四川盆地中部前震旦系裂谷及对上覆地层成藏的控制

The pre-Sinian rift in central Sichuan Basin and its control on hydrocarbon accumulation in the overlying strata

利用最新地震、大地电磁、野外露头和钻探等资料,分析四川盆地中部基底构造特征及其对震旦系—寒武系油气成藏的控制作用。研究发现,四川盆地中部发育北东走向的前震旦系裂谷,裂谷内部受一系列与裂谷走向平行的正断层控制,发育地垒-地堑结构,大型垒-堑结构及控制垒-堑结构的边界断层后期活动对上覆地层滩体有利相带具有重要的控制作用。基底差异性升降导致垒-堑结构的形成,地垒导致局部高地貌的形成,有利于滩体的发育,并在长期海相沉积环境中继承性发育,在震旦系—寒武系甚至二叠系中形成一系列上下叠置的丘滩体,形成大面积的有利沉积相带。前震旦系裂谷及相关正断层后期活动控制了上覆震旦系—寒武系颗粒滩和岩溶储集层以及烃源岩的规模发育并形成构造-岩性圈闭。通过综合评价,优选出高石梯—磨溪以北和高石梯—磨溪以南2个大型构造-岩性复合圈闭有利勘探区,有望成为安岳特大型气田发现后重要的天然气勘探领域。

Based on the latest seismic data,resistivity profile,outcrop evidence and logging data,the structural features of basement in Sichuan Basin and its control on the hydrocarbon accumulation in the Sinian-Cambrian strata was discussed.It was found that a NE striking pre-Sinian rift was developed across the whole basin.Controlled by a series of rift-parallel normal faults,horst-graben structures were developed inside the rift,large horst-graben structures and later activity of their boundary faults controlled the distribution of beach facies of the overlying strata.The horst-graben structures induced the formation of local highs of ancient landform and controlled the successive development of overlapped bioherm beach facies in long-term marine setting from the Sinian period to the Permian period,and as a result a widely distributed favorable sedimentary facies belt was developed.The pre-Sinian rift and later activities of related normal faults controlled the development of the grain beach and karst reservoirs and the deposition of high quality source rock,which form structural-lithologic traps.Through comprehensive evaluation,two large structural-lithologic composite trap favorable exploration areas in the south and north of the Gaoshiti-Moxi area,were selected.