沿不同时期断裂运移的油气被泥岩盖层封闭所需条件的差异性——以三肇凹陷青一段和南堡凹陷5号构造东二段为例

Analysis on the different sealing conditions required by mudstone caprock at different fault evolution stages: A case study on the 1st member of Qingshankou Formation in the Sanzhao Depression and 2nd member of Dongying Formation in the structure No.5 of t

为了研究含油气盆地下生上储式断裂发育区油气分布规律,在不同时期断裂本身特征及其附近压力条件差异性研究的基础上,对油气沿断裂运移特征及其泥岩盖层封闭运移油气所需条件进行了研究。结果表明,泥岩盖层封闭沿不同时期断裂运移油气所需的条件不同。油气沿活动断裂运移的动力既有地层剩余压力,又有油气本身浮力;以伴生和诱导裂缝为输导通道,孔渗性相对较好,阻力相对较小,易于油气穿过泥岩盖层运移;泥岩盖层封闭沿活动断裂运移油气的条件是断裂在泥岩盖层内上下不连接。而油气沿静止期断裂运移的动力仅为油气本身浮力;以断层岩孔隙为输导通道,孔隙性相对较差,阻力相对较大,不易于油气穿过泥岩盖层运移,泥岩盖层封闭沿静止期断裂运移油气所需的条件是断层岩排替压力大于或等于其下储层剩余压力。

To decipher the hydrocarbon distribution pattern of oil bearing basins with hydrocarbon generating in the deeper formations and then migrating along faults upwards to the shallower reservoirs,we have studied hydrocarbon migration characteristics along faults and mudstone caprock sealing conditions required for accumulating hydrocarbon.Fault characteristics at different evolution stages were studied and corresponding pressure conditions were depicted.The results showed that to seal hydrocarbons migrating along faults,different conditions were required at various stages.The hydrocarbon migration along active faults was driven by both buoyancy and formation overpressure.While the carrier system is associated cracks and induced fractures,the corresponding porosity and permeability were relatively good.In this case,the hydrocarbon migration resistance crossing through the mudstone caprock was lower.Therefore,only when faults above the caprock are disconnected with those below,can the caprock seal the migrating hydrocarbon.In contrast,the hydrocarbon migration along static faults was driven only by buoyancy,while the carrier system was of fault rock pores.In this case,the corresponding porosity is relatively poor with higher migration resistance for the hydrocarbon to break through the mudstone caprock.Therefore,to seal hydrocarbon migrating along faults,the displacement pressure of fault rock should be equal to or greater than the reservoir overpressure.