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Oil-source correlation study in northeastern Alaska
Advances in Organic Geochemistry 1985
Org. Geochem. Vol. I0, pp. 407-415, 1986
0146-6380/86 $3.00 + 0.00 Pergamon Journals Ltd
Printed in Great Britain
Oil-source correlation study in northeastern Alaska DONALD E. ANDERSl and LESLIE B. MAGOON2 ~U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, U.S.A. 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, U.S.A.
(Received 19 September 1985; accepted 5 March 1986) Abstract--The occurrence of numerous oil-seeps and oil-stained outcrops across the coastal plain of the Arctic National Wildlife Refuge (ANWR) in northeastern Alaska indicates that commercial hydrocarbons could be present in the subsurface of this region. In addition, this region is flanked by two important oil provinces--the Prudhoe Bay area to the west and the Mackenzie delta to the east. To begin to understand the petroleum resource potential of ANWR, we evaluated the source rock quality and thermal maturity of five rock units ranging in age from Triassic to early Tertiary: Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale and Canning Shale. We also compared ANWR oils using stable carbon isotope ratios, tricyclic terpane ratios, and saturate/aromatic hydrocarbon ratios. The organic carbon content of the five rock units range from an average of 1.6 to 4.0 wt%. Cretaceous rocks from the coastal plain are thermally immature (vitrinite reflectance <0.5%) and in the southern mountains thermally mature to overmature (vitrinite reflectance 1.0--1.8%). In general, type III organic matter predominates in the Kingak Shale, pebble shale unit, and Canning Shale, and types II and III in the Hue Shale. ANWR oils are divided into three groups: (1) Jago oil type, includes oils from Angun Point, Katakturuk River and Jago River; (2) Manning oil type, from Manning Point near the coast of the Beaufort Sea; and (3) Kavik oil type, from Kavik west of the Canning River. None of the three oil types of ANWR compares favorably with the economically important oils from Prudhoe Bay and the National Petroleum Reserve of Alaska (NPRA). The most promising source rock for oils of the Jago River type is the organic rich type II units of the Hue Shale. Possible source rocks for the other ANWR oil types could not be established.
Key words: oil-source correlation, Alaska, Prudhoe Bay, Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, Canning Shale
INTRODUCTION
Six oil-seeps or oil-stained outcrops in or adjacent to the Alaska National Wildlife Refuge (ANWR) coastal plain in northeastern Alaska indicate that commercial hydrocarbons could be present in the subsurface. This area is flanked by two important petroleum provinces, the Prudhoe Bay area on the west which has estimated recoverable resources of 17-21 billion barrels of oil and 31 trillion cubic feet of gas, and the Mackenzie delta on the east which has estimated recoverable resources of 0.74 billion barrels of oil and 10 trillion cubic feet of gas. The character and source of the hydrocarbons, as well as the geology in these two adjoining provinces, are distinctly different from each other making direct extrapolation from either side into the A N W R coastal plain difficult. This study examines the oil and rock samples in northeastern Alaska to determine the source or sources of the ANWR oil-seeps or stains, and to determine if the oil type(s) is similar to the oils being produced in Prudhoe Bay (Seifert et al., 1979) and the National Petroleum Reserve of Alaska (Magoon and Claypool, 1981, in press). The oil-and-gas potential of five rock units: the Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale are evaluated. These 407
five rock units was selected on the basis of preliminary geological and geochemical evidence which suggests that they are the most likely source rocks for the ANWR oil seeps and stains. Four types of analyses are used to evaluate the resource potential of these units: (1) organic-carbon content (wt%), (2) Rock-Eval pyrolysis (organic matter type and hydrogen richness), (3) C~5 + hydrocarbon content (ppm), and (4) vitrinite reflectance (% Ro). Oil-oil and oil-source rock comparisons of the following geochemical properties, carbon isotopes of the saturate and aromatic hydrocarbon fractions, gas chromatography of the saturate hydrocarbon fractions, and GC/MS relative abundances of specific tricyclic and pentacyclic terpanes, are used to establish genetic oil types and principle source rocks for the oil types. Subsurface geochemical information on the North Slope is published by Morgridge and Smith (1972), Jones and Speers 0976), Seifert et al. 0979), Magoon and Claypool (1981, 1984, in press), Carman and Hardwick (1983), and Magoon and Bird (in press), Magoon et al. (in press) for both rocks and oils. Preliminary source-rock information on outcrops in northeastern Alaska is reported by Palmer et aL (1979), Lyle et aL (1980), Molenaar (1983) and Molenaar et aL (in press).
408
DONALD E. ANDERS and LESLIE B. MAGOON ~UOHOE
0
L
BAY
BEAsU~ART
BARTER ~SLANO~
~
b
Fig. I. Map showing the general location of rock samples analyzed in this northeastern Alaska study. Numbers on map correspond to sample reference column in Table 1. SAMPLE DISTRIBUTION
The reliability of oil and gas source-rock assessment depends upon "adequate" geochemical characterization of the stratigraphic interval(s) considered; adequate characterization is a sampling problem dependent upon the thickness, aerial extent, and internal geochemical variability. In this study, the stratigraphic intervals range in thickness from less than one hundred meters to several hundred meters and most extend aerially across the North Slope. Many more samples (586) were used to characterize each stratigraphic unit than is presented in this paper on Table i. West of the Canning River, most of the rock samples are from industry exploratory wells; east of the Canning River all the rocks are surface from the Sadlerochit and Shublik Mountains and the A N W R coastal plain (Fig. 1). The distribution of the oil samples in this report is restricted to the Prudhoe Bay oil field, Cape Simpson and Umiat oil fields and oil from the South Barrow gas field in the National Petroleum Reserve in Alaska (NPRA), and six seeps and stains in or adjacent to A N W R (Fig. 2).
GEOLOGIC FRAMEWORK This study is restricted to five stratigraphic intervals: the Triassic Shublik Formation, the Jurassic and
-i•~
~
Lower Cretaceous Kingak Shale, the Lower Cretaceous pebble shale unit, the Lower and Upper Cretaceous Hue Shale, and the Upper Cretaceous and lower Tertiary Canning Shale (Fig. 3). The structural configuration of these rock units in northeastern Alaska differs on either side of the Canning River. West of the river, rock units older than the Canning Shale dip gently to the south, while the basin clinoform strata of the Canning Shale dip gentle to the northeast. East of the river, steep dips and deformation are common to coastal plain sediments as well as to strata in the Sadlerochit and Shublik Mountains. In northeastern Alaska, an unconformity at the base of the pebble shale unit truncates both the Shublik Formation and the Kingak Shale north of the Sadlerochit and Shublik Mountains. A brief description of each rock units follows. Shublik Formation: The Shublik Formation is a distinctive unit consisting of calcareous and sooty shale and fossiliferous dark, phosphatic limestone. It crops out in the Sadlerochit and Shublik Mountains and along the mountain front to the east and occurs in parts of the subsurface to the west. Kingak Shale: The Kingak Shale crops out along the mountain front and occurs in parts of the subsurface to the west. It consists predominantly of dark gray marine shale ranging in thickness from zero where truncated by the pebble shale unconformity to 1200 m.
BEAUFORT SEA
NATIONALPETROLEUM
UMIAT # 4 ~ .
Fig. 2. Map showing the general location of analyzed oil-seeps and stained rocks in northeastern Alsaka and selected North Slope oils. Numbers on map correspond to sample reference column in Table 2.
Ref.
Pebble Sh. Kupt r u k P~u. RtnKak S h .
3
,, ShubI 1k Fu.
Klngak ST~.
12 19
PI
569 539
5?6 406 426 462 560
538 502
431 437 405
411 406 409 408 450
424 438 432 435 404
429 412 639
420 432 437 418 423
434 431 418 429 429
(C)
Tm~x
2.1 1.8
1.5 0.5 1.4 1.9
1.0 1.1 0.5 1.6 1.8
0.5 0.5
1.0 1.0 1.2
0.5 0.5 0.4
0.4 0.5 0.5 0.4 0.4
0.5 0.5 0.5 0.5 0.3
Z
Ro
V~_~f~
214 I37
848 2144 205 68 129
791 715 425 254 507
8673 9707 3062 7500 947
202 1376 1012 1220 ROgk
3480 7778 691
3140 1645 6741 2531 3533
407 323 2991 8302 1546
1.0 0.5
1.8 4.8 0.8 0.8 0.6
3.2 1.6 0.7 0.7 1.2
10.8 6.8 5.2 4.1 2.4
1.3 5.8 3.3 2.4 5.2
7.3 77.8 6.6
6.2 14.2 9.6 10.5 8.8
3.4 2.9 5.5 20.8 5.0
Z
EOt4/TOC
108 71
0.5 0.3
0.9 2.9 0.6 0.5 0.4
439 1323 106 41 76
2.3 l.l 0.1 0.3 0.6
7.8 3.8 3.1 1.3 1.8
0.6 3.7 2.3 1.8 2.7
4.5 57.7 3.2
3.3 9.6 6.5 7.0 4.8
1.8 1.4 4.2 14.4 3.3
2
tlC/TOC
5113 301 80 88 247
6266 5388 1838 2392 697
83 993 703 903 4209
5772 338
2130
1706 1242 6543 1689 1909
212 133 2212 5771 1013
ppa
tIC
4.1 3.4
1.1 3.6 1.6 0.8 2.9
2.2 0.6 0.1 1.0
3.1
1.9 1.3 1.5 0.9 2.1
1.4 2.1 1.3 3.5 1.2
2.7 k.0 2.0
2.3 3.7 1.8 2.3 1.0
2.2 1.3 2.9 3.2 3.0
S/A
-27.4 -29.1
-24.9 -28.9 -28.3 -26.3 -27.3
-27.4 --25.3 -23.6
-27.1
-29.0 -28.4 -30.0 -28.6 -27.k
-28.6 -28.7 -27.6 -23.9 --
-26.1 -27.9
-2~_.2 -27.6 -27.3 -25.5 -28.1
-26.6 -25.2 -22.4 -22.3
-26.9
-28.0 -28.8 --27.6 -27.9
-27.7 -28.5 -27.0 -26.2 --
-30.6 -29.7 -27.4
-30.0 -30.6 -30.1 -29.8 -30.2
-30.6 -30.5 -30.6 -30.1 -29.2 -30.8 -30.1 -27.9
-26.8 -2 6 0 6 -28.9 -29.4 -30.9
A r o a . KC
6 t3C
-28.3 -28.5 -29.4 -29.9 -31.2
S a t .RC
6 13C
,l~otope Data
4aaaC292OS/a~C292OS+~oaC2920R s t e r a n e s ;
55 60
221 392 57 15 44
137 137 312 59 109
1/~1 3808 1077 4202 182
78 321 187 161 3280
873 1793 154
990 272 1353 950 1503
147 127 786 3248 337
pl~a
non HC
E x c r a c t t o ~ Oat~
1.5 1.6
1.8 1.5 0.6 2.8 1.6
2.0 0.8 1.9 2.7
2.9
1.5 0.4 0.2 0.3 4.6
0.3 1.7 2.8 3.7 0.3
1.4 0.9 3.9
1.1 1.8 1.2 1.7 2.9
1.5 1.2 0.8 1.8 1.0
1.7 1.3
2.3 1.9 2.5 1.3 1.2
1.5 3.4 1.3 2.0
[.8
2.0 t.q 1. 5 1.2 2.0
1.7 1. 4 1. 6 1. 7 1ol
2.3 l.I 1.2
2. 7 1. 8 2.0 1. 7 1.4
2.3 2.7 2.4 1. 5 2.6
Pr/Ph 2
value <0.I
nCI7/Pr
steranes', 6C2820R t rt~romatLc/C2820R triaro~t t,: + C2920R mnoaromat tc steranes; 7negligible; 81mture,
cerpane;
ppm
EOM
terpane/C23 crtcycltc
0.11 0.07
0.07 O.2~ 0.07 O.10 0.06
0.07 0.10
0.08 0.09 0.03
0.10 0.03 0.06 0.03 0.O4
0.03 0.04 0.16 0.05 0.03
0.06 0.50 0.22
O.05 0.07 0.07 0.10 0.04
0.11 0.11 0.11 0.31 0.04
3CI 9 c r i c y c t t c
0.36 0.42
23
32
0.99 1.22 0.73 0.44 0.50
0.39 1.20
0.92 0.79 0.62
38.04 66.82 20.30 88.40 2.60
0.76 4.93 0.93 2.10 80.84
21.61 6.29 0.75
17.50 5.36 42.22 8.54 42.89
0.97 0.62 13.65 7.36 11.15
Kg/H con
S l + S2
R o c k - E v a l ~sta
18 58 75 27 19
27 16
38 62 gO
19 19 24 23 12
90 17 41 12 27
13 4t 219
19 20 14 13~
23 32 18 69 17
Ol
s~,~ P t g u r e 1; 2 p r l s t a n e / g h y t a n e ;
2.1 2.5
19 ~0 25 35 17
5B£C292OS+SBC292OR/~C2920S+BBC2920R+~C2920S+~aC292OR
I g o r sample l o c a t / o n s ,
14 35
30 31 32 33
4.8 4.5 Z.7 0.9 2.1
29
53 19 I1
2.5 4.6 6.3
19 24
429 456 326 471 51
69 167 26 ~5
518 300 88
466 306 586 357 720
240 162 399
~3
HI
8.0 14.2 5.9 18.3 3.9
1 .5 2.7 3.1 5.0 15 .6
4.8 1 .0 1.1
5.1 1 .3 7.0 2.4 4.0
1.2 1.1 5.3 4.0 3.1
X
TOC
3.5 4.3
" pebble sh.
"
"
(~ccrop
8910 8921 9533-9536
8868 8885 8900 8930 8985
8531 8386 8956-9085 6643 U53
ft.
Depth
27 28
26
25
24
19 20 21 22 23
14 13 16 17 18
C a n n i u g Sh. " Hue S h a l e
I v i s h a k Sg.
II 12 13
#.t~qt locks
S h u b l i k Yu. "
6 7 8 9 10
4 5
Canal u g S h .
1 2
Prudhoe Ba7 Rocks
Rock
Unit
sample I
Sample D e s c r t p t ton
Table I. Geochemical properties of Prudhoe Bay and ANWR rocks
* 0.2
0.9 1.0 2.0 0.4 0.2
0.9 3.8 0.2 2.1
1.4
0.4 0.5 0.4 0.3 1.2
1.3 0.8 0.6 0.9 0.4
0.4 <0.1 0.3
0.2 0.3 0.2 0.1 0.2
0.9 0.9 0.2 <0.1 0.2
C23Trt
C19Trl/3
* 0.5
0.7 13.8 55.0 0.1 0.1
0.3 114.0 0.2 t
0.5
10.8 22.0 8.0 t9.0 0.4
13.0 0,8 0.3 0.6 28.0
3.9 2.9 0.6
5.7 4.1 5.7 1.6 | .0
2.2 5.1 2.8 2.2 12.7
C23Trt
Ropane/
*
07.
*
0.6
•
flat, 0.6 0.6
0.4
0.6
*
0.4 0.5 lit* 0.4
0.5 0.4 0.3 0.4 0.5
lmt. 0.6 0*6 0.6 0.4
0.5 0.6 0.4
1.5
0.5
0.2 (0.1 0.6 0.6
1.5
0.5
*
0.4 0.5 (O.I 0.3
0.4 O .I 0.1 0.1 0.5
<0.1 0.4 0.5 0.4 0.1
0.5 t.5 1.5
•
1.2
0.5
1.5 1.5
0.8 0.3 1.0 0.2 1.5
,7 15 1o5 1.3 0.Z
0.5 0.4
0.4 0.5
0.4 0.4
0.5
0.5
1.5 1.3
0.3 0.5
0.5
0*5 0.5 0.3 0.5 0.3
8
~BB EgB÷E~o
0.4 0.5
0.3 0.3 0.4 0.4 0.4
acm20R
~2OS 4 ao~20S+
1.4
1.5 1.5 1.5 1.5 1.3
1.3 1.4 1.4 1.4 1.5
S/R
C3ihopanes
8 1 o s ~ r k e r Data
(.0
1.0
0.4 1.0 1.0
0.5
t°O
1.0 1.O
0*5
1.0 1.0
* 0.0 0.1 0.0 1.0
O.I 1.O I.O I°O O.O
0.7 0.8 0.6
0.8 0.8
O.q
0.7 0.8
0.6 0.6 0.7 0*9 0.8
C2920 k
02820R6 C282011 ÷
410
DONALDE. ANDERSand LESLIEB. MAGOON
AGE
QUATERNARY
S'rRATIGRAPfllC uNrT
li
ORGANIC GEOCHEMISTRY
LffHO.OGY qSw)~t]
Rocks
SURF~IAL DEPOSITS
PLIOCENE
MIOCENE
SAGAVANIRICTOK .~'._~m~. FORMATION ~,.~:i~.~ ~ . .
Qua.
"22272--'
EOCENEI~ PALE~IENE
'7!;
....
~
CANNING SHALE
LATE CRETACEOUS EARLY
-
" ~ _ _ T 2'
!
HUE SHALE
•
A A it-:
Glcnma--rly ~' ~ - ' ~ " - ~ ' zo~ u CRETACEOUS ~.. >IEIIIILE SHALE UNiT (LATE NEOCOMIAN U KEMIK SS MIR EARLY
i
- -- -- ~ ~-- -- -- -
CRETACEOUS
AND
KINGAK SHALE
JUFIASSIC
........ ........
KAREN CREEK SS
:",T : i '
:
SHUBUK FORMATION
"---"-2---
PE~IAN
~
ECHOOKA FORMATION
I
' " ~" "
"I
Fig. 3. Generalized stratigraphic column for the northern part of the Arctic National Wildlife Refuge (ANWR). Pebble shale unit: The pebble shale unit is an Early Cretaceous regional rock unit that can be mapped across the entire North Slope. In the Sadlerochit and Shublik Mountains area, the pebble shale unit is 60-90m thick and consists of dark-gray to black, noncalcareous, clayey to silty shale containing scattered pebbles or grains of chert and quartzite (Molenaar, 1983). Canning Shale and Hue Shale: These two shales are a sequence of silici-clastic rocks deposited by a northeasterly prograding delta of which only the fine-grained sediments will be discussed. The Hue Shale, which contains a radioactive shale at the base, is a distal condensed shale facies that crops out around the Sadlerochit Mountains and in the Niguanak River area on the ANWR coastal plain. It is usually less than 300 m thick and consists of black, fissile, noncalcareous, clay shale and bentonite (Molenaar et al., in press). The Canning Shale gradationally overlies in the Hue Shale and consists of 1200 to 1800m of darkgray to gray-brown bentonitic shale and siltstone with thin turbidite sandstone beds in the lower part (Molenaar et al., in press). It exists in the subsurface west of the Canning River and crops out around the Sadlerochit Mountains.
Thermal maturity: According to Seifert et al. (1979), the principle source rocks for the Prudhoe Bay oils are the Kingak Shale and Shublik Formation. Our work on the thermal maturity for these two units at Prudhoe Bay indicate that the organic matter is immature to marginally mature with respect to hydrocarbon generation to depths up to 2750m (Tin,X 412-438°C, vitrinite reflectance 0.3-0.5% Ro; Table 1). Because of the low thermal maturity of the source rocks at Prudhoe Bay, the oil in this region probably migrated from stratigraphically equivalent but more deeply buried rocks to the south. Thermal maturity data for the organic matter in the potential source rocks of A N W R is not a simple function of present day burial depths. For example, all rock units, regardless of age, exposed at the Ignek Valley section (15-17, 23-25, 27, 29 and 32-35, Table 1) as a result of the Sadlerochit and Shublik Mountain uplift are thermally mature to post mature with respect to hydrocarbon generation (Tin, x, 432-560°C; 1.0-2.0% Ro, Table 1). Whereas, 100 km northeast of the Ignek Valley section, in the Jago River and Niguanak River area of the ANWR coastal plain (18-22, 26, 30 and 31, Table l), the same rock units are thermally immature ( Tmax, 401-409°C; <0.6% RO, Table 1). Organic matter type and quality: Magoon and Bird (in Press) indicate that the pebble shale unit tends toward type III organic matter across the entire North Slope but that the Kingak Shale and Shublik Formation are predominantly type II/III across NPRA and type II/I south of and in the Prudhoe Bay area. Data presented in Table 1 for the potential source rocks in the Prudhoe Bay area (samples 1-13) agree with the Magoon and Bird (in press) conclusions. Average organic carbon content for the Kingak Shale and Shublik Formation is 2.0 wt%. Within ANWR, the only rock unit sampled with sufficient organic matter and hydrogen rich kerogen to generate commercial quantities of liquid hydrocarbons is the Hue Shale. Immature samples (0.5% Ro) of the Hue Shale 08-22, Table 1) from the Jago River and Niguanak River sections of the coastal plain give hydrogen index values (HI = 324-505 mg HC/gC) indicative of type II/III organic matter and organic carbon content up to 18 wt% (av. 4.0 wt%). As further proof of the hydrocarbon generating capacity of the Hue Shale at the Jago River and Niguanak River sections, samples 19 and 22 (Table 1) produce abundant liquid hydrocarbons during hydrous pyrolysis (50-51, Table 2). In the Ignek Valley section of the Sadlerochit and Shublik Mountains of ANWR, it is more difficult to determine the organic matter type in the Hue Shale because of its advanced thermal maturity (1.0-1.2% Ro; 16, 17, 23-25, Table l). This increased thermal
Oil-source correlation study in N.E. Alaska maturity of the Hue Shale at the Ignek Valley section relative to the Hue Shale at the Jago and Niguanak River sections is not sufficient in itself to explain the extraordinary drop of the hydrogen index from an average of 400 mg HC/gC at the Jago and Niguanak River sections to < 50 mg HC/gC at the Ignek Valley section. The low hydrogen indices, coupled with low production indices and low hydrocarbon yields, for the Hue Shale at Ignek Valley relative to higher values for this unit at the Jago River and Niguanak River sections, may indicate a northeast-southwest change in organic matter type within these two units from type II on the northeast coastal plain to type III at the southwest Ignek Valley section. The organic carbon content of the Kingak Shale, pebble shale unit, and Canning Shale samples from the Jago and Niguanak River section of the ANWR coastal plain average 2.0, 3.0 and 2.0wt%, respectively. The organic matter type in these three rock units is predominantely type III based on their low hydrogen indices (11 to 69 mgHC/gC) and high C29 sterane content relative to their C27 and C28 sterane content (3:1). Further, the low hydrocarbon generating capacity (0.62-1.22 kg/metric ton) of these units is in agreement with an organic matter type III assignment. At the Ignek Valley section, the Kingak Shale and the pebble shale unit are in the late stages of thermal generation of hydrocarbons and cannot be evaluated with certainty as to their organic matter type. However, the low hydrocarbon yield ( < 1.2 kg/ metric ton), low production index (<0.1) and high pristane/phytane ratio ( > 1.8) for these thermally mature units suggest that the dominate organic matter in the rock units to the south are also type III. Immature pebble shale unit and Kingak Shale samples 26 and 31 (Table 1) from the Niguanak River (52, 53, Table 2) produce predominantly gas during hydrous pyrolysis. The Canning Shale at the Ignek Valley section contains predominately type III organic matter with an occasional thin section of type II organic matter. Since the Shublik Formation is overmature (> 1.8% Ro, Table 1) in ANWR, the resource potential of this unit in northeastern Alaska cannot be evaluated except by cautiously extrapolating values from marginally mature samples in the Prudhoe Bay area. Based on organic carbon content, organic matter type or hydrogen richness, and hydrocarbon yield from hydrous pyrolysis and Rock-Eval, the upper Kingak Shale, pebble shale unit, and Canning Shale are gas prone, and the Hue Shale is oil prone in ANWR. Cj5+ hydrocarbons: The material most like petroleum in sedimentary rocks is the solvent extractable hydrocarbons. The relationship between C~5 + extractable hydrocarbons and organic carbon content was first established by Hunt (1979). In the Hunt model, oil stained rocks or reservoir rocks contain more than 100 mg HC/g OC (> 10 wt%), immature
411
and metamorphosed rocks contain less than 10 mg HC/g OC ( < 1.0 wt%) and source rocks fall between these upper and lower limits. Two Prudhoe Bay samples (4, 12, Table l) and seven ANWR samples (41-44, 46, 47, 49, Table 2) contain more than 100 mg HC/g OC and are probably stained by migrated hydrocarbons. Nine A N W R samples 04, 26-29, 33-35) contain less than 10 mg HC/g OC; three are immature (<0.6% Ro) and six have obtained a high degree of thermal maturity ( > 1.5% Ro). The remaining samples from Prudhoe Bay and ANWR fall in the range for oil source rocks and show the expected trend of increasing hydrocarbon content with increasing carbon content.
Oils Two oil-seeps and seven oil-stained rocks from six locations in or adjacent to the ANWR coastal plain (Fig. 2) were geochemically compared. The results of the solvent extraction of the oil-stained rocks are reported on Table 2. All seven of the hydrocarbon stained rocks from ANWR contain more than 100 mg HC/g OC and five contain more than 300 mg HC/g OC. With the exception of sample 42, hydrocarbons from the ANWR oil seeps and stained rocks (41-49, Table 2) are biodegraded--containing no measureable amounts of n-alkanes or regular chain isoprenoids. Four of the samples (41, 43-45, Table 2) are severely biodegraded (hydrocarbon content <25 wt%). The severely biodegraded hydrocarbon samples are dominated by hydrocarbons with boiling points > n-Cz0, while the lesser biodegraded samples (46--49, Table 2) are dominated by hydrocarbons boiling < n-C20. Carbon isotope values for the northeastern Alaska seeps and stained rocks show distinct differences that help organize the oils into genetic types. For example, when the delta 13C values of the saturated hydrocarbon fractions of the oils are plotted vs the delta ~3C values of their aromatic hydrocarbon fractions, three genetic oil types are suggested by the results (Fig. 4). For comparison purposes, carbon isotope values for the saturated and aromatic hydrocarbon fractions from the Prudhoe Bay oil types (Seifert et al., 1979) and NPRA oil types (Magoon and Claypool, 1981) are also plotted on Fig. 4. ANWR oils from the Katakturuk River, Jago River and Angun Point are isotopically similar (613C = -29.2 + 0.3 for the saturate fractioins and -28.5 ___0.4 for the aromatic fractions) and are designated the Jago oil type; whereas, the hydrocarbon fractions from the Manning Point samples are about 1.0 per mil heavier and for the Kavik area sample adjacent to ANWR, about 2.5 per mil heavier than the oils of the Jago type and are designated the Manning and Kavik types, respectively. Based on these carbon isotopic differences, two oil types, Jago and Manning, are suggested for oils on the ANWR coastal plain and one type, Kavik, is adjacent to the ANWR coastal plain west of the Canning River.
Unit
Rock
299 -1556-1639
7702-10 10,~17-535
Outcrop " Sutfa~e Outcrop
wt. X
TO~
-
-
-
44.7 75.9 87.6
-
_
19.9 12.9 26.~ 11.7
9.3 73.8 77.9 73.6
~0.9
-
1.9
**
**
3.0
2.5 2.2 5.2 5.t
5.2 2.6 3.0 2.9
,.8
~.0 ~.1 3.1
3.8 I.~
S/A
**
8
35.8 66.1 77.t
76.9 23.1 19.4 -
,,.0
2
~C/TOC
~t
80.1 87.1 73.2 M.3
90.7 26.2 22.1 24.~
19.1
98.8 9~.3 88.0
91.8 79.8
Wt. I
tiC
-
-
-28.3
-27.9
-28.8 -28.9 -27.5 -27.6
-28.8 -28.1 -28.1 -28.3
-27.8
-26.7 -27.$ -28.7
-30.$ -29.1
Arom.HC
~ 13 C
1.8 0.7
1.6
2.6
* s * *
* * *
* * ~ *
I. 3
* * *
•
2.2 2.1 1.2
2.S 1.5
Pr/Ph 2
O.&
.
2 07 * 0.9
1.~ 2.0
uC17/Pr
781odegraded and ~emthered; 8~cee hydrocarbons f l o a t i n g
on the ~ a t ~
s u r f a c e ~ f t e c hydrous p y r o l y s i s :
8teranes;
0.3
0.5
0.5 0.5 2.1 1.9
0.3 0.~ 0.6
0.6
0.1
1.9 0.6 0.2
0.2 <0.1
C23Tri
ClgTri/3
Data
8L~t,:r~,
15.0
9.0
8.~ 7.1 15.7 13.8
13.8 * *
9.0
•
2.3 ~.$ 0.~
19.0 ~.1
C23Tri
0.4 0.~ 0.4 0.t
0.4 a *
0. S
•
0.5 0.~ 0.S
0.S 0.$
~a20l
~ o 20S+
aoa 20S t
* ~ u e <0.1
0.8
1.0
1.4 1.2 1.2 1.2
1.~ * *
1.3
•
1.2 1.3 1.7
1.~ I .~
S/!
Daphne/ C31Hop~nes
l/mrker
simple 19 (2392 ppll), sample 22 (2409 ppm), samples 26 and 31 (<100 ppu).
4o~aC2920S/oa~C2920S+~aac292OR
-28.9
-29.0
-29.~ -29.2 -28.2 -28.&
-29.5 -29.3 -29.0 -28.9
-2,.7
-28.0 -28.~ -29.1
-31.8 -29.6
Sut.I~
~ 13c
l a o t o ~ e Data
terpane;
8,500 20,500 use 9 ~,~00
9,., 8&.8 88.0 88.0 -
1.2 5.7 12.0
8.2 20.2
wt. X
non HC
. ,
trtaroma¢tc ÷ C292QKIonoaro~l¢ic stetanes; 7negligible;
22 sh. 26 Sh. 31
1.9 2.7 11.O
4.240 20,2~0 69,320 s~p
28,,00
-
-
~
KO~/TOC
D~&
1For sample L o c a t i o n s , nee Figure 2; 2 p r l a t a n e / P h y t a n e ; 3CI9 c r l c y c L t c terpmne/C23 o r * c y c l i c
8ample pebble sample Kia~mk sample
2.8
0.$ 2.3 7.9
-
-
pqm
~0N
8xtraetioa
5~C292OS÷~C2920K/~aC2920S÷~C2920K÷~C29203÷~C2920~ ~¢exanea; 6C2820R t r t ~ r o ~ t i c / C 2 8 2 0 R
53
~2
~e
St
~ha~e
Hue ShaI~ amlple 19
50
Hydrous P y r o l y s i s
Quateremry
Surface
Tertiary
"
outo.o,
A6 47 ~8 49
-
C o l v i l l e Gp. Tertiary Quaternary
&2 ~3 44 43
,1
Pebble Sh.
Ilmmshedc Cp.
K l q a k Sh. Smdlerochit
ft.
Depth
OiL S t t £ ~ ' d O ' ~ t c r o ~ L S~v~tee S e e p a
38 34) ~0
NPU O i l s
36 37
Prudhoe l a ~ O i l s
Suf.
Sample 1
Sample D e s c r i p t i o n
Table 2. Geochemical properties of A N W R oil-stained rocks and seeps, and selected Prudhoe Bay and NPRA oils
ZBB~
C282~
0.5 0.6 0.5 0.6 0.6
t
t
C2920R
C2820l +
0.5 0.S 0.4 0.4
0.5
0.',
0.6 0.5 0.6
O.S 0.5
EB~+~aa
Z
Z
Z
4~ t,O
Oil-source correlation study in N.E. Alaska
ANWR CANNINGAND HUE S
H
(J "r
~
.....
_
S BARROW20(NPRA) OIL
l--
(n
L (NPf~A}
PRUDHOEBAY
U3
~'~MANNINGPOINTOIL{AN~) I S H UPSON W , O~L INPRA) SHUW.IK FORMAllON
~
FORMATION
ANGUN PT, KATAKTURUKRV, JAGO flV 011.5(ANW~)
~ P R -30
413
":•:. '~{i:;?:' ~.:i"
BAY OILS OPRUDHOE BAY SAG OELTAO~L UDHOE BAY KiNGAK SHALE
PRUOHOEBAY KAVEARAKOIL
-
,
,
.,2,
,
,
.;,
,
,
6~SC, AROMATIC HC
Fig. 4. Oil-oil and oil-source rock correlation based on carbon isotopes of the C,5 + saturate and aromatic hydrocarbon fractions. Isotopic comparison of the oils indicate two distinct oil types within ANWR (1) Jago Rv., Katakturuk Rv. and Angun Pt., and (2) Manning Pt. and one oil type adjacent to ANWR (Kavik). The Jago Rv., etc. oil type correlates best with the type II facies of the Hue Shale. The Jago oil type (42-47, Table 2) is isotopically most like the NPRA oil recovered from a sandstone within the pebble shale unit penetrated in the South Barrow No. 20 well (Fig. 4). The Manning oil type is isotopically similar to the oil recovered from the seismic shot point on the Simpson Peninsula in NPRA. The Kavik oil type is unlike any oil recovered to date on the North Slope and the Jago River and Manning Point oil types of A N W R are isotopically heavier than the Prudhoe Bay oil types of Seifert et aL (1979). Tricyclic terpane distributions were also useful in establishing three oil types within and adjacent to ANWR. For example, when the CI9/C23 tricyclic terpane ratio of the A N W R oils are plotted vs their delta ~3C values for the saturated fraction (Fig. 5), the same three oil types appear as were observed in the carbon isotope plot (Fig. 4). Oil-stained rocks from the Katakturuk River, Jago River, and Angun Point area (42-47) all group together as one type (Jago oil type), and the Manning Point (48, 49) and Kavik (41) samples each form their own separate type (Table 2, Fig. 5). Most of the oils on the North Slope have relatively low C19/C23 tricyclic terpane ratios, falling in the range of 0.1 to 0.6 (Table 2). Within this narrow range, the Prudhoe Bay oil types cannot be separated from the Kavik and S. Barrow 20 oil types, but can be differentiated from the consistantly higher
ratios of the Jago, Simpson, Manning and Umiat 4 oil types (Table 2, Fig. 5). The ANWR (Jago and Manning) and Kavik oil types (41-49) are easily distinguished from all other North Slope oils (37-40) except the Kavearak Point oil (36), by their high pentacyclic terpane content relative to their tricyclic terpane content (Table 2). Hopane/C23 tricyclic terpane ratios for the ANWR, Kavik, and Kavearak Point oils are all greater than seven, while all other North Slope oils are less than five. The saturate/aromatic hydrocarbon ratios of the biodegraded oils within or adjacent to ANWR fall into three ranges: (1) Jago oil type (43-47; Table 2), which includes samples from Katakturuk River near the Marsh Anticline, Jago River, and Angun Point, have ratios that range from 2.2 to 3.0; (2) Manning oil type (48, 49; Table 2) from Manning Point with a ratio of 5.3; and (3) Kavik oil type (41; Table 2) from Kavik west of the Canning River with an intermediate ratio of 3.8. As expected, nonbiodegraded oil sample 42 (Table 2) from the Katakturuk River near the Sadlerochit Mts. has a ratio twice as large as its biodegraded companion oil (43; Table 2). Oil-source rock correlation
Oil-source rock geochemical correlation provide
414
DONALDE. ANDERSand LESLIEB. MAGOON
CANNI,NG AND HU~ SHALES (ANWR}
~"
~
~
,
)
/
(
A
N
~
)
KINGAK SHALE (ANWR)
JAGO [~t, KA'rAk"TURUK qRV,
t
I 0.2
I 0.6 C19/C23
I 1.0 TRICYCLIC
I 1.4 TERPANE
1 1.8
i
r
2,2
RATIO
Fig. 5. Oil-oil and oil-source rock correlation based on carbon isotopes of the Ct5 + saturate hydrocarbon fraction and ratios of the C~9/C~3tricyclic terpanes. The distribution of values suggest two different oil types within ANWR (I) Jago Rv., Katakturuk Rv., and Angun Pt., and (2) Manning Pt. and one oil type adjacent to ANWR (Kavik). The Jago Rv. etc. oil type correlates well with the type II facies of the Hue Shale unit.
units except the pebble shale unit could be ruled out as potential source rocks for the northeastern Alaska seeps and oil-stained rocks. However, it is the type II organic facies of the Hue Shale and Canning Shale, and the Shublik Formation that are isotopically most like the Jago and Manning oil types. The plot of the 6 ~3C values for the saturate hydrocarbon vs C19/C23 tricyclic terpane ratios, found useful in distinguishing the ANWR oil types, is compared in Fig. 5 with the 6~3C and C19/C23 ratios in the bitumen extracts from the various ANWR rock units. In this plot (Fig. 5), as with isotope plot (Fig. 4), the rock units with the greatest similarity to the Jago oil type were the Shublik Formation and the type II facies (15, 18-22; Table 1) of the Hue and Canning Shales. Since the isotope vs Ct9/C23 tricyclic terpane values for the Manning and Kavik oil types lie outside the values for the rocks, the source of these two oil types remain unknown. The high Hopane/C23 tricyclic terpane ratios (> 7) that characterize the A N W R oils were also found to be high in all of the thermally immature rock extracts but low ( < I ) in all the thermally mature rock extracts (Tables 1 and 2). Because this ratio is not expected to change dramatically during oil biodegradation, but can change to lower values with migration, the much lower Hopane/C23 tricyclic ratios in the mature rocks in comparison to the higher values in the oils suggest that expulsion had to have begun quite early in catagenesis and the migrational effects had too have been minimal in order for the values in the oils to remain so high. CONCLUSIONS
the best rational for concluding which rock unit is the source of a particular oil type. In the current study, five rock units, the Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale, were evaluated as possible source rocks for the A N W R (Jago and Manning) and Kavik oil types. A comparison of 613C values for the saturate and aromatic hydrocarbon fractions from the ANWR rocks and oils is seen in Fig. 4. For comparison purposes, the ~ ~3C values for the hydrocarbon fractions from the principle Prudhoe Bay source rocks (Kingak Shale and Shublik Formation) are also shown. In Fig. 4, the A N W R Hue Shale and Canning Shale are shown plotted as one unit because they are lithologically similar and stratigraphically adjacent (Molenaar et al., in press). Isotopic variation within the Hue and Canning Shales is largely a function of organic matter type. The type II facies (15, 18-22, Table 1) are isotopically the lightest (fi~3C = -28.7 + 0.3 saturate HC and - 2 8 . 2 + 0.6 aromatic HC) and the type III facies (14, 16, 17, 23-25; Table 2) are isotopically heaviest and have a broader range of values (613C= --27.3 + 1.3 saturate HC and -27.1 +0.8 aromatic HC). Based on the observed carbon isotopic similarities and dissimilarities between the rocks and oils (Fig. 4), none of the rock
Three distinct oil types within and adjacent to ANWR are identified from geochemical differences in their carbon isotope values of the saturate and aromatic hydrocarbon fractions, saturate/aromatic hydrocarbon ratios, C19/C23 tricyclic terpane ratios, and Hopane/Cz3 tricyclic terpane ratios. The three oil types are as follows: (1) Jago oil type, includes samples from the Katakturuk River, Jago River and Angun Point; (2) Manning oil type from the Manning Point adjacent to the Beaufort Sea; and (3) Kavik oil type from the Kavik area west of the Canning River near ANWR. Based on geochemical correlation criteria, none of the three northeastern Alaska oil types compares favorably with the commerically important Prudhoe Bay on NPRA oil types. Five rock units, Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale are evaluated, as to their oil source quality and maturity, In the coastal plain of eastern ANWR, the Kingak Shale, pebble shale unit, and Canning Shale are thermally immature (< 0.6% Ro), dominated by type III organic matter, and give poor yields of liquid hydrocarbons during pyrolysis ( < 1.2 kg/metric ton). In western ANWR, the Shublik Formation and Kingak Shale are truncated north of the Shublik
Oil-source correlation study in N.E. Alaska Mountains, and in outcrops of the Ignek Valley section these units could not be adequately evaluated because of the advanced thermal maturity of their organic matter. The most promising source rocks within A N W R are the type II (marine) facies of the Hue Shale as this unit contains up to 18 wt% organic carbon, is hydrogen rich, and gives yields of up to 88 kgHC/metric ton of rock during pyrolysis. Oil-source rock correlation suggests that the most promising source rocks for the Jago oil type are the type II organic facies of the Hue Shale based on similarities in carbon isotope values of the saturate and aromatic hydrocarbon fractions and their CI9/C23 tricyclic terpane ratios. The Canning Shale, pebble shale unit, and upper part of the Kingak Shale can be ruled out as potential source rocks for the A N W R oils on the basis that their organic matter is gas prone and their geochemical properties do not correlate well with the oils. Geochemically, the M a n n i n g and Kavik oil types are sufficiently different from the bitumens extracted from the five rock units so as to suggest a source that has not been evaluated as yet.
415
REFERENCES
Magoon L. B. and Bird K. J. (in press) Alaska North Slope Petroleum Geochemistry for the Shublik Formation, Kingak Shale, pebble shale unit and Torok Formation. In Alaska North Slope Oil-Rock Correlation Stud), (Edited by Magoon L. B. and Claypool G. E.). Am. Assoc. Pet. Geol. Spec. Stud. Geol. No. 20. Magoon L. B., Bird K. J., Claypool G. E., Weitzman D. E. and Thompson R. H. (in press) Organic geochemistry, hydrocarbon occurrence, and geology of government drilled wells, North Slope, Alaska. In Geology of the National Petroleum Reserve in Alaska (Edited by Gryc G.). U.S. Geol. Surv. Prof. Pap. Magoon L. B. and Claypool G. E. (1981) Two oil types on North Slope of Alaska--Implications for exploration. Am. Assoc. Pet. Geol. Bull. 65, 644-652. Magoon L. B. and Claypool G. E. (1984) The Kingak Shale of Northern Alsaka--Regional variations in organic geochemical properties and petroleum source rock quality. Advances in Organic Geochemistry 1983 (Edited by Schenck P. A., De Leeuw J. W. and Lijmbach G. W. M.). Org. Geochem. 6, 533-542. Pergamon Press, Oxford. Magoon L. B. and Claypool G. E. (in press) Geochemistry of oils, National Petroleum Reserve in Alaska. In Geology of the National Petroleum Reserve in Alaska (Edited by Gryc C.) U.S. Geol. Surv. Prof. Pap. Molenaar C. M. (1983) Depositional relations of Cretaceous and Lower Tertiary rocks, northeastern Alaska. Am. Assoc. Pet. Geol. Bull. 67, 10661080. Molenaar C. M., Bird K. J. and Kirk A. R. (in Press)
Carman G. J. and Hardwick P. (1983) Geology and regional setting of the Kuparuk oil field, Alaska. Am. Assoc. Pet. Geol. Bull. 67, 1014~1031. Hunt J. M. (1979) In Petroleum geochemistry and geology, 617 pp. W. H. Freeman, San Francisco. Jones H. P. and Speers R. G. (1976) Permo-Triassic reservoirs of Prudhoe Bay field, North Slope, Alaska. In North American oil and gasfields (Edited by Braunstein, J.). pp. 23 50. Am. Assoc. Pet. Geol. Mem. 24. Lyle W. M., Palmer I. F. Bolm J. G. and Maxey L. R. (1980) Post-Early Triassic Formations of northeastern Alaska and their petroleum reservoir and source-rock potential. Alaska Division of Geological and Geophysical Surveys Geologic Report 76.
Morgridge D. L. and Smith W. B. (1972) Geology and discovery of Prudhoe Bay field, eastern Arctic Slope, Alaska. In Stratigraphic Oil and Gas Fields (Edited by King R. E.), pp, 489-501. Am. Assoc. Pet. Geol. Mem. 16. Palmer I. F., Bolm J. G., Maxey L. R. and Lyle W. M. (1979) Petroleum source rock and reservoir quality data from outcrop samples, onshore North Slope of Alaska east of Prudhoe Bay. U.S. Geol. Surv. Open-File Rep. 79-1634. Seifert W. K., Moldowan J. M. and Jones J. W. (1979) Application of biological marker chemistry to petroleum exploration, lOth World petroleum Congress in Bucharest, pp. 425~t40. Heyden & Son, London.
Cretaceous and Tertiary Stratigraphy of Northeastern Alaska.
Org. Geochem. Vol. I0, pp. 407-415, 1986
0146-6380/86 $3.00 + 0.00 Pergamon Journals Ltd
Printed in Great Britain
Oil-source correlation study in northeastern Alaska DONALD E. ANDERSl and LESLIE B. MAGOON2 ~U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, U.S.A. 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, U.S.A.
(Received 19 September 1985; accepted 5 March 1986) Abstract--The occurrence of numerous oil-seeps and oil-stained outcrops across the coastal plain of the Arctic National Wildlife Refuge (ANWR) in northeastern Alaska indicates that commercial hydrocarbons could be present in the subsurface of this region. In addition, this region is flanked by two important oil provinces--the Prudhoe Bay area to the west and the Mackenzie delta to the east. To begin to understand the petroleum resource potential of ANWR, we evaluated the source rock quality and thermal maturity of five rock units ranging in age from Triassic to early Tertiary: Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale and Canning Shale. We also compared ANWR oils using stable carbon isotope ratios, tricyclic terpane ratios, and saturate/aromatic hydrocarbon ratios. The organic carbon content of the five rock units range from an average of 1.6 to 4.0 wt%. Cretaceous rocks from the coastal plain are thermally immature (vitrinite reflectance <0.5%) and in the southern mountains thermally mature to overmature (vitrinite reflectance 1.0--1.8%). In general, type III organic matter predominates in the Kingak Shale, pebble shale unit, and Canning Shale, and types II and III in the Hue Shale. ANWR oils are divided into three groups: (1) Jago oil type, includes oils from Angun Point, Katakturuk River and Jago River; (2) Manning oil type, from Manning Point near the coast of the Beaufort Sea; and (3) Kavik oil type, from Kavik west of the Canning River. None of the three oil types of ANWR compares favorably with the economically important oils from Prudhoe Bay and the National Petroleum Reserve of Alaska (NPRA). The most promising source rock for oils of the Jago River type is the organic rich type II units of the Hue Shale. Possible source rocks for the other ANWR oil types could not be established.
Key words: oil-source correlation, Alaska, Prudhoe Bay, Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, Canning Shale
INTRODUCTION
Six oil-seeps or oil-stained outcrops in or adjacent to the Alaska National Wildlife Refuge (ANWR) coastal plain in northeastern Alaska indicate that commercial hydrocarbons could be present in the subsurface. This area is flanked by two important petroleum provinces, the Prudhoe Bay area on the west which has estimated recoverable resources of 17-21 billion barrels of oil and 31 trillion cubic feet of gas, and the Mackenzie delta on the east which has estimated recoverable resources of 0.74 billion barrels of oil and 10 trillion cubic feet of gas. The character and source of the hydrocarbons, as well as the geology in these two adjoining provinces, are distinctly different from each other making direct extrapolation from either side into the A N W R coastal plain difficult. This study examines the oil and rock samples in northeastern Alaska to determine the source or sources of the ANWR oil-seeps or stains, and to determine if the oil type(s) is similar to the oils being produced in Prudhoe Bay (Seifert et al., 1979) and the National Petroleum Reserve of Alaska (Magoon and Claypool, 1981, in press). The oil-and-gas potential of five rock units: the Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale are evaluated. These 407
five rock units was selected on the basis of preliminary geological and geochemical evidence which suggests that they are the most likely source rocks for the ANWR oil seeps and stains. Four types of analyses are used to evaluate the resource potential of these units: (1) organic-carbon content (wt%), (2) Rock-Eval pyrolysis (organic matter type and hydrogen richness), (3) C~5 + hydrocarbon content (ppm), and (4) vitrinite reflectance (% Ro). Oil-oil and oil-source rock comparisons of the following geochemical properties, carbon isotopes of the saturate and aromatic hydrocarbon fractions, gas chromatography of the saturate hydrocarbon fractions, and GC/MS relative abundances of specific tricyclic and pentacyclic terpanes, are used to establish genetic oil types and principle source rocks for the oil types. Subsurface geochemical information on the North Slope is published by Morgridge and Smith (1972), Jones and Speers 0976), Seifert et al. 0979), Magoon and Claypool (1981, 1984, in press), Carman and Hardwick (1983), and Magoon and Bird (in press), Magoon et al. (in press) for both rocks and oils. Preliminary source-rock information on outcrops in northeastern Alaska is reported by Palmer et aL (1979), Lyle et aL (1980), Molenaar (1983) and Molenaar et aL (in press).
408
DONALD E. ANDERS and LESLIE B. MAGOON ~UOHOE
0
L
BAY
BEAsU~ART
BARTER ~SLANO~
~
b
Fig. I. Map showing the general location of rock samples analyzed in this northeastern Alaska study. Numbers on map correspond to sample reference column in Table 1. SAMPLE DISTRIBUTION
The reliability of oil and gas source-rock assessment depends upon "adequate" geochemical characterization of the stratigraphic interval(s) considered; adequate characterization is a sampling problem dependent upon the thickness, aerial extent, and internal geochemical variability. In this study, the stratigraphic intervals range in thickness from less than one hundred meters to several hundred meters and most extend aerially across the North Slope. Many more samples (586) were used to characterize each stratigraphic unit than is presented in this paper on Table i. West of the Canning River, most of the rock samples are from industry exploratory wells; east of the Canning River all the rocks are surface from the Sadlerochit and Shublik Mountains and the A N W R coastal plain (Fig. 1). The distribution of the oil samples in this report is restricted to the Prudhoe Bay oil field, Cape Simpson and Umiat oil fields and oil from the South Barrow gas field in the National Petroleum Reserve in Alaska (NPRA), and six seeps and stains in or adjacent to A N W R (Fig. 2).
GEOLOGIC FRAMEWORK This study is restricted to five stratigraphic intervals: the Triassic Shublik Formation, the Jurassic and
-i•~
~
Lower Cretaceous Kingak Shale, the Lower Cretaceous pebble shale unit, the Lower and Upper Cretaceous Hue Shale, and the Upper Cretaceous and lower Tertiary Canning Shale (Fig. 3). The structural configuration of these rock units in northeastern Alaska differs on either side of the Canning River. West of the river, rock units older than the Canning Shale dip gently to the south, while the basin clinoform strata of the Canning Shale dip gentle to the northeast. East of the river, steep dips and deformation are common to coastal plain sediments as well as to strata in the Sadlerochit and Shublik Mountains. In northeastern Alaska, an unconformity at the base of the pebble shale unit truncates both the Shublik Formation and the Kingak Shale north of the Sadlerochit and Shublik Mountains. A brief description of each rock units follows. Shublik Formation: The Shublik Formation is a distinctive unit consisting of calcareous and sooty shale and fossiliferous dark, phosphatic limestone. It crops out in the Sadlerochit and Shublik Mountains and along the mountain front to the east and occurs in parts of the subsurface to the west. Kingak Shale: The Kingak Shale crops out along the mountain front and occurs in parts of the subsurface to the west. It consists predominantly of dark gray marine shale ranging in thickness from zero where truncated by the pebble shale unconformity to 1200 m.
BEAUFORT SEA
NATIONALPETROLEUM
UMIAT # 4 ~ .
Fig. 2. Map showing the general location of analyzed oil-seeps and stained rocks in northeastern Alsaka and selected North Slope oils. Numbers on map correspond to sample reference column in Table 2.
Ref.
Pebble Sh. Kupt r u k P~u. RtnKak S h .
3
,, ShubI 1k Fu.
Klngak ST~.
12 19
PI
569 539
5?6 406 426 462 560
538 502
431 437 405
411 406 409 408 450
424 438 432 435 404
429 412 639
420 432 437 418 423
434 431 418 429 429
(C)
Tm~x
2.1 1.8
1.5 0.5 1.4 1.9
1.0 1.1 0.5 1.6 1.8
0.5 0.5
1.0 1.0 1.2
0.5 0.5 0.4
0.4 0.5 0.5 0.4 0.4
0.5 0.5 0.5 0.5 0.3
Z
Ro
V~_~f~
214 I37
848 2144 205 68 129
791 715 425 254 507
8673 9707 3062 7500 947
202 1376 1012 1220 ROgk
3480 7778 691
3140 1645 6741 2531 3533
407 323 2991 8302 1546
1.0 0.5
1.8 4.8 0.8 0.8 0.6
3.2 1.6 0.7 0.7 1.2
10.8 6.8 5.2 4.1 2.4
1.3 5.8 3.3 2.4 5.2
7.3 77.8 6.6
6.2 14.2 9.6 10.5 8.8
3.4 2.9 5.5 20.8 5.0
Z
EOt4/TOC
108 71
0.5 0.3
0.9 2.9 0.6 0.5 0.4
439 1323 106 41 76
2.3 l.l 0.1 0.3 0.6
7.8 3.8 3.1 1.3 1.8
0.6 3.7 2.3 1.8 2.7
4.5 57.7 3.2
3.3 9.6 6.5 7.0 4.8
1.8 1.4 4.2 14.4 3.3
2
tlC/TOC
5113 301 80 88 247
6266 5388 1838 2392 697
83 993 703 903 4209
5772 338
2130
1706 1242 6543 1689 1909
212 133 2212 5771 1013
ppa
tIC
4.1 3.4
1.1 3.6 1.6 0.8 2.9
2.2 0.6 0.1 1.0
3.1
1.9 1.3 1.5 0.9 2.1
1.4 2.1 1.3 3.5 1.2
2.7 k.0 2.0
2.3 3.7 1.8 2.3 1.0
2.2 1.3 2.9 3.2 3.0
S/A
-27.4 -29.1
-24.9 -28.9 -28.3 -26.3 -27.3
-27.4 --25.3 -23.6
-27.1
-29.0 -28.4 -30.0 -28.6 -27.k
-28.6 -28.7 -27.6 -23.9 --
-26.1 -27.9
-2~_.2 -27.6 -27.3 -25.5 -28.1
-26.6 -25.2 -22.4 -22.3
-26.9
-28.0 -28.8 --27.6 -27.9
-27.7 -28.5 -27.0 -26.2 --
-30.6 -29.7 -27.4
-30.0 -30.6 -30.1 -29.8 -30.2
-30.6 -30.5 -30.6 -30.1 -29.2 -30.8 -30.1 -27.9
-26.8 -2 6 0 6 -28.9 -29.4 -30.9
A r o a . KC
6 t3C
-28.3 -28.5 -29.4 -29.9 -31.2
S a t .RC
6 13C
,l~otope Data
4aaaC292OS/a~C292OS+~oaC2920R s t e r a n e s ;
55 60
221 392 57 15 44
137 137 312 59 109
1/~1 3808 1077 4202 182
78 321 187 161 3280
873 1793 154
990 272 1353 950 1503
147 127 786 3248 337
pl~a
non HC
E x c r a c t t o ~ Oat~
1.5 1.6
1.8 1.5 0.6 2.8 1.6
2.0 0.8 1.9 2.7
2.9
1.5 0.4 0.2 0.3 4.6
0.3 1.7 2.8 3.7 0.3
1.4 0.9 3.9
1.1 1.8 1.2 1.7 2.9
1.5 1.2 0.8 1.8 1.0
1.7 1.3
2.3 1.9 2.5 1.3 1.2
1.5 3.4 1.3 2.0
[.8
2.0 t.q 1. 5 1.2 2.0
1.7 1. 4 1. 6 1. 7 1ol
2.3 l.I 1.2
2. 7 1. 8 2.0 1. 7 1.4
2.3 2.7 2.4 1. 5 2.6
Pr/Ph 2
value <0.I
nCI7/Pr
steranes', 6C2820R t rt~romatLc/C2820R triaro~t t,: + C2920R mnoaromat tc steranes; 7negligible; 81mture,
cerpane;
ppm
EOM
terpane/C23 crtcycltc
0.11 0.07
0.07 O.2~ 0.07 O.10 0.06
0.07 0.10
0.08 0.09 0.03
0.10 0.03 0.06 0.03 0.O4
0.03 0.04 0.16 0.05 0.03
0.06 0.50 0.22
O.05 0.07 0.07 0.10 0.04
0.11 0.11 0.11 0.31 0.04
3CI 9 c r i c y c t t c
0.36 0.42
23
32
0.99 1.22 0.73 0.44 0.50
0.39 1.20
0.92 0.79 0.62
38.04 66.82 20.30 88.40 2.60
0.76 4.93 0.93 2.10 80.84
21.61 6.29 0.75
17.50 5.36 42.22 8.54 42.89
0.97 0.62 13.65 7.36 11.15
Kg/H con
S l + S2
R o c k - E v a l ~sta
18 58 75 27 19
27 16
38 62 gO
19 19 24 23 12
90 17 41 12 27
13 4t 219
19 20 14 13~
23 32 18 69 17
Ol
s~,~ P t g u r e 1; 2 p r l s t a n e / g h y t a n e ;
2.1 2.5
19 ~0 25 35 17
5B£C292OS+SBC292OR/~C2920S+BBC2920R+~C2920S+~aC292OR
I g o r sample l o c a t / o n s ,
14 35
30 31 32 33
4.8 4.5 Z.7 0.9 2.1
29
53 19 I1
2.5 4.6 6.3
19 24
429 456 326 471 51
69 167 26 ~5
518 300 88
466 306 586 357 720
240 162 399
~3
HI
8.0 14.2 5.9 18.3 3.9
1 .5 2.7 3.1 5.0 15 .6
4.8 1 .0 1.1
5.1 1 .3 7.0 2.4 4.0
1.2 1.1 5.3 4.0 3.1
X
TOC
3.5 4.3
" pebble sh.
"
"
(~ccrop
8910 8921 9533-9536
8868 8885 8900 8930 8985
8531 8386 8956-9085 6643 U53
ft.
Depth
27 28
26
25
24
19 20 21 22 23
14 13 16 17 18
C a n n i u g Sh. " Hue S h a l e
I v i s h a k Sg.
II 12 13
#.t~qt locks
S h u b l i k Yu. "
6 7 8 9 10
4 5
Canal u g S h .
1 2
Prudhoe Ba7 Rocks
Rock
Unit
sample I
Sample D e s c r t p t ton
Table I. Geochemical properties of Prudhoe Bay and ANWR rocks
* 0.2
0.9 1.0 2.0 0.4 0.2
0.9 3.8 0.2 2.1
1.4
0.4 0.5 0.4 0.3 1.2
1.3 0.8 0.6 0.9 0.4
0.4 <0.1 0.3
0.2 0.3 0.2 0.1 0.2
0.9 0.9 0.2 <0.1 0.2
C23Trt
C19Trl/3
* 0.5
0.7 13.8 55.0 0.1 0.1
0.3 114.0 0.2 t
0.5
10.8 22.0 8.0 t9.0 0.4
13.0 0,8 0.3 0.6 28.0
3.9 2.9 0.6
5.7 4.1 5.7 1.6 | .0
2.2 5.1 2.8 2.2 12.7
C23Trt
Ropane/
*
07.
*
0.6
•
flat, 0.6 0.6
0.4
0.6
*
0.4 0.5 lit* 0.4
0.5 0.4 0.3 0.4 0.5
lmt. 0.6 0*6 0.6 0.4
0.5 0.6 0.4
1.5
0.5
0.2 (0.1 0.6 0.6
1.5
0.5
*
0.4 0.5 (O.I 0.3
0.4 O .I 0.1 0.1 0.5
<0.1 0.4 0.5 0.4 0.1
0.5 t.5 1.5
•
1.2
0.5
1.5 1.5
0.8 0.3 1.0 0.2 1.5
,7 15 1o5 1.3 0.Z
0.5 0.4
0.4 0.5
0.4 0.4
0.5
0.5
1.5 1.3
0.3 0.5
0.5
0*5 0.5 0.3 0.5 0.3
8
~BB EgB÷E~o
0.4 0.5
0.3 0.3 0.4 0.4 0.4
acm20R
~2OS 4 ao~20S+
1.4
1.5 1.5 1.5 1.5 1.3
1.3 1.4 1.4 1.4 1.5
S/R
C3ihopanes
8 1 o s ~ r k e r Data
(.0
1.0
0.4 1.0 1.0
0.5
t°O
1.0 1.O
0*5
1.0 1.0
* 0.0 0.1 0.0 1.0
O.I 1.O I.O I°O O.O
0.7 0.8 0.6
0.8 0.8
O.q
0.7 0.8
0.6 0.6 0.7 0*9 0.8
C2920 k
02820R6 C282011 ÷
410
DONALDE. ANDERSand LESLIEB. MAGOON
AGE
QUATERNARY
S'rRATIGRAPfllC uNrT
li
ORGANIC GEOCHEMISTRY
LffHO.OGY qSw)~t]
Rocks
SURF~IAL DEPOSITS
PLIOCENE
MIOCENE
SAGAVANIRICTOK .~'._~m~. FORMATION ~,.~:i~.~ ~ . .
Qua.
"22272--'
EOCENEI~ PALE~IENE
'7!;
....
~
CANNING SHALE
LATE CRETACEOUS EARLY
-
" ~ _ _ T 2'
!
HUE SHALE
•
A A it-:
Glcnma--rly ~' ~ - ' ~ " - ~ ' zo~ u CRETACEOUS ~.. >IEIIIILE SHALE UNiT (LATE NEOCOMIAN U KEMIK SS MIR EARLY
i
- -- -- ~ ~-- -- -- -
CRETACEOUS
AND
KINGAK SHALE
JUFIASSIC
........ ........
KAREN CREEK SS
:",T : i '
:
SHUBUK FORMATION
"---"-2---
PE~IAN
~
ECHOOKA FORMATION
I
' " ~" "
"I
Fig. 3. Generalized stratigraphic column for the northern part of the Arctic National Wildlife Refuge (ANWR). Pebble shale unit: The pebble shale unit is an Early Cretaceous regional rock unit that can be mapped across the entire North Slope. In the Sadlerochit and Shublik Mountains area, the pebble shale unit is 60-90m thick and consists of dark-gray to black, noncalcareous, clayey to silty shale containing scattered pebbles or grains of chert and quartzite (Molenaar, 1983). Canning Shale and Hue Shale: These two shales are a sequence of silici-clastic rocks deposited by a northeasterly prograding delta of which only the fine-grained sediments will be discussed. The Hue Shale, which contains a radioactive shale at the base, is a distal condensed shale facies that crops out around the Sadlerochit Mountains and in the Niguanak River area on the ANWR coastal plain. It is usually less than 300 m thick and consists of black, fissile, noncalcareous, clay shale and bentonite (Molenaar et al., in press). The Canning Shale gradationally overlies in the Hue Shale and consists of 1200 to 1800m of darkgray to gray-brown bentonitic shale and siltstone with thin turbidite sandstone beds in the lower part (Molenaar et al., in press). It exists in the subsurface west of the Canning River and crops out around the Sadlerochit Mountains.
Thermal maturity: According to Seifert et al. (1979), the principle source rocks for the Prudhoe Bay oils are the Kingak Shale and Shublik Formation. Our work on the thermal maturity for these two units at Prudhoe Bay indicate that the organic matter is immature to marginally mature with respect to hydrocarbon generation to depths up to 2750m (Tin,X 412-438°C, vitrinite reflectance 0.3-0.5% Ro; Table 1). Because of the low thermal maturity of the source rocks at Prudhoe Bay, the oil in this region probably migrated from stratigraphically equivalent but more deeply buried rocks to the south. Thermal maturity data for the organic matter in the potential source rocks of A N W R is not a simple function of present day burial depths. For example, all rock units, regardless of age, exposed at the Ignek Valley section (15-17, 23-25, 27, 29 and 32-35, Table 1) as a result of the Sadlerochit and Shublik Mountain uplift are thermally mature to post mature with respect to hydrocarbon generation (Tin, x, 432-560°C; 1.0-2.0% Ro, Table 1). Whereas, 100 km northeast of the Ignek Valley section, in the Jago River and Niguanak River area of the ANWR coastal plain (18-22, 26, 30 and 31, Table l), the same rock units are thermally immature ( Tmax, 401-409°C; <0.6% RO, Table 1). Organic matter type and quality: Magoon and Bird (in Press) indicate that the pebble shale unit tends toward type III organic matter across the entire North Slope but that the Kingak Shale and Shublik Formation are predominantly type II/III across NPRA and type II/I south of and in the Prudhoe Bay area. Data presented in Table 1 for the potential source rocks in the Prudhoe Bay area (samples 1-13) agree with the Magoon and Bird (in press) conclusions. Average organic carbon content for the Kingak Shale and Shublik Formation is 2.0 wt%. Within ANWR, the only rock unit sampled with sufficient organic matter and hydrogen rich kerogen to generate commercial quantities of liquid hydrocarbons is the Hue Shale. Immature samples (0.5% Ro) of the Hue Shale 08-22, Table 1) from the Jago River and Niguanak River sections of the coastal plain give hydrogen index values (HI = 324-505 mg HC/gC) indicative of type II/III organic matter and organic carbon content up to 18 wt% (av. 4.0 wt%). As further proof of the hydrocarbon generating capacity of the Hue Shale at the Jago River and Niguanak River sections, samples 19 and 22 (Table 1) produce abundant liquid hydrocarbons during hydrous pyrolysis (50-51, Table 2). In the Ignek Valley section of the Sadlerochit and Shublik Mountains of ANWR, it is more difficult to determine the organic matter type in the Hue Shale because of its advanced thermal maturity (1.0-1.2% Ro; 16, 17, 23-25, Table l). This increased thermal
Oil-source correlation study in N.E. Alaska maturity of the Hue Shale at the Ignek Valley section relative to the Hue Shale at the Jago and Niguanak River sections is not sufficient in itself to explain the extraordinary drop of the hydrogen index from an average of 400 mg HC/gC at the Jago and Niguanak River sections to < 50 mg HC/gC at the Ignek Valley section. The low hydrogen indices, coupled with low production indices and low hydrocarbon yields, for the Hue Shale at Ignek Valley relative to higher values for this unit at the Jago River and Niguanak River sections, may indicate a northeast-southwest change in organic matter type within these two units from type II on the northeast coastal plain to type III at the southwest Ignek Valley section. The organic carbon content of the Kingak Shale, pebble shale unit, and Canning Shale samples from the Jago and Niguanak River section of the ANWR coastal plain average 2.0, 3.0 and 2.0wt%, respectively. The organic matter type in these three rock units is predominantely type III based on their low hydrogen indices (11 to 69 mgHC/gC) and high C29 sterane content relative to their C27 and C28 sterane content (3:1). Further, the low hydrocarbon generating capacity (0.62-1.22 kg/metric ton) of these units is in agreement with an organic matter type III assignment. At the Ignek Valley section, the Kingak Shale and the pebble shale unit are in the late stages of thermal generation of hydrocarbons and cannot be evaluated with certainty as to their organic matter type. However, the low hydrocarbon yield ( < 1.2 kg/ metric ton), low production index (<0.1) and high pristane/phytane ratio ( > 1.8) for these thermally mature units suggest that the dominate organic matter in the rock units to the south are also type III. Immature pebble shale unit and Kingak Shale samples 26 and 31 (Table 1) from the Niguanak River (52, 53, Table 2) produce predominantly gas during hydrous pyrolysis. The Canning Shale at the Ignek Valley section contains predominately type III organic matter with an occasional thin section of type II organic matter. Since the Shublik Formation is overmature (> 1.8% Ro, Table 1) in ANWR, the resource potential of this unit in northeastern Alaska cannot be evaluated except by cautiously extrapolating values from marginally mature samples in the Prudhoe Bay area. Based on organic carbon content, organic matter type or hydrogen richness, and hydrocarbon yield from hydrous pyrolysis and Rock-Eval, the upper Kingak Shale, pebble shale unit, and Canning Shale are gas prone, and the Hue Shale is oil prone in ANWR. Cj5+ hydrocarbons: The material most like petroleum in sedimentary rocks is the solvent extractable hydrocarbons. The relationship between C~5 + extractable hydrocarbons and organic carbon content was first established by Hunt (1979). In the Hunt model, oil stained rocks or reservoir rocks contain more than 100 mg HC/g OC (> 10 wt%), immature
411
and metamorphosed rocks contain less than 10 mg HC/g OC ( < 1.0 wt%) and source rocks fall between these upper and lower limits. Two Prudhoe Bay samples (4, 12, Table l) and seven ANWR samples (41-44, 46, 47, 49, Table 2) contain more than 100 mg HC/g OC and are probably stained by migrated hydrocarbons. Nine A N W R samples 04, 26-29, 33-35) contain less than 10 mg HC/g OC; three are immature (<0.6% Ro) and six have obtained a high degree of thermal maturity ( > 1.5% Ro). The remaining samples from Prudhoe Bay and ANWR fall in the range for oil source rocks and show the expected trend of increasing hydrocarbon content with increasing carbon content.
Oils Two oil-seeps and seven oil-stained rocks from six locations in or adjacent to the ANWR coastal plain (Fig. 2) were geochemically compared. The results of the solvent extraction of the oil-stained rocks are reported on Table 2. All seven of the hydrocarbon stained rocks from ANWR contain more than 100 mg HC/g OC and five contain more than 300 mg HC/g OC. With the exception of sample 42, hydrocarbons from the ANWR oil seeps and stained rocks (41-49, Table 2) are biodegraded--containing no measureable amounts of n-alkanes or regular chain isoprenoids. Four of the samples (41, 43-45, Table 2) are severely biodegraded (hydrocarbon content <25 wt%). The severely biodegraded hydrocarbon samples are dominated by hydrocarbons with boiling points > n-Cz0, while the lesser biodegraded samples (46--49, Table 2) are dominated by hydrocarbons boiling < n-C20. Carbon isotope values for the northeastern Alaska seeps and stained rocks show distinct differences that help organize the oils into genetic types. For example, when the delta 13C values of the saturated hydrocarbon fractions of the oils are plotted vs the delta ~3C values of their aromatic hydrocarbon fractions, three genetic oil types are suggested by the results (Fig. 4). For comparison purposes, carbon isotope values for the saturated and aromatic hydrocarbon fractions from the Prudhoe Bay oil types (Seifert et al., 1979) and NPRA oil types (Magoon and Claypool, 1981) are also plotted on Fig. 4. ANWR oils from the Katakturuk River, Jago River and Angun Point are isotopically similar (613C = -29.2 + 0.3 for the saturate fractioins and -28.5 ___0.4 for the aromatic fractions) and are designated the Jago oil type; whereas, the hydrocarbon fractions from the Manning Point samples are about 1.0 per mil heavier and for the Kavik area sample adjacent to ANWR, about 2.5 per mil heavier than the oils of the Jago type and are designated the Manning and Kavik types, respectively. Based on these carbon isotopic differences, two oil types, Jago and Manning, are suggested for oils on the ANWR coastal plain and one type, Kavik, is adjacent to the ANWR coastal plain west of the Canning River.
Unit
Rock
299 -1556-1639
7702-10 10,~17-535
Outcrop " Sutfa~e Outcrop
wt. X
TO~
-
-
-
44.7 75.9 87.6
-
_
19.9 12.9 26.~ 11.7
9.3 73.8 77.9 73.6
~0.9
-
1.9
**
**
3.0
2.5 2.2 5.2 5.t
5.2 2.6 3.0 2.9
,.8
~.0 ~.1 3.1
3.8 I.~
S/A
**
8
35.8 66.1 77.t
76.9 23.1 19.4 -
,,.0
2
~C/TOC
~t
80.1 87.1 73.2 M.3
90.7 26.2 22.1 24.~
19.1
98.8 9~.3 88.0
91.8 79.8
Wt. I
tiC
-
-
-28.3
-27.9
-28.8 -28.9 -27.5 -27.6
-28.8 -28.1 -28.1 -28.3
-27.8
-26.7 -27.$ -28.7
-30.$ -29.1
Arom.HC
~ 13 C
1.8 0.7
1.6
2.6
* s * *
* * *
* * ~ *
I. 3
* * *
•
2.2 2.1 1.2
2.S 1.5
Pr/Ph 2
O.&
.
2 07 * 0.9
1.~ 2.0
uC17/Pr
781odegraded and ~emthered; 8~cee hydrocarbons f l o a t i n g
on the ~ a t ~
s u r f a c e ~ f t e c hydrous p y r o l y s i s :
8teranes;
0.3
0.5
0.5 0.5 2.1 1.9
0.3 0.~ 0.6
0.6
0.1
1.9 0.6 0.2
0.2 <0.1
C23Tri
ClgTri/3
Data
8L~t,:r~,
15.0
9.0
8.~ 7.1 15.7 13.8
13.8 * *
9.0
•
2.3 ~.$ 0.~
19.0 ~.1
C23Tri
0.4 0.~ 0.4 0.t
0.4 a *
0. S
•
0.5 0.~ 0.S
0.S 0.$
~a20l
~ o 20S+
aoa 20S t
* ~ u e <0.1
0.8
1.0
1.4 1.2 1.2 1.2
1.~ * *
1.3
•
1.2 1.3 1.7
1.~ I .~
S/!
Daphne/ C31Hop~nes
l/mrker
simple 19 (2392 ppll), sample 22 (2409 ppm), samples 26 and 31 (<100 ppu).
4o~aC2920S/oa~C2920S+~aac292OR
-28.9
-29.0
-29.~ -29.2 -28.2 -28.&
-29.5 -29.3 -29.0 -28.9
-2,.7
-28.0 -28.~ -29.1
-31.8 -29.6
Sut.I~
~ 13c
l a o t o ~ e Data
terpane;
8,500 20,500 use 9 ~,~00
9,., 8&.8 88.0 88.0 -
1.2 5.7 12.0
8.2 20.2
wt. X
non HC
. ,
trtaroma¢tc ÷ C292QKIonoaro~l¢ic stetanes; 7negligible;
22 sh. 26 Sh. 31
1.9 2.7 11.O
4.240 20,2~0 69,320 s~p
28,,00
-
-
~
KO~/TOC
D~&
1For sample L o c a t i o n s , nee Figure 2; 2 p r l a t a n e / P h y t a n e ; 3CI9 c r l c y c L t c terpmne/C23 o r * c y c l i c
8ample pebble sample Kia~mk sample
2.8
0.$ 2.3 7.9
-
-
pqm
~0N
8xtraetioa
5~C292OS÷~C2920K/~aC2920S÷~C2920K÷~C29203÷~C2920~ ~¢exanea; 6C2820R t r t ~ r o ~ t i c / C 2 8 2 0 R
53
~2
~e
St
~ha~e
Hue ShaI~ amlple 19
50
Hydrous P y r o l y s i s
Quateremry
Surface
Tertiary
"
outo.o,
A6 47 ~8 49
-
C o l v i l l e Gp. Tertiary Quaternary
&2 ~3 44 43
,1
Pebble Sh.
Ilmmshedc Cp.
K l q a k Sh. Smdlerochit
ft.
Depth
OiL S t t £ ~ ' d O ' ~ t c r o ~ L S~v~tee S e e p a
38 34) ~0
NPU O i l s
36 37
Prudhoe l a ~ O i l s
Suf.
Sample 1
Sample D e s c r i p t i o n
Table 2. Geochemical properties of A N W R oil-stained rocks and seeps, and selected Prudhoe Bay and NPRA oils
ZBB~
C282~
0.5 0.6 0.5 0.6 0.6
t
t
C2920R
C2820l +
0.5 0.S 0.4 0.4
0.5
0.',
0.6 0.5 0.6
O.S 0.5
EB~+~aa
Z
Z
Z
4~ t,O
Oil-source correlation study in N.E. Alaska
ANWR CANNINGAND HUE S
H
(J "r
~
.....
_
S BARROW20(NPRA) OIL
l--
(n
L (NPf~A}
PRUDHOEBAY
U3
~'~MANNINGPOINTOIL{AN~) I S H UPSON W , O~L INPRA) SHUW.IK FORMAllON
~
FORMATION
ANGUN PT, KATAKTURUKRV, JAGO flV 011.5(ANW~)
~ P R -30
413
":•:. '~{i:;?:' ~.:i"
BAY OILS OPRUDHOE BAY SAG OELTAO~L UDHOE BAY KiNGAK SHALE
PRUOHOEBAY KAVEARAKOIL
-
,
,
.,2,
,
,
.;,
,
,
6~SC, AROMATIC HC
Fig. 4. Oil-oil and oil-source rock correlation based on carbon isotopes of the C,5 + saturate and aromatic hydrocarbon fractions. Isotopic comparison of the oils indicate two distinct oil types within ANWR (1) Jago Rv., Katakturuk Rv. and Angun Pt., and (2) Manning Pt. and one oil type adjacent to ANWR (Kavik). The Jago Rv., etc. oil type correlates best with the type II facies of the Hue Shale. The Jago oil type (42-47, Table 2) is isotopically most like the NPRA oil recovered from a sandstone within the pebble shale unit penetrated in the South Barrow No. 20 well (Fig. 4). The Manning oil type is isotopically similar to the oil recovered from the seismic shot point on the Simpson Peninsula in NPRA. The Kavik oil type is unlike any oil recovered to date on the North Slope and the Jago River and Manning Point oil types of A N W R are isotopically heavier than the Prudhoe Bay oil types of Seifert et aL (1979). Tricyclic terpane distributions were also useful in establishing three oil types within and adjacent to ANWR. For example, when the CI9/C23 tricyclic terpane ratio of the A N W R oils are plotted vs their delta ~3C values for the saturated fraction (Fig. 5), the same three oil types appear as were observed in the carbon isotope plot (Fig. 4). Oil-stained rocks from the Katakturuk River, Jago River, and Angun Point area (42-47) all group together as one type (Jago oil type), and the Manning Point (48, 49) and Kavik (41) samples each form their own separate type (Table 2, Fig. 5). Most of the oils on the North Slope have relatively low C19/C23 tricyclic terpane ratios, falling in the range of 0.1 to 0.6 (Table 2). Within this narrow range, the Prudhoe Bay oil types cannot be separated from the Kavik and S. Barrow 20 oil types, but can be differentiated from the consistantly higher
ratios of the Jago, Simpson, Manning and Umiat 4 oil types (Table 2, Fig. 5). The ANWR (Jago and Manning) and Kavik oil types (41-49) are easily distinguished from all other North Slope oils (37-40) except the Kavearak Point oil (36), by their high pentacyclic terpane content relative to their tricyclic terpane content (Table 2). Hopane/C23 tricyclic terpane ratios for the ANWR, Kavik, and Kavearak Point oils are all greater than seven, while all other North Slope oils are less than five. The saturate/aromatic hydrocarbon ratios of the biodegraded oils within or adjacent to ANWR fall into three ranges: (1) Jago oil type (43-47; Table 2), which includes samples from Katakturuk River near the Marsh Anticline, Jago River, and Angun Point, have ratios that range from 2.2 to 3.0; (2) Manning oil type (48, 49; Table 2) from Manning Point with a ratio of 5.3; and (3) Kavik oil type (41; Table 2) from Kavik west of the Canning River with an intermediate ratio of 3.8. As expected, nonbiodegraded oil sample 42 (Table 2) from the Katakturuk River near the Sadlerochit Mts. has a ratio twice as large as its biodegraded companion oil (43; Table 2). Oil-source rock correlation
Oil-source rock geochemical correlation provide
414
DONALDE. ANDERSand LESLIEB. MAGOON
CANNI,NG AND HU~ SHALES (ANWR}
~"
~
~
,
)
/
(
A
N
~
)
KINGAK SHALE (ANWR)
JAGO [~t, KA'rAk"TURUK qRV,
t
I 0.2
I 0.6 C19/C23
I 1.0 TRICYCLIC
I 1.4 TERPANE
1 1.8
i
r
2,2
RATIO
Fig. 5. Oil-oil and oil-source rock correlation based on carbon isotopes of the Ct5 + saturate hydrocarbon fraction and ratios of the C~9/C~3tricyclic terpanes. The distribution of values suggest two different oil types within ANWR (I) Jago Rv., Katakturuk Rv., and Angun Pt., and (2) Manning Pt. and one oil type adjacent to ANWR (Kavik). The Jago Rv. etc. oil type correlates well with the type II facies of the Hue Shale unit.
units except the pebble shale unit could be ruled out as potential source rocks for the northeastern Alaska seeps and oil-stained rocks. However, it is the type II organic facies of the Hue Shale and Canning Shale, and the Shublik Formation that are isotopically most like the Jago and Manning oil types. The plot of the 6 ~3C values for the saturate hydrocarbon vs C19/C23 tricyclic terpane ratios, found useful in distinguishing the ANWR oil types, is compared in Fig. 5 with the 6~3C and C19/C23 ratios in the bitumen extracts from the various ANWR rock units. In this plot (Fig. 5), as with isotope plot (Fig. 4), the rock units with the greatest similarity to the Jago oil type were the Shublik Formation and the type II facies (15, 18-22; Table 1) of the Hue and Canning Shales. Since the isotope vs Ct9/C23 tricyclic terpane values for the Manning and Kavik oil types lie outside the values for the rocks, the source of these two oil types remain unknown. The high Hopane/C23 tricyclic terpane ratios (> 7) that characterize the A N W R oils were also found to be high in all of the thermally immature rock extracts but low ( < I ) in all the thermally mature rock extracts (Tables 1 and 2). Because this ratio is not expected to change dramatically during oil biodegradation, but can change to lower values with migration, the much lower Hopane/C23 tricyclic ratios in the mature rocks in comparison to the higher values in the oils suggest that expulsion had to have begun quite early in catagenesis and the migrational effects had too have been minimal in order for the values in the oils to remain so high. CONCLUSIONS
the best rational for concluding which rock unit is the source of a particular oil type. In the current study, five rock units, the Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale, were evaluated as possible source rocks for the A N W R (Jago and Manning) and Kavik oil types. A comparison of 613C values for the saturate and aromatic hydrocarbon fractions from the ANWR rocks and oils is seen in Fig. 4. For comparison purposes, the ~ ~3C values for the hydrocarbon fractions from the principle Prudhoe Bay source rocks (Kingak Shale and Shublik Formation) are also shown. In Fig. 4, the A N W R Hue Shale and Canning Shale are shown plotted as one unit because they are lithologically similar and stratigraphically adjacent (Molenaar et al., in press). Isotopic variation within the Hue and Canning Shales is largely a function of organic matter type. The type II facies (15, 18-22, Table 1) are isotopically the lightest (fi~3C = -28.7 + 0.3 saturate HC and - 2 8 . 2 + 0.6 aromatic HC) and the type III facies (14, 16, 17, 23-25; Table 2) are isotopically heaviest and have a broader range of values (613C= --27.3 + 1.3 saturate HC and -27.1 +0.8 aromatic HC). Based on the observed carbon isotopic similarities and dissimilarities between the rocks and oils (Fig. 4), none of the rock
Three distinct oil types within and adjacent to ANWR are identified from geochemical differences in their carbon isotope values of the saturate and aromatic hydrocarbon fractions, saturate/aromatic hydrocarbon ratios, C19/C23 tricyclic terpane ratios, and Hopane/Cz3 tricyclic terpane ratios. The three oil types are as follows: (1) Jago oil type, includes samples from the Katakturuk River, Jago River and Angun Point; (2) Manning oil type from the Manning Point adjacent to the Beaufort Sea; and (3) Kavik oil type from the Kavik area west of the Canning River near ANWR. Based on geochemical correlation criteria, none of the three northeastern Alaska oil types compares favorably with the commerically important Prudhoe Bay on NPRA oil types. Five rock units, Shublik Formation, Kingak Shale, pebble shale unit, Hue Shale, and Canning Shale are evaluated, as to their oil source quality and maturity, In the coastal plain of eastern ANWR, the Kingak Shale, pebble shale unit, and Canning Shale are thermally immature (< 0.6% Ro), dominated by type III organic matter, and give poor yields of liquid hydrocarbons during pyrolysis ( < 1.2 kg/metric ton). In western ANWR, the Shublik Formation and Kingak Shale are truncated north of the Shublik
Oil-source correlation study in N.E. Alaska Mountains, and in outcrops of the Ignek Valley section these units could not be adequately evaluated because of the advanced thermal maturity of their organic matter. The most promising source rocks within A N W R are the type II (marine) facies of the Hue Shale as this unit contains up to 18 wt% organic carbon, is hydrogen rich, and gives yields of up to 88 kgHC/metric ton of rock during pyrolysis. Oil-source rock correlation suggests that the most promising source rocks for the Jago oil type are the type II organic facies of the Hue Shale based on similarities in carbon isotope values of the saturate and aromatic hydrocarbon fractions and their CI9/C23 tricyclic terpane ratios. The Canning Shale, pebble shale unit, and upper part of the Kingak Shale can be ruled out as potential source rocks for the A N W R oils on the basis that their organic matter is gas prone and their geochemical properties do not correlate well with the oils. Geochemically, the M a n n i n g and Kavik oil types are sufficiently different from the bitumens extracted from the five rock units so as to suggest a source that has not been evaluated as yet.
415
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Cretaceous and Tertiary Stratigraphy of Northeastern Alaska.