川西坳陷复合-联合构造及其对油气的控制

Structural superimposition and conjunction and its effects on hydrocarbon accumulation in the Western Sichuan Depression

据不整合和岩相记录及古构造分析,川西坳陷中新生代陆相地层中至少存在11个构造运动界面。受西缘龙门山冲断带、北缘米仓山构造带和西南缘川滇构造带影响,川西坳陷发育北东向、近东西向和近南北向3组主要构造,其中北东向构造在多数构造活动中都有不同程度发育,而近东西向和近南北向构造则分别形成于燕山期和喜马拉雅期。同时,3组构造在多期次构造活动中相互叠加,形成了同轴复合、横跨复合、斜接复合、多向复合和联合等5种主要形式的叠加构造。川西坳陷构造对油气的控制表现在构造适时性、构造控位和构造改造3个方面,原生气藏形成及油气分布主要受控于早期构造(印支—燕山期),而晚期构造(主要是喜马拉雅期)仅对早期气藏起改造作用,表现为早期构造变位、储集层改善、原生气藏破坏或次生气藏形成。印支—燕山期古构造的精确恢复以及多期、多组构造叠加过程中裂缝活动特征是该区今后油气勘探应重点关注的两个方面。

Records of unconformities and lithologic facies and analysis of paleo-structure show that at least eleven tectonic boundaries exist in the Meso-Cenozoic continental strata in the Western Sichuan Depression.Affected by the Longmenshan thrust belt on the west side,Micangshan structural belt on the north side and Chuandian structural belt on the southwest side,NE-trending,sub-EW-trending and sub-NS-trending structures were developed correspondingly in the Western Sichuan Depression.The NE-trending structures were developed in varying degrees in most tectonic movements,while the sub-EW-trending and sub-NS-trending structures were formed in the Yanshanian and Himalayan,respectively.The three groups of structures were superimposed by one another in multi-stage tectonic movements,producing mainly five types of structural complexes,i.e.coaxial superimposition,orthogonal superimposition,oblique superimposition,multi-direction superimposition,and structural conjunction.Structural controls on hydrocarbon accumulation in the Western Sichuan Depression can be expressed as the following three aspects,i.e.timing,location and modification.Hydrocarbon distribution and the formation of primary gas pools were mostly controlled by early structures（in the Indosinian and Yanshanian）,whereas late structures（mainly in the Himalayan） only had modification effects on early gas pools,resulting in structural displacement,reservoir improvement,the destruction of primary gas pools and the formation of secondary oil pools.Accurate reconstruction of the Indosinian-Yanshanian paleo-structures and fracture behaviors during the multi-stage and multi-direction structural superimposition are two important aspects that need to be paid more attention to in the future hydrocarbon exploration in this region.