构造作用对常规-非常规油气连续聚积耦合成藏控制机制——以川东南平桥地区为例

Control mechanism of tectonic action on continuous accumulation and coupling of conventional-unconventional oil and gas reservoirs:a case study of Pingqiao area,southeastern Sichuan Basin

为探索川东南平桥地区构造作用对常规和非常规气藏成藏过程的动态控制作用及差异,基于地震、地质和包裹体等资料,根据断层相关褶皱理论,系统剖析了该区构造特征及演化过程、常规气藏和非常规气藏动态成藏过程及构造对两者影响的差异性,建立了典型常规—非常规油气连续聚集耦合成藏模式。平桥地区位于川东南SE-NW前展式递进变形带中,受多套滑脱层和江南—雪峰造山带联合控制,发育断展构造和背冲构造。平桥背斜构造形成于燕山期。中燕山期,受江南—雪峰构造体系前展式扩展影响,研究区发生NE向强烈断褶作用。晚燕山期—喜马拉雅期川中隆起阻挡和青藏高原隆升使平桥背斜不断抬升;寒武系筇竹寺组和奥陶系五峰组—志留系龙马溪组烃源岩在早燕山期及以前主要经历了长期的埋藏生烃,中燕山期构造变形扩展至研究区,常规气藏储层(洗象池群)、盖层、油气圈闭及运移均受到影响,气藏保存条件较差。非常规气层被改造成为背斜构造,页岩气向背斜核部聚集,整体保存条件较好。晚燕山期—喜马拉雅期,地层隆升泄压,两类气藏保存条件继续变差。因此,构造作用对常规气藏和非常规气藏成藏控制差异体现在控制方式和改造时间上:中燕山期侧向供烃是常规气藏成藏的关键;晚白垩世构造活动改造和晚燕山期—喜马拉雅期构造抬升影响了页岩气的保存。

This study explored the dynamic control and differences of tectonic action on the formation of conven-tional and unconventional gas reservoirs in Pingqiao area,southeastern Sichuan Basin.Based on seismic,geolo-gical,inclusion,and other relevant data,together with fault-related fold theory,this study systematically analyzed the structural characteristics and evolution processes of the area,as well as the dynamic accumulation processes of conventional and unconventional gas reservoirs and the differences in structural impacts on both.A coupled accu-mulation model of typical conventional and unconventional oil and gas continuous aggregation was established.The Pingqiao area,located in the SE-NW foreland progressive deformation zone of southeastern Sichuan,is controlled by multiple detachment layers and the Jiangnan-Xuefeng orogenic belt,developing fault extension structures and back-thrust structures.The Pingqiao anticline structure was formed during the Yanshanian period.During the middle Yanshanian period,influenced by the foreland expansion of the Jiangnan-Xuefeng tectonic system,the study area experienced intense NE-directed fault-folding.From the late Yanshanian to the Himalayan period,the uplift of central Sichuan and the rise of the Qinghai-Tibet Plateau caused the Pingqiao anticline to continuously uplift.The Cambrian Qiongzhusi Formation and Ordovician Wufeng Formation to Silurian Longmaxi Formation source rocks mainly experienced long-term burial and hydrocarbon generation in the early Yanshanian period and before.In the middle Yanshanian period,tectonic deformation extended to the study area,affecting the conventional gas reservoir(Xixiangchi Group),cap rocks,hydrocarbon traps,and migration,resulting in poor preservation conditions of gas reservoirs.Unconventional gas layers were transformed into anticline struc-tures,with shale gas accumulating towards the core of the anticline,resulting in better overall preservation condi-tions.From the late Yanshanian to the Himalayan period,strata uplift and depressurization continued to deterio-rate the preservation conditions of both types of gas reservoirs.Therefore,this study suggests that the difference in tectonic control on conventional and unconventional gas reservoirs is reflected in the control methods and transfor-mation timing:the lateral hydrocarbon supply during the middle Yanshanian period is the key for conventional gas reservoir formation;tectonic activity in the Late Cretaceous and tectonic uplift from the late Yanshanian to the Himalayan period affect the preservation of shale gas.