湖相致密白云岩不均一油藏特征及主控因素

The Reservoir Heterogeneity Characteristics and Affecting Factors of Tight Lacustrine Dolomite Reservoirs

渤海湾盆地塘沽地区沙三5亚段发育湖相含油泥质白云岩层系,油藏顶面埋深2 800~3 600m,属于中深-深层的断块-岩性油藏,储层为致密裂缝白云岩.本文通过岩心观察、实验室分析、压力测试、裂缝分析等手段,重点研究了致密白云岩储层岩石相、储集性、复杂含油性和油藏不均一性特征,分析了成藏主控因素及成藏模式.研究表明:储层岩性以白云岩、泥质白云岩为主,为中-低孔、低渗-特低渗的裂缝-孔隙型储层,储集空间主要为晶间孔、溶孔、裂缝及溶缝;超压与含油性密切相关,超压断块井均中高产、含水率低于20%且呈持续降低趋势,常压断块井均低产、含水率高于55%且稳定-上升趋势;白云岩层系内厚层泥岩为优质烃源岩,提供充足油源;断层封闭性控制油气聚集,进而控制生烃型超压的分布,超压成为油气富集的重要标志;油气充注晚于断块-岩性圈闭形成时间,使油气充注有效.

Lacustrine argillaceous dolomite reservoir has been found theⅢ-5 Member of Shahejie Formation,Tanggu District,Bohai Bay Basin,China,which buried depth is 2 800-3 600 mand keeps oil in the fault block-lithologic argillaceous dolomite reservoir.Considering structure and sedimentary background,the research summarizes reservoir characteristics mainly includes lithologic character,reservoir property and hydrocarbon distribution.At the same time,the paper provides the controlling factors and pattern of hydrocarbon accumulation through integrated analysis of source-reservoir-seal combination and evolution of tectonics,diagenesis and hydrocarbon accumulation.The results show that reservoir lithologic is mainly dolomite and argillaceous dolomite and belongs to fracture-pore reservoir of ultra low porosity and permeability,whose reservoir space,to a large extent,includes intercrystalline pore,secondary dissolved pore,dissolved fractures and fractures.Overpressure is closely correlated with the hydrocarbon distribution.The overpressure wells show medium-high production and their water cuts are under20% with a continuing downward trend;while instead,the normal wells show low production and water cuts are above 55%owning a smooth or upward trend.Mudstone is high-quality source rocks and can supply enough oil to dolomite reservoir.The quantity of hydrocarbon generation and reserves capacity of dolomite are both closely relevant to abundant algae laminae.Faultsealing controls the hydrocarbon accumulation and distribution of overpressure,whose one of the main driving force is hydrocarbon generation.The overpressure has been the significant mark of hydrocarbon enrichment.The hydrocarbon-charging time is behind the fault sealing,thus hydrocarbon-charging is effective.