Recognising biodegradation in gas/oil accumulations through the δ13C compositions of gas components

被引:216
作者
Pallasser, RJ [1 ]
机构
[1] CSIRO Petr, N Ryde, NSW 1670, Australia
关键词
natural gas; secondary biogenic gas; CO2; carbon isotopes; anaerobic biodegradation; methanogenesis;
D O I
10.1016/S0146-6380(00)00101-7
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
A large suite of natural gases (93) from the North West Shelf and Gippsland and Otway Basins in Australia have been characterised chemically and isotopically resulting in the elucidation of two types of gases. About 26% of these gases have anomalous stable carbon isotope compositions in the C-1-C-4 hydrocarbons and CO2 components, and are interpreted to have a secondary biogenic history. The characteristics include unusually large isotopic separations between successive n-alkane homologues (up to + 29 parts per thousand PDB) and isotopically heavy CO2 (up to + 19.5 parts per thousand PDB). Irrespective of geographic location, these anomalous gases are from the shallower accumulations (600-1700 m) where temperatures are lower than 75 degreesC. The secondary biogenic gases are readily distinguishable from thermogenic gases (74% of this sample suite), which should assist in the appraisal of hydrocarbons during exploration where hydrocarbon accumulations are under 2000 m. While dissolution effects may have contributed to the high C-13 enrichment of the CO2 component in the secondary biogenic gases, the primary signature of this CO2 is attributed to biochemical fractionation associated with anaerobic degradation and methanogenesis. Correlation between biodegraded oils and biodegraded "dry" gas supports the concept that gas is formed from the bacterial destruction of oil, resulting in "secondary biogenic gas" Furthermore, the prominence of methanogenic CO2 in these types of accumulations along with some isotopically-depleted methane provides evidence that the processes of methanogenesis and oil biodegradation are linked. It is further proposed that biodegradation of oil proceeds via a complex anaerobic coupling that is integral to and supports methanogenesis. (C) 2000 Elsevier Science Ltd. All rights reserved.
引用
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页码:1363 / 1373
页数:11
相关论文
共 38 条
[1]  
Alexander R., 1981, ADV ORG GEOCHEM, P76
[2]  
[Anonymous], 1967, PETROLEUM MICROBIOLO
[3]  
[Anonymous], P AAPG HEDB RES C 6
[4]  
BAILIE PW, 1997, J AUSTR PETROLEUM EX, V37, P117
[5]  
CAROTHERS W, 1980, GEOCHIMICA COSMOCHIM, V3, P53
[6]   ORIGIN OF GASEOUS HYDROCARBONS IN SUBSURFACE ENVIRONMENTS - THEORETICAL CONSIDERATIONS OF CARBON ISOTOPE DISTRIBUTION [J].
CHUNG, HM ;
GORMLY, JR ;
SQUIRES, RM .
CHEMICAL GEOLOGY, 1988, 71 (1-3) :97-103
[7]  
Clark I., 1997, ENV ISOTOPES HYDROLO, DOI DOI 10.1201/9781482242911
[8]   Alteration of natural gas during leakage from a North Sea salt diapir field [J].
Clayton, CJ ;
Hay, SJ ;
Baylis, SA ;
Dipper, B .
MARINE GEOLOGY, 1997, 137 (1-2) :69-80
[9]  
CONNAN J, 1997, 18 INT M ORG GEOCH 1, P5
[10]  
Cord-Ruwisch R, 1998, APPL ENVIRON MICROB, V64, P2232