四川盆地南部双龙—罗场地区龙马溪组构造裂缝特征及形成期次

Tectonic fracture characteristics and formation stages of Longmaxi Formation in Shuanglong-Luochang areas,southern Sichuan Basin

四川盆地南部双龙—罗场地区龙马溪组是深层页岩气勘探开发的重点区域,构造裂缝的发育特征及形成期次对页岩含气性及产能具有重要影响。综合运用岩心、FMI成像测井、裂缝充填物流体包裹体测试、岩石声发射实验及埋藏—热演化史分析等,对页岩构造裂缝的发育特征及形成时期开展综合研究。结果表明:龙马溪组构造裂缝主要以构造成因的高角度缝、直立缝和复合缝为主,岩心裂缝具有间距大、密度小、倾角大、充填程度高等特征;成像测井裂缝倾角与岩心具有较好的一致性,延伸方位以近EW向、NNE向和NWW向为主,次为NNW向。岩心裂缝切割关系、成像测井裂缝产状匹配关系、裂缝充填物流体包裹体测试以及岩石声发射实验均证实,双龙—罗场地区龙马溪组构造裂缝经历了3期以上的构造运动改造。结合埋藏—热演化史分析,厘定了构造裂缝的形成时期为燕山运动中晚期—喜马拉雅运动早期(78~56 Ma)、喜马拉雅运动中期(56~29 Ma)、喜马拉雅运动晚期—现今(29 Ma至今),对应的裂缝充填物流体包裹体均一温度分别为165~198℃、115~146℃、74~105℃。基于构造地质学原理,建立了双龙—罗场地区龙马溪组构造裂缝的成因机制。

Longmaxi Formation in Shuanglong-Luochang areas,southern Sichuan Basin is a key area for deep shale gas exploration and development. The development characteristics and formation stages of tectonic fractures have an important influence on shale gas bearing and productivity. By using core,FMI imaging logging,fracture filling fluid inclusion testing,rock acoustic emission experiments and burial thermal evolution history analysis,the development characteristics and formation period of shale structural fractures are comprehensively studied. The study results have shown that the tectonic fractures of Longmaxi Formation are mainly high angle fractures,vertical fractures and composite fractures of tectonic origin. The core fractures have the characteristics of large spacing,small density,large dip angle and high filling degree. The fracture dip angle of imaging logging is consistent with the core,and the extension orientation is mainly near EW,NNE and NWW directions,followed by NNW direction. The core fracture cutting relationship,fracture occurrence matching relationships of imaging logging,fracture filling fluid inclusion testing and rock acoustic emission experiment all confirm that the Longmaxi Formation structural fractures in Shuanglong-Luochang areas underwent more than three periods of tectonic movement transformation. Combined with the analysis of burial-thermal evolution history,it is determined that the formation periods of tectonic fractures are mid-late Yanshan Movement and early Himalayan Movement(78-56 Ma),middle Himalayan Movement(56-29 Ma)and late Himalayan Movement-present(29-0 Ma). The homogenization temperatures of the corresponding fluid inclusions are 165-198 ℃,115-146 ℃ and 74-105 ℃,respectively. Based on the principle of structural geology,genetic mechanism of tectonic fractures in the Longmaxi Formation in Shuanglong-Luochang areas is established.