Oil and Gas Charge History of Eastern Baiyun Sag,Pearl River Mouth Basin
Zhang Lili
Zhang Xiangtao
Liu Keyu
Zhai Puqiang
Sun Hui
Zhang Yinglin
Yang Peng
Abstract：The Baiyun Sag,situated in the southern part of the Pearl River Mouth Basin,is an area for active deep-water oil and gas exploration in China.Insight into the oil and gas charge history in the area is crucial for further oil and gas exploration.Based on detailed investigation of oil and gas reservoirs in the eastern Baiyun Sag,this study aims to provide a better understanding of the oil and gas charge history through an integrated fluid inclusion analysis,PVT and basin modeling.The results indicate that:(1)The eastern Baiyun Sag is dominated by gas condensate with some locally developed oil reservoirs.The overall distribution pattern shows that gas occurs in the shallow reservoirs while oil in the deeper reservoirs.In structural highs,gas condensate reservoirs are characterized by relatively high gas dryness coefficient and gas-oil ratio(GOR).(2)Two different types of oil inclusion assemblages(OIAs)have been identified in the reservoirs:Type Ⅰ OIA is characterized by gas-liquid phases at room temperature,emitting yellowish white and yellowish green fluorescence.The vapor filling degree is generally less than 10％,and the homogenization temperature(Th)is 86.2-93.2 ℃.The Th and final ice-melting temperature(Tm)of the coeval aqueous inclusions are 100.9-104.1 ℃ and-4.3 ℃ to—4.2 ℃,respectively.Type Ⅱ OIA is featured by gas-liquid or gas-liquid-solid phases at room temperature,with yellowish green,blue-green,and blue-white fluorescence.The vapor filling degree ranges from 10％to 30％,and the Th values are in the range of 71.1 ℃ to 112.4 ℃.The Th and Tm values of the coeval aqueous inclusions are 96.8-108.6 ℃ and-3.2 ℃ to—2.7 ℃,respectively.(3)The oil and gas charge event corresponding to Type Ⅰ OIA occurred at approximately 10.8 Ma under a normal hydrostatic pressure condition,whereas the equivalent oil and gas charge timing of Type Ⅱ OIA was around 2.8 Ma,under a weak overpressure condition.(4)Some oil reservoirs were entrapped in the eastern Baiyun Sag during the Zhujiang-Hanjiang Formation depositional periods.From the Yuehai Formation depositional period to the present,deep hydrocarbons,mainly in over-pressured gas,migrated vertically along faults upwards to the regional caprock,and then migrated laterally along interconnected sandbodies to accumulate in early traps,altering early oil accumulations and forming a series of condensate gas reservoirs via compositional fractionation during migration.
Keywords：oil and gas charge historymigration fractionationfluid inclusionPVT modelingBaiyun SagPearl River Mouth Basinpetroleum geology
Publication Date：2025-01-14
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：14( 158-171 )