Geochemical Characteristics of Ancient Oil Reservoirs in Sairen Area,Qiangtang Basin
The Sairen region,situated in the Qiangtang Basin,a large marine oil and gas basin in the northern part of the Qinghai-Tibet Plateau,is located in the southern Qiangtang Depression.This area has seen limited research and a relatively low level of understanding in the field of oil and gas geochemistry.The group composition and the geochemical characteristics of steroidal terpenes in oil reservoir samples were summarized,and a conclusion was drawn by integrating various biomarker parameters.The paleo-reservoir in this region,as a whole,are in a stage ranging from low to mature maturity.C27 steranes predominate over C29 steranes,and tricyclic terpanes,with C23 as the main peak,indicate a predominant marine organic matter source with some contribution from terrestrial organic matter.The reservoir samples exhibit a low pristane/phytane ratio(Pr/Ph＜1).In non-hydrocarbon compounds,gammacerane is detected in certain abundance,along with a relatively high C35/C34 hopane ratio,suggesting that the paleo-reservoir formed in a sedimentary environment with relatively deep deposition,strong reducing conditions,and a certain salinity.The geochemical analysis of paleo-reservoir in this region lays the foundation for the study of hydrocarbon accumulation and understanding the laws of oil and gas enrichment.It establishes the sedimentary environment and organic matter source of paleo-reservoir in this area,with a predominant marine organic matter source and a sedimentary environment characterized as relatively reducing.
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