川中—川西地区茅口组顶部地震相特征与成因

Characteristics and causes of seismic facies of Middle Permian Maokou Formation in central-western Sichuan Basin,China

为解决川中-川西地区钻井资料匮乏、受玄武岩喷发影响地层纵横向分布发生变化等问题,利用地震资料开展中二叠统茅口组及上覆地层地震相特征分析。通过地震识别,茅口组顶界在地震剖面上主要表现为强波峰地震反射,川中-川西地区茅口组顶界存在明显的弱振幅杂乱地震反射特征连片分布。根据沉积背景分析,认为川西南部地区、川西中部地区、川西北部地区、川中地区茅口组顶界弱振幅地震异常响应特征为火山喷发、火山沉积与碳酸盐岩喀斯特等不同地质作用所引起;结合茅口组上覆地层的差异,将川西-川中分为4个地震相区域。四川盆地上二叠统玄武岩在成都-简阳地区分布,早期可能为火山口爆发区,为油气勘探有利区带。

The characterist ics of seismic facies data of Middle Permian Maokou Formation and its overlying strata are analyzed in order to solve such problems as lack of drilling data in western-central Sichuan Basin and the heterogeneous distribution of stratum resulted from the basalt eruption. Seismic identification reveals that the mainly seismic reflection on the top of Maokou Formation in Sichuan Basin is strong and has obvious weak amplitude clutter as well as contiguous distribution. The analyses of drilling data and sedimentary background show that the characteristics of seismic anomaly response of the top Maokou Formation in the south, middle and north sections of Sichuan Basin are resulted from different geological processes, such as volcanic eruption, volcanic sedimentation and carbonate karstfication. 4 seismic facies zone in central-western Sichuan Basin are classified according to the differences of the overlying strata. It is considered that the Chengdu-Jianyang area likely to be a volcanic eruption zone during late Permian period because of the development of the basalt in this area, which is favorable for the evaluation of oil and gas.