东营凹陷沙三—沙四段砂岩储层超压成因与演化

渤海湾盆地东营凹陷沙三—沙四段砂岩储层发育中-强幅度超压,钻井实测压力换算的最大压力系数为2.0,最大剩余压力达40 MPa。分析发现,储层含油性与超压发育程度具有相关性,认为现今储层超压主要源自烃源岩生油超压流体传递。综合盆地模拟技术和流体包裹体分析,恢复了沙三—沙四段砂岩储层古压力的演化历史,认为沙三段—东营组沉积末期的快速沉降作用是导致孔隙流体排出受阻而形成第一期储层流体超压的主要原因,但东营组沉积末期—馆陶组沉积初期构造抬升的泄压作用可使孔隙流体压力降低至常压;在明化镇组沉积末期—现今,由于烃源岩主体仍然处于主油阶段,烃源岩生烃作用产生的大量含油气超压流体充注砂岩储层是形成第二期储层超压的主导成因。

Overpressure genesis and evolution of sandstone reservoirs in the 3rd and 4th members of Shahejie Formation,the Dongying Depression

The sandstone reservoirs within the 3^rd and 4^th members of Shahejie Formation in Dongying Depression, the Bohai Bay Basin are moderately to strongly overpressured with the maximum pressure coefficient of 2.0 and the maximum excessive pressure of 40 MPa calculated based on the measured pressures.Analysis indicates that oil-bearing properties of the reservoirs correlate to the development degree of overpressure,and current reservoir overpressure is mainly caused by the overpressured fluids from source rocks.Integrated with basin modeling and fluid inclusions analysis,this paper reconstructed the geo-pressure evolutionary history of the sandstone reservoirs in the 3^rd and 4^th member of Shahejie Formation.The first stage reservoir overpressure was mainly caused by the rapid subsidence during the deposition of the 3^rd member of Shahejie Formation to the end of Dongying Formation that blocked pore fluid discharging.The overpressure might be released to hydrostatic pressure along with the tectonic uplifting during the late Dongying Formation to early Guantao Formation.From the late Minghuazhen Formation to the present,the bulk of the source rock is still at peak oil generation and large amount of oil/gas-bearing overpressured fluid generated by the source rocks charge into the sandstone reservoirs,leading to the second stage overpressure.