首页|Geochemical evidence for secondary microbial gas in deep hot reservoirs of the Tarim Basin

Geochemical evidence for secondary microbial gas in deep hot reservoirs of the Tarim Basin

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  • NSTL
  • Elsevier
It is hard to determine secondary microbial gas from deep burial reservoirs with multiple generations of petroleum charge. Herein, oils at depths from 5000 m to 6500 m in the Ordovician carbonate reservoirs, Tarim basin, are found to have been biodegraded to secondary microbial gas. These oils experienced severe biodegradation and thus contain abundant 25-norhopanes and 17-nortricyclic terpanes. The associated gases have methane δ~(13)C_1 from -51.9‰ to -47.3‰ and δ~2H_1 from -327.8‰ to -192.4‰, and CO_2 δ~(13)C_(CO_2) from -0.7‰ to +15.3‰. These features suggest that the gases are secondary microbial gas, generated predominantly via CO_2 reduction with preferential reduction of ~(13)C-depleted CO_2 and contribution of methane hydrogen from formation water in closed environments. The secondary microbial gas may have generated from biodegradation of oils at reservoir temperatures of about <75?C during the Late Permian, and has subsequently mixed with a later charge of non-biodegraded oils and wet gas during the Late Cretaceous. Consequently, the present gas shows relatively low dryness (C_1/ΣC_(1-4) < 0.87) and has varied δ~(13)C_1 and δ~2H_1 values in methane. The study implies that the signatures of secondary microbial gas can easily be masked by thermogenic gas and thus more secondary microbial gas has yet to be identified.

Secondary microbial gasBiodegradationMethanogenesisMixingTarim Basin

Daowei Wang、Chunfang Cai、Lu Yun、Zicheng Cao、Jun Zhang、Yu Qi、Jingyan Liu、Ziwen Jiang、Yongjie Hu

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School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Northwest Petroleum Company, SINOPEC, Urumqi 830011, China

Research Institute of Petroleum Exploration and Development, SINOPEC, Beijing 100728, China

International Petroleum Exploration and Production Corporation, SINOPEC, Beijing 100029, China

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2022

10.1016/j.chemgeo.2021.120630

Chemical geology

Chemical geology

EISCI
ISSN：0009-2541
年,卷(期)：2022.587
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