四川盆地东缘寒武系盐下油气勘探领域探讨

Study on the structural inheritance of Dengying Formation in Sichuan Basin

地球物理资料显示四川盆地东缘齐岳山附近寒武系高台组膏盐岩层下深部存在逆冲构造,其形成过程以及油气地质意义未见深入研究。笔者等综合四川盆地东部石柱地区线束三维和建南地区二维地震反射资料,并结合钻井资料以及区域地质研究成果,从构造继承性的角度探讨四川盆地震旦系灯影组台缘带类型,并分析了川东地区寒武系盐下油气圈闭特征。研究获得如下认识:①川东齐岳山北段构造变形强烈,普遍发育基底卷入构造,构造样式受青白口纪—南华纪裂谷与转换带构造位置的控制。②依据构造继承关系将盆内灯影组台缘带划分为德阳—安岳地区原生型台缘带、万源—达州地区继承型台缘带以及石柱地区继承—改造型台缘带。③依据青白口纪—南华纪裂谷的分布和后期构造作用影响大小,认为沿齐岳山向南至南川一带存在与石柱地区相似的灯影组继承—改造型台缘带,忠县、南川以西存在灯影组继承型台缘带。④研究区新元古界—下寒武统烃源岩、灯影组—龙王庙组滩相白云岩储层与寒武系膏盐岩层系构成完整的生储盖组合。⑤寒武系盐下基底逆冲可形成成排、成带的构造,与灯影组继承—改造型台缘带、龙王庙组滩相白云岩储层配置,形成断层相关的构造—岩性圈闭带,成为川东地区油气规模聚集有利区。研究认为四川盆地东部石柱地区震旦纪—早寒武世早期继承了青白口纪—南华纪裂谷构造特征,燕山期构造反转,高台组盐下形成基底卷入逆冲构造,具备生储盖等基本石油地质条件,具有重要的油气勘探现实意义。

Objectives:Geophysical data show that there are thrusts deep under the salt-rock layer of the Cambrian Gaotai Formation near Qiyue Mountain in the eastern margin of Sichuan Basin,the formation process of the thrusts and the geological significance of oil and gas have not been deeply studied.Methods:Based on the swath 3D and two-dimensional seismic reflection data in Shizhu and Jiannan area of eastern Sichuan Basin,combined with drilling datas and regional geological research results.Results:①The tectonic deformation of the northern Qiyue Mountains in eastern Sichuan is strong,and the basement involved structure is widely developed.The structural style is controlled by the tectonic location of the Qingbaikou-Nanhua rift and transition belt.②According to the structural inheritance relationship,Dengying Formation platform boundary belt can be divided into Deyang-Anyue primary type platform boundary belt,Wanyuan-Dazhou inherited type platform boundary belt and Shizhu inheritance-modified type platform boundary belt.③Based on the distribution of Qingbaikou-Nanhua rift and the influence of late tectonics,it is believed that there are inheritance-modified platform margin belts of Dengying Formation similar to Shizhu area along Qiyue Mountain southward to Nanchuan,and there are inheritance-modified platform margin belts of Dengying Formation in Zhongxian and the west of Nanchuan.④A complete reservoir-cap association is formed by Neoproterozoic Lower Cambrian source rock,Dengying Formation and Longwangmiao Formation beach facies dolomite reservoir and Cambrian salt-rock layer in the study area.⑤The pre-salt basement thrusts of Cambrian can form rows and belts,and the fault-related tectonic-lithologic trap with Dengying Formation's succinction-reformed platform margin belt and Longwangmiao Formation's shoal facies dolomite reservoir configuration has become a favorable area for oil and gas accumulation in east Sichuan.Conclusions:The Sinian-Early Cambrian in Shizhu area of eastern Sichuan Basin inherited the characteristics of Qingbaikou-Nanhua rift,while the Yanshanian tectonic inversion.The formation of the basement involved thrust structure under salt in the Gaotai Formation,which has the basic petroleum geological conditions such as reservoir cap,and has important practical significance for oil and gas exploration.