恩平凹陷中央断裂构造带超压发育及成藏意义

Overpressure forming and its effect on petroleum accumulation in central faulted structural belt of Enping depression, China

基于钻井实测压力数据和气烟囱现象,结合泥岩声波时差及地震层速度预测结果,对恩平凹陷中央断裂构造带超压的分布特征及成因进行研究,并探讨超压发育对油气成藏的作用和意义。研究区纵向上划分为2套压实压力系统:恩平组及以上地层为正常压实常压系统,文昌组为欠压实超压系统;平面上超压主要分布于EP17洼内,EP18洼次之,EP12洼基本不发育。超压形成是生烃增压和不均衡压实共同作用的结果,其中生烃作用为主要因素,不均衡压实为次要因素。超压未对有机质热演化产生影响,但在一定程度上改善深部储层的性能,加强对烃类的封盖作用,同时可以产生微裂缝,并为油气运移提供动力。在压力控制下,中央断裂带油气主要聚集在文昌组和恩平组内,其中文昌组具有近源成藏、自生自储的优越条件,是研究区油气勘探的有利层位。

With observed pressure of drills,phenomena of gas chimney and prediction from shale acoustic travel time and seismic data,overpressure forming and its effect on petroleum accumulation in central faulted structural belt of Enping depression were studied.In the longitudinal direction,two reservoir pressure systems were identified： Normal compaction-normal pressure system in Enping and upper formation and uncompacted-overpressure system in Wenchang formation.On vertical,overpressure is mainly distributed in EP17 sag,secondly in EP18 sag.The main driving mechanism of overpressure is hydrocarbon,and disequilibrium compaction is the minor factor.Overpressure has little effect on thermal degradation of kerogens,but it improves the performance of deep reservoir to some extent,strengthens the capability to seal gas and produces micro-fissure for hydrocarbon expulsion.Under the control of overpressure,oil and gas accumulate mainly in Wenchang and Enping formations.Wenchang reservoirs are characterized by near-source accumulation,self-generating and self-preserving.These advantages make it a favorable strata for petroleum explorations.