鄂尔多斯盆地西峰油田延长组长8段岩性油藏动态成藏过程

Research on Oil Accumulation Process of Lithologic Reservoir in Chang 8 Member of Yanchang Formation,Xifeng Oilfield

运用定量方法对西峰油田地层埋藏史、热史、生排烃史、成岩史、孔隙度演化史、油气充注期、圈闭形成史及成藏动力窗口演化史分别进行了模拟,并对成藏关键条件的时空匹配关系进行了综合分析。结果表明,从早白垩世开始,区域构造沉降及伴随的大规模盆地热事件引发了烃源岩的生排烃,为油气成藏创造了优越油源条件;成藏之前,有机酸的溶蚀作用极大地改善了长8段储层的物性,从而奠定了油气成藏所需的空间基础;随时空演化,源储压差的持续增大使油气充注进入储层成为了可能;从成藏期开始,成藏动力窗口和岩性圈闭窗口的持续发育,不但保障了油气的高效充注,而且使已形成的油藏能够很好地保存下来。成藏关键条件的时空匹配关系表明,西峰地区长8段储层油气成藏是一个自然的过程,成藏期储层物性良好,成藏后在压实和胶结作用下储层逐渐致密。

Using quantitative methods,the evolution process of formations,geothermal field,hydrocarbon generation and drainage,diagenesis,porosity,accumulation times,traps and the driving force window are simulated,and the space-time matching of key accumulation factors are further analyzed. Results show that beginning form the Early Cretaceous,the regional structural subsidence and incidental significant geothermal event triggered the generation and drainage of source rocks. Dissolution of organic acid before accumulation period dramatically improved the porosity of Chang 8 reservoir which provides enough space for oil accumulation. Following time-space evolution,the increasing pressure difference between source rocks and reservoirs makes the oil injected into reservoirs possible. Beginning at the accumulation period,the steady development of driving-force window and trap window not only promotes the efficiency of oil injection but also makes those already accumulated oil preserved safely. The time-space matching of key conditions of oil accumulation shows that oil accumulation in Xifeng oilfield is a natural process,namely,the porosity in Chang 8 reservoirs is perfect before the oil accumulation period,and after which,becomes denser and denser under compaction and cementation.