鄂尔多斯盆地陇东地区长7 段烃源岩排烃机制及成藏意义

通过鄂尔多斯盆地陇东地区延长组泥岩综合压实曲线对比,明确研究区长7段烃源岩普遍存在欠压实现象,利用等效深度法计算了泥岩最大埋深时期的过剩压力,结果表明,欠压实产生的过剩压力是长7段烃源岩排烃的重要动力。由此,根据过剩压力的纵向分布特征划分了3种排烃方式,并叠合烃源岩的分布、源储压力差得出长7段烃源岩向其上下地层有利的排烃范围。结果表明,当源储压力差不小于储层的毛管压力时,排烃才可能发生;有利的排烃区受优质烃源岩分布、排烃方式和动力条件的综合控制;长7段烃源岩向下伏地层排烃的条件优于向上覆地层,是现今油藏选择在长8段大规模分布的主要原因;长6段小规模的油藏基本分布在长7段烃源岩向上有利排烃范围之内。

Hydrocarbon expulsion dynamic conditions and accumulation significance of petroleum of source rocks in Longdong area,Ordos Basin

Mechanisms and conditions of primary migration of petroleum affect the distribution of oil and gas reservoirs to some extent.Through the comparison of comprehensive compaction curve in Yanchang formation of Longdong area,Chang7 hydrocarbon source rocks are universally compacted;the overpressure of mudstone in the largest buried depth period is calculated by means of equivalent depth method,and the result indicates that the overpressure of the Chang7 hydrocarbon source rocks is an important hydrocarbon-expulsion power.According to the study above,and based on the distribution of the overpressure curve vertical shape,hydrocarbon-expulsion way is divided into three kinds,and considering the distribution of source rocks and the differential overpressure,the scope of favorable hydrocarbon expulsion area is mapped.Research shows that,when the differential overpressure between the source rock and reservoir is not less than the capillary pressure of reservoir,the hydrocarbon-expulsion occurs;favorable hydrocarbon expulsion area is comprehensively controlled by the distribution of high-quality hydrocarbon source rocks,hydrocarbon-expulsion way and dynamic conditions;the condition of hydrocarbon-expulsion in Chang7 hydrocarbon source rocks to the lower strata is better than that of the overlying strata,this is the reason that the large-scale reservoirs is distributed in Chang8 instead of in Chang6;the small reservoirs in Chang6 is mostly confined in the scope from hydrocarbon-expulsion of Chang7 hydrocarbon source rocks to the overlying strata.