rojas et
45 782
al. (2015), from the pseudo-porosity volumes of the Perla Limestone produced by Marini and
783
Spadafora (2014) (Fig. 23).
784 785 786
Figure 23. Pseudo-porosity map of the lower Miocene unit M-2 obtained by Rojas et al. (2015) from the pseudo-porosity volumes done by Marini and Spadafora (2014).
787
Although dissolution porosity created by inorganic CO2-degassing has been extensively reported
788
in the literature (e.g. Beavington-Penney et al., 2008), the impact of this model enhancing
789
reservoir quality was strongly criticized by Ehrenberg et al. (2012). These authors argued
790
problems related to mass balance constraints and lack of quantitative treatment. However, Biehl
791
et al. (2016), from experimental studies on late Permian carbonates (Lower Saxony Basin,
792
Germany), noticed that even if the CO2-dissolved in water has the potential to dissolve only
793
minor amounts of carbonate in closed-systems; their impact in open-systems with inflow and
794
outflow of fluids, becomes important. In the Perla Limestone, the relative absence of late
795
cements postdating an important burial dissolution process could suggest alternating conditions,
46 796
from open to closed system, driven by tectonic events that discharged super-saturated fluids out
797
of the reservoir during open-system stages (e.g. Shen et al., 2016).
798
Moreover, quantitative porosity and permeability data from Perla Limestone cores (Table 4; Fig.
799
16), show a strong correlation between the presence of chalky-like patches, created by burial
800
dissolution processes, and the high reservoir-quality zones.
801
6. CONCLUSIONS
802
The Perla Limestone has undergone a complex sequence of diagenetic events. The primary
803
mineralogy and pore texture set up the initial conditions for the diagenetic evolution of the
804
carbonate succession in the near-surface and shallow-burial environment. Nevertheless, in the
805
deeper burial realm, where carbonates are commonly in equilibrium with the adjacent formation
806
waters, an important event of dissolution and microporosity development occurred. This process
807
was induced by hot CO2-rich fluids coming from the basement to the reservoir, likely during
808
middle Miocene times. The ability of these fluids to create high reservoir-quality zones was
809
controlled by the presence of fault corridors, fractures and pressure-dissolution surfaces that
810
served as a conduit to the carbonate succession. Also, the presence of grain-supported lithofacies
811
and previously dolomitized lithofacies probably favored the dissolution process by the higher
812
permeable networks.
813
Based on this study, the reservoir quality in the Perla Limestone is expected to increase in
814
poorly/non-cemented lithofacies, in the vicinity of major basement-rooted faults. As well, in
815
areas located in paleo-topographic highs where the crystalline basement is directly in contact
816
with the carbonate succession. Similar models can be also applicable to many more examples
817
around the world, such as Baturaja Formation (lower Miocene carbonates) in the North West
47 818
Java Basin (Widodo, 2018), among others. Next steps for diagenetic modelling should consider
819
the combination of these conceptual diagenetic models with 3-D geomechanical fault-system
820
modelling and depositional facies distribution, to establish a powerful tool for porosity and
821
permeability predictions in carbonate reservoirs.
822
7. ACKNOWLEDGEMENTS
823
Authors thank Cardon IV, S.A. for the permission to publish. This study was originated from an
824
M.Sc. thesis project (Valencia, 2016) financially supported by Cardon IV, S.A. We especially
825
thank Ornella Borromeo for her valuable support and ideas about the diagenesis of the Perla
826
Limestone that served as the basis of this research. We would like to acknowledge the referees
827
for their constructive comments to improve the manuscript. Strong support, in terms of data and
828
discussions, was received by the Perla teams of Eni S.p.A/EPLAB, Repsol Technology Center,
829
Cardon IV, S.A, PDVSA, José Méndez Baamonde, Ana Cabrera and Marvin Baquero. Likewise,
830
we thank Mark Wilson, Luis Buatois and Gabriela Mángano for their support with the borings
831
ichnotypes identification.
832
8. REFERENCES
833
Albert-Villanueva, E., Gonzalez, L., Bover-Arnal, T., Ferrandez-Cañadell, C., Esteban, M., Fernandez-Carmona, J.,
834
Calvo, R., Salas, R., 2017. Geology of the Falcón Basin (NW Venezuela). Journal of Maps 13 (2), p. 491-
835
501. https://doi.org/10.1080/17445647.2017.1333969
836 837
Ali, S.A., Clark, W.J., Moore, W.R., Dribus, J.R., 2010. Diagenesis and Reservoir Quality. Oilfield Review 22, p. 14-27.
838
André, L., Audigane, P., Azaroual, M., Menjoz, A., 2007. Numerical modeling of fluid–rock chemical interactions
839
at the supercritical CO2–liquid interface during CO2 injection into a carbonate reservoir, the Dogger
48 840
aquifer
841
https://doi.org/10.1016/j.enconman.2007.01.006
842 843
(Paris
Basin,
France).
Energy
Conversion
and
Management
48,
p.
1782–1797.
Audemard, F., 1993. Neotectonique, sismotectonique et alea sismique du Nord-Ouste du Venezuela (Systeme de failles d’Oca-Ancon). PhD thesis, Universite Montpellier II. 369 p.
844
Audemard, F., 2009. Key issues on the post-Mesozoic Southern Caribbean Plate boundary. In: James, K. H.,
845
Lorente, M. A. & Pindell, J. L. (eds) The Origin and Evolution of the Caribbean Plate. Geological Society,
846
London, Special Publications, 328, 569–586.
847
Baines, S.J., Worden, R.H., 2004. The long-term fate of CO2 in the subsurface: natural analogues for CO2 storage.
848
Geological
849
https://doi.org/10.1144/GSL.SP.2004.233.01.06
Society,
London,
Special
Publications
233,
p.
59–85.
850
Ballentine, C.J., Holland, G., 2008. What CO2 well gases tell us about the origin of noble gases in the mantle and
851
their relationship to the atmosphere. Philosophical Transactions of the Royal Society A: Mathematical,
852
Physical and Engineering Sciences 366, p. 4183–4203. https://doi.org/10.1098/rsta.2008.0150
853 854
Baquero, M., 2015. Evolución geodinámica del Noroccidente de Venezuela, basado en nuevos datos de geocronología, geoquímica e isotópicos. PhD thesis, Universidad Central de Venezuela. 259 p.
855
Baquero, M., Grande, S., Urbani, F., Cordani, U., Hall, C., Armstrong, R., 2015. New Evidence for Putumayo Crust
856
in the Basement of the Falcon Basin and Guajira Peninsula, Northwestern Venezuela, in: Bartolini, C.,
857
Mann, P. (Eds.), Memoir 108: Petroleum Geology and Potential of the Colombian Caribbean Margin.
858
AAPG. https://doi.org/10.1306/13531933M1083639
859
Barnett, A.J., Wright, V.P., Chandra, V.S., Jain, V., 2015. Distinguishing between eogenetic, unconformity-related
860
and mesogenetic dissolution: a case study from the Panna and Mukta fields, offshore Mumbai, India.
861
Geological Society, London, Special Publications, 435, http://doi.org/10.1144/SP435.12
862
Bastin, E.S., 1939. Theories of formation of ore deposits. Scientific American 49 (6), p. 538–547.
863
Bathurst, R.G., 1975. Carbonate Sediment and Their Diagenesis. Development in Sedimentology, Elsevier,
864
Amsterdam. 658 p.
865
Beavington-Penney, S.J., Nadin, P., Wright, V.P., Clarke, E., McQuilken, J., Bailey, H.W., 2008. Reservoir quality
866
variation on an Eocene carbonate ramp, El Garia Formation, offshore Tunisia: Structural control of burial
867
corrosion
and
dolomitisation.
Sedimentary
Geology
209,
p.
42–57.
49 868
https://doi.org/10.1016/j.sedgeo.2008.06.006
869
Biehl, B.C., Reuning, L., Schoenherr, J., Lewin, A., Leupold, M., Kukla, P.A., 2016. Do CO2-charged fluids
870
contribute to secondary porosity creation in deeply buried carbonates? Marine and Petroleum Geology 76,
871
p. 176–186. https://doi.org/10.1016/j.marpetgeo.2016.05.005
872 873
Bischoff, W.D., Bertram, M.A., Mackenzie, F.T., Bishop, F.C., 1993. Diagenetic stabilization pathways of magnesian calcites. Carbonates Evaporites 8, p. 82–89. https://doi.org/10.1007/BF03175165
874
Borromeo, O., Miraglia, S., Santorio, D., Bolla, E., Ortenzi, A., Reali, S., Castellanos, C., Villalobos, R., 2011. The
875
Perla World-Class Giant Gas Field, Gulf of Venezuela: Depositional and Diagenetic Controls on Reservoir
876
Quality in Early Miocene Carbonates. AAPG International Conference and Exhibition, Milan, Italy. Article
877
#90135.
878
Borromeo, O., Miraglia, S., Reali, S., Santorio, D., Ortega, S., Villalobos, R., Castillo, V., Esteban, M., Benkovics,
879
L., 2013. The Perla Gas Field, Gulf of Venezuela: Geological Model of an Oligo-Miocene Carbonate Bank.
880
AAPG International Conference and Exhibition, Cartagena, Colombia. Article #90166.
881 882
Budd, D.A., 1992. Dissolution of high-Mg calcite fossils and the formation of biomolds during mineralogical stabilization. Carbonates and Evaporites 7, p. 74–81. https://doi.org/10.1007/BF03175394
883
Castillo, V., Benkovics, L., Cobos, C., Demuro, D., Franco, A., 2017. Perla Field: The Largest Discovery Ever in
884
Latin America, in: Merrill, R., Sternbach, C. (Eds.), Memoir 113: Giant fields of the decade 2000–2010.
885
AAPG, p. 141–152.
886
Checconi, A., Bassi, D., Carannante, G., Monaco, P., 2010. Re-deposited rhodoliths in the Middle Miocene
887
hemipelagic deposits of Vitulano (Southern Apennines, Italy): Coralline assemblage characterization and
888
related trace fossils. Sedimentary Geology 225, p. 50–66. https://doi.org/10.1016/j.sedgeo.2010.01.001
889
Choquette P.W., Pray, L.C., 1970. Geologic Nomenclature and Classification of Porosity in Sedimentary
890
Carbonates.
891
8645000102C1865D
892 893 894 895
AAPG
Bulletin
54.
207-205.
https://doi.org/10.1306/5D25C98B-16C1-11D7-
Clayton, J.L., Spencer, C.W., Koncz, I., Szalay, A., 1990. Origin and migration of hydrocarbon gases and carbon dioxide, Békés Basin, southeastern Hungary. Organic Geochemistry 15 (3), p. 233-247. Collins, J., Narr, W., Harris, P., Playton, T., Jenkins, S., Tankersley, T., Kenter, J., 2013. SEPM Special Publication 105, p. 50-83. https://doi.org/10.2110/sepmsp.105.11
50 896
Corbella, M., Ayora, C., Cardellach, E., 2004. Hydrothermal mixing, carbonate dissolution and sulfide precipitation
897
in Mississippi Valley-type deposits. Mineralium Deposita 39, p. 344–357. https://doi.org/10.1007/s00126-
898
004-0412-5
899
Craig, H., 1965. The measurement of oxygen isotopes paleotemperatures, in: Tongiorgi, E. (Eds.), Proceedings
900
Spoleto Conference on Stable Isotopes in Oceanographic Studies and Paleotemperatures 3, P. 3-24.
901
de Boer, R.B., 1977. Stability of Mg-Ca carbonates. Geochimica et Cosmochimica Acta 41, p. 265–270.
902
https://doi.org/10.1016/0016-7037(77)90234-4
903
Croizet, D., Renard, F., Gratier, J.P., 2013. Compaction and Porosity Reduction in Carbonates: A Review of
904
Observations, Theory, and Experiments, in: Advances in Geophysics. Elsevier, p. 181–238.
905
https://doi.org/10.1016/B978-0-12-380940-7.00003-2
906 907
Davies, G.R., Smith, L.B., 2006. Structurally controlled hydrothermal dolomite reservoir facies: An overview. AAPG Bulletin 90 (11), p. 1641–1690.
908
Decker, D.D., Polyak, V.J., Asmerom, Y., 2015. Depth and timing of calcite spar and “spar cave” genesis:
909
Implications for landscape evolution studies, in: Geological Society of America Special Papers, p. 103–
910
111. https://doi.org/10.1130/2015.2516(08)
911 912
Diaz De Gamero, M. L., 1977. Estratigrafía y micropaleontología del Oligoceno y Mioceno Inferior del centro de la cuenca de Falcon, Venezuela. GEOS-Universidad Central de Venezuela 22, p. 3–60.
913
Domingo, C., García-Carmona, J., Loste, E., Fanovich, A., Fraile, J., Gómez-Morales, J., 2004. Control of calcium
914
carbonate morphology by precipitation in compressed and supercritical carbon dioxide media. Journal of
915
Crystal Growth 271, p. 268–273. https://doi.org/10.1016/j.jcrysgro.2004.07.060
916
Ehrenberg, S.N., Aagaard, P., Wilson, M.J., Fraser, A.R., Duthie, D.M.L., 1993. Depth-Dependent Transformation
917
of Kaolinite to Dickite In Sandstones of the Norwegian Continental Shelf. Clay Mineral. 28, p. 325–352.
918
https://doi.org/10.1180/claymin.1993.028.3.01
919 920 921 922 923
Ehrenberg, S.N., Walderhaug, O., Bjørlykke, K., 2012. Carbonate porosity creation by mesogenetic dissolution: Reality or illusion? AAPG Bulletin 96, p. 217–233. https://doi.org/10.1306/05031110187 Enos, P., Sawatzky, L., 1981. Pore networks in Holocene carbonate sediments. Journal of Sedimentary Petrology, v. 51/3, p. 961-985. Escalona, A., Mann, P., 2011. Tectonics, basin subsidence mechanisms, and paleogeography of the Caribbean-South
51 924
American
925
https://doi.org/10.1016/j.marpetgeo.2010.01.016
plate
boundary
zone.
Marine
and
Petroleum
Geology
28,
p.
8–39.
926
Esteban, M., Taberner, C., 2003. Secondary porosity development during late burial in carbonate reservoirs as a
927
result of mixing and/or cooling of brines. Journal of Geochemical Exploration 78–79, p. 355–359.
928
https://doi.org/10.1016/S0375-6742(03)00111-0
929
Folk, R. L., 1965, Some aspects of recrystallization in ancient limestones, in L. C. Pray and R. C. Murray, eds.,
930
Dolomitization and limestone diagenesis: A symposium: Society of Economic Paleontologists and
931
Mineralogists Special Publication 13, p. 14–48.
932 933 934 935 936 937 938 939
Hamilton, E.L., 1976. Variations of Density and Porosity with Depth in Deep-sea Sediments. SEPM J. Sediment. Res. Vol. 46. https://doi.org/10.1306/212F6F3C-2B24-11D7-8648000102C1865D Hashim, M.S., Kaczmarek, S.E., 2019. A review of the nature and origin of limestone microporosity. Marine and Petroleum Geology 107, 527–554. https://doi.org/10.1016/j.marpetgeo.2019.03.037 Heydari, E., 2000. Porosity loss, fluid flow, and mass transfer in limestone reservoirs: application to the Upper Jurassic Smackover Formation, Mississippi. AAPG Bulletin (2000) 84 (1), p. 100-118. Hudson, J.D., 1977. Stable isotopes and limestone lithification. Journal of the Geological Society 133, p. 637–660. https://doi.org/10.1144/gsjgs.133.6.0637
940
Jiang, L., Pan, W., Cai, C., Jia, L., Pan, L., Wang, T., Li, H., Chen, S., Chen, Y., 2015. Fluid mixing induced by
941
hydrothermal activity in the ordovician carbonates in Tarim Basin, China. Geofluids 15, p. 483–498.
942
https://doi.org/10.1111/gfl.12125
943
Kaczmarek, S.E., Fullmer, S.M, Hasiuk, F.J. (2015). A universal classification scheme for the microcrystals that
944
host
945
http://dx.doi.org/10.2110/jsr.2015.79
946 947
limestone
microporosity.
Journal
of
Sedimentary
Research
85,
p.
1197-1212.
Kim, S.T. and O’Neil, J. R., 1997. Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates. Geochim. Cosmochim. Acta 61, p. 3461–3475.
948
Knoerich, A.C., Mutti, M., 2003. Controls of facies and sediment composition on the diagenetic pathway of
949
shallow-water Heterozoan carbonates: the Oligocene of the Maltese Islands. International Journal of Earth
950
Sciences 92, p. 494–510. https://doi.org/10.1007/s00531-003-0329-8
951
Lambert, L., Christophe, D., Jean-Paul, L., Gerard, M., 2006. Burial dissolution of micrite in Middle East carbonate
52 952
reservoirs (Jurassic–Cretaceous): keys for recognition and timing. Marine and Petroleum Geology 23, p.
953
79–92.
954
Lavoie, D., Chi, G., Brenan-Alpert, P., Desrochers, A., Bertrand, R., 2005. Hydrothermal dolomitization in the
955
Lower Ordovician Romaine Formation of the Anticosti Basin: significance for hydrocarbon exploration.
956
Bulletin of Canadian Petroleum Geology 53, p. 454–471. https://doi.org/10.2113/53.4.454
957
Liu, L.H., Ma, Y.S., Liu, B., Wang, C.L., 2017. Hydrothermal dissolution of Ordovician carbonates rocks and its
958
dissolution mechanism in Tarim Basin, China. Carbonates and Evaporites 32, p. 525–537.
959
https://doi.org/10.1007/s13146-016-0309-2
960 961 962 963 964 965
Longman, M.W., 1977. Factors Controlling the Formation of Microspar in the Bromide Formation. SEPM Journal of Sedimentary Research Vol. 47. https://doi.org/10.1306/212F716C-2B24-11D7-8648000102C1865D. Longman, M.W., 1980. Carbonate diagenetic textures from near surface diagenetic environments. AAPG Bulletin 64, p. 461- 487. Lonnee, J.S., 1999. Sedimentology, Dolomitization and Diagenetic Fluid Evolution of the Middle Devonian Sulphur Point Formation, Northwestern Alberta. PhD thesis. University of Windsor. 137 p.
966
Lonnee, J., Machel, H.G., 2006. Pervasive dolomitization with subsequent hydrothermal alteration in the Clarke
967
Lake gas field, Middle Devonian Slave Point Formation, British Columbia, Canada. AAPG Bulletin 90, p.
968
1739–1761. https://doi.org/10.1306/03060605069
969 970 971 972
Lucia, F.J., 1995. Rock-Fabric/Petrophysical Classification of Carbonate Pore Space for Reservoir Characterization. AAPG Bulletin 79. https://doi.org/10.1306/7834D4A4-1721-11D7-8645000102C1865D Lucia, F.J., Loucks, R.G., 2013. Micropores in Carbonate Mud: Early Development and Petrophysics. GCAGS Journal 2, p. 1-10.
973
Macellari, C.E., 1995. Cenozoic Sedimentation and Tectonics of the Southwestern Caribbean Pull-Apart Basin,
974
Venezuela and Colombia, in: Tankard, A.; Suarez, R., Welsink, H. (Eds.), Memoir 62: Petroleum basins of
975
South America. AAPG, p. 757–780.
976 977 978 979
Machel, H.G., 2001. Bacterial and thermochemical sulfate reduction in diagenetic settings - old and new insights. Sedimentary Geology 33, p. 143-175. Machel, H.G., Lonnee, J., 2002. Hydrothermal dolomite—a product of poor definition and imagination. Sedimentary Geology 152, p. 163–171. https://doi.org/10.1016/S0037-0738(02)00259-2
53 980
Malavé, B.J., Contreras, O.J., 2013. New Contributions to the Geodynamics of the Caribbean through Structural
981
Transects in the Gulf of Venezuela and its Implications in the Definition of Petroleum Systems. AAPG
982
International Conference and Exhibition, Cartagena, Colombia. Article #30286.
983
Marini, A.I., Spadafora, E., 2014. GandG Data Integration to model a Carbonate Giant Field: Predicting and
984
Managing Reservoir properties in an Underexplored Basin till Production phase. Abu Dhabi International
985
Petroleum Exhibition and Conference, Society of Petroleum Engineers, Abu Dhabi, UAE.
986
https://doi.org/10.2118/171963-MS
987
Mazzullo, S.J., Harris, P.M., 1992. Mesogenetic Dissolution: Its Role in Porosity Development in Carbonate
988
Reservoirs.
989
8645000102C1865D
990 991
AAPG
Bulletin
76,
p.
607-620.
https://doi.org/10.1306/BDFF8880-1718-11D7-
Melim, L.A; Swart, P.K; Maliva, R.G., 1995. Meteoric-like fabrics forming in marine waters: Implications for the use of petrography to identify diagenetic environments. Geology 23, p. 893-896.
992
Melim, L.A.; Westphal, H; Swart, P.K.; Eberli, G.P.; Munnecke, A., 2002. Questioning Carbonate Diagenetic
993
Paradigms: Evidence from the Neogene of the Bahamas. Marine Geology 185, no. 1–2, p .27–53.
994
https://doi.org/10.1016/S0025-3227(01)00289-4.
995 996 997 998
Moore, C.H., 2001. Carbonate reservoirs: porosity evolution and diagenesis in a sequence stratigraphic framework, 3. impr. ed, Developments in sedimentology 55. Elsevier, Amsterdam. Moore, C.H., Wade, W.J., 2013. Carbonate reservoirs porosity and diagenesis in a sequence stratigraphic framework, 2. impr. ed, Developments in sedimentology 67. Elsevier, New York.
999
Morad, D., Paganoni, M., Al Harthi, A., Morad, S., Ceriani, A., Mansurbeg, H., Al Suwaidi, A., Al-Aasm, I.S,
1000
Ehrenberg, S.N., 2018. Origin and evolution of microporosity in packstones and grainstones in a Lower
1001
Cretaceous carbonate reservoir, United Arab Emirates. Geological Society, London, Special Publications
1002
435, 47–66. https://doi.org/10.1144/SP435.20
1003
Moscariello, A., Pinto, D., Agate, M., 2018. Revisited play concept for distally-steepened carbonate ramps: the
1004
relevance of sediment density flows in the stratigraphic record. AAPG Search and Discovery Article
1005
#51514. AAPG Annual Convention and Exhibition, Salt Lake City, Utah.
1006
Munnecke, A., Westphal, H., Reijmer, J.J.G., Samtleben, C., 1997. Microspar development during early marine
1007
burial diagenesis: a comparison of Pliocene carbonates from the Bahamas with Silurian limestones from
54 1008
Gotland (Sweden). Sedimentology 44,p. 977–990. https://doi.org/10.1111/j.1365-3091.1997.tb02173.x
1009
Nash, M.C., Troitzsch, U., Opdyke, B.N., Trafford, J.M., Russell, B.D., Kline, D.I., 2011. First discovery of
1010
dolomite and magnesite in living coralline algae and its geobiological implications. Biogeosciences 8, p.
1011
3331–3340. https://doi.org/10.5194/bg-8-3331-2011
1012 1013
Orr, W., 1977. Geologic and geochemical controls on the distribution of hydrogen sulfide in natural gas, in: Campos, R.; Goni, J. (Eds.). Advances in Organic Geochemistry 1975, p. 571-97.
1014
Paganoni, M., Al Harethi, A., Morad, D., Morad, S., Ceriani, A., Mansurbeg, H., Al Suwaidi, A., Al-Aasm, I.S.,
1015
Ehrenberg, S.N., Sirat, M., 2015. Impact of Stylolitization on Diagenesis and Reservoir Quality: A Case
1016
Study from an Early Cretaceous Reservoir in a Giant Oilfield, Abu Dhabi, United Arab Emirates. Abu
1017
Dhabi International Petroleum Exhibition and Conference, Society of Petroleum Engineers, Abu Dhabi,
1018
UAE. https://doi.org/10.2118/177944-MS
1019
Palinkaš, S.S., Šoštarić, S.B., Bermanec, V., Palinkaš, L., Prochaska, W., Furić, K., Smajlović, J., 2009. Dickite and
1020
kaolinite in the Pb-Zn-Ag sulphide deposits of northern Kosovo (Trepča and Crnac). Clay miner. 44, 67–
1021
79. https://doi.org/10.1180/claymin.2009.044.1.67
1022
Pinto, J., Ortega, S., Martin, Z., Berrios, I., Perez, A., Pirela, M., 2011, Controls on the newly-discovered gas
1023
accumulations in the Miocene “Perla” carbonate bank, Gulf of Venezuela: A preliminary assessment: I
1024
South American Oil and Gas Congress, p. 1–4.
1025
Pirela, M., 2017. Caracterización de fluidos y estimación de la posible dirección de llenado de yacimiento. caso de
1026
estudio: Campo Perla, Cuenca del Golfo de Venezuela. Masters tesis. Universidad Central de Venezuela.
1027
134 p.
1028 1029
Plummer, L.N., 1975. Mixing of Sea Water with Calcium Carbonate Ground Water. Geological Society of America Memoir 142, p. 219-236.
1030
Pomar, L., Esteban, M., Martinez, W., Espino, D., Castillo, V., Benkovics, L., Leyva, T.C., 2015. Oligocene–
1031
Miocene Carbonates of the Perla Field, Offshore Venezuela: Depositional Model and Facies Architecture,
1032
in: Bartolini, C., Mann, P. (Eds.), Memoir 108: Petroleum Geology and Potential of the Colombian
1033
Caribbean Margin. AAPG. https://doi.org/10.1306/13531952M1083655
1034
Pöppelreiter, M., Balzarini, M.A., De Sousa, P., Engel, S., Galarraga, M., Hansen, B., Marquez, X., Morell, J.,
1035
Nelson, R., Rodriguez, F., 2005. Structural control on sweet-spot distribution in a carbonate reservoir:
55 1036
Concepts and 3-D models (Cogollo Group, Lower Cretaceous, Venezuela). AAPG Bulletin 89, p. 1651–
1037
1676. https://doi.org/10.1306/08080504126
1038 1039
Radke, B.M. and Mathis, R.L., 1980. On the Formation and Occurrence of Saddle Dolomite. Journal of Sedimentary Research, 50, p. 1149-1168.
1040
Richard, J., Sizun, J., Machhour, L., 2007. Development and compartmentalization of chalky carbonate reservoirs:
1041
the Urgonian Jura-Bas Dauphine´ platform model (Ge´nissiat, southeastern France). Sedimentary Geology
1042
198, p. 195–207.
1043
Rojas, G., Avendaño, M., De Visintini, P., Rampersad, A., Tomasi, A. Palmeri, G., Valencia, F., Pirela, J., Guaipo,
1044
M., 2015. Perla field – Cardon IV West Block: Integrated Geological and Static model. Internal Report -
1045
Cardon IV S.A. 283 p.
1046
Ronchi, P., Jadoul, F., Ceriani, A., Di Giulio, A., Scotti, P., Ortenzi, A., Previde Massara, E., 2011. Multistage
1047
dolomitization and distribution of dolomitized bodies in Early Jurassic carbonate platforms (Southern Alps,
1048
Italy):
1049
https://doi.org/10.1111/j.1365-3091.2010.01174.x
Multistage
dolomitization,
Southern
Alps.
Sedimentology
58,
p.
532–565.
1050
Rosenbauer, R.J., Koksalan, T., Palandri, J.L., 2005. Experimental investigation of CO2–brine–rock interactions at
1051
elevated temperature and pressure: Implications for CO2 sequestration in deep-saline aquifers. Fuel
1052
Processing Technology 86, p. 1581–1597. https://doi.org/10.1016/j.fuproc.2005.01.011
1053
Salas, J., Taberner, C., Esteban, M., Ayora, C., 2007. Hydrothermal dolomitization, mixing corrosion and deep
1054
burial porosity formation: numerical results from 1-D reactive transport models. Geofluids 7, p. 99–111.
1055
https://doi.org/10.1111/j.1468-8123.2006.00167.x
1056 1057 1058 1059
Saller, A., 2013. Diagenetic evolution of porosity in carbonates during burial. AAPG Search and Discovery Article #50779, Tulsa Geological Society Luncheon Meeting. Saller, A., Moore, C., 1989. Meteoric diagenesis, marine diagenesis, and microporosity in Pleistocene and Oligocene limestones, Enewetak Atoll, Marshall Islands. Sedimentary Geology 63, p. 253–272.
1060
Schulz, H.-M., Wirth, R., Schreiber, A., 2016. Organic-inorganic rock-fluid interactions in stylolitic micro-
1061
environments of carbonate rocks: a FIB-TEM study combined with a hydrogeochemical modelling
1062
approach. Geofluids 16, p. 909–924. https://doi.org/10.1111/gfl.12195
1063
Shen, A., She, M., Hu, A., Pan, L., Lu, J., 2016. Scale and distribution of marine carbonate burial dissolution pores.
56 1064 1065 1066
Journal of Natural Gas Geoscience 1, p. 187–193. https://doi.org/10.1016/j.jnggs.2016.08.003 Shinn, E., Robbin, D.M., 1983. Mechanical and chemical compaction in fine-grained shallow-water limestones. Journal of Sedimentary Petrology, v. 53 (2), p. 595-618.
1067
Skalinski, M., Kenter, J.A.M., 2014. Carbonate petrophysical rock typing: integrating geological attributes and
1068
petrophysical properties while linking with dynamic behaviour. Geological Society, London, Special
1069
Publications 406, p. 229–259. https://doi.org/10.1144/SP406.6
1070 1071
Schmoker, J. W., Halley, R. B., 1982, Carbonate porosity versus depth: a predictable relation for south Florida: Am. Assoc. Petroleum Geologists Bull., v. 66, p. 2561-2570.
1072
Spycher, N., Pruess, K., Ennis-King, J., 2003. CO2-H2O mixtures in the geological sequestration of CO2. I.
1073
Assessment and calculation of mutual solubilities from 12 to 100°C and up to 600 bar. Geochimica et
1074
Cosmochimica Acta 67, p. 3015–3031. https://doi.org/10.1016/S0016-7037(03)00273-4
1075 1076 1077 1078
Swart, P.K., 2015. The geochemistry of carbonate diagenesis: The past, present and future. Sedimentology 62, p. 1233–1304. https://doi.org/10.1111/sed.12205 Tarduno, J., Duncan, R., Scholl, D., 2002. Proc. ODP, Init. Repts., 197 p.: College Station, TX (Ocean Drilling Program) 89. https://doi.org/10.2973/odp.proc.ir.197.2002
1079
Tosca, N.J., Wright, P., 2015. Diagenetic pathways linked to labile Mg-clays in lacustrine carbonate reservoirs: a
1080
model for the origin of secondary porosity in the Cretaceous pre-salt Barra Velha Formation, offshore
1081
Brazil. Geological Society, London, Special Publications, 435, p. 33-46. https://doi.org/10.1144/SP435.1
1082
Truesdell, A.H., Kennedy, B.M., Walters, M.A., D’Amore, F., 1994. New evidence for a magmatic origin of some
1083
gases in the geysers geothermal reservoir. Proceedings, Nineteenth Workshop on Geothermal Reservoir
1084
Engineering Stanford University, Stanford, California, SGP-TR-14, p. 297-301.
1085 1086
Valencia, F., 2016. Diagénesis de los carbonatos del Campo Perla, Golfo de Venezuela: Implicaciones en las propiedades petrofísicas. Master thesis. Universidad Simón Bolívar. 178 p.
1087
Valencia, F., d’Alterio, F., 2014. Aplicaciones de la geoquímica isotópica para la determinación del origen de los
1088
gases no hidrocarburos del Campo Perla, Sub-bloque Cardón IV-Oeste. Revista Visión Tecnológica,
1089
Memorias del I Congreso Venezolano de Gas Natural (ICVGAS). Article # EX-14.
1090
Volery, C., Davaud, E., Foubert, A., Caline, B., 2009. Shallow-marine microporous carbonate reservoir rocks in the
1091
Middle East: relationship with seawater Mg/Ca ratio and eustatic sea level. Journal of Petroleum Geology
57 1092
32, p. 313–326.
1093
Wei, W., Chen, D., Qing, H., Qian, Y., 2017. Hydrothermal Dissolution of Deeply Buried Cambrian Dolomite
1094
Rocks and Porosity Generation: Integrated with Geological Studies and Reactive Transport Modeling in the
1095
Tarim Basin, China. Geofluids 2017, 1–19. https://doi.org/10.1155/2017/9562507
1096 1097
Widodo, R. W., 2018. Evolution of The Early Miocene Carbonate: Baturaja Formation in Northwest Java Basin, Indonesia [Ph.D.: Texas A&M University, 235 p.
1098
Worden, R.H., Armitage, P.J., Butcher, A.R., Churchill, J.M., Csoma, A.E., Hollis, C., Lander, R.H., Omma, J.E.,
1099
2018. Petroleum reservoir quality prediction: overview and contrasting approaches from sandstone and
1100
carbonate
1101
http://dx.doi.org/10.1144/SP435.21
communities.
Geological
Society
London
Special
Publications
435(1).
1102
Wright, P., Harris, P., 2013. Carbonate Dissolution and Porosity Development in the Burial (Mesogenetic)
1103
Environment. AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania. Article #50860.
1104
Wycherley, H., Fleet, A., Shaw, H., 1999. Some observations on the origins of large volumes of carbon dioxide
1105
accumulations
1106
https://doi.org/10.1016/S0264-8172(99)00047-1
in
sedimentary
basins.
Marine
and
Petroleum
Geology
16,
p.
489–494.
•
Deep-burial dissolution linked to basement-related hydrothermal CO2-rich fluids.
•
Microporosity development due to acid-driven dissolution mechanism.
•
Faults, fractures and dissolution seams controlling burial diagenetic alterations.
Fernando L. Valencia: Conceptualization, Methodology, Data curation, Writing- Original draft preparation, Visualization, Investigation and Editing. Juan C. Laya: Supervision, Conceptualization and Reviewing.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0264-8172(19)30596-3
DOI:
https://doi.org/10.1016/j.marpetgeo.2019.104144
Reference:
JMPG 104144
To appear in:
Marine and Petroleum Geology
Received Date: 18 September 2019 Revised Date:
15 November 2019
Accepted Date: 18 November 2019
Please cite this article as: Valencia, F.L., Laya, J.C., Deep-burial dissolution in an OligoceneMiocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development, Marine and Petroleum Geology (2019), doi: https://doi.org/10.1016/ j.marpetgeo.2019.104144. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
1 1 2 3 4 5 6 7 8 9
Deep-burial dissolution in an Oligocene-Miocene giant carbonate reservoir (Perla Limestone), Gulf of Venezuela Basin: Implications on microporosity development. FERNANDO L. VALENCIAa and JUAN C. LAYAb a Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada (e-mail: [email protected]) b Department of Geology and Geophysics, Texas A&M University, College Station, U.S.A.
10
ABSTRACT
11
Sedimentary rocks tend to progressively lose porosity with depth due to mechanical and
12
chemical compaction. In carbonates, this trend is hard to predict since many factors can create
13
porosity in the burial setting. The Oligocene-Miocene Perla Limestone, a giant gas reservoir
14
located in the Gulf of Venezuela Basin, shows a complex porosity system marked by a strong
15
diagenetic control. Despite exhaustive depositional facies modelling carried out in the carbonate
16
reservoir, inconsistencies remained when distributing petrophysical properties with depositional
17
facies. These inconsistencies become more important in areas strongly affected by intense
18
diagenetic processes. After the initial investigation, burial dissolution was identified as the main
19
diagenetic process affecting porosity in this succession. To understand the origin of the burial
20
dissolution process and its distribution along the reservoir, detailed petrographic, mineralogical
21
and isotopic studies were carried out on recovered cores from different exploration wells. Results
22
show a series of diagenetic features which were associated with the evolution of the strata
23
including burial dissolution, dolomitization and compaction as the main processes. After testing
24
several hypotheses, the results support an inorganic-CO2 model as responsible for the burial
25
dissolution process in the Perla Limestone. According to this model, deep-burial dissolution
26
created pervasive microporosity, with subordinated moldic and vuggy pores that enhanced the
27
reservoir quality in localized areas of the carbonate succession. These features are located where
2 28
the ascent of hydrothermal CO2-rich fluids funneled by discontinuity surfaces (faults, fractures,
29
stylolites, etc.) reached the Perla Limestone.
30
Keywords: Inorganic-CO2; Deep-burial dissolution; Microporosity; Diagenetic model;
31
Carbonate reservoir; Perla Limestone.
32
1. INTRODUCTION
33
The petrophysical behaviour of carbonate reservoirs is controlled by depositional and diagenetic
34
processes and their spatial interrelationship and trends (Skalinski and Kenter, 2014).
35
Depositional processes determine the initial pore-size distribution and the permeability of the
36
individual depositional facies (Choquette and Pray 1970; Lucia, 1995). Diagenetic processes are
37
responsible for most of the primary porosity and permeability modifications of the evolving
38
limestones (Moore and Wade, 2013).
39
Modern carbonate sediments are characterized by porosities of around 40 to 80 % (Enos and
40
Sawatzky, 1981), while ancient carbonate rocks usually have 3 to 35 % of porosity (Saller,
41
2013). This porosity reduction is often associated to compactional processes that occur in
42
response to the progressive increase of overburden thickness (e.g. Hamilton, 1976; Schmoker
43
and Halley, 1982; Shinn and Robbin, 1983; Croizet et al., 2013; Worden et al. 2018).
44
Nevertheless, in carbonate rocks, the expected compactional porosity loss can be substantially
45
affected by diagenetic processes creating significant volumes of porosity in the burial realm
46
(Moore, 2001).
47
Among the diagenetic processes, carbonate dissolution is considered a major controlling factor
48
of the reservoir quality in carbonate successions (Moore, 2001). It may occur at any point on the
49
diagenetic evolution of a carbonate deposit as a response to important changes in the pore-fluid
3 50
chemistry, such as variations in salinity, pCO2, pH, temperature and many other factors (Moore
51
and Wade, 2013). Carbonate dissolution is considered particularly significant in the meteoric
52
setting since meteoric waters are usually undersaturated with respect to most carbonate mineral
53
species, stimulating dissolution of metastable minerals and creating porosity (Bathurst, 1975;
54
Longman, 1980; Moore, 2001). In contrast, in the burial setting where pore water is commonly
55
in equilibrium with the host rock, processes such as acidification, fluid mixing, changes in
56
temperature or pressure are required to generate dissolution of already-stabilized minerals
57
(Moore, 2001; Esteban and Taberner, 2003; Ali et al., 2010).
58
The importance of burial dissolution creating significant porosity is a matter of a long-standing
59
debate in the literature. Several studies have reported enhanced porosity and permeability in
60
carbonate reservoirs due to burial dissolution (e.g. Pöppelreiter et al., 2005; Corbella et al., 2004;
61
Beavington-Penney et al., 2008; etc.). In contrast, Ehrenberg et al. (2012) conclude that burial
62
dissolution models are unsupported by empirical data and violate important chemical constraints
63
on mass transport. Nevertheless, recent studies on the Tarim Basin in China, reflect an
64
unquestionable impact of burial dissolution processes in the development of good reservoir zones
65
(e.g. Jiang et al., 2015; Liu et al., 2017; Wei et al., 2017).
66
The aim of this research is to understand the controls on dissolution of the Oligocene-Miocene
67
Perla Limestone reservoir, the largest gas reservoir in Latin America (Castillo et al., 2017), since
68
it shows some clear evidence of a dissolution process creating significant secondary porosity in
69
the burial realm (Borromeo et al., 2011; Castillo et al., 2017). The origin of this process is still
70
under discussion, however, several elements support the hypothesis of a burial dissolution
71
process induced by the rising of hydrothermal acidic-fluids from the basement. This research
72
included a detailed petrographic, mineralogical and geochemical study of cores recovered from
4 73
the Perla Limestone, aimed at understanding the impact of burial dissolution on the reservoir
74
quality. The results of this study will represent a novel and well-documented example of the
75
importance of burial dissolution in producing carbonate reservoirs, as well as, promote further
76
integration of diagenetic models with reservoir characterization studies in general.
77
2. GEOLOGICAL CONTEXT
78
2.1.
79
The Gulf of Venezuela Basin is characterized by a wide continental shelf limited to the north by
80
the Caribbean Sea; to the south, by the Falcón and Maracaibo basins; to the west, by the Guajira
81
Peninsula and the east, by the Paraguaná Peninsula (Fig. 1). The tectonic history of the Gulf of
82
Venezuela Basin is intrinsically connected to the evolution of the interaction between the
83
Caribbean and South American plates (Macellari, 1995). Its history shows evidence of six main
84
tectonic phases: (1) Cretaceous passive margin development, (2) late Paleocene–early Eocene
85
foredeep and consequent forebulge erosion, (3) late Eocene tectonic flexure and faulting phase,
86
(4) Oligocene–early Miocene transtensional faulting phase, (5) middle-late Miocene
87
transpressional regime and (6) Pliocene to Present Andean uplift (Audemard, 1993; Macellari,
88
1995; Escalona and Mann, 2011; Castillo et al., 2017). Because of this complex tectonic
89
evolution, two distinct structural provinces were established: the Dabajuro-Guajira and the
90
Urumaco provinces, which are separated by the Urumaco Trough (Malave and Contreras, 2013;
91
see Fig. 1).
92
The Urumaco Province comprises a thick Paleogene-Neogene sedimentary succession resting
93
directly on a Meso-Neoproterozoic granodioritic basement, with a structural style dominated by
94
NW-SE high-angle normal faults, in which the basement is involved (Baquero, 2015; Baquero et
Tectonic evolution
5 95
al., 2015; Castillo et al., 2017). During Oligocene-Miocene times, the tectonic evolution of the
96
Urumaco Province favored the deposition of the Perla Limestone atop of a Paleogene siliciclastic
97
succession; on a basement-high defined by an NW-SE trending faulted-anticline-like structure
98
(Castillo et al., 2017).
99 100 101 102
Figure 1. Structural map showing the Perla field location and the structural provinces of the Gulf of Venezuela Basin (yellow area) (modified from Malave and Contreras, 2013).
103
2.2.
104
The Gulf of Venezuela Basin is a relatively unexplored area compared with the rest of the
105
Venezuelan hydrocarbon basins and consequently lacks formal lithostratigraphy. Nevertheless,
106
some authors (e.g. Díaz de Gamero et al., 1993; Macellari, 1995; Castillo et al., 2017) have
107
integrated seismic and well data from exploration wells and correlated the stratigraphy with the
108
adjacent Falcón Basin (Fig. 2).
109
Locally in the Perla field area, the Gulf of Venezuela-strata consists of three major units
110
deposited atop of the Meso-Neoproterozoic basement (Fig. 3): (1) a Paleogene, mostly Oligocene
Stratigraphy
6 111
siliciclastic succession; (2) an upper Oligocene to lower Miocene carbonate deposit (Perla
112
Limestone); and (3) a siliciclastic-dominated succession deposited from the lower Miocene to the
113
Present (Rojas et al., 2015).
114 115 116 117 118
119
Figure 2. Chronostratigraphic chart showing the correlation between the Falcón Basin and the Gulf of Venezuela Basin in the Perla field area (compiled from Díaz de Gamero et al., 1993; Macellari, 1995; Castillo et al., 2017).
7 120 121 122
Figure 3. Seismic section showing the stratigraphic succession of the Perla field area, with the exploration wells drilled by Cardon IV, S.A. (modified from Rojas et al., 2015). An inset map in the lower-right corner indicates the orientation of the seismic section.
123
The Perla Limestone is an ca 250 m-thick carbonate succession composed by branching red-
124
algae, rhodoliths (nodular coralline red-algae) and large benthic foraminifera (LBF), with a
125
minor contribution of corals, mollusks, echinoderms, barnacles, green algae, bryozoans and
126
planktonic foraminifera (Pinto et al., 2011; Borromeo et al., 2011, 2013; Pomar et al., 2015).
127
Internally, the Perla Limestone can be subdivided into two main chronostratigraphic units, the
128
Oligocene and the lower Miocene successions (Pinto et al., 2011; Moscariello et al., 2018). The
129
Oligocene unit (upper Rupelian to Chattian) comprises inner to middle-ramp deposits, with
130
occasional interbeds of siliciclastic sediments at the bottom. In contrast, the lower Miocene unit
131
(Aquitanian-Burdigalian) is formed by middle to outer-ramp carbonates, stacked and cyclically
132
organized, that pass upward to outer-ramp facies dominated by rhodoliths with abundant
133
nannofossils and planktonic foraminifera (Borromeo et al., 2013). Based on core analysis, Pomar
134
et al. (2015) identified twelve different depositional facies in the Perla Limestone (Table 1).
135
These facies conform a distally-steepened carbonate ramp, developed in an isolated bank,
136
vertically marked by an overall deepening-upward trend, with the characteristic transgressive
137
backstepping-pattern (Pinto et al., 2011; Borromeo et al., 2013; Pomar et al., 2015).
138 139
Table 1. Depositional facies of the Perla Limestone described by Pomar et al. (2015).
SS MS PS CF SPG FG GSG CBRA FBRA RF RR
Depositional Facies Siliciclastic sandstones Mixed sandstone-carbonates Packstones-wackestones with siliciclastics Coral floatstone-rudstone Skeletal packstones and grainstones Fine skeletal grainstones Gray skeletal grainstones Coarse branching red algae floatstone-rudstone Fine branching red algae floatstone-rudstone Rhodolith floatstones Rhodolith rudstones
8 LBFR
Larger benthic foraminifer rudstones
140 141
Based on the integration of well-logs, sedimentological data, chronostratigraphic and seismic-
142
stratigraphic interpretations, Rojas et al. (2015) subdivided the Perla Limestone into seven
143
reservoir-units. From the base to top, these are the Oligocene units “O-3”, “O-4” and “O-5”;
144
overlain by the lower Miocene units “M-1”, “M-2”, “M-3” and “M-4”. O-4 is the only unit not
145
cored yet despite recognition on seismic. The reservoir units of the Perla Limestone comprise
146
different lithofacies associations and have variable thickness and geometry (see Fig. 4).
147 148 149 150
Figure 4. Reservoir units and exploration wells of the Perla Limestone. A: Oligocene and lower Miocene reservoir units of the Perla Limestone from Rojas et al. (2015). B: Structural map of the Perla Limestone showing the location of the exploration wells.
151
3. SAMPLING AND METHODS
152
Since the exploration campaign up to the present, a total of nine wells have been drilled in the
153
Perla field, by the operating company Cardon IV, S.A. Four exploration wells (P-AX, P-BX, P-
154
CX and P-DX) and five development wells. After the discovery well, P-AX, three cores were
9 155
recovered from P-BX, P-CX and P-DX wells. P-CX is placed in the crest of the structure, while
156
P-BX and P-DX are positioned in the transition to the flanks-area (Fig. 4).
157
A total of 277 samples were collected from cores and prepared for petrographic analysis (Table
158
2). The sampling was determined by the thickness of the carbonate succession in each well,
159
ensuring the coverage of the different reservoir units, as well as, a high sedimentological
160
resolution (see Table 2 for more detail). In specific cases, the sampling was incremented in zones
161
with microporosity patches (see Dissolution porosity section on the results).
162
Thin sections were impregnated with blue-epoxy and examined by conventional petrography.
163
Porosity types were identified and estimated using a comparison chart for visual percentage
164
estimation (Tarduno et al., 2002). Specific samples in areas with a higher density of
165
microporosity patches were analyzed by backscatter-electron microscopy (SEM) and
166
cathodoluminescence (CL). Additionally, core-plug helium porosity and horizontal permeability
167
data reported by Valencia (2016) were collected for later comparison and interpretations.
168
A representative subset (193 powdered samples) was selected for bulk rock stable isotope
169
analysis carbon (δ13C) and oxygen (δ18O), using isotope-ratio mass spectrometry (IRMS). The
170
isotope ratio measurement precision is ± 0.08 ‰ for δ13C and ± 0.1 ‰ for δ18O. Sub-samplings
171
via acid digestion and micro-drilling were performed, to analyze dolomites and calcite cements,
172
respectively (Table 2). All these analyses were carried out in the laboratory facilities of Eni
173
S.p.A., Repsol Technology Center and the Intevep at Petróleos de Venezuela, S.A.
174 175 176 177 178 179 180
10 181 182 183 184 185 186 187
Table 2. Sampling detail in the different cores and reservoir units. BC=blocky spar calcite cement and DOL=dolomite cement.
Analysis
Reservoir unit
M-4 M-3 M-2 Petrography M-1 O-5 O-3 M-4 M-3 M-2 Stable isotopes (C and O)
P-BX # samples [unit thickness] (sub-samples) 3 [26 m] 14 [36 m] 13 [39 m] 25 [106 m] 17 [56 m] 10 [37 m] 3 14 10 (+ 2 BC)
M-1
13
O-5
8
O-3
3 (+ 2 BC)
Core P-CX # samples [unit thickness] (sub-samples) 2 [10 m] 12 [26 m] 14 [41 m] 40 [94 m] 16 [37 m] 6 [5 m] 2 12 14 (+ 5 DOL) 39 (+ 15 DOL + 7 BC) 16 (+ 5 DOL + 1 BC) 2 (+ 2 BC)
P-DX # samples [unit thickness] (sub-samples) Not present 4 [21 m] Not present 2 [6 m] 28 [72 m] 21 [44 m] Not present 4 Not present 2 (+ 1 DOL) 28 (+ 12 DOL) 23 (+ 5 DOL)
188 189
4. RESULTS
190
4.1.
191
4.1.1. Main components (particles/grains and cements)
192
The samples analyzed contain bioclasts and carbonate cements, with minor amounts of a micritic
193
matrix, non-carbonate cements, non-carbonate grains, peloids and intraclasts. Bioclasts are
194
mostly composed by rhodoliths, branching red-algae (Corallinaceae and Sporalithaceae) and
Petrography and mineralogy
11 195
LBF (Miogypsina, Amphistegina, Heterostegina, etc.); subordinated by echinoids, planktonic
196
foraminifera, mollusks, bryozoans, barnacles, green algae and corals (Fig. 5).
197 198 199 200 201 202 203
Figure 5. Main components of the Perla Limestone. A: Ellipsoidal rhodolith (arrowed) with encrusting foraminifera. B: Red algae fragments in a bioclastic matrix (arrowed). C: LBF bioclasts (arrowed). D: Bryozoan bioclast (arrowed). E: Re-worked barnacle fragments (arrowed). F: Coral fragment almost completely replaced by calcite cement (arrowed). Scale bar is 2.5 millimeters-size.
204
Five main types of calcite cement were identified: blocky spar, microspar, syntaxial, bladed and
205
dogtooth spar calcite.
206
Blocky: Blocky calcite is the dominant cement in the Perla Limestone. It is usually not
207
luminescent under CL, with dull to bright red luminescence in very few samples of the
4.1.1.1.
Calcite cements
12 208
Oligocene units (Fig. 6b). This cement is mainly distributed in O-3, O-5 and M-1, where it can
209
reach up to 40 % volume of some samples. Blocky cement can be subdivided in blocky-1 and
210
blocky-2, based on crystal-size and occurrence. Blocky-1 consists of subhedral to anhedral
211
limpid-crystals, with diameters ranging from 50 to 250 µm (Fig. 6, 7a). It is found void-filling
212
primary inter- and intraparticle porosity, as well as, moldic-pores and post-compactional
213
features. Alternatively, blocky-2 corresponds to a scarcer version of this cement, which is
214
characterized by larger crystal-sizes (up to 2 mm in diameter) exclusively observed void-filling
215
large secondary pores and post-compactional features, such as tension gashes (Fig. 7b, d).
216 217 218 219 220 221
Figure 6. Blocky-1 under transmitted-light and CL petrography. A: Transmitted-light petrography showing blocky-1 precipitated in moldic-pore (green arrow), as well as, filling post-compactional feature (blue arrow). B: CL petrography showing blocky-1 with dull red luminescence (green arrow) and bright red luminescence (blue arrow). Scale bar is 500 micrometers-size.
222
Microspar: Microspar occurs as subhedral to anhedral microcrystals, with crystal-sizes from 5 to
223
20 µm. It is not luminescent under CL. Microspar is found either as aggregates of micropeloidal
224
matrix (microspar-1) or void-filling secondary pores (microspar-2); see Fig. 7c, 7d and 8b. Both
225
microspars are scarce but microspar-1 can be locally abundant in O-3 and O-5.
226
Syntaxial: Syntaxial rim cement appears as overgrown-crystals on echinoid spines and plates,
227
with diameters up to 250 µm-size (Fig. 7f). It is usually not luminescent under CL, except for
13 228
few samples with bright red luminescence. This cement is scarce, and its abundance is controlled
229
by the presence of echinoderms, which are more abundant in O-3 and O-5.
230
Bladed and dogtooth spar: They consists of non-isopachous crystal rims growing around the
231
external and internal walls of determined bioclasts, such as of foraminifera tests and echinoids
232
spines (Fig. 7f). Also, they are occasionally preserved like internal rims within macroborings
233
(Fig. 8). Bladed cement has individual crystal-sizes under 10 µm in diameter, while, dogtooth
234
consists of larger crystals (up to 20 µm), with a more prismatic habit that locally develops
235
scalenohedral geometry (Fig. 7e). Under CL, these cements are non-luminescent. Bladed and
236
dogtooth cement are rare but scattered along the Perla Limestone.
237 238 239
Figure 7. Calcite cements identified in the Perla Limestone samples. A: Blocky-1 filling mollusk mold (arrowed). B: Blocky-2 precipitated in tension gashes (arrowed). C: Microspar-1 replacing the micritic-
14 240 241 242 243
matrix (arrowed). D: Blocky-2 and microspar-2 void-filling secondary porosity in red-algal fragment. E: Bladed calcite cement well-preserved in a benthic foraminifera bioclast (internally and externally). F: Syntaxial and dogtooth cement developed in echinoderm fragments. Scale bar is 200 micrometers-size.
244 245 246 247 248
Figure 8. Bladed and microspar cements. A: Bladed cement (green arrow) as internal rim in Gastrochaenolites ichnotaxon (red arrow) that preserves its producer (bivalve; blue arrow). B: Microspar1 (green arrow) associated with a rounded pellet (blue arrow), engulfed by Blocky-1 (red arrow). Scale bar is 500 micrometers-size.
249 250
4.1.1.2.
Dolomite
251
Petrography and SEM analysis allowed the recognition of three types of dolomite based on
252
crystal-size and textural features: DOL-1, DOL-2 and DOL-3.
253
DOL-1: DOL-1 consists of replacive microcrystalline dolomite, with anhedral to subhedral
254
crystals less than 5 µm in size. It is precipitated as internal rims within the red-algae cell-walls
255
(Fig. 9a). Under CL, DOL-1 shows bright red luminescence (Fig. 10). DOL-1 is scarce (< 5 % of
256
rock volume) but scattered throughout the carbonate succession.
257
DOL-2: DOL-2 refers to a microcrystalline to finely crystalline dolomite cement, with euhedral
258
to subhedral crystals up to 30 µm-size. It is both void-filling red-algae moldic-pores and partially
259
replacing the micritic-matrix nearby pressure-dissolution seams (Fig. 9b, c, d). Under CL, DOL-
260
2 crystals show a non-luminescent to dull red luminescent core, with a bright red luminescent
261
rim of variable size (Fig. 10). DOL-2 is visibly the dominant type of dolomite in the Perla
15 262
Limestone. In general, it accounts for less than 5 % of the rock volume in M-4 and M-3, 5 to 10
263
% in M-2 and 10 to 30 % in the underlying units. It can be locally abundant (≈ 30 % of rock
264
volume) in specific zones of the Oligocene units with high-concentration of pressure-dissolution
265
seams.
266
DOL-3: DOL-3 consists of a medium to coarse-crystalline dolomite cement, with individual
267
crystals in size from 30 to 100 µm (Fig. 9d). It is typically found void-filling moldic-pores
268
adjacent to pressure-dissolution seams, in association with DOL-2. Under CL, DOL-3 shows
269
zoned rhombs with four zones, a non-luminescent to bright red luminescent core, a bright red
270
luminescent middle zone and a dull red outer zone, with a lighter red luminescent overgrowth
271
rim (Fig. 10). DOL-3 is volumetrically minor and usually accounts for less than 5 % of the total
272
rock volume. Rare samples have warped crystal wedges than can suggest a saddle dolomite
273
variety (e.g. Radke and Mathis, 1980).
274 275 276
Figure 9. SEM images showing the dolomites recognized in the Perla Limestone samples. A: DOL-1 precipitated as rims within the red algae cell-walls. B: DOL-2 void-filling enlarged intraparticle pores in
16 277 278 279
280 281 282 283 284 285 286 287
red algae fragment. C: DOL-2 and DOL-3 void-filling intraparticle pore in red algae fragment. D: DOL-2 filling a stylolite-surface, accompanied by framboidal pyrite. Scale bar is 30 micrometers-size.
Figure 10. Dolomites of the Perla Limestone under CL. A: Enlarged-intraparticle pore within a red algae fragment, void-filled by DOL-2 crystals engulfed by blocky-1. The DOL-2 crystals show a nonluminescent to dull red luminescent core, with bright red luminescent rim. B: Fracture filled by DOL-3 crystals showing rhombs with four zones, a non-luminescent to bright red luminescent core, a bright red luminescent middle zone and a dull red outer zone, with a lighter red luminescent overgrowth rim. C: Red algae bioclast partially replaced by bright red luminescent DOL-1 crystals, associated with DOL-2. Scale bar is 50 micrometers-size.
288 289
4.1.1.3.
Other cements
290
Non-carbonate cements in the Perla Limestone include pyrite, fluorite, sphalerite, galena, barite,
291
clays, iron-oxyhydroxides, apatite and quartz. Pyrite cements occur in framboidal and finely
292
crystalline forms. The framboidal pyrite occurs along pressure-dissolution surfaces and void-
293
filling primary/secondary micropores. In contrast, the finely crystalline pyrite is strictly
17 294
precipitated in the vicinity of pressure-dissolution seams (Fig. 11a, b, d, e). Pyrite is scattered but
295
relatively more abundant in M-3 and M-4.
296
Fluorite cement occurs as traces in O-3, O-5, M-1 and M-2. It consists of fine crystals and
297
aggregates up to 50 µm-size, which are usually filling secondary pores (Fig. 11f). Likewise,
298
microcrystalline traces of sphalerite, galena and barite cement occur within secondary pores (Fig.
299
11b and e). In general, sphalerite, galena, barite and pyrite occur as ephemeral mineralization
300
halos. These halos show parallel to sub-vertical spatial disposition respect the main pressure-
301
dissolution surfaces. Also, they are usually found in association with DOL-2 (Fig. 11c).
302
Traces of kaolinite, illite, smectite and rare organic matter are frequently accumulated along
303
pressure-dissolution surfaces. On the other hand, a kaolinite-polytype recognized as dickite is
304
found filling intraparticle pores and stylolite-related microfractures (Fig. 11c, d). Dickite differs
305
from other kaolinite-polytypes due to its blockier and more euhedral crystals (Ehrenberg et al.,
306
1993).
307 308 309 310
18
311 312 313 314 315 316 317 318 319 320 321
Figure 11. SEM photomicrographs showing different non-carbonate cements present in the Perla Limestone. A: framboidal pyrite cement precipitated along stylolite-surface filled with blocky-2. B: Finely crystalline pyrite with galena inclusions precipitated along a vein, in the vicinity of a stylolite filled with DOL-2. C: Dickite crystals with a blocky-booklet habit, precipitated in interparticle pore filled with blocky-2. D: Framboidal pyrite, DOL-2 and dickite precipitated in dissolution-enlarged interparticle pore. E: Sphalerite, DOL-2 and pyrite precipitated in vuggy pore. F: Vein filled with DOL-2 and fluorite cement. Scale bar is 100 micrometers-size.
19 322
4.1.2. Porosity types
323
Petrographic analyses allowed the identification and quantitative estimation of nine main pore-
324
types (Table 4). They were classified using the carbonate porosity classifications of Choquette
325
and Pray (1970), Kaczmarek et al. (2015) and Hashim and Kaczmarek (2019), as guides. From a
326
total of nine pore types, two represent primary depositional porosity (interparticle and
327
intraparticle), while the rest corresponds to secondary porosity.
328 329 330 331 332 333
Table 3. Pore-type distribution in the Perla Limestone. A (abundant) = 20–30 %, C (common) = 10-20 %, F (frequent) = 5-10 %, O (occasional) = 1-5 %; n/p = traces or not present. IP: interparticle porosity; WP: intraparticle porosity; MO-A: moldic porosity associated with former aragonitic bioclasts; MO-HMC: moldic porosity associated with former high-Mg calcite bioclasts; VUG: vuggy porosity; IX: intercrystalline porosity (dolomites); mFr: microfracture porosity; BO: boring porosity. Porosity types
P-BX
Unit M-4 M-3 M-2 M-1 O-5 O-3
P-CX
Unit M-4 M-3 M-2 M-1 O-5 O-3
P-DX
Unit M-3 M-1 O-5 O-3
IP
WP
MO-A
Microporosity
C C O O O n/p
C C O O O n/p
O O O O n/p n/p
F F C F F O
IP
WP
MO-A
Microporosity
C C O O n/p n/p
C C O O O n/p
n/p O O n/p n/p n/p
F C A C F O
IP
WP
MO-A
Microporosity
n/p n/p n/p n/p
n/p n/p n/p n/p
O O n/p n/p
O O F F
MO-HMC
VUG
IX
mFR
BO
n/p n/p O O n/p n/p
n/p O O O O F
O O n/p O O n/p
O n/p n/p n/p n/p n/p
VUG
IX
mFR
BO
n/p n/p F O n/p O
n/p O O F O F
O O n/p n/p O O
O O O n/p n/p n/p
MO-HMC
VUG
IX
mFR
BO
O O O O
n/p n/p n/p n/p
n/p O O O
O O O O
n/p n/p n/p n/p
F O C F O O Porosity types MO-HMC
O F C F O O Porosity types
Total porosity (%, by visual estimation) 30 - 40 20 - 30 20 - 30 15 - 25 10 - 20 5 - 10 Total porosity (%, by visual estimation) 30 - 40 30 - 40 40 - 50 20 - 30 10 - 20 5 - 10 Total porosity (%, by visual estimation) 5 - 10 5 - 10 10 - 15 10 - 15
20
334 335 336 337 338 339 340 341 342 343
Figure 12. Thin-section photomicrographs of porosities in the Perla Limestone. A: Interparticle porosity (IP) between bioclasts and intraparticle porosity (WP) within LBF bioclasts, barnacles, among others. B: Vuggy porosity (VUG), moldic porosity associated with former HMC-bioclasts (MO-HMC) and intercrystalline porosity (IX) in partially dolomitized red-algal rich sample; the opaque mineral was identified as pyrite. C: Moldic porosity related to aragonitic bioclasts (MO-A) developed from former gastropods. D: Pervasive microporosity indistinctly affecting bioclasts, matrix and cement and forming dissolution vugs. E: Microporosity and vuggy porosity (VUG) developed from the dissolution of blocky-1 cement. Scale bar is 500 micrometers-size.
4.1.2.1.
Primary porosity
344
The interparticle porosity is abundant in the uppermost lower Miocene units (Table 3). It consists
345
of pore-space with diameters ranging from 10 to 500 µm; depending on both the associated type
346
of bioclasts and the degree of mechanical compaction (Fig. 12a). Likewise, the intraparticle
21 347
porosity shows different sizes depending on the type of bioclast. It usually ranges from 10 to 30
348
µm in diameter in red algae, 50 to 100 µm in LBF and 100 to 250 µm in larger bioclasts such as
349
bryozoans (Fig. 12a). The intraparticle pores show a similar distribution pattern than the
350
interparticle pores (Table 3). Both pore-types remain very well preserved in P-BX and P-CX but
351
obliterated in P-DX.
352
4.1.2.2.
Dissolution porosity
353
The porosity associated with dissolution processes is the focus of this article. Petrographic
354
observations on the Perla Limestone recognized four main types of dissolution porosity:
355
(1) a fabric-selective dissolution porosity characterized by molds up to 600 µm-size, created by
356
dissolution and collapse of aragonitic fossils (Fig. 12c).
357
(2) a fabric-selective dissolution porosity characterized by molds ranging from less than 10 to
358
200 µm-size, formed by dissolution-enlarged intraparticle pores within former high-Mg calcite
359
(HMC) bioclasts such as red-algae fragments and LBF (Fig. 12b, 13a, 13b).
360
(3) a non-fabric selective microporosity, with pore-sizes under 10 µm, associated with granular-
361
subhedral textures, which is indistinctly affecting bioclasts, matrix and cements (Fig. 12d, 12e,
362
13a, 14, 21c, 21d).
363
(4) a non-fabric selective vuggy porosity, with pores ranging from 5 to 250 µm in diameter,
364
derived by dissolution-enlarged interparticle and intercrystalline pores (Fig. 12b, 12d, 12e, 13b,
365
13c, 14).
366
Microporosity is the dominant secondary pore type in the Perla Limestone (Table 3). This
367
microporosity could be classified as granular microporosity, due to its textural similarities with
368
the petrophysical pore type (granular microporosity - Type I) defined by Kaczmarek et al.
22 369
(2015). The microporosity is mainly distributed in the lower Miocene units of the P-CX and P-
370
BX; specifically, in the section between the topmost part of M-1 and the basal area of M-3. In
371
contrast, in the P-DX it is scarce but present in the Oligocene units (Table 3). Moreover,
372
microporosity is frequently observed in association with vuggy porosity, intercrystalline porosity
373
and moldic porosity in former HMC bioclasts (Fig. 12d, 12e and 13a). These porosities form
374
microporous to finely porous assemblages that can be macroscopically recognizable in cores, by
375
the presence of light beige to whitish patches, characterized by chalky-like texture (Fig. 14, 15a,
376
15b). These microporous patches are commonly associated with major stylolitic surfaces (Fig.
377
15b). However, in the P-CX core, they do not show any preferential distribution but instead, are
378
rather broad and diffuse (Fig. 15a).
379
On the other hand, the moldic porosity created by dissolution and collapse of aragonitic fossils is
380
poorly preserved. It tends to be scarce in the lower Miocene units and very rare in the Oligocene
381
units of the Perla Limestone (Table 3).
382
4.1.2.3.
Dolomite-related porosity
383
This porosity corresponds to a fabric-selective intercrystalline microporosity, with less than 10
384
µm pore-size, developed between dolomite crystals that partially replaced the micritic-matrix
385
(Fig. 12b). It is mainly distributed in O-3, O-5, M-1 and M-2, specifically in areas dominated by
386
pressure-dissolution surfaces.
387
4.1.2.4.
Other types of porosity
388
In addition to the pore-types described above, two other minor secondary pore-types were
389
identified (Table 3). These are boring porosity and microfracture porosity. The boring porosity is
390
characterized by a rounded shape, with pore sizes from 30 to 500 µm and is locally present in red
391
algae fragments (Fig. 8a, 13c). The microfracture porosity is formed by 5 to 50 µm-size pores,
23 392
typically in elongated bioclasts, as well as, cross-cutting blocky-1 cement and stylolites (Fig.13a,
393
c, d).
394 395 396 397 398 399
Figure 13. Thin-section photomicrographs of porosities in the Perla Limestone. A: Coeval microporosity, moldic (MO-HMC) and microfracture porosity (mFR). B: Vuggy porosity (VUG) postdating blocky-1 and a preceding syntaxial cement associated with an echinoderm. C: Boring (BO), microfracture (mFR) and vuggy (VUG) porosities associated with red-algal fragment. D: Late generation of microfractures cross-cutting bioclasts, stylolites and blocky-1 (red-arrow). Scale bar is 500 micrometers-size.
24
400 401 402 403 404
Figure 14. Macrograph and photomicrograph (magnification = 1000x) of the P-CX core affected by the dissolution porosity (chalky-like texture), with occurrences of microporosity and vuggy porosity. Corroded non-sutured dissolution seam with clayey infilling is arrowed. The core is 10 centimeters wide.
405 406 407 408 409
Figure 15. Macrographs of the P-CX (left) and P-BX (right) cores. A: Area in the M-2 unit of the P-CX affected by dissolution porosity (delimited by dashed lines). B: Area in the M-2 unit of the P-BX affected by dissolution porosity (delimited by dashed lines) linked to pressure-dissolution surfaces (red arrow). Individual bottom-cores are 10 centimeters-wide.
25 410
4.1.3. Porosity and permeability data from core-plugs
411
Helium porosity and horizontal permeability data from core-plugs analysis were collected and
412
plotted to compare values and trends along with the different units of the carbonate succession
413
(see Fig. 16 and Table 4). The P-CX well has the highest reservoir quality of the analyzed wells,
414
followed by the P-BX and the P-DX, respectively. Also, in general, the lower Miocene units
415
show the highest porosities and permeabilities of the carbonate succession. However, in the P-
416
DX the higher porosity and permeability values belong to the Oligocene reservoir units.
417
Moreover, it is also interesting to notice that highly microporous zones (chalky-like texture) tend
418
to have higher porosity and permeability values (Fig. 16).
26
419 420 421 422 423 424 425 426 427 428 429 430 431 432
Figure 16. Helium porosity and horizontal permeability data from core analysis performed on the Perla Limestone (compiled from Valencia, 2016). Superimposed zones with higher abundance of microporosity (chalky-like patches) were visually recognized in the present study.
27 433 434 435 436 437
Table 4. Range of distribution, median and average of helium porosity and horizontal permeability by reservoir unit in the Perla Limestone (reported by Valencia, 2016). Core
P-BX
P-CX
P-DX
Unit
Thickness (m)
M-4 M-3 M-2 M-1 O-5 O-3 M-4 M-3 M-2 M-1 O-5 O-3 M-3 M-1 O-5 O-3
26 36 39 106 56 37 10 26 41 94 37 5 4 2 28 21
Helium Porosity (%) Range Median Average 14 - 28 24.1 22.4 8 - 29 15.6 16.1 7 - 38 17.6 19.6 8 - 37 18.0 18.7 5 - 35 19.3 19.3 4 - 28 16.0 15.7 19 - 31 28.7 27.7 10 - 31 22.0 21.4 13 - 42 29.3 27.3 8 - 38 21.4 21.4 7 - 34 17.3 18.5 4 - 20 11.2 11.0 2 - 12 6.8 6.9 5 - 12 7.3 8.3 6 - 32 20 20.4 3 - 36 15 14.4
Horizontal permeability (mD) Range Median Average 3 - 57 17.8 24.5 0 - 484 2.9 27.8 0 - 96 0.8 4.5 0 - 23 0.7 1.4 0 - 11 0.8 1.6 0-6 0.4 0.4 6 - 322 14.4 40.5 1 - 671 15.0 50.8 0 - 278 12.1 28.4 0 - 37 0.8 2.4 0-3 0.5 0.8 0 - 21 0.3 2.4 0 - 25 0.0 2.0 0-4 0.0 0.5 0 - 122 0.8 2.0 0-4 0.2 0.5
438
4.1.4. Other diagenetic features
439
In addition to the diagenetic cements and neomorphic textures described above, several other
440
diagenetic features such as borings, fractures, pressure-dissolution surfaces and overgrowth pores
441
were recognized in the Perla Limestone.
442
4.1.4.1.
Borings
443
Petrographic analyses allowed the identification of macroborings, microborings and micritic
444
envelopes caused by microbial micritization. Based on morphological analysis, macroborings
445
ichnotypes such as Entobia isp., Trypanites isp. and Gastrochaenolites isp. occur in the Perla
446
Limestone. The Entobia traces seem to be most abundant. They show single and multiple
447
chambers, with an irregular-rounded to sub-angular shape. Diameter ranges from 0.5 to 2 mm-
448
size (Fig. 17a). The Trypanites is represented by a singular elongated and straight boring tube,
449
with an approximately constant diameter (0.5 to 1 mm) and rounded termination (Fig. 17a). The
28 450
Gastrochaenolites traces are characterized by a sub-ellipsoidal chamber that can reach up to 2
451
mm in diameter (Fig. 8a, 17b).
452 453 454 455 456 457 458
Figure 17. Thin-section photomicrographs showing the different macroboring ichnotypes in red algae bioclasts from the Perla Limestone. A: Trypanites and Entobia ichnotypes in red algae fragment. B: Gastrochaenolites ichnotaxon containing valves of its producer (bivalve shells). Scale bar is 2.5 millimeters-size.
459
The deformation features observed in the Perla Limestone have been classified into two major
460
groups: fractures and pressure-dissolution surfaces. Fractures with variable length were
461
recognized (Fig. 13a, c, d). Most of them correspond to microfractures (grain breakages)
462
affecting elongated or flat grains, such as branching red-algae, mollusks and barnacles. They are
463
usually infilled by blocky-1, however, in the uppermost units, they are frequently open and
464
connecting previously isolated pores. A later generation of microfractures is found cross-cutting
465
stylolites and blocky-1 cement (Fig. 13d).
466
Pressure-dissolution surfaces comprise sets of non-sutured seams and stylolites. The non-sutured
467
seams are dominant. They are laterally continuous on core-scale (cm-size), with wispy-surfaces
468
parallel to sub-parallel to the bedding plane (Fig. 18a, c). Also, they are sporadically associated
4.1.4.2.
Deformation features
29 469
with secondary networks of micro-stylolites. In contrast, the stylolite surfaces are characterized
470
by horizontal to pseudo-horizontal sets of low to high-amplitude jagged-surfaces, which are
471
laterally continuous at the core-scale (Fig. 18b, d). Tension gashes and microfractures are often
472
associated with the stylolite-surfaces. Likewise, rare vertical stylolites are also present. Variable
473
amounts of non-carbonate cements and rare organic matter were preferentially accumulated in
474
both non-sutured seams and stylolites (Fig. 18a, b, c).
475 476 477 478 479 480 481
Figure 18. Thin-section photomicrographs and photo-macrographs showing pressure-dissolution features in the Perla Limestone. A (photomicrograph) and C (phot-macrograph): Non-sutured dissolution seams (arrowed), with parallel to sub-parallel surfaces infilled by insoluble material. B: Saturated contact between LBF bioclasts. D: High-amplitude sub-parallel to sub-perpendicular stylolites: Yellow-scale bar is 500 micrometers-size.
482
4.2.
483
δ13C and δ18O isotope analysis were performed on bulk samples (Fig. 19). Therefore, these
484
isotopic values only represent a mixture of original values (unaltered grains), variably altered
Stable carbon and oxygen isotopes
30 485
grains and cements. However, in some instances, it was possible to separate and analyze
486
dolomites (undifferentiated) and blocky-2 cement.
487
δ13C ratios in the bulk samples vary from -8.89 to +1.10 ‰ (V-PDB), with an average of slightly
488
positive values (+0.12 ‰), and a few strongly depleted values in the Oligocene units. The δ18O
489
composition varies from -7.48 to -0.72 ‰ (V-PDB), with most of the samples ranging from -3.00
490
to -1.5 ‰.
491 492 493 494
Figure 19. δ18O vs. δ13C ratios in calcite (bulk), dolomites and blocky-2 cement from the Perla Limestone. Group A, B and C denote possible dolomite families. Green dashed-line include strongly depleted 13C values from the O-3 unit in the P-DX.
495
Blocky-2 samples show δ13C ratios from -1.62 to +0.69 ‰ (V-PDB). While the δ18O values
496
range from -8.15 to -4.51 ‰ (V-PDB). The 18O values are strongly depleted compared with the
497
host rock (Fig. 19). The average δ18O ratio of blocky-2 cement is -6.2 ‰ (V-PDB), while the
498
average of the bulk samples analyzed is -3.1 ‰ (V-PDB). On the other hand, δ13C ratios are
499
comparatively similar to their analogue bulk samples.
31 500
Dolomite samples show δ13C ratios from -8.51 to +1.33 ‰ (V-PDB). While the δ18O values
501
range from -12.51 to -0.02 ‰ (V-PDB). When these values are plotted in a δ18O vs. δ13C cross-
502
plot graph, they show a positive correlation and seem to be clustered into three main groups:
503
Group-A, Group-B and Group-C (Fig. 19). Group-A (δ13C: -0.10 to +1.33 ‰; δ18O: -1.65 to -
504
0.02 ‰) is characterized by slightly positive δ13C ratios and less negative δ18O values, compared
505
with the host rock. Group-B (δ13C: -2.97 to -0.13 ‰; δ18O: -6.34 to -2.49 ‰) consists of
506
dolomites with more depleted 13C and slightly depleted 18O than the bulk samples. On the other
507
hand, Group-C (δ13C: -8.51 to -4.22 ‰; δ18O: -12.51 to -8.82 ‰) is characterized by dolomites
508
strongly depleted in 13C and 18O, when compared with the host rock. The dolomites from Group-
509
A are distributed along the entire carbonate column, while dolomites from Group-B and Group-C
510
are mainly distributed from O-3 to M-2.
511 512 513 514 515 516
32 517
5. DISCUSSION
518
5.1.
519
The Perla Limestone has experienced a complex sequence of diagenetic modifications associated
520
with four main diagenetic environments: marine, meteoric, shallow-burial and deep-burial
521
environment (Fig. 20).
Paragenesis of the Perla Limestone
522 523 524
Figure 20. Paragenetic scheme of the diagenetic processes occurred in the near-surface, shallow-burial and deep-burial environments that modified the petrophysical properties of the Perla Limestone.
525
5.1.1. Early diagenetic stages (marine and ephemeral meteoric environment)
526
Diagenetic processes started early in the depositional setting. The first diagenetic modifications
527
in the marine environment were bioerosion and microbial micritization, evidenced by the
33 528
presence of different boring ichnotypes in red-algae fragments (Fig. 17). The boring activity
529
predates most of the early marine cementation, as per the presence of bladed and dogtooth
530
cements precipitated within macroborings (Fig. 8a). The bioerosion process was dominated by
531
the activity of sponges (Entobia), while the microbial micritization process was probably
532
induced by the activity of fungus/bacteria (e.g. Checconi et al., 2010). These diagenetic events
533
enhanced the primary porosity in the red algae-rich facies of the Perla Limestone. In contrast,
534
early marine cementation reduced porosity. However, considering the scarcity of early marine
535
cements, their impact on the pore network is considered minor.
536
An early, fabric-selective dissolution process was also documented. This process was responsible
537
for creating moldic pores as the result of mineral stabilizations in the early diagenetic
538
environment. However, during the mineral stabilization process, the aragonite and HMC
539
bioclasts did not follow the same alteration pathway. The dissolution of aragonite skeletal
540
fragments created complete molds of the former bioclasts, resulting in no preservation of the
541
original texture (Fig. 12c). In contrast, the stabilization of HMC bioclasts (red-algae and LBF)
542
resulted in excellent preservation of the primary texture (Fig. 12b, 13a, 13d). The textural
543
preservation of HMC bioclasts during diagenesis is commonly explained by an incongruent
544
dissolution process, which considers that the dissolution of HMC grains and subsequent
545
precipitation of calcite with lower concentration of Mg, occur across thin reaction films, with the
546
two reactions barely separated in time (Bathurst, 1975; Budd, 1992; Bischoff et al., 1993).
547
Although the mineral stabilization process is typical of the meteoric environment (Bathurst,
548
1975; Longman, 1980; Moore, 2001), the absence of substantial meteoric alteration, only locally
549
identified in the Oligocene units, suggests a dissolution process that occurred in marine or
34 550
slightly modified marine waters at or near the sea-floor (e.g. Melim et al., 1995; Knoerich and
551
Mutti, 2003; Swart, 2015).
552
Scarce to rare meteoric alterations are present at some levels in the Oligocene units O-3 and O-5
553
in the P-CX well, and the O-3 unit in the P-Bx and P-DX. The main evidence of these shallowing
554
episodes includes: (1) rare dissolution macro-cavities infilled either by mixed carbonate-
555
siliciclastic deposits in the P-BX and P-CX cores; and (2) strongly depleted
556
lowermost section (O-3) of the P-DX (Fig. 17). Depleted
557
occurrence of greenish siliciclastic sandstones lithofacies (SS), associated with ephemeral
558
subaerial exposures episodes during the Oligocene, according to Pomar et al. (2015). However,
559
given the scarcity of the meteoric alterations in the Perla Limestone, their impact on the reservoir
560
quality seems to be limited.
561
Petrographic and SEM analysis also allowed the recognition of an early dolomitization process
562
(DOL-1). This dolomitization pre-dates the precipitation of blocky-1, in accordance with spatial
563
relationships (Fig. 8a). Presumably, this dolomitization process has occurred by redistribution of
564
available magnesium coming from red-algal mineralogical stabilization (e.g. Land and Epstein,
565
1970). However, a primary origin, biologically mediated by the red algae is not discarded (e.g.
566
Nash et al., 2011).
567
Unfortunately, it was not possible to physically separate the three different types of dolomite
568
recognized by petrography and SEM, for geochemical purposes (δ18O and δ13C). Interestingly,
569
however, three groups of dolomites can be defined based on their isotopic print: Group-A,
570
Group-B and Group-C (Fig. 17). On the basis that the δ18O ratio in carbonates is considered
571
inversely proportional to the temperature of crystallization (Hudson, 1977; Swart, 2015), it
572
would be reasonable to assume that the earliest stage of dolomitization (DOL-1) corresponds to
13
13
C values in the
C values are consistent with the
35 18
573
the Group-A. Whereas, more
O-depleted groups, would correspond to later diagenetic
574
dolomites (DOL-2 and DOl-3).
575
Assuming that DOL-1 precipitated from the same waters than the host-rock, the “average DOL-
576
1” would have precipitated at similar but slightly higher precipitation temperature than the
577
“average bulk calcite” in the Perla Limestone (36
578
O’Neil, 1997 and Craig, 1965).
579
5.1.2. Shallow-burial environment
580
The dissolution process of unstable minerals eventually leads to supersaturation of the fluid with
581
respect to low-Mg calcite (LMC) and to the subsequent precipitation of LMC-cement (Moore,
582
2001). As a result, significant precipitation of calcite cement should occur in the transition
583
between the near-surface to the shallow-burial environment. This process is documented in the
584
Perla Limestone by the precipitation of blocky-1 within pre-existent interparticle, intraparticle,
585
moldic (aragonitic grains), boring pores, as well as, filling post-compactional features (Fig. 6,
586
7a). Blocky-1 destroyed most of the primary and early-secondary porosity in the lowermost
587
units. In contrast, in the uppermost units (M-3 and M-4), the primary and early-secondary
588
porosity remained well preserved.
589
Microspar formation is believed to have occurred in two different diagenetic stages. Petrographic
590
evidence suggests an early version of microspar (microspar-1), which is the product of
591
replacement process, with the partial dissolution of a precursor micritic-matrix and subsequent
592
microspar precipitation (e.g. Folk, 1965; Longman, 1977; Lucia and Loucks, 2013). The
593
presence of microspar-1 engulfed by blocky-1 reveals its early diagenetic nature (Fig. 8b). In
594
contrast, a later version of microspar (microspar-2), considered a primary microspar cement (e.g.
C vs. 30
C; using the equations in Kim and
36 595
Munnecke et al., 1997; Melim et al., 2002), is found precipitated in dissolution-enlarged
596
intraparticle pores in association with DOL-2 (Fig. 7d).
597
The progressive and increased incidence of mechanical compaction generated an expected
598
porosity-reduction in the Perla Limestone (e.g. Hamilton, 1976; Croizet et al., 2013). However,
599
this process affected the reservoir in different ways. Early-cemented units (e.g. O-3 and O-5)
600
were generally less compacted than the poorly/non-cement units (e.g. M-3 and M-4). Also, in
601
these poorly/non-cemented units, the microfractures were usually found connecting previously
602
isolated interparticle and intraparticle pores; thus, increasing permeability (Fig. 13c).
603
Microfractures and fractures occurred at different diagenetic stages in the Perla Limestone. Some
604
early microfractures predate the blocky-1 precipitation. While others are found orthogonally
605
cross-cutting pressure-dissolution features (Fig. 13d); thus, representing a later diagenetic event.
606
5.1.3. Deep-burial environment
607
Postdating the first stages of mechanical compaction, the Perla Limestone started to experience
608
an intense chemical compaction process that created numerous pressure-dissolution features,
609
such as non-sutured seams and stylolites, at both microscopic and macroscopic level (Fig. 14,
610
15b, 18). This process reduced the porosity volume in the Perla Limestone (e.g. Croizet et al.,
611
2013). However, it could also have created discontinuity surfaces that served as conduits for
612
diagenetic fluids responsible for later dissolution processes (e.g. Paganoni et al., 2015; Barnett et
613
al., 2015). This can be supported by the presence of some corroded pressure-dissolution seams
614
constraining the dissolution timing to be post-stylolitization (Fig. 13a, 14, 15b).
615
The presence of DOL-2 and DOL-3 associated with ephemeral base-metal sulphide
616
mineralization in the vicinity of pressure-dissolution surfaces, as well as, in dissolution pores
37 617
created during the first stages of pressure-dissolution deformation, suggests a dolomitization and
618
sulphide mineralization either coeval or post-dating the chemical compaction process. This
619
interpretation can be supported by dolomite samples with depleted 18O values (Group-B and C in
620
Fig. 19), which reveals their late diagenetic origin (e.g. Lavoie et al., 2005; Lonnee and Machel,
621
2006).
622
CL analysis revealed that DOL-3 crystals are composed by zoned rhombs that seem to be DOL-2
623
crystals with an overgrown dull red middle-outer zone and lighter red luminescent rim (Fig.
624
10b). Based on this assumption, DOL-3 would be a late diagenetic overgrown phase of DOL-2.
625
This interpretation can be also supported by the fact that the DOL-3 crystals are not affected by
626
the late burial dissolution process compared to the DOL-2 crystals (21a, b); thus, representing a
627
later diagenetic phase. The dolomites with strongly depleted
628
could represent the DOL-3 observed in thin sections. However, more analyses are required.
629
Interestingly, the occurrence of high-temperature dolomites (DOL-2 and DOL-3), seems to be
630
genetically controlled not only by the presence of pressure-dissolution features but the red-algae
631
content. Moreover, it can be noticed that dolomite-replaced matrix is only present in the
632
surrounding areas of red-algae bioclasts when these are affected by the pressure-dissolution
633
process. Base on that, a compactional dolomitization model, where the increment of temperature
634
with depth, favors dolomitization by removing the kinetic barriers that inhibit dolomitization is
635
considered. A common weakness of the burial compaction model is the supply and transport of
636
magnesium ions (Lonne, 1999). However, in the case of the Perla Limestone, remobilized
637
magnesium ions from red-algal rich facies and/or Mg-rich compactional brines from the
638
underlying Paleogene-siliciclastic succession, funneled by pressure-dissolution features and/or
18
O values (Group-C in Fig. 19)
38 639
fault and fractures are considered to have induced the burial dolomitization process (e.g. Ronchi
640
et al., 2011).
641
An alternative structurally controlled hydrothermal dolomitization model (e.g. Davies and Smith,
642
2006) is not discarded. However, the absence of saddle dolomite (only present as traces in some
643
dolomitized samples) seems not to be compatible with this model. The authors consider that
644
further investigation regarding fluid inclusions, isotopes and epifluorescence in the Perla
645
Limestone dolomites is required.
646
The burial dolomitization process was responsible for the creation of intercrystalline porosity,
647
which is an important type of porosity in the Perla Limestone. It is mainly distributed in units O-
648
3, O-5, M-1 and M-2 (see Table 3). The burial environment was also the site of a significant
649
dissolution process that created pervasive microporosity. This topic will be discussed later in
650
detail in the burial dissolution section.
651
The arrival of organic gases from the source rock to the reservoir seems not to have a major
652
impact in the diagenetic evolution of the carbonate succession. Physical evidence of bitumen was
653
not recorded in the Perla Limestone samples. However, epifluorescence imaging analysis would
654
be required to confirm its absence. According to Pirela (2017), the source rock of the
655
hydrocarbons present in the Perla field is a geochronologic equivalent of the Agua Clara Fm.
656
(Falcón Basin) that reached the hydrocarbon generative window in the deepest zone of the
657
Urumaco Trough, located at the south-eastern area of the structure (see Fig. 1 and 2 for spatial
658
and stratigraphic reference). In addition, Castillo et al. (2017) based on geochemical data
659
indicated that the gas present in the Perla field was generated from the latest late Miocene to the
660
Holocene. This suggests that the timing of hydrocarbon charge would have occurred somewhere
661
between ca 5.3 m.y.a. to the Present. During this period, the Perla Limestone was buried by at
39 662
least 1.3 km of a lower to late Miocene succession, according to the stratigraphic markers from
663
Rojas et al. (2015). Based on this information, it would be reasonable to assume that the
664
hydrocarbon migration occurred after most of the diagenetic events observed in the Perla
665
Limestone.
666
5.2.
667
Deep-burial dissolution creating microporosity: Petrographic, mineralogical
and geochemical evidence
668
A line of evidence confirmed the presence of an important dissolution process that created a
669
pervasive non-fabric selective microporosity, with subordinate moldic and vuggy porosities in
670
the lower Miocene units of the P-CX and P-BX cores (Table 3). This dissolution process is
671
interpreted to have occurred in the deep-burial setting based on genetic relationships with post-
672
compactional features and late diagenetic cements. Post-compactional features such as fractures,
673
stylolites and non-sutured seams, are usually micro-corroded. Likewise, late diagenetic cements
674
such as blocky-1, blocky-2, DOL-2, pyrite, fluorite, among others are partial to totally micro-
675
corroded (Fig. 21a, b, c, 14).
676
Moreover, LMC bioclasts such as echinoderms, which are usually stable in the diagenetic
677
environment (de Boer, 1977), are also micro-corroded (Fig. 21d), thus implying the inflow of
678
corrosive diagenetic fluids. In addition, the presence of non-carbonate cements such as dickite,
679
pyrite, sphalerite, barite and fluorite, is also a potential indication of high-temperature exotic
680
fluids (e.g. Palinkas et al., 2009; Liu et al., 2017). The fact that these non-carbonate minerals are
681
coeval with DOL-2 (Fig. 11), as well as, precipitated within secondary porosity and post-
682
compactional features, reveal their late diagenetic origin.
40 683
The origin of microporosity in limestones is subject of a long-standing debate in the literature.
684
However, most authors agree with a mineral stabilization process as the main driver for
685
microporosity development (e.g. Saller and Moore, 1989; Richard et al., 2007; Volery et al.,
686
2010; Morad et al., 2018; Hashim and Kaczmareck, 2019). In contrast, in the Perla Limestone,
687
our study suggests microporosity development as a result of an acid-driven dissolution
688
mechanism associated with external corrosive-fluids. Similar cases of microporosity related to
689
burial diagenetic fluids have been reported (e.g. Lambert et al., 2006).
690 691 692 693 694
Figure 21. SEM and thin-section photomicrographs showing the evidence of the late nature of the burial dissolution process. A: Corroded DOL-2, pyrite and blocky-2 cement. B: Corroded DOL-2, pyrite and quartz cement. C: Corroded Fluorite and blocky-1 cement. D: Highly corroded LMC-echinoderm (echinoid spine). Scale bar is 50 micrometers-size.
695
In addition to the evidence collected in this study, Valencia and d’Alterio (2014) performed a
696
geochemical analysis of gas samples from the Perla Limestone reservoir. They reported δ13CCO2
697
ratios from -2.7 to -6.9 ‰ (PDB), with an average of -4.2 ‰ (PDB), and the less depleted 13CCO2
698
values in the P-CX well. These isotopic values are considered typical of inorganic origin
41 699
(δ13CCO2 from 0 to -10 ‰ PDB, sensu Wycherley et al., 1999). Within the inorganic sources of
700
CO2, Valencia and d’Alterio (2014) considered that the CO2 from the Perla field was originated
701
from magmatic/mantle degassing and carbonate dissolution sources (-4 to -7 ‰ PDB and -2 to
702
+3 ‰ PDB, sensu Clayton et al., 1990 and Baines and Worden, 2004; respectively). According
703
to these authors, the burial dissolution of the Perla Limestone would have shifted the normal
704
mantle-derived CO2 print to relatively heavy-values in some areas of the reservoir. Moreover,
705
they also reported a
706
concentration. This is characteristic of magmatic/mantle-derived gases (e.g. Truesdell et al.,
707
1994; Ballentine and Holland, 2008). The presence of both mantle-derived fluids and CO2
708
product of carbonate dissolution is considered a clear indication of the interaction between the
709
Perla Limestone and CO2-charged basement-related fluids.
710
5.3.
711
Aggressive fluids unconnected to active hydrologic systems could create burial dissolution
712
(Machel and Lonnee, 2002; Wright and Harris, 2013). These fluids are commonly introduced
713
into the carbonate system through discontinuity surfaces such as faults, fractures, bedding planes
714
and stylolites (Esteban and Taberner, 2003; Salas et al., 2007). From a reservoir perspective, it is
715
important to understand the nature of these fluids capable of carbonate dissolution in the burial
716
realm, to predict the possible geometry of diagenetic geobodies. Several models have been
717
proposed in the literature, where the most common are: (1) the kerogen-related fluids model (e.g.
718
Mazzullo and Harris, 1992; Schulz et al., 2016), (2) the thermochemical sulfate reduction model
719
(e.g. Orr, 1977; Machel, 2001), (3) the mixing-corrosion (e.g. Plummer, 1975; Esteban and
720
Taberner, 2003), (4) the inorganic-CO2 model (e.g. Corbella et al., 2004; Beavington-Penney et
721
al., 2008), (5) the retrograde solubility model (e.g. Heydari, 2000), (6) the pressure-change
3
He-enrichment in the Perla Limestone respect the standard air
Deep-burial dissolution model
42 722
model (e.g. Collins et al., 2013) and (7) the clay-mineral decomposition model (Tosca and
723
Wright, 2015). In the case of the Perla Limestone, petrographic, mineralogical and geochemical
724
evidence supports an inorganic-CO2 model.
725
5.3.1. Inorganic-CO2 model for the Perla Limestone
726
Burial pervasive microporosity (corrosion) in bioclasts, matrix, cements, as well as, in late
727
diagenetic features, was documented in the Perla Limestone. The origin of this secondary
728
porosity is considered the result of an acid-driven dissolution mechanism, associated with the
729
upward migration of hydrothermal CO2-charged fluids from the basement to the reservoir. The
730
mobilization of these fluids was mediated by basement-root faults, fractures and stylolites
731
corridors that allowed the development of pervasive secondary porosity in the vicinity of the
732
major discontinuity surfaces (Fig. 22).
733 734 735
Figure 22. Mechanism of the inorganic-CO2 model proposed for the burial dissolution porosity observed in the Perla Limestone.
43 736
In the following section, a simplified hypothetical sequence of events producing the burial
737
dissolution of the Perla Limestone is proposed:
738
(1) During the middle Miocene to late Miocene, a major tectonic reactivation of the Gulf of
739
Venezuela Basin occurred (Albert-Villanueva et al., 2017; Audemard 2009). At that time,
740
the Perla Limestone was buried by at least 500 m (up to 1300 m) of a siliciclastic-
741
dominated succession, based on stratigraphic markers from Rojas et al. (2015).
742
(2) Because of the active tectonic regime, some antecedent faults and fractures were
743
reactivated favouring the entrance of diagenetic fluids from the crystalline basement up
744
to the reservoir. Pressure-dissolution surfaces also helped to enhance the invasion of
745
these diagenetic fluids (e.g. Paganoni et al., 2015; Barnett et al., 2015). At that depth (≥
746
300 m), assuming a normal geothermal and geobaric gradient (25
747
MPa/km, respectively), the CO2 could have been in the supercritical phase; which is a
748
superfluid phase theoretically reached by the CO2 at 31 C and 7.4 MPa (André et al.,
749
2007). This phase has a low resistance to flow, 6 % lower density than liquid water
750
(Spycher et al., 2003); allowing an easy displacement from the parent magma to the
751
reservoir rock (Domingo et al., 2004).
C/km and 25
752
(3) During the migration towards the Perla Limestone, the supercritical CO2 could also have
753
encountered basinal brines in the underlying Paleogene-siliciclastic unit and mixed with
754
it, creating even more aggressive fluids (e.g. Decker et al., 2015), or reducing its
755
dissolution potential due to high-sulfate content in the basinal brines (e.g. Rosenbauer et
756
al. 2005).
757
(4) Once in contact with the carbonate succession, the acidic fluids were responsible for the
758
creation of extensive dissolution and microporosity development in the Perla Limestone.
44 759
This process was favored by the presence of basement-root faults, fractures and other
760
discontinuity surfaces that funneled the ascending fluids into the carbonate succession.
761
5.3.2. Key considerations for the inorganic-CO2 model
762
Even though it was noticed that the burial dissolution process was not directly related to any
763
specific depositional facies, the fact that it is more frequent in the lower Miocene units (M-2 >
764
M-3 > M-1 > M-4), suggests a connection between the burial dissolution process and these
765
geological units. The more frequent mud-lean or poorly cemented lithofacies in the lower
766
Miocene units might favor the fluid migration on these strata compared to the Oligocene units
767
(Borromeo et al., 2013; Pomar et al., 2015). On the other hand, the diminishing of micro-
768
corrosion from the middle M-3 unit to the top-reservoir (M-4), can be explained by a chemical
769
reaction shut-down due to the limited acidic-fluid input, followed by a rapid chemical-
770
equilibrium with the carbonate formation.
771
The impact of burial dissolution is higher in P-CX well compared with P-BX and P-DX wells.
772
This could be explained by the fact that the P-CX is located in a paleo-topographic basement
773
high, close to a major fault system, with the carbonate succession directly in contact with the
774
basement-rock since the Paleogene-siliciclastic succession (present in P-BX and P-DX) is
775
missing (Fig. 3). The relatively shallower position of the P-CX (paleo-topographic high) with
776
respect to the other wells, might have contributed to a greater flow of diagenetic fluids, due to
777
the naturally expected fluid-flow migration towards lower-pressure zones. Moreover, the
778
stratigraphic omission of the underlying Paleogene-siliciclastic sequence provided a direct
779
contact between the basement and reservoir, and a more efficient pathway for the entrance of
780
diagenetic fluids from the basement-root faults and fractures. A relationship between high-
781
porosity zones and major faults system is evidenced in pseudo-porosity maps created by Rojas et
45 782
al. (2015), from the pseudo-porosity volumes of the Perla Limestone produced by Marini and
783
Spadafora (2014) (Fig. 23).
784 785 786
Figure 23. Pseudo-porosity map of the lower Miocene unit M-2 obtained by Rojas et al. (2015) from the pseudo-porosity volumes done by Marini and Spadafora (2014).
787
Although dissolution porosity created by inorganic CO2-degassing has been extensively reported
788
in the literature (e.g. Beavington-Penney et al., 2008), the impact of this model enhancing
789
reservoir quality was strongly criticized by Ehrenberg et al. (2012). These authors argued
790
problems related to mass balance constraints and lack of quantitative treatment. However, Biehl
791
et al. (2016), from experimental studies on late Permian carbonates (Lower Saxony Basin,
792
Germany), noticed that even if the CO2-dissolved in water has the potential to dissolve only
793
minor amounts of carbonate in closed-systems; their impact in open-systems with inflow and
794
outflow of fluids, becomes important. In the Perla Limestone, the relative absence of late
795
cements postdating an important burial dissolution process could suggest alternating conditions,
46 796
from open to closed system, driven by tectonic events that discharged super-saturated fluids out
797
of the reservoir during open-system stages (e.g. Shen et al., 2016).
798
Moreover, quantitative porosity and permeability data from Perla Limestone cores (Table 4; Fig.
799
16), show a strong correlation between the presence of chalky-like patches, created by burial
800
dissolution processes, and the high reservoir-quality zones.
801
6. CONCLUSIONS
802
The Perla Limestone has undergone a complex sequence of diagenetic events. The primary
803
mineralogy and pore texture set up the initial conditions for the diagenetic evolution of the
804
carbonate succession in the near-surface and shallow-burial environment. Nevertheless, in the
805
deeper burial realm, where carbonates are commonly in equilibrium with the adjacent formation
806
waters, an important event of dissolution and microporosity development occurred. This process
807
was induced by hot CO2-rich fluids coming from the basement to the reservoir, likely during
808
middle Miocene times. The ability of these fluids to create high reservoir-quality zones was
809
controlled by the presence of fault corridors, fractures and pressure-dissolution surfaces that
810
served as a conduit to the carbonate succession. Also, the presence of grain-supported lithofacies
811
and previously dolomitized lithofacies probably favored the dissolution process by the higher
812
permeable networks.
813
Based on this study, the reservoir quality in the Perla Limestone is expected to increase in
814
poorly/non-cemented lithofacies, in the vicinity of major basement-rooted faults. As well, in
815
areas located in paleo-topographic highs where the crystalline basement is directly in contact
816
with the carbonate succession. Similar models can be also applicable to many more examples
817
around the world, such as Baturaja Formation (lower Miocene carbonates) in the North West
47 818
Java Basin (Widodo, 2018), among others. Next steps for diagenetic modelling should consider
819
the combination of these conceptual diagenetic models with 3-D geomechanical fault-system
820
modelling and depositional facies distribution, to establish a powerful tool for porosity and
821
permeability predictions in carbonate reservoirs.
822
7. ACKNOWLEDGEMENTS
823
Authors thank Cardon IV, S.A. for the permission to publish. This study was originated from an
824
M.Sc. thesis project (Valencia, 2016) financially supported by Cardon IV, S.A. We especially
825
thank Ornella Borromeo for her valuable support and ideas about the diagenesis of the Perla
826
Limestone that served as the basis of this research. We would like to acknowledge the referees
827
for their constructive comments to improve the manuscript. Strong support, in terms of data and
828
discussions, was received by the Perla teams of Eni S.p.A/EPLAB, Repsol Technology Center,
829
Cardon IV, S.A, PDVSA, José Méndez Baamonde, Ana Cabrera and Marvin Baquero. Likewise,
830
we thank Mark Wilson, Luis Buatois and Gabriela Mángano for their support with the borings
831
ichnotypes identification.
832
8. REFERENCES
833
Albert-Villanueva, E., Gonzalez, L., Bover-Arnal, T., Ferrandez-Cañadell, C., Esteban, M., Fernandez-Carmona, J.,
834
Calvo, R., Salas, R., 2017. Geology of the Falcón Basin (NW Venezuela). Journal of Maps 13 (2), p. 491-
835
501. https://doi.org/10.1080/17445647.2017.1333969
836 837
Ali, S.A., Clark, W.J., Moore, W.R., Dribus, J.R., 2010. Diagenesis and Reservoir Quality. Oilfield Review 22, p. 14-27.
838
André, L., Audigane, P., Azaroual, M., Menjoz, A., 2007. Numerical modeling of fluid–rock chemical interactions
839
at the supercritical CO2–liquid interface during CO2 injection into a carbonate reservoir, the Dogger
48 840
aquifer
841
https://doi.org/10.1016/j.enconman.2007.01.006
842 843
(Paris
Basin,
France).
Energy
Conversion
and
Management
48,
p.
1782–1797.
Audemard, F., 1993. Neotectonique, sismotectonique et alea sismique du Nord-Ouste du Venezuela (Systeme de failles d’Oca-Ancon). PhD thesis, Universite Montpellier II. 369 p.
844
Audemard, F., 2009. Key issues on the post-Mesozoic Southern Caribbean Plate boundary. In: James, K. H.,
845
Lorente, M. A. & Pindell, J. L. (eds) The Origin and Evolution of the Caribbean Plate. Geological Society,
846
London, Special Publications, 328, 569–586.
847
Baines, S.J., Worden, R.H., 2004. The long-term fate of CO2 in the subsurface: natural analogues for CO2 storage.
848
Geological
849
https://doi.org/10.1144/GSL.SP.2004.233.01.06
Society,
London,
Special
Publications
233,
p.
59–85.
850
Ballentine, C.J., Holland, G., 2008. What CO2 well gases tell us about the origin of noble gases in the mantle and
851
their relationship to the atmosphere. Philosophical Transactions of the Royal Society A: Mathematical,
852
Physical and Engineering Sciences 366, p. 4183–4203. https://doi.org/10.1098/rsta.2008.0150
853 854
Baquero, M., 2015. Evolución geodinámica del Noroccidente de Venezuela, basado en nuevos datos de geocronología, geoquímica e isotópicos. PhD thesis, Universidad Central de Venezuela. 259 p.
855
Baquero, M., Grande, S., Urbani, F., Cordani, U., Hall, C., Armstrong, R., 2015. New Evidence for Putumayo Crust
856
in the Basement of the Falcon Basin and Guajira Peninsula, Northwestern Venezuela, in: Bartolini, C.,
857
Mann, P. (Eds.), Memoir 108: Petroleum Geology and Potential of the Colombian Caribbean Margin.
858
AAPG. https://doi.org/10.1306/13531933M1083639
859
Barnett, A.J., Wright, V.P., Chandra, V.S., Jain, V., 2015. Distinguishing between eogenetic, unconformity-related
860
and mesogenetic dissolution: a case study from the Panna and Mukta fields, offshore Mumbai, India.
861
Geological Society, London, Special Publications, 435, http://doi.org/10.1144/SP435.12
862
Bastin, E.S., 1939. Theories of formation of ore deposits. Scientific American 49 (6), p. 538–547.
863
Bathurst, R.G., 1975. Carbonate Sediment and Their Diagenesis. Development in Sedimentology, Elsevier,
864
Amsterdam. 658 p.
865
Beavington-Penney, S.J., Nadin, P., Wright, V.P., Clarke, E., McQuilken, J., Bailey, H.W., 2008. Reservoir quality
866
variation on an Eocene carbonate ramp, El Garia Formation, offshore Tunisia: Structural control of burial
867
corrosion
and
dolomitisation.
Sedimentary
Geology
209,
p.
42–57.
49 868
https://doi.org/10.1016/j.sedgeo.2008.06.006
869
Biehl, B.C., Reuning, L., Schoenherr, J., Lewin, A., Leupold, M., Kukla, P.A., 2016. Do CO2-charged fluids
870
contribute to secondary porosity creation in deeply buried carbonates? Marine and Petroleum Geology 76,
871
p. 176–186. https://doi.org/10.1016/j.marpetgeo.2016.05.005
872 873
Bischoff, W.D., Bertram, M.A., Mackenzie, F.T., Bishop, F.C., 1993. Diagenetic stabilization pathways of magnesian calcites. Carbonates Evaporites 8, p. 82–89. https://doi.org/10.1007/BF03175165
874
Borromeo, O., Miraglia, S., Santorio, D., Bolla, E., Ortenzi, A., Reali, S., Castellanos, C., Villalobos, R., 2011. The
875
Perla World-Class Giant Gas Field, Gulf of Venezuela: Depositional and Diagenetic Controls on Reservoir
876
Quality in Early Miocene Carbonates. AAPG International Conference and Exhibition, Milan, Italy. Article
877
#90135.
878
Borromeo, O., Miraglia, S., Reali, S., Santorio, D., Ortega, S., Villalobos, R., Castillo, V., Esteban, M., Benkovics,
879
L., 2013. The Perla Gas Field, Gulf of Venezuela: Geological Model of an Oligo-Miocene Carbonate Bank.
880
AAPG International Conference and Exhibition, Cartagena, Colombia. Article #90166.
881 882
Budd, D.A., 1992. Dissolution of high-Mg calcite fossils and the formation of biomolds during mineralogical stabilization. Carbonates and Evaporites 7, p. 74–81. https://doi.org/10.1007/BF03175394
883
Castillo, V., Benkovics, L., Cobos, C., Demuro, D., Franco, A., 2017. Perla Field: The Largest Discovery Ever in
884
Latin America, in: Merrill, R., Sternbach, C. (Eds.), Memoir 113: Giant fields of the decade 2000–2010.
885
AAPG, p. 141–152.
886
Checconi, A., Bassi, D., Carannante, G., Monaco, P., 2010. Re-deposited rhodoliths in the Middle Miocene
887
hemipelagic deposits of Vitulano (Southern Apennines, Italy): Coralline assemblage characterization and
888
related trace fossils. Sedimentary Geology 225, p. 50–66. https://doi.org/10.1016/j.sedgeo.2010.01.001
889
Choquette P.W., Pray, L.C., 1970. Geologic Nomenclature and Classification of Porosity in Sedimentary
890
Carbonates.
891
8645000102C1865D
892 893 894 895
AAPG
Bulletin
54.
207-205.
https://doi.org/10.1306/5D25C98B-16C1-11D7-
Clayton, J.L., Spencer, C.W., Koncz, I., Szalay, A., 1990. Origin and migration of hydrocarbon gases and carbon dioxide, Békés Basin, southeastern Hungary. Organic Geochemistry 15 (3), p. 233-247. Collins, J., Narr, W., Harris, P., Playton, T., Jenkins, S., Tankersley, T., Kenter, J., 2013. SEPM Special Publication 105, p. 50-83. https://doi.org/10.2110/sepmsp.105.11
50 896
Corbella, M., Ayora, C., Cardellach, E., 2004. Hydrothermal mixing, carbonate dissolution and sulfide precipitation
897
in Mississippi Valley-type deposits. Mineralium Deposita 39, p. 344–357. https://doi.org/10.1007/s00126-
898
004-0412-5
899
Craig, H., 1965. The measurement of oxygen isotopes paleotemperatures, in: Tongiorgi, E. (Eds.), Proceedings
900
Spoleto Conference on Stable Isotopes in Oceanographic Studies and Paleotemperatures 3, P. 3-24.
901
de Boer, R.B., 1977. Stability of Mg-Ca carbonates. Geochimica et Cosmochimica Acta 41, p. 265–270.
902
https://doi.org/10.1016/0016-7037(77)90234-4
903
Croizet, D., Renard, F., Gratier, J.P., 2013. Compaction and Porosity Reduction in Carbonates: A Review of
904
Observations, Theory, and Experiments, in: Advances in Geophysics. Elsevier, p. 181–238.
905
https://doi.org/10.1016/B978-0-12-380940-7.00003-2
906 907
Davies, G.R., Smith, L.B., 2006. Structurally controlled hydrothermal dolomite reservoir facies: An overview. AAPG Bulletin 90 (11), p. 1641–1690.
908
Decker, D.D., Polyak, V.J., Asmerom, Y., 2015. Depth and timing of calcite spar and “spar cave” genesis:
909
Implications for landscape evolution studies, in: Geological Society of America Special Papers, p. 103–
910
111. https://doi.org/10.1130/2015.2516(08)
911 912
Diaz De Gamero, M. L., 1977. Estratigrafía y micropaleontología del Oligoceno y Mioceno Inferior del centro de la cuenca de Falcon, Venezuela. GEOS-Universidad Central de Venezuela 22, p. 3–60.
913
Domingo, C., García-Carmona, J., Loste, E., Fanovich, A., Fraile, J., Gómez-Morales, J., 2004. Control of calcium
914
carbonate morphology by precipitation in compressed and supercritical carbon dioxide media. Journal of
915
Crystal Growth 271, p. 268–273. https://doi.org/10.1016/j.jcrysgro.2004.07.060
916
Ehrenberg, S.N., Aagaard, P., Wilson, M.J., Fraser, A.R., Duthie, D.M.L., 1993. Depth-Dependent Transformation
917
of Kaolinite to Dickite In Sandstones of the Norwegian Continental Shelf. Clay Mineral. 28, p. 325–352.
918
https://doi.org/10.1180/claymin.1993.028.3.01
919 920 921 922 923
Ehrenberg, S.N., Walderhaug, O., Bjørlykke, K., 2012. Carbonate porosity creation by mesogenetic dissolution: Reality or illusion? AAPG Bulletin 96, p. 217–233. https://doi.org/10.1306/05031110187 Enos, P., Sawatzky, L., 1981. Pore networks in Holocene carbonate sediments. Journal of Sedimentary Petrology, v. 51/3, p. 961-985. Escalona, A., Mann, P., 2011. Tectonics, basin subsidence mechanisms, and paleogeography of the Caribbean-South
51 924
American
925
https://doi.org/10.1016/j.marpetgeo.2010.01.016
plate
boundary
zone.
Marine
and
Petroleum
Geology
28,
p.
8–39.
926
Esteban, M., Taberner, C., 2003. Secondary porosity development during late burial in carbonate reservoirs as a
927
result of mixing and/or cooling of brines. Journal of Geochemical Exploration 78–79, p. 355–359.
928
https://doi.org/10.1016/S0375-6742(03)00111-0
929
Folk, R. L., 1965, Some aspects of recrystallization in ancient limestones, in L. C. Pray and R. C. Murray, eds.,
930
Dolomitization and limestone diagenesis: A symposium: Society of Economic Paleontologists and
931
Mineralogists Special Publication 13, p. 14–48.
932 933 934 935 936 937 938 939
Hamilton, E.L., 1976. Variations of Density and Porosity with Depth in Deep-sea Sediments. SEPM J. Sediment. Res. Vol. 46. https://doi.org/10.1306/212F6F3C-2B24-11D7-8648000102C1865D Hashim, M.S., Kaczmarek, S.E., 2019. A review of the nature and origin of limestone microporosity. Marine and Petroleum Geology 107, 527–554. https://doi.org/10.1016/j.marpetgeo.2019.03.037 Heydari, E., 2000. Porosity loss, fluid flow, and mass transfer in limestone reservoirs: application to the Upper Jurassic Smackover Formation, Mississippi. AAPG Bulletin (2000) 84 (1), p. 100-118. Hudson, J.D., 1977. Stable isotopes and limestone lithification. Journal of the Geological Society 133, p. 637–660. https://doi.org/10.1144/gsjgs.133.6.0637
940
Jiang, L., Pan, W., Cai, C., Jia, L., Pan, L., Wang, T., Li, H., Chen, S., Chen, Y., 2015. Fluid mixing induced by
941
hydrothermal activity in the ordovician carbonates in Tarim Basin, China. Geofluids 15, p. 483–498.
942
https://doi.org/10.1111/gfl.12125
943
Kaczmarek, S.E., Fullmer, S.M, Hasiuk, F.J. (2015). A universal classification scheme for the microcrystals that
944
host
945
http://dx.doi.org/10.2110/jsr.2015.79
946 947
limestone
microporosity.
Journal
of
Sedimentary
Research
85,
p.
1197-1212.
Kim, S.T. and O’Neil, J. R., 1997. Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates. Geochim. Cosmochim. Acta 61, p. 3461–3475.
948
Knoerich, A.C., Mutti, M., 2003. Controls of facies and sediment composition on the diagenetic pathway of
949
shallow-water Heterozoan carbonates: the Oligocene of the Maltese Islands. International Journal of Earth
950
Sciences 92, p. 494–510. https://doi.org/10.1007/s00531-003-0329-8
951
Lambert, L., Christophe, D., Jean-Paul, L., Gerard, M., 2006. Burial dissolution of micrite in Middle East carbonate
52 952
reservoirs (Jurassic–Cretaceous): keys for recognition and timing. Marine and Petroleum Geology 23, p.
953
79–92.
954
Lavoie, D., Chi, G., Brenan-Alpert, P., Desrochers, A., Bertrand, R., 2005. Hydrothermal dolomitization in the
955
Lower Ordovician Romaine Formation of the Anticosti Basin: significance for hydrocarbon exploration.
956
Bulletin of Canadian Petroleum Geology 53, p. 454–471. https://doi.org/10.2113/53.4.454
957
Liu, L.H., Ma, Y.S., Liu, B., Wang, C.L., 2017. Hydrothermal dissolution of Ordovician carbonates rocks and its
958
dissolution mechanism in Tarim Basin, China. Carbonates and Evaporites 32, p. 525–537.
959
https://doi.org/10.1007/s13146-016-0309-2
960 961 962 963 964 965
Longman, M.W., 1977. Factors Controlling the Formation of Microspar in the Bromide Formation. SEPM Journal of Sedimentary Research Vol. 47. https://doi.org/10.1306/212F716C-2B24-11D7-8648000102C1865D. Longman, M.W., 1980. Carbonate diagenetic textures from near surface diagenetic environments. AAPG Bulletin 64, p. 461- 487. Lonnee, J.S., 1999. Sedimentology, Dolomitization and Diagenetic Fluid Evolution of the Middle Devonian Sulphur Point Formation, Northwestern Alberta. PhD thesis. University of Windsor. 137 p.
966
Lonnee, J., Machel, H.G., 2006. Pervasive dolomitization with subsequent hydrothermal alteration in the Clarke
967
Lake gas field, Middle Devonian Slave Point Formation, British Columbia, Canada. AAPG Bulletin 90, p.
968
1739–1761. https://doi.org/10.1306/03060605069
969 970 971 972
Lucia, F.J., 1995. Rock-Fabric/Petrophysical Classification of Carbonate Pore Space for Reservoir Characterization. AAPG Bulletin 79. https://doi.org/10.1306/7834D4A4-1721-11D7-8645000102C1865D Lucia, F.J., Loucks, R.G., 2013. Micropores in Carbonate Mud: Early Development and Petrophysics. GCAGS Journal 2, p. 1-10.
973
Macellari, C.E., 1995. Cenozoic Sedimentation and Tectonics of the Southwestern Caribbean Pull-Apart Basin,
974
Venezuela and Colombia, in: Tankard, A.; Suarez, R., Welsink, H. (Eds.), Memoir 62: Petroleum basins of
975
South America. AAPG, p. 757–780.
976 977 978 979
Machel, H.G., 2001. Bacterial and thermochemical sulfate reduction in diagenetic settings - old and new insights. Sedimentary Geology 33, p. 143-175. Machel, H.G., Lonnee, J., 2002. Hydrothermal dolomite—a product of poor definition and imagination. Sedimentary Geology 152, p. 163–171. https://doi.org/10.1016/S0037-0738(02)00259-2
53 980
Malavé, B.J., Contreras, O.J., 2013. New Contributions to the Geodynamics of the Caribbean through Structural
981
Transects in the Gulf of Venezuela and its Implications in the Definition of Petroleum Systems. AAPG
982
International Conference and Exhibition, Cartagena, Colombia. Article #30286.
983
Marini, A.I., Spadafora, E., 2014. GandG Data Integration to model a Carbonate Giant Field: Predicting and
984
Managing Reservoir properties in an Underexplored Basin till Production phase. Abu Dhabi International
985
Petroleum Exhibition and Conference, Society of Petroleum Engineers, Abu Dhabi, UAE.
986
https://doi.org/10.2118/171963-MS
987
Mazzullo, S.J., Harris, P.M., 1992. Mesogenetic Dissolution: Its Role in Porosity Development in Carbonate
988
Reservoirs.
989
8645000102C1865D
990 991
AAPG
Bulletin
76,
p.
607-620.
https://doi.org/10.1306/BDFF8880-1718-11D7-
Melim, L.A; Swart, P.K; Maliva, R.G., 1995. Meteoric-like fabrics forming in marine waters: Implications for the use of petrography to identify diagenetic environments. Geology 23, p. 893-896.
992
Melim, L.A.; Westphal, H; Swart, P.K.; Eberli, G.P.; Munnecke, A., 2002. Questioning Carbonate Diagenetic
993
Paradigms: Evidence from the Neogene of the Bahamas. Marine Geology 185, no. 1–2, p .27–53.
994
https://doi.org/10.1016/S0025-3227(01)00289-4.
995 996 997 998
Moore, C.H., 2001. Carbonate reservoirs: porosity evolution and diagenesis in a sequence stratigraphic framework, 3. impr. ed, Developments in sedimentology 55. Elsevier, Amsterdam. Moore, C.H., Wade, W.J., 2013. Carbonate reservoirs porosity and diagenesis in a sequence stratigraphic framework, 2. impr. ed, Developments in sedimentology 67. Elsevier, New York.
999
Morad, D., Paganoni, M., Al Harthi, A., Morad, S., Ceriani, A., Mansurbeg, H., Al Suwaidi, A., Al-Aasm, I.S,
1000
Ehrenberg, S.N., 2018. Origin and evolution of microporosity in packstones and grainstones in a Lower
1001
Cretaceous carbonate reservoir, United Arab Emirates. Geological Society, London, Special Publications
1002
435, 47–66. https://doi.org/10.1144/SP435.20
1003
Moscariello, A., Pinto, D., Agate, M., 2018. Revisited play concept for distally-steepened carbonate ramps: the
1004
relevance of sediment density flows in the stratigraphic record. AAPG Search and Discovery Article
1005
#51514. AAPG Annual Convention and Exhibition, Salt Lake City, Utah.
1006
Munnecke, A., Westphal, H., Reijmer, J.J.G., Samtleben, C., 1997. Microspar development during early marine
1007
burial diagenesis: a comparison of Pliocene carbonates from the Bahamas with Silurian limestones from
54 1008
Gotland (Sweden). Sedimentology 44,p. 977–990. https://doi.org/10.1111/j.1365-3091.1997.tb02173.x
1009
Nash, M.C., Troitzsch, U., Opdyke, B.N., Trafford, J.M., Russell, B.D., Kline, D.I., 2011. First discovery of
1010
dolomite and magnesite in living coralline algae and its geobiological implications. Biogeosciences 8, p.
1011
3331–3340. https://doi.org/10.5194/bg-8-3331-2011
1012 1013
Orr, W., 1977. Geologic and geochemical controls on the distribution of hydrogen sulfide in natural gas, in: Campos, R.; Goni, J. (Eds.). Advances in Organic Geochemistry 1975, p. 571-97.
1014
Paganoni, M., Al Harethi, A., Morad, D., Morad, S., Ceriani, A., Mansurbeg, H., Al Suwaidi, A., Al-Aasm, I.S.,
1015
Ehrenberg, S.N., Sirat, M., 2015. Impact of Stylolitization on Diagenesis and Reservoir Quality: A Case
1016
Study from an Early Cretaceous Reservoir in a Giant Oilfield, Abu Dhabi, United Arab Emirates. Abu
1017
Dhabi International Petroleum Exhibition and Conference, Society of Petroleum Engineers, Abu Dhabi,
1018
UAE. https://doi.org/10.2118/177944-MS
1019
Palinkaš, S.S., Šoštarić, S.B., Bermanec, V., Palinkaš, L., Prochaska, W., Furić, K., Smajlović, J., 2009. Dickite and
1020
kaolinite in the Pb-Zn-Ag sulphide deposits of northern Kosovo (Trepča and Crnac). Clay miner. 44, 67–
1021
79. https://doi.org/10.1180/claymin.2009.044.1.67
1022
Pinto, J., Ortega, S., Martin, Z., Berrios, I., Perez, A., Pirela, M., 2011, Controls on the newly-discovered gas
1023
accumulations in the Miocene “Perla” carbonate bank, Gulf of Venezuela: A preliminary assessment: I
1024
South American Oil and Gas Congress, p. 1–4.
1025
Pirela, M., 2017. Caracterización de fluidos y estimación de la posible dirección de llenado de yacimiento. caso de
1026
estudio: Campo Perla, Cuenca del Golfo de Venezuela. Masters tesis. Universidad Central de Venezuela.
1027
134 p.
1028 1029
Plummer, L.N., 1975. Mixing of Sea Water with Calcium Carbonate Ground Water. Geological Society of America Memoir 142, p. 219-236.
1030
Pomar, L., Esteban, M., Martinez, W., Espino, D., Castillo, V., Benkovics, L., Leyva, T.C., 2015. Oligocene–
1031
Miocene Carbonates of the Perla Field, Offshore Venezuela: Depositional Model and Facies Architecture,
1032
in: Bartolini, C., Mann, P. (Eds.), Memoir 108: Petroleum Geology and Potential of the Colombian
1033
Caribbean Margin. AAPG. https://doi.org/10.1306/13531952M1083655
1034
Pöppelreiter, M., Balzarini, M.A., De Sousa, P., Engel, S., Galarraga, M., Hansen, B., Marquez, X., Morell, J.,
1035
Nelson, R., Rodriguez, F., 2005. Structural control on sweet-spot distribution in a carbonate reservoir:
55 1036
Concepts and 3-D models (Cogollo Group, Lower Cretaceous, Venezuela). AAPG Bulletin 89, p. 1651–
1037
1676. https://doi.org/10.1306/08080504126
1038 1039
Radke, B.M. and Mathis, R.L., 1980. On the Formation and Occurrence of Saddle Dolomite. Journal of Sedimentary Research, 50, p. 1149-1168.
1040
Richard, J., Sizun, J., Machhour, L., 2007. Development and compartmentalization of chalky carbonate reservoirs:
1041
the Urgonian Jura-Bas Dauphine´ platform model (Ge´nissiat, southeastern France). Sedimentary Geology
1042
198, p. 195–207.
1043
Rojas, G., Avendaño, M., De Visintini, P., Rampersad, A., Tomasi, A. Palmeri, G., Valencia, F., Pirela, J., Guaipo,
1044
M., 2015. Perla field – Cardon IV West Block: Integrated Geological and Static model. Internal Report -
1045
Cardon IV S.A. 283 p.
1046
Ronchi, P., Jadoul, F., Ceriani, A., Di Giulio, A., Scotti, P., Ortenzi, A., Previde Massara, E., 2011. Multistage
1047
dolomitization and distribution of dolomitized bodies in Early Jurassic carbonate platforms (Southern Alps,
1048
Italy):
1049
https://doi.org/10.1111/j.1365-3091.2010.01174.x
Multistage
dolomitization,
Southern
Alps.
Sedimentology
58,
p.
532–565.
1050
Rosenbauer, R.J., Koksalan, T., Palandri, J.L., 2005. Experimental investigation of CO2–brine–rock interactions at
1051
elevated temperature and pressure: Implications for CO2 sequestration in deep-saline aquifers. Fuel
1052
Processing Technology 86, p. 1581–1597. https://doi.org/10.1016/j.fuproc.2005.01.011
1053
Salas, J., Taberner, C., Esteban, M., Ayora, C., 2007. Hydrothermal dolomitization, mixing corrosion and deep
1054
burial porosity formation: numerical results from 1-D reactive transport models. Geofluids 7, p. 99–111.
1055
https://doi.org/10.1111/j.1468-8123.2006.00167.x
1056 1057 1058 1059
Saller, A., 2013. Diagenetic evolution of porosity in carbonates during burial. AAPG Search and Discovery Article #50779, Tulsa Geological Society Luncheon Meeting. Saller, A., Moore, C., 1989. Meteoric diagenesis, marine diagenesis, and microporosity in Pleistocene and Oligocene limestones, Enewetak Atoll, Marshall Islands. Sedimentary Geology 63, p. 253–272.
1060
Schulz, H.-M., Wirth, R., Schreiber, A., 2016. Organic-inorganic rock-fluid interactions in stylolitic micro-
1061
environments of carbonate rocks: a FIB-TEM study combined with a hydrogeochemical modelling
1062
approach. Geofluids 16, p. 909–924. https://doi.org/10.1111/gfl.12195
1063
Shen, A., She, M., Hu, A., Pan, L., Lu, J., 2016. Scale and distribution of marine carbonate burial dissolution pores.
56 1064 1065 1066
Journal of Natural Gas Geoscience 1, p. 187–193. https://doi.org/10.1016/j.jnggs.2016.08.003 Shinn, E., Robbin, D.M., 1983. Mechanical and chemical compaction in fine-grained shallow-water limestones. Journal of Sedimentary Petrology, v. 53 (2), p. 595-618.
1067
Skalinski, M., Kenter, J.A.M., 2014. Carbonate petrophysical rock typing: integrating geological attributes and
1068
petrophysical properties while linking with dynamic behaviour. Geological Society, London, Special
1069
Publications 406, p. 229–259. https://doi.org/10.1144/SP406.6
1070 1071
Schmoker, J. W., Halley, R. B., 1982, Carbonate porosity versus depth: a predictable relation for south Florida: Am. Assoc. Petroleum Geologists Bull., v. 66, p. 2561-2570.
1072
Spycher, N., Pruess, K., Ennis-King, J., 2003. CO2-H2O mixtures in the geological sequestration of CO2. I.
1073
Assessment and calculation of mutual solubilities from 12 to 100°C and up to 600 bar. Geochimica et
1074
Cosmochimica Acta 67, p. 3015–3031. https://doi.org/10.1016/S0016-7037(03)00273-4
1075 1076 1077 1078
Swart, P.K., 2015. The geochemistry of carbonate diagenesis: The past, present and future. Sedimentology 62, p. 1233–1304. https://doi.org/10.1111/sed.12205 Tarduno, J., Duncan, R., Scholl, D., 2002. Proc. ODP, Init. Repts., 197 p.: College Station, TX (Ocean Drilling Program) 89. https://doi.org/10.2973/odp.proc.ir.197.2002
1079
Tosca, N.J., Wright, P., 2015. Diagenetic pathways linked to labile Mg-clays in lacustrine carbonate reservoirs: a
1080
model for the origin of secondary porosity in the Cretaceous pre-salt Barra Velha Formation, offshore
1081
Brazil. Geological Society, London, Special Publications, 435, p. 33-46. https://doi.org/10.1144/SP435.1
1082
Truesdell, A.H., Kennedy, B.M., Walters, M.A., D’Amore, F., 1994. New evidence for a magmatic origin of some
1083
gases in the geysers geothermal reservoir. Proceedings, Nineteenth Workshop on Geothermal Reservoir
1084
Engineering Stanford University, Stanford, California, SGP-TR-14, p. 297-301.
1085 1086
Valencia, F., 2016. Diagénesis de los carbonatos del Campo Perla, Golfo de Venezuela: Implicaciones en las propiedades petrofísicas. Master thesis. Universidad Simón Bolívar. 178 p.
1087
Valencia, F., d’Alterio, F., 2014. Aplicaciones de la geoquímica isotópica para la determinación del origen de los
1088
gases no hidrocarburos del Campo Perla, Sub-bloque Cardón IV-Oeste. Revista Visión Tecnológica,
1089
Memorias del I Congreso Venezolano de Gas Natural (ICVGAS). Article # EX-14.
1090
Volery, C., Davaud, E., Foubert, A., Caline, B., 2009. Shallow-marine microporous carbonate reservoir rocks in the
1091
Middle East: relationship with seawater Mg/Ca ratio and eustatic sea level. Journal of Petroleum Geology
57 1092
32, p. 313–326.
1093
Wei, W., Chen, D., Qing, H., Qian, Y., 2017. Hydrothermal Dissolution of Deeply Buried Cambrian Dolomite
1094
Rocks and Porosity Generation: Integrated with Geological Studies and Reactive Transport Modeling in the
1095
Tarim Basin, China. Geofluids 2017, 1–19. https://doi.org/10.1155/2017/9562507
1096 1097
Widodo, R. W., 2018. Evolution of The Early Miocene Carbonate: Baturaja Formation in Northwest Java Basin, Indonesia [Ph.D.: Texas A&M University, 235 p.
1098
Worden, R.H., Armitage, P.J., Butcher, A.R., Churchill, J.M., Csoma, A.E., Hollis, C., Lander, R.H., Omma, J.E.,
1099
2018. Petroleum reservoir quality prediction: overview and contrasting approaches from sandstone and
1100
carbonate
1101
http://dx.doi.org/10.1144/SP435.21
communities.
Geological
Society
London
Special
Publications
435(1).
1102
Wright, P., Harris, P., 2013. Carbonate Dissolution and Porosity Development in the Burial (Mesogenetic)
1103
Environment. AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania. Article #50860.
1104
Wycherley, H., Fleet, A., Shaw, H., 1999. Some observations on the origins of large volumes of carbon dioxide
1105
accumulations
1106
https://doi.org/10.1016/S0264-8172(99)00047-1
in
sedimentary
basins.
Marine
and
Petroleum
Geology
16,
p.
489–494.
•
Deep-burial dissolution linked to basement-related hydrothermal CO2-rich fluids.
•
Microporosity development due to acid-driven dissolution mechanism.
•
Faults, fractures and dissolution seams controlling burial diagenetic alterations.
Fernando L. Valencia: Conceptualization, Methodology, Data curation, Writing- Original draft preparation, Visualization, Investigation and Editing. Juan C. Laya: Supervision, Conceptualization and Reviewing.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: