四川盆地东南缘向斜构造五峰组-龙马溪组常压页岩气富集主控因素

Main controlling factors on normal pressure shale gas enrichments in Wufeng-Longmaxi Formations in synclines,southeastern Sichuan Basin

四川盆地东南部地区盆缘槽档转换带和盆外隔槽式构造带向斜发育,由于其整体抬升时间长,构造运动强烈,剥蚀量大,区域保存条件相对复杂,导致不同向斜五峰组—龙马溪组为常压且页岩气含气性差异较大。在研究区向斜构造五峰组—龙马溪组页岩发育特征、后期保存条件、含气性等差异的基础上,分析了向斜构造页岩气富集主控因素,并总结了3种有利于页岩气保存富集的构造样式。研究结果表明:优质页岩发育是页岩含气性的物质基础,川东南地区盆缘和盆外向斜五峰组—龙马溪组优质页岩发育,页岩气物质条件相似;保存条件是影响页岩含气性差异的关键因素,页岩地层埋深大、地层倾角小、远离剥蚀区和发育反向逆断层,有利于页岩气的保存,总体上盆缘槽档转换带内向斜构造保存条件更好,盆外隔槽式构造带内向斜较差;盆缘槽档转换带复向斜构造内"洼中隆"断背斜、宽缓残留向斜中心、逆断层侧向遮挡向斜3种构造样式有利于页岩气的富集。

The synclines develop well in transferring belt from wide spaced synclines to anticlines at the edge of southeastern Sichuan Basin and in the belt of wide spaced synclines outside Sichuan Basin.Due to the uplifting for long time,serious structural movements and great amount of erosion,the regional preservation condition is complex,there exists great differences in gas contents in Wufeng-Longmaxi Formations in various anticlines.On the basis of studies on the features of shales from Wufeng-Longmaxi Formations,preservation conditions and gas contents in anticlines,the article analyzes the main controlling factors on shale gas enrichments in anticlines and makes a conclusion on structural patterns favorable for shale gas preservation and enrichments.The studies show that quality shales are the bases for shale gas,and the quality shales either at the edge of Sichuan Basin or out of Sichuan Basin have similar hydrocarbon rock conditions;preservation condition is the key for gas contents in shales,great depth of shale layers,small dip angle of strata,great distance away from eroded areas and developed over-thrusting faults are favorable for the preservation of shale gas.All in all,the preservation conditions of synclines in transferring belt from wide spaced synclines at the edge of Sichuan Basin are better than that of the belt of wide spaced synclines out of Sichuan Basin.Three kind of structural patterns as uplifts develop in synclines in transferring belt from wide spaced synclines to anticlines,the central part of wide gentle synclines and the synclines covered by over-thrusting faults are favorable for shale gas enrichments.