Carboxylic acid anions in formation waters, San Joaquin Basin and Louisiana Gulf Coast, U.S.A.—Implications for clastic diagenesis

Applied Geochemistry,Vol. 5, pp. 687-701, 1990

0883-2927/90 $3.00+ .00 Pergamon Press plc

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Carboxylic acid anions in formation waters, San Joaquin Basin and Louisiana Gulf Coast, U.S.A.--Implications for clastic diagenesis DONALD B. MACGOWAN Enhanced Oil Recovery Institute, Box 3006, The University of Wyoming, Laramie, WY 82071, U.S.A.

and RONALD C. SURDAM Department of Geology and Geophysics, The University of Wyoming, Laramie, WY 82071, U.S.A.

(Received 22 September 1989; accepted in revised form 26 April 1990) Abstraet--Carboxylic acid anions (CAA) in formation waters are of interest to studies of clastic diagenesis because of their ability to buffer formation water Eh and pH (and thus substantially contribute to controls on carbonate mineral stability), and their ability to complex and transport AI and Si from the site of aluminosilicate mineral dissolution during diagenesis. Carboxylic acid anions are also extremely important to the aqueous geochemistry of Ca, Fe, Mn, Pb and Zn. Some formation waters from sedimentary basins contain high concentrations of CAAs. The analyses of 20 formation waters from the San Joaquin Basin, California and 20 formation waters from the Louisiana Gulf Coast Basin presented in this study, show concentrations as high as 8100 ppm monofunctional and 370 ppm difunctional CAA; by comparison, previously reported analyses indicate monofunctional CAA occur in concentrations up to 10,000 ppm and difunctional CAA may occur in concentrations up to 2610 ppm. Analyses of drilling muds and scale soaps presented in this study show that few if any difunctional CAA in the study area can be attributed to contamination from these sources. Additionally, aqueous extracts of crude oils contain both mono- and difunctional acid anions, as do the aqueous and petroleum phases of hydrous pyrolysates. Previously unreported dissolution experiments, equilibrium computer simulations, and hydrous pyrolysis experiments support those already published and suggest that CAA are generated during thermal maturation of kerogen and expelled from the shale along oil-wet microfractures. Upon entering the water-wet sandstone pore, the hydrophilic CAA partition into the aqueous phase. Organic-inorganic reactions may occur which form CAA-metal complexes. Because the complexes are hydrophobic, they partition in the petroleum phase, where present. Carboxylic acid anions are of great importance to clastic diagenesis over the temperature range in which they dominate fluid alkalinity; certainly, no other viable mechanism has been advanced which adequately explains the observed aluminosilicate mineral dissolution with subsequent mass transfer of Al, as well as the carbonate mineral diagenetic successions observed in sand-shale systems world-wide. The utility of modeling these observations of organic-inorganic diagenesis is limited only by the ability to model the concentration and distribution of CAA through space and time.

INTRODUCTION CARBOXYLIC acid anions ( C A A ) have been known from formation waters since before the turn of the century (see references in ROGERS,1917; ZINGERand KRAVCHIK, 1973; nATION and HANOR, 1984). Indeed, a host of aqueous organic species have been identified in formation waters, including: hydrocarbons, mono-, di- and tricarboxylic acids, amino acid anions, various phenols, cresols, and hydroxybenzoic acid anions (COLLINS, 1975; KELLEY and MERIWEATHER, 1985; KHARAKAet al., 1986; SURDAMand MAcGOWAN, 1987; MAcGOWAN and SURDAM, 1988; BRANTHAVERet al., 1988; FISHER and BOLES, 1990). Initially, C A A in formation waters were suggested

as the precursors to petroleum, and possibly the agents of primary migration of petroleum (BAKER, 1959, 1967; MEINSCnEIN, 1959; SHVETS, 1970; MATUSEVlCHand ScnvExs, 1973; CORDELL, 1972, 1973) and as proximity indicators of petroleum reservoirs ( Z I N G E R and KRAVCHIK, 1973; KARTSEV, 1974; COLLINS, 1975; MATUSEVICHand PROKOPEVA,1977). They have also been identified as an important component of formation water alkalinity (WILEYet al., 1975) and as aqueous precursors of natural gas (CAROTHERSand KHARAKA,1978). Carboxylic acid anions have been shown to be the product of the thermal maturation of kerogen (VANDENBROUCKE, 1980; ROUXHET et al., 1980; VANDERGRIFTet al., 1980; SURDAMet al., 1984; CROSSLY,1985; KAWAMURAet al., 1986; KAWAMURA

687

688

D.B. MacGowan and R. C. Surdam

and KAPLAN,1987; MAcGOWAN and SURDAM, 1987;

intermediate zone of clastic diagenesis is discussed. The analytical technique is presented in the SURDAM and MAcGOWAN, 1987; LUNDEGARD and Appendix. SENFrLE, 1987; MAcGOwAN et al., 1988b), of hydrous pyrolysis of liquid petroleum (KriARAKAet al., 1989), and of mineral oxidation of sedimentary organic RESULTS AND DISCUSSION material (CRosSEY et al., 1986). Several authors have proposed C A A as the agents of metal transport which form ore deposits (BARTON, 1967; SCHVETS, Composition o f the formation waters 1970; NISSENBAUMand SWAINE, 1976; SAXaY, 1976; Locations of the sampled wells are given in Table GIORDANO and BARNES, 1981; DRUMMOND and PALMER, 1986; HENNET, 1987; HENNET et al., 1988a; 1; more detailed data are available in FISHER and BOLES, (1990) and LAND and MACPHERSON, (1989). DRUMMONDet al., 1989; GIORDANO, 1989). The results of the analyses for C A A in the formation Recently, it has been documented that short-chain waters are given in Table 2 and Fig. 1, C A A (particularly the difunctional species) are These waters show the typical dominance of monocapable of complexing and transporting A1 and Si functional species over difunctional species that has from the site of silicate and aluminosilicate framework mineral grain dissolution in subsurface waters (SURDAMet al., 1984; CROSSEY, 1985; HANSLEY, 1987; Table 1. BENNETT and SIEGEL, 1987; SURDAM and MACSample No. Field Descriptor GOWAN, 1987; BENNETTet al., 1988; MAcGOWANand SURDAM, 1988; KHARAKAet al., 1989; MACGOWANet Louisiana Gulf Coast Basin al., 1988a; BEVAN and SAVAGE,1989). This process 1 Eugene Island Block 313a has been invoked as the mechanism for the develop2 Eugene Island Block 205 3 Mound Point -ment of the widespread enhancement of sandstone 4 Vermillion 31-15 porosity resulting from aluminosilicate mineral dis5 Mound Point -solution (where no subsequent authigenic alumino6 Mound Point -silicate phase is precipitated), a texture frequently 7 South Marsh Island II-B1 observed in clastic successions (SIEBERTet HI., 1984; 8 Eugene Island Block 338 9 Eugene Island Block 313b SURDAMand CROSSEY, 1987). The capacity of C A A to 10 Eugene Island Block 313c buffer solution pH is typically orders of magnitude 11 Mound Point -more effective than the carbonate species. As a 12 Mount Point -consequence, C A A can exert a major control on the 13 Rabbit Island 183 14 Mount Point -stability of carbonate minerals over the temperature 15 Lighthouse Point A-4 range in which they dominate solution alkalinity 16 South Marsh Island I1 1-A (SURDAM et al., 1984; CROSSEY, 1985; SURDAMand 17 South Marsh Island lI-B3 CROSSEY, 1985a, b; LUNDEGARD and LAND, 1989). 18 South Marsh Island 33 From 50 to 100% of porosity in some clastic suc19 Point Barre 114 20 Vermillion B-53 cessions has been attributed to carbonate cement and/or aluminosilicate mineral dissolution (SURDAM San Joaquin Basin and CROSSEY, 1987). The geochemistry of Fe and Fe1 San Emidio Nose KC1-H35-10 bearing authigenic minerals also may be strongly 2 Rosedale Unit 2 No. 2 affected by organic complexation of Fe (KHARAKAet 3 Rosedale Unit ! No. 6 4 Yowlumne 81 x 14 al., 1986; SURDAMand MAcGOWAN, 1987; DIXON et 5 Greely KCI No. 63 21-20 al., 1989; SURDAM et al., 1989c; KHARARA et al., 6 Greely 45-19 1989). Therefore, holistic models of clastic diagenesis 7 Rio Viejo 86 x 33 have recognized the importance of C A A in buffering 8 Greely Treater 9* Coles Levee 12-3 l formation water pH and mass transfer (e.g. SURDAM 111 Paloma 24 x 2 et al., 1989b, c). 11 Paloma 66 x 2 Analyses of C A A are presented for 40 formation 12 Paloma 62 x I 1 waters from the southern San Joaquin Basin, Cali13 Paloma 24 x 11 fornia and the off-shore Louisiana Gulf Coast Basin 14 Coles Levee 43-31 15 Coles Levee ColeFee 24 as well as from water-flood samples, injection-well 16 Kern Front Young No. 63 formation water and receiving-well formation water. 17 Kern Front Young No. 63 Analyses of C A A in aqueous extracts of crude oils (resampled) from these basins, hydrous pyrolysates, and of some 18 Rosedale Ranch KCI 1 17-1 19 Kern River Apollo WD-1 drilling fluids are also presented. Results from dis21 Mt Poso Glide 6 solution experiments and computer simulations involving artificial brines or formation waters, crude - - location data unavailable. petroleum, andesine mineral grains or whole-core *SJB-1, MAcGOWANand SURDAM(1988); DM-5, SURDAM material are also presented. The role of C A A in the et al. (1989a).

Carboxylic acid anions in formation waters

689

been noted by other researchers who have reported should be expected to occur in formation waters difunctional C A A in produced formation waters associated with maturing sedimentary organic mat(SURDAM et al., 1984; KHARAKAet al., 1985; BARTH, ter. Indeed, based upon their experiments, KAWA1987a, b; MAcGOWAN and SU~DAM, 1988); also, as MURA and KAPLAN (1987) calculate up to 3000 ppm expected in produced formation fluids from first- ethanedioate (oxalate) would occur in formation cycle basins currently at maximum levels of thermal waters where conditions are conducive to their generexposure, and where formation water mixing is not ation and preservation. important, they show the dominance of ethanoate The mono- and difunctional C A A are also found in over other species in most samples (FISHER, 1987; aqueous extracts of crude oil and the petroleum MAcGOWAN and SURDAM,1988). phase of hydrous pyrolysates (Table 5). In this exDifunctional C A A have only been recognized in a periment, 50 ml of crude oil or 1 ml of hydrous few instances to exist in high concentrations in the pyrolysate petroleum phase was shaken into 200 ml diagenetic environment. SURDAM et al. (1984) distilled water (or in the hydrous pyrolysate experireported the presence of propanedioic (malonic) and ments, into 5 ml distilled water) for 6 h. The resultant Z-butenedioic (maleic) acid anions, and KHARAKAet emulsion was broken by centrifugation and the water al. (1985) reported the presence of C4-C10 difunc- phase analyzed for C A A by ion chromatography (see tional C A A in formation waters; however, in both Appendix). Interestingly, the composition and districases reported concentrations were low. BARTH bution of C A A in the water washes of crude oils are (1987a, b) reported the concentration of ethanedioic dissimilar to those of formation waters from the same (oxalic) and propanedioic (malonic) acid anions in basin. However, the distribution of C A A from exproduced formation waters in concentrations up to 38 tracts of crude oil from hydrous pyrolysis experiand 102 ppm, respectively. MAcGOWAN and SURDAM ments is similar to that seen in the aqueous phase of (1988) report concentrations of difunctional C A A > those experiments. By comparison, SIEFERT and 2500 ppm in California formation waters. The pres- HOWELLS (1969) reported the presence of up to 2.5 ent study (Table 2) shows total difunctional C A A wt% C A A in California crude oils. SIEFERT (1975) concentrations up to 370 ppm (107 ppm ethanedioic reported up to 3 wt% C A A in crude oil from the San [oxalic] and 216 propanedioic [malonic] and 47 ppm Joaquin Basin; the acid anions analyzed in this study Z-butenedioic [maleic]), although most concen- comprise <<1 wt% of the crude petroleum sample. trations of total difunctional C A A are well below 200 Considering the foregoing discussion, it is not ppm. BARTH (1987a, b) attributed the presence of surprising (given proper analytical and sampling difunction acid anions in formation waters to con- techniques, MAcGOWAN and SURDAM, 1988) that tamination by drilling fluids; however, aqueous or- both mono- and difunctional C A A should be obganic geochemistry of drilling fluids and scale soaps served in formation waters associated with petfrom the study areas reported in this study (Table 3) roleum, especially from reservoirs which are curshow little or no difunctional C A A in the drilling rently at maximum levels of thermal exposure and in muds or scale soap solutions which were available for the 80 to 130°C window (SURDAMand MAcGOWAN, analysis. 1987; MAcGOWAN and SURDAM,1988; SURDAMet al., The high concentration of C A A in some formation 1989b, c). waters has also been attributed to injection of C A A MAcGOWAN and SURDAM(1989a) show maximum rich waters during enhanced-recovery water-floods. reported concentrations of C A A in formation waters Every effort was made to collect samples for this from basins presently undergoing intense C A A genstudy from wells which had not been affected by eration and expulsion based on recent literature water-flooding. In fact, analyses of injection waters (BOLES and RAMSEYER,1988; FISCHERand SURDAM, used in the San Joaquin Basin (Table 3), show them 1988; KHARAKAet al., 1985; MAcGOWAN and SURto be very low in C A A . Waters from both the DAM, 1988; MAcGOWAN et al., 1990). They assert production and injection wells are compositionally that, in sedimentary basins currently undergoing similar, as well as being similar to other formation intermediate burial diagenesis concomitant with inwaters from that basin (Table 4 and MAcGOWAN and tense generation and expulsion of C A A , formation SURDAM,1988, and FISHER and BOLES, 1990). waters will have C A A concentrations similar to those Difunctional as well as monofunctional carboxylic maximum values. Although diagenetic modeling as and hydroxybenzoic acid anions have been recognized well as geological and geochemical assessment of the in the liquid phase of kerogen hydrous pyrolysates reservoir conditions of formation waters demon(KAWAMURA et al., 1986; KAWAMURAand KAPLAN, strates that this condition may be quite restricted in 1987; SURDAM and MAcGOWAN, 1987; LUNDEGARD time-temperature space (MAcGOWAN and SURDAM, and SENFTLE,1987; MAcGOWAN and SURDAM,1987, 1987; SURDAMet al., 1989b, c), this pulse of C A A into 1988; MAcGOWAN et al., 1988b; THYNE et al., 1988), the diagenetic system is very important in terms of as well as the aqueous phase of liquid petroleum which subsequent diagenetic pathways are taken by hydrous pyrolysis experiments (KHARAKA et al., the sandstone-shale system (SURDAMe t al., 1989b). 1989); these indicate that they are natural products Because most formation waters are not sampled from of the thermal maturation of kerogen and thus units presently undergoing generation and expulsion

690

D . B . MacGowan and R. C. Surdam

Table 2. Carboxylic acid anions (ppm) in San Joaquin Basin and Louisiana Gulf Coast Basin formation water Sample No.

Temperature (°C)

Methanoic

Louisiana Gulf Coast Basin 1 94 Tr 2 83 ND 3 -19.2 4 110 60.5 5 86 80.4 6 106 45.7 7 104 57.8 8 72 97.2 9 83 107 10 78 9.70 11 96 87.2 12 101 174 13 121 ND 14 86 ND 15 91 102 16 96 Tr 17 88 Tr 18 98 ND 19 89 ND 20 121 27.2 San Joaquin Basin 1 125 23.8 2 63 21.7 3 57 22.4 4 99 16.2 5 85 32.3 6 138 21.0 7 121 3.00 8 129 22.2 9 101 50.2 10 134 25.8 11 160 24.3 12 132 37.5 13 114 13.2 14 114 21.7 15 -Tr 16 -1.13 17 -Tr 18 4538.2 19 -6.30 20 -3.60

Ethanoic

Propanoic

Propeneoic

1820 1220 1040 6420 5150 5920 1270 1340 4750 115 5920 5750 2400 6250 3720 1120 1090 1220 984 164

97.1 647 965 1050 1130 975 276 109 627 ND 1240 1420 297 645 216 110 156 114 126 28.6

--ND ND ND ND ND ND ND ND 2.62 ND ND 10.3 ND ND ND ND ND ND

3400 175 677 6320 1030 6080 2650 6400 897 2620 2710 1500 1040 1114 92 278 292 475 400 297

238 ND Tr 816 706 171 392 318 352 503 345 210 150 207 ND ND ND ND ND 32.5

ND ND ND 12.1 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 2.70

Butanoic

Pentanoic

Hexanoic

Heptanoic

26.2 60.1 45.2 197 114 72.5 29.7 12.1 89.7 ND 39.7 91.7 44.2 97.1 311 142 39.2 16.2 87.2 32.1

ND 22.4 30.1 215 99.2 120 Tr Tr 78.2 ND 64.2 104 12.7 106 20.1 ND 32.9 19.7 64.5 Tr

ND 19.2 10.7 106 107 62.3 Tr Tr 42.1 ND 32.1 65.7 ND 42.2 30.6 Tr 16.1 6.25 Tr Tr

ND ND ND 32.1 82.6 98.7 Tr Tr Tr ND 19.6 Tr ND 27.1 19.2 Tr Tr Tr ND ND

60.1 ND ND 298 156 682 19.1 19.7 107 78.9 62.3 32.5 27.2 40.2 ND ND ND ND ND ND

19.2 ND ND 356 65.2 49.5 18.7 54.0 109 Tr 175 49.2 351 371 ND ND ND ND ND ND

Tr ND ND 8.10 46.2 Tr 9.10 9.20 ND Tr 8.20 Tr Tr 16.5 ND ND ND ND ND ND

Tr ND ND 9.20 47.1 Tr 10.1 7.60 ND ND 8.90 Tr ND ND ND ND ND ND ND ND

ND = none detected, Tr = trace detected, - - = no data available.

of C A A or are f r o m fields which have b e e n waterflooded or have u n d e r g o n e f o r m a t i o n fluid mixing, bacterial d e g r a d a t i o n etc., they may show C A A c o n c e n t r a t i o n s m u c h lower than those given by MAcGOWAN and SURDAM (1989a). I n d e e d , it has b e e n s p e c u l a t e d that due to the rate of decarboxylation of these species, c o n c e n t r a t i o n s of C A A r e p o r t e d in f o r m a t i o n waters may have b e e n significantly higher in the geological past (KHARAKAe t al., 1989). D i a g e n e t i c m o d e l s which are b a s e d u p o n fluids which are i m m a t u r e with respect to C A A o r which are relict fluids (those which have u n d e r g o n e decarboxylation o f C A A ) or f o r m a t i o n waters which have b e e n subject to bacterial alteration in the reservoir, f o r m a t i o n fluid mixing or water-flooding, will drasti-

cally u n d e r s t i m a t e the i m p o r t a n c e these species play during clastic diagenesis (MAcGOWAN and SURDAM, 1988, 1989a; KHAgAr~ et al., 1989; HARRmON and TnYNE, 1989; SURDAMet al., 1989a, b, c).

Formation waters and diagenesis In the past, conventional w i s d o m held that secondary o r e n h a n c e d porosity was caused by carbonic acid dissolution of c a r b o n a t e s and aluminosilicate framework grains (e.g. SCHMIDT and McDONALD, 1979; LUNDEGARD and LAND, 1986). This is p r o b a b l y the case in instances w h e r e feldspars have b e e n altered in situ to kaolinite or o t h e r aluminosilicate minerals, a c o m m o n p e t r o g r a p h i c texture (ScHMIDT and

Carboxylic acid anions in formation waters

691

Table 2. Continued Octanoic

Ethanedioic

Propanedioic

Z-Butenedioic

O-Hydroxybenzoic

ND ND ND ND 41.7 ND Tr Tr Tr ND 16.2 Tr ND 30.6 6.72 ND ND ND ND ND

ND ND Tr 11.1 25.2 Tr ND ND ND ND 107 119 ND Tr Tr ND ND ND ND ND

ND ND 46.2 21.2 113 75.2 ND ND ND ND 216 115 Tr 65.7 Tr ND ND ND ND ND

ND ND ND 16.3 ND ND Tr 65.7 Tr ND 47.1 Tr ND Tr ND ND ND ND ND ND

ND ND ND ND 41.6 32.1 ND ND Tr ND 64.7 ND ND 10.2 ND ND ND ND ND ND

1939 2160 2160 8130 6980 7400 1630 1610 5690 125 7860 7840 2750 7280 4430 1370 1300 1370 1260 252

ND ND Tr ND Tr ND ND ND ND ND 21.3 ND ND ND ND 6.20 Tr ND Tr ND

ND ND ND ND ND ND ND ND Tr 16.2 Tr ND 29.7 26.1 ND ND ND ND ND ND

3810 198 697 7860 2100 6400 3110 6740 1580 3280 3400 1840 1330 1880 96.0 287 298 513 422 314

ND ND ND 12.6 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

52.2 Tr ND ND Tr Tr ND ND 16.5 30.1 49.7 12.6 31.1 34.2 1.80 Tr Tr ND Tr 8.10

12.5 Tr Tr 13.5 15.6 12.6 10.1 10.1 42.1 10.9 Tr ND Tr 42.1 2.10 2.03 Tr ND 15.6 3.30

McDorqALO, 1979). H o w e v e r , in m a n y cases t h e r e are few or n o o b s e r v a b l e aluminosilicate r e a c t i o n p r o d u c t s in p r o x i m i t y to dissolved aluminosilicate grains (SIEBERT et al., 1984; SURDAM a n d CROSSEY, 1987). This indicates a c e r t a i n d e g r e e of AI mobility a b o v e the inorganic solubility of AI a n d Si a n d has b e e n e x p l a i n e d in t e r m s of organic c o m p l e x a t i o n of AI a n d Si (for a r e c e n t review, see MAcGOWAN a n d SORDAM, 1989a). T h e ability of c a r b o n i c acid ( a n d its dissociated c o n j u g a t e bases) to mobilize m e t a l s by c o m p l e x a t i o n in f o r m a t i o n waters is e x t r e m e l y low (HENNETe t al., 1988b). T h u s it c a n n o t t r a n s p o r t the less-soluble p r o d u c t s (e.g. A1 a n d Si) of aluminosilicate dissolution away from t h e site of dissolution. C o m p l e x a t i o n of A1 a n d Si by organic c o m p l e x i n g species has b e e n d e m o n s t r a t e d to b e a viable m e c h -

Total CAA

Total difunctional CAA 0.0 0.0 46.2 68.6 138 75.2 0.0 0.0 0.0 0.0 370 234 0.0 65.7 0.0 0.0 0.0 0.0 0.0 0.0 64.7 0.0 0.0 13.5 15.6 12.6 10.1 10.1 58.6 41.0 71.0 12.6 31.1 76.3 3.90 8.23 0.0 0.0 15.6 11.4

anism for t h e e l e v a t i o n of AI a n d Si solubility a n d the t r a n s p o r t of these e l e m e n t s in f o r m a t i o n waters at reservoir conditions (SuP,DAM et al., 1984). BJORLYKKE (1984), LUNDEGARD a n d LAND (1986) a n d GtLES a n d MARSHALL (1986) c o n c l u d e d t h a t t h e r e was insufficient O in k e r o g e n to g e n e r a t e sufficient acids ( H 2 C O 3 a n d carboxylic) to b e effective at dissolving feldspar in s a n d s t o n e s associated with shales. T h e s e calculations were b a s e d in p a r t u p o n e l e m e n t a l O analyses p e r f o r m e d o n k e r o g e n isolated f r o m source rocks. H o w e v e r , VANDERGRIFT et al. (1980) d e m o n s t r a t e d t h a t a significant p e r c e n t a g e of the organic O originally p r e s e n t in t h e k e r o g e n is lost during this isolation p r o c e d u r e a n d thus is n e v e r m e a s u r e d in t h e e l e m e n t a l analysis. It is i n t e r e s t i n g to n o t e t h a t the molecules c o n t a i n i n g this "lost" O have

692

D.B. MacGowan and R. C. Surdam

been identified by VANDERGRIFT et HI. (1980) as monofunctional, difunctional and keto-aliphatic carboxylic acids as well as aromatic carboxylic acids. From these considerations, it is apparent that caution should be exercised in constructing mass balance calculations of C A A available to diagenetic systems based upon the amount of organic O in kerogen, as determined in standard elemental analyses of kerogen isolates. These may be of limited value in constraining the possible extent of organic-inorganic interactions in clastic successions in that they considerably underestimate the amount of organic O available. Furthermore, KAWAMURA and KAPLAN (1987) have documented both mono- and dicarboxylic acids released to the hydrocarbon phase of hydrous pyrolysates during laboratory maturation of source rocks. Using the methodology of GILES and MARSHALL (1986) they showed that extremely high concentrations of dicarboxylic acids would be available to the diagenetic system during kerogen maturation; up to 3000 ppm as ethanedioate (oxalate). Additionally, GILES and MARSHALL(1986) calculated that all CO 2 and C A A would be reacted during primary migration from the source rock. Hydrous pyrolysis experiments and shale petrology have shown, however, that C A A are generated during incipient oil generation and move from the source rock along oil-wet microfractures and do not react with the shale (LEWAN, 1989; FISHER and LEWAN, 1989). Once they encounter the water-wet sandstone pores, the C A A partition into the aqueous phase, because they are strongly hydrophilic (MAcGOWAN 10,000

Total Carboxylic Acid A n i o n s • LGC • • SJB

9,000 8,000 A

E

~

7,~

C

0

6,000

~

5,~

C O ¢ J 4,000 O U •A

2,000

1,000 :

40

60

.

so

•

loo

12o

14o

1so

T e m p e r a t u r e (°C)

FI6. 1. The distribution of total concentration of organic acid anions with temperature from recently published data, showing the data from the present study (WILEYet al., 1975; CAROTHERSand KHARAKA,1978; HATTONand HANOR,1984; SURDAM et al., 1984; KELLEY and MERIWEATHER, 1985; KHARAKAetal., 1985, 1986; BARTH,1987a, b; FISHER,1987; BRANTHAVERet HI., 1988; MAcGOWANand SUROAM,1988). LGC = Louisiana Gulf Coast, SJB = San Joaquin Basin.

and SURDAM,1989a, b; SURDAM and MAcGOWAN, 1989; FISHER and LEWAN, 1989). Although organic-inorganic interactions in sedimentary rocks have long been postulated (e.g. THOMPSON, 1925), their contribution to the diagenetic environment has not been studied in great detail until recently (e.g. WILEYet al., 1975; CAROTHERSand KHARAKA,1978; CURTIS, 1978; SURDAMet HI., 1984). To date, the only hypothesis advanced to explain the widespread dissolution of aluminosilicates and subsequent transport of Al observed in clastic successions is the complexation of Al by organic complexing species (SURDAM and CROSSLY, 1987); certainly, large amounts of Al must somehow be mobilized in the subsurface to explain the widespread porosity enhancement due to feldspar dissolution without subsequent precipitation of an authigenic aluminosilicate phase. There is a growing body of experimental evidence to support this hypothesis (Figs 2 and 3; Table 5; and HUANG and KELLER, 1970; SURDAM et al., 1984; CROSSLY, 1985; HANSLEY, 1987; SURDAM and MACGOWAN, 1987; MAcGOWAN and SURDAM,1988; BENNETT et al., 1988; DRUMMONDet HI., 1989; GIORDANO, 1989; MAcGOWAN et al., 1990). A series of dissolution experiments similar to those previously described (SURDAMet HI., 1984; CROSSLY,1985; SURDAM and MAcGOWAN, 1987; MAcGOWAN and SURDAM, 1988; MAcGOWAN etal., 1990) were carried out using artificial brines, formation waters (for compositions, see MAcGOWAN and SURDAM,1989a, b; and FISHER and BOLES,1990), andesine mineral grains, Stevens Sandstone (a plagioclase-rich litharenite [FISCHER, 1986]) and crude oil. The results are shown in Table 6 and are similar to previous experiments of this type. It should be noted that no detectable A1 was in either the aqueous or hydrocarbon phases prior to these dissolution experiments. Earlier mass balance calculations (e.g. BJORLYKKE, 1984; LUNDE6ARD and LAND, 1986; GILES and MARSHALL, 1986) and earlier computer simulations (e.g. KHARAKA et al., 1985; HARRISON, 1989) tended to downplay the importance of C A A in clastic diagenesis due to erroneous estimates of the amounts of C A A available to the diagenetic system and lack of thermodynamic data at temperatures >25°C for computer simulation. Recent thermodynamic measurements at elevated temperatures (DRUMMONDet al., 1989; GIORDANO,1989) suggest that both mono- and difunctional species may be very important in the complexation and transportation of A1, as well as Zn, Pb, Fe, Mn and Ca in the diagenetic system (KHARAKA et HI., 1989; HARRISON and THYNE, 1989; MACGOWAN et al., 1990). Contrary to the abundant published experimental evidence, as well as recent thermodynamic equilibrium computer modeling cited above, STOESSEL and PITrMAN (1990) present some dissolution experimental evidence calling into question the Al concentrations from results of earlier dissolution experiments. STOESSEL and PITrMAN

Carboxylic acid anions in formation waters

693

Table 3. Analyses of drilling fluids (ppm) Sample

Methanoate

Ethanoate

Propanoate

Ethanedioate

Propanedioate

San Joaquin Basin drilling mud San Joaquin drilling mud San Joaquin scale soap Louisiana Gulf Coast Basin drilling mud

2.1 1.9 1.6 2.8

104 121 116 42.1

4.1 ND ND ND

ND ND ND Tr

Tr ND ND ND

ND = none detected; Tr = trace. Table 4. Carboxylic acid anions (ppm) in injection water, water flood and receiving-well formation waters, San Joaquin Basin Well Injection water Injection well formation water Production well formation water

T e m p e r a t u r e (°C)

Methanoate

Ethanoate

Propanoate

Butanoate

Pentanoate

Hexanoate

Heptanoate

Ethanedioic

Propanedioate

50 1130

3.0 15.0

10.8 2270

Tr 96.2

ND 107

ND 86. I

ND 9.2

ND 5.7

ND 28.5

5~; 15.9

1.90

6.7

2620

265.0

152

97.1

12.1

4.2

ND

6.7

N D = none detected; T r = trace detected.

Table 5. Carboxylic acid anions (ppm in aqueous phase) in aqueous extracts of crude oils and associated formation waters Basin

Sample

Total Monofunctional

Total Difunctional 373 31.1

San Joaquin (Paloma)

Extract Formation water

950 1270

(Coles Levee)

Extract Formation water*

4620 2460

Gulf Coast (Vermillion)

Extract Formation water*

1200 2740

(Rabbit Island)

Extract Formation water*

436 1630

Extract Formation water

942 993

Hydrous pyrolysis experiment HP88-39

1320 2640 31.8 15.0 10

148 92.6 101

*From MAcGOWANand SURDAM(1988).

(1990) attempted to duplicate the results of SURDAM et al. (1984); however, instead of carrying-out the experiments in Teflon reaction vessels (as did SrORDAMet al., 1984) they used Ti reaction vessels. STOESSEL and P1TTMAN (1990) did note the Ti reaction vessels were severely etched. Due to this reactivity of the reaction vessel walls toward the experimental fluids, their assertions on the relative reactivity of C A A , aluminosilicate minerals and metallic Ti may not be especially applicable to studies of clastic diagenesis. It is instructive to note in Fig. 3 that the C A A do not complex any metal to the exclusion of other cationic species, although there appears to be a preference to complexing Fe, which occurs only up to 0.5 wt% in the andesine mineral grains used in the experiments (MAcGOWAN et al., 1988a). Because experimental solutions are cooled to room temperature before analysis, precipitation of an aluminosilicate gel occurs on the surface of the mineral grains (see also SURDAMet al., 1984; MAcGOWAN and SUR-

DAM, 1988). In dissolution experiments where crude oil was added to the liquid phase, no such aluminosilicate gel precipitation was observed on the solid reactant material (see also MAcGOwAN et al., 1990). In fact, X-ray diffractograms of the > 0.22/.t filtrate from the crude oil after the experiment show the presence of amorphous aluminosilicates in the oil which were not present at the beginning of the experiment (MAcGOWAN and SURDAM, 1989a). Further, X-ray fluorescence analyses showed the concentration of Al in the oil increased from nondetectable to > 100 ppm during the same experimental runs (Table 6). It should be noted that the oil, formation waters and core material were taken from reservoirs currently in the 80-120°C window, and from active diagenetic systems. It has long been the practice among analytical chemists analyzing for trace amounts of aqueous Al to complex the Al with an organic chelating agent and then extract the complexes into an organic phase,

694

D.B. MacGowan and R. C. Surdam

which is then analyzed for Al. Based upon this, and the behavior of the complexes in the experiments, we hypothesize that the complexes are more hydrophobic than hydrophilic. Thus, dissolution experiments indicate elevated Al and Si (as well as Ca and Fe) concentrations may be expected in experiments using aqueous solutions of C A A in artificial NaCl brines and formation waters which contain high concentrations of Na, Ca, Mg and K (MAcGowAN et al., 1990). However, when an organic (petroleum) phase is present, little elevation of Al or Si is noted, although the organic phase shows increases of >100 ppm in Al concentration (Table 6), and the solid phase shows clear dissolution textures (MAcGOWAN et al., 1990). Carboxylic acid anions are generated during thermal maturation of source rocks and are probably transported through the source-rock via oil-wet microfractures into the reservoir rock (LEWAN, 1989; FISHER and LEWAN, 1989) and then, due to their hydrophilic nature, partitioned into the formation

u

o ~ ~ -2

-3iiiii.

i

,

i

. ~nO~nc~on°~

i

i

[

.:iiiii i

:,i!iiiiiiii!i!i!iii

Results of Dissolution Experiments 'rom the data of Surdam and MacGowan, 1967

~

AI

12

8

~

12s ~E

Si

0.. 100 o .

32o

Ca

Fe

2O A1

B1

C1

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a.

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A) 10000ppmacetalein 20000ppm NaC:I B) A + 2500 ppm malocmle C) B + 50 ppm ImllCyillte D) Stevens~landstoneformationwater 1) Ande~nemineralgroins 2) StevensSandstonewholecorematerial

FIG. 3. Graphical presentation of results of the dissolution experiments of SUROAMand MAcGOWAN(1987) illustrating that no cation is complexed to the exclusion of other cations by organic acid anions. Note that although it only represents about 5 wt% of the andesine used, Fe is strongly complexed into solution.

water in water-wet sandstone pores (MAcGOWANand SURDAM, 1989a, b; FISHERand LEWAN, 1989). Figure 4 shows data from hydrous pyrolysis experiments of a 4 iiiiiiiii . . . . . iiiiiiiiiiiil!iiiii!iiiii!ii!ii moderate S, Type II kerogen which supports this. Note that at least some free oil is present in the bomb -5 ": when CAA are present in detectable quantities in the ~ ii iii???ii?iiiiiiii!iii?ii?ii?i!i:!???i!iiiiiiiii!!i!ii!iii?iii!!iii!ii aqueous phase, indicating the expulsion of CAA and ii;?iiiiiiii!iiiiiii?iiiiiiiii?iiiii[iii?iiii??iiiii!?iil;ii)ii?iil;! oil were simultaneous in the experiments. Once par2 3 4 5 6 7 8 titioned into the aqueous phase, the CAA are free to pH interact with aluminosilicate minerals. If aluminosilio D a t a f r o m S u r d a m et al., 1 9 8 4 ; C r o s s e y , 1985. cate dissolution takes place and organic-Al com• D a t a f r o m M a c G o w a n and S u r d a m , 1 9 8 8 ; plexes are formed, due to their hydrophobic nature S u r d a m and M a c G o w a n , 1 9 8 7 and present study. the complexes will partition into an oil phase if • D a t a from dissolution e x p e r i m e n t s with c r u d e o i l ; present (MAcGOWAN and SURDAM, 1989a). This M a c G o w a n and S u r d e m , 1 9 8 9 and present study. hypothesis is supported by data on the generation FIG. 2. Log [AI ppm] normalized to the concentration of and destruction of organic acid anions from hydrous CAA ppm vs pH for experiments from SURDAMetal., 1984; pyrolysis experiments (LEWAN, 1989; FISHER and CROSSEr, 1985; SURDAMand MAcGOWAN,1987; and MAC- LEWAN, 1989; MAcGOWAN and SURDAM, 1989a, b) GOWANand SURDAM,1988. Shown are a model data line and dissolution experiments with a crude oil phase using SOLM1NEQ.88 (KHAv,Ar,A et al., 1988) with an (MAcGOWAN et al., 1988b, 1990; MAcGOWAN and expanded organic/inorganic reaction data base (HARRISON and THYNE, 1989); results from high difuctional CAA dis- SURDAM,1989a, b, and this study). Such a scenario solution experiments (SuRDAM and MAcGowAN, 1987; also explains the low analytical A1 concentration in MAcGOWANand SURDAM,1988, 1990); and the inorganic formation waters produced from active organicsolubility of kaolinite (saturated with respect to amorphous inorganic diagenetic systems associated with petsilica) as calculated by SOLM1NEQ.88. Data from the experiments and formation waters of the present study and roleum reservoirs which have high concentrations of SURDAMet al., 1984; CROSSEY, 1985; SURDAMand MAC- CAA. GOWAN, 1987; MAcGOWANand SURINAM,1988. Computer simulations using SOLMINEQ.88

Carboxylic acid anions in formation waters (KrtARAKA et al., 1988) with an expanded organicinorganic interaction data base (HARRISON and THYNE, 1989) and results from various high-CAA dissolution experiments (SuRDAM et al., 1984; CROSSEY, 1985; SURDAM and MAcGOwAr~, 1987; MACGOWAN and SURDAM, 1988 and this study) shown in Fig. 2 indicate that organic complexation of Al due to aluminosilicate dissolution at 100°C is extremely important to elastic diagenesis and is even more critical than suggested by the dissolution experiments. Additionally, they illustrate that even solutions high in Na, Ca, Mg, K and Fe (such as the Stevens Sandstone formation water used in the dissolution experiments) will complex appreciable quantities of Al if CAA are present (SURDAMand MAcGOwAN, 1987, 1989; MAcGOWAN and SURDAM, 1989b; MACGOWANet al., 1990). Structures which have been proved for the C A A Si complex (BENNE~ et al., 1988) and postulated for the organo-Al complex (SURDAMet al., 1984; DRUMMONDetal., 1989; GIORDANO,1989) indicate that, due to the nature of the organic chelate, the ratio of organic chelate to inorganic cation is of the order of 1 to 3. The Al concentrations in dissolution experiments are 2-3 orders of magnitude above the inorganic solubility of A1 at neutral pH (SURDAMet al., 1984; CROSSEY, 1985; SURDAM and MAcGOwAN, 1987; MAcGOWAN and SURDAM, 1988) and an order of magnitude above the highest measured formation water A1 concentrations (MAcGOWAN and SURDAM, 1988; FISHERand BOLES, 1990). Therefore, the concentrations of C A A involved in the mobilization of Al is likely <100 ppm (inasmuch as formation water samples show <6 ppm Al at a maximum and the experimental solutions show <100 ppm A1). This

695

leaves the majority of the mono- and difunctional CAA free to complex Fe, Ca, Si and others (Fig. 3), as well as to buffer pH. Without this component of organic alkalinity, aluminosilicate minerals alter in situ to clays or zeolites (SURDAMe t al., 1989c). Carboxylic acid anions may also have a pronounced effect upon the stability of carbonate minerals over the temperature range (typically 80-130°C) in which they dominate formation water alkalinity (SURDAMet al., 1984; SURDAMand CROSSEY,1985a, b). In such instances, the formation water pH is buffered by CAA (SURDAMet al., 1984; SURDAMand CROSSEY, 1985a, b; MESHRI, 1986; KHARAKAet al., 1989). As pointed-out by SURDAMet al. (1984), carbonate minerals will actually be stabilized as Pco2 increases over the temperature range in which CAA dominate alkalinity. Thus, the stability of carbonate minerals in this case will depend upon the balance between the concentration of CAA and Pco_, in formation waters. SMITHand EHRENBERO (1989) and ABERCROMBIE (1988) point out that aluminosilicate minerals may be more effective at buffering pH, under certain conditions. It is more useful, however, to consider the entire buffer system than a single component when evaluating carbonate mineral stability in clastic systems. As an example, LUNDEGARDand LAND (1989), in a first attempt at modeling this system calculated the pH-buffer crossover points in the system Ca 2+-Na+-CH3COOH-CaCO3-HzO using the P H R E E Q E and EQ-3/EQ-6 computer codes with varying fluid Pco_, values. Although some of the dissociation and complexation constants needed to make these calculations are unknown at temperatures >25°C, they attempted to calculate the buffer

Table 6. Al concentrations in aqueous and hydrocarbon phases of dissolution experiments at 100°C Fluid

Solid

1

A

1 2 2 3 3 4 4 5 5

B A B A B A B A B

Aqueous phase Al (ppm)

Organic phase A1 (ppm)

ND ND 37.2 21.6 5.7 ND 33.6 42.4 ND ND

NP NP NP NP 31.2 ND NP NP 106 9.6

pH* 6.12

6.23 6.54 6.76 6.45 6.29 6.85 7.01 6.97 7.11

Fluid compositions: (1) 20,000 ppm NaC1 (organic blank); (2) 1 + 3000 ppm acetate + 200 ppm malonate + 50 ppm salicylate; (3) 2 + 0.5 ml Paloma Field, San Joaquin Basin, crude oil; (4) Stevens Sandstone formation water, Coles Levee Field (SJB-1, MAcGOWAN and SURDAM,1988); (5) 4 + 0.5 ml Paloma Field, San Joaquin Basin, crude oil. Solid phases: (A) Andesine mineral grains; (B) Whole-core Stevens Sandstone material, Coles Levee, San Joaquin Basin. *Final pH measured at room temperature. NP = No organic phase present. ND = None detected.

696

D.B. MacGowan and R. C. Surdam HYDROUS PYROLYSIS OF A TYPICAL TYPE II

..•IO0

MODERATE

SULFUR

KEROGEN

2:

Z

0275 INCREASING

b TEMPERATURE

350 (°C)

FIG. 4. Carboxylic acid anions and oil generation during

hydrous pyrolysis of whole source-rock sample of a moderate S, Type II kerogen. Note at least some free oil is present in the bomb when CAA are present in detectable quantity. Data shown have not been normalized to source rock TOC.

crossover points at various temperatures up to 150°C. In the simulations, pH was calculated as a dependent variable, although initial and final pH values for the simulations were not reported. They found that, in order for ethanoate to stabilize carbonates as Pco_, is increased, 10,500 ppm ethanoate were required at 50°C, 3660 ppm ethanoate at 100°C, and 1140 ppm ethanoate at 150°C (Fig. 5). They further found that addition of Na into the model simulation had a negligible affect upon the crossover concentration. Addition of Ca from a source other than calcite dissolution, however, had a dramatic effect upon the crossover concentration: the addition of just 400 ppm Ca (about the concentration in normal marine waters; DREVER,1988) lowered the crossover concentration by 14%. A survey of Ca concentrations in formation waters shows they range from a few hundred parts per million to >100,000 ppm Ca, with most in the range of several hundred to a few thousand parts per million, and that Ca generally increases with increasing burial depth (COLLINS, 1975). Additionally, SCHUL/Z et al. (1990) demonstrated that, at least in the Stevens Sandstone formation waters of the San Joaquin Basin, plagioclase dissolution and not calcite dissolution was the major contributor to Ca concentration. It is therefore probable that the crossover concentration would be drastically reduced by using more realistic initial Ca concentrations in the model simulations. Further, all the initial conditions were set with ethanoic acid, rather than ethanoate. LUNDEGARDand LAND (1989) stated that in all simulations, final ethanoate concentrations greatly exceeded final ethanoic acid concentrations, indicating dissociation of the acid to protons and the acid anion. The only reaction available to consume the protons produced by dissociation of ethanoic acid in the simple system modeled by LUNDEGARD and LAND (1989) is the dissolution of calcite (CaCO 3 + H ÷ --~ Ca 2÷ + HCO3). In the natural system (or a

more complete model), dissolution or hydration of aluminosilicate minerals would consume these protons (SMITH and EHRENBERG, 1989; ABERCROMBIE, 1988), making the crossover concentration required for ethanoate to stabilize carbonate minerals with increasing Pco2 several times less than that calculated by LUNDEGARDand LAND (1989). LUNDEGARDand LAND (1989) conclude that, inasmuch as only a very few reported analyses of formation waters have concentrations in excess of their calculated crossover concentrations, ethanoate buffering of formation water pH is not an operative mechanism in most basins and therefore, Pco2 and not ethanoate concentration would be the dominant control on carbonate mineral stability. However, in addition to the analyses cited by LUNDEGARD and LAND (1989), other recently reported analyses have demonstrated ethanoate concentrations in excess of their calculated crossover point (SURDAMel al., 1984; FISHER, 1987; MAcGOWAN and SURDAM, 1988, and the present study). Figure 5 presents total C A A concentration vs temperature for the formation waters analyzed in this study. Superimposed on this diagram are the lines of Ca = 0 ppm and Ca = 400 ppm calculated by LUNDEGARDand LAND (1989) and the envelope of reported C A A concentrations vs temperature from Fig. 1. Note that nearly half the analyses reported herein fall above the calculated crossover lines. Thus, in these waters carbonates would be stabilized by increasing POD,., presuming the correctness of the lines calculated by LUNDEGARD and LAND (1989). For the above reasons, caution should be exercised in extrapolating the results of

10,000

~

DH pH buffered

/ %\

Itlb~ {Luealglr e / ff~~bYS©lq|lo'~lc"l ind Llnd lw~) / / /

9,000

Total Csrbo3(ytIc Acld Anions

\

oI LGC, L~C, pHnolbufferod pH bufkr~ A ~B, pH ~t buHo,sd * SJB.pH bufferld

~ •

\\

l/ e~ il° •

8,000

\\\

7,000 ~. -

)

pHI©m|m, n*~ bu ~lCNI Dy ° . . . . . . . . . ~:;:,. 6,000 ind Lind, 1~B9)

~,

I~

"

, I

5'000

~lglon 01feporW~~ t l l e

1~B9) j ~

c°~nlratl°n" wh*rt ~l¢lll ts ~

3,000

\.

~,ooo ....

~/~

"

.- i 40

L 60

*

,

~

o

20

\\

% 80

°

, 100

Temperature

, 120

, 140

, 160

(°C)

FIG. 5. The concentration of total CAA from analyses in this study. Superimposed upon this plot is the envelope containing all reported analyses of CAA (modified from Fig. 1) and the acetate-carbonate pH-buffer crossover lines from LUNDEGARDand LAND(1989). LGC = Louisiana Gulf Coast, SJB = San Joaquin Basin.

Carboxylic acid anions in formation waters their computer simulations to clastic systems not completely dominated by carbonate minerals. It is apparent that the C A A in formation waters can have a pronounced effect upon the porosity of sandstone and petroleum migration conduits. Because of their ability to complex and transport A1 and Si (as well as other metals) from the site of aluminosilicate dissolution, and their control upon carbonate mineral stability (SURDAMetal., 1984; CROSSEY, 1985; SURDAM and CROSSEY, 1985a, b; SURDAM and MACGOWAN, 1987; MAcCOWAN and SURDAM,1988; LDNOEGARD and LAND, 1989; KHARAKAet al., 1989), the evolution and destruction of the diagenetically important C A A in clastic rocks is of great importance to the study of clastic diagenesis.

697

mineral dissolution event as Pco2 increases without an organic buffer (in basins achieving higher temperature than the southern San Joaquin Basin, -120°C; e.g. SURDAMet al., 1989b, c). The utility of these observations in modeling diagenesis in sandstone-shale successions is limited only by the knowledge of the concentration and distribution of C A A through space and time. SURDAM el al. (1989b) present a methodology for evaluating temporal concentrations and distributions of C A A and the modeling of organic-inorganic diagenetic pathways through space and time.

SUMMARY

In the present study of 40 formation waters from the San Joaquin Basin, California and the Louisiana Gulf Coast Basin, the maximum concentration of In formation waters that are either immature with monofunctional C A A is 8100 ppm and the maximum respect to the generation of C A A or depleted with concentration of difunctional C A A is 370 ppm. respect to C A A (via decarboxylation, bacterial Although several authors have reported the presence action, formation fluid mixing, etc.), carbonate of difunctional C A A in produced formation waters mineral stability will be a function of the Pco2, (SURDAMet al., 1984; KHARAKAet al., 1985; BARTH activities of Ca 2+ , Mg 2+ and Fe 2+, and solution pH 1987a, b; MAcGOWAN and SURDAM, 1988), BARTH (which may be controlled by aluminosilicate mineral (1987a, b) postulated that the presence of difunctiobuffers; SMITH and EHRENBERG,1989; ABERCROMBIE, hal C A A in formation waters indicated contami1988). In solutions where C A A dominate fluid alka- nation by drilling fluids. Analyses of drilling muds linity (generally between 80 and 140°C), carbonate and scale soap used within the study area which were mineral stability will be a function mainly of the available for this study show few or no difunctional balance between aluminosilicate hydration, organic C A A . Additionally, both mono- and difunctional alkalinity and Pcoe, due to the capacity of C A A s to C A A were detected in aqueous extracts of crude oils buffer pH (SURDAMet al., 1984). Depending upon the and the petroleum phase of hydrous pyrolysates. P c o : configuration of the solution, in a formation Difunctional and monofunctional C A A have also water whose alkalinity is dominated by C A A , car- been reported in the liquid products of laboratory bonate minerals will be stabilized by increasing Pco: kerogen hydrous pyrolysis experiments (KAWAMURA (SURDAMet al., 1984; SURDAMand CROSSEr, 1985a, b; et al., 1986; KAWAMURAand KAPLAN, 1987: MACLUNDECARD and LAND, 1989). Decarboxylation of GOWAN and SURDAM, 1987; SURDAM and MACC A A will simultaneously increase the ~2CO3 of the GOWAN, 1987; MAcGOWAN et al., 1988b; KHARAKAet formation water, and lower the capacity of the or- al., 1989); therefore, it is not surprising that they ganic species in the solution to buffer pH. When should be detected in produced formation waters carbonate species again dominate formation water associated with petroleum reservoirs. Carboxylic alkalinity (typically at temperatures > 140°C, Fig. 1 ), acid anions are important in clastic diagenenc reacif Pco: increases (from final kerogen decarboxy- tions; not only do they buffer formation water pH lation) a late-calcite dissolution event may occur. over the temperature range in which they dominate This evolution of pore waters may help explain the fluid alkalinity, and thus participate in the control on diagenetic sequence documented in the southern San carbonate mineral stability (typically over the 80Joaquin Basin, California (e.g. BOLES, 1984; 140°C temperature range; SURDAM and CROSSEr, FISCHER, 1986; RAMSEYER and BOLES, 1986; BOLES 1985a, b), but they are also capable of complexing and RAMSEYER, 1987, 1988; FISCHER and SURDAM, and transporting the less-soluble components of alu1988: FISHER and BOLES, 1990) and Gulf Coast Basin minosilicates (notably AI and Si) from the site of (SHARP et al., 1988), a diagenetic sequence also seen aluminosilicate dissolution in the subsurface. Hydin sandstone-shale successions in many other basins: rous pyrolysis and dissolution experiments as well as early carbonate cement (calcite. dolomite or siderite) thermodynamic equilibrium computer simulations precipitated at formation temperatures between - 4 0 show these organic-inorganic interactions to be critiand 80°C, followed by an aluminosilicate dissolution cal to the study of clastic diagenesis. Certainly, no and carbonate mineral dissolution (or nonprecipi- other viable, holistic mechanism has been advanced ration) events ( - 8 0 to 120°C). This is followed by a that adequately accounts for the observed widelate-carbonate cementation event (typically ankerite spread dissolution of aluminosilicate minerals and or dolomite) with a possible late-stage carbonate the transportation of AI and Si in subsurface diageDiagenetic s u m m a r y

698

D.B. MacGowan and R. C. Surdam

netic systems as well as the distribution of c a r b o n a t e mineral c e m e n t a t i o n / d e c e m e n t a t i o n z o n e s which are o b s e r v e d in s a n d s t o n e / s h a l e successions.

Acknowledgements--R. C. Surdam wishes to acknowledge the financial assistance of Texaco Inc., Phillips Petroleum, Amoco, Conoco and British Petroleum. D. B. MacGowan thanks the Enhanced Oil Recovery Institute of The University of Wyoming for support. In addition, we wish to thank Texaco, Mobil, Shell, Arco, Amoco and Dr J. R. Boles (University of California at Santa Barbara) for formation water samples. We would especially like to thank Michael D. Hogg (Texaco, New Orleans, Louisiana) for arranging for formation water samples and much help and advice, as well as T. L. Dunn (Department of Geology and Geophysics, the University of Wyoming) for creative input and thoughtful discussions. The authors are also grateful to P. Braithwaite of Mobil Oil Research and Development for arranging for elemental analysis of some of the oil samples. We are indebted to Dr W. J. Harrison (Colorado School of Mines) and Geoffrey D. Thyne (University of Wyoming) for allowing us to use their temperature extrapolations for organic-inorganic complex association logK values. We also thank A. Rush and A. Diess for their patience in the many drafts the manuscript and figures have seen. Reviews by .1. R. Boles (University of California, Santa Barbara) and an anonymous reviewer as well as comments by Y. K. Kharaka greatly improved this manuscript. Editorial handling: Y. K. Kharaka.

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APPENDIX

Great care was taken to sample only wells that had not undergone unusual organic chemical treatments during completion or production, or that had experienced any secondary or enhanced oil recovery stimulations or floods. Formation water samples were taken at the wellhead, upstream of the separator. After the oil-water mixture had separated, the samples were filtered through 0.45/,, divided into several 100-ml aliquots, and placed in polycarbonate or polyethylene bottles so that preservative could be added. Samples for CAA analysis had 200 ppm mercuric chloride added as a bacteriacide. All samples were then stored in the dark and kept as cool as possible until shipped to the laboratory. Carboxylic acid anions were analyzed directly by ion chromatography exclusion (ICE), using a Dionex 14 ol Dionex 12 ion chromatograph equipped with a conductivity detector. Table A.1 contains the instrumental conditions. Separation of ionic species was achieved in a separatol column which effects separation on the basis of diffusion of charged species in and out of resin pores. Strongly charged species (such as mineral acids) are prevented from entering the resin pores by Donnan exclusion and elute immediateb in the void-volume peak. Non- ol weakly-charged species (such as CAA) are free to diffuse in and out of resin pores: the separation of the species is mostly dependent upon concentration, eluent pH, cluatc pK a. resin hydrophilicity. and temperature (DIONEX CORP., 1982). The high conductivity of the eluant and resultant high background is avoided by ion exchange in a fibrous suppressor column, which exchanges a tetrabutylammoniumhydroxide (TBAOH 4 ) ion for the H + ion in the eluent because the TBAOH+C! pair has a much lower conductivity than does the H+/CI pair. Each acid anion species was individually identified by serial internal spiking of the samples. Table A.2 shows the various inorganic and organic interferences encountered

Carboxylic acid anions in formation waters

70/

during the course of analysis. These interferences were resolved by altering the resin hydrophilicity; this was achieved by increasing the eluent strength or adding 1-4% isopropanol to the eluent (DIONEX CORP., 1982).

Table A.2. Interferences in the analysis of orgamc acid anions during ICE analyses

Table A.I. Instrumental conditions for the ICE analyses of formation waters

Difunctional Ethanedioate

Instrument: Dionex System 12 or 14 Ion Chromatograph,

Species

Propanedioate

interferences water dip, salt peak, sulfide, phosphate O-hydroxybenzoatc

Flow rate: 2 ml/min. Separator column: polystyrenedivinylbenzene (Dionex ICE AS-1 separator 30580) Eluent: 5.10- 4 M to 1.2.10 3 M HCI; _+4% (by volume) isopropanol as conditions dictate. Suppressor regenerant: 2.0.10 3 M to 4.0-10 3 M tetrabutylammoniumhydroxide.

Monofunctional Methanoate Ethanoate Hydroxybenzoates O-hydroxybenzoic acid

O-hydroxybenzoate bicarbonate propanedioate, methanoate