断裂对页岩气保存条件的影响机制——以渝东南地区五峰组-龙马溪组为例

上扬子地区广泛发育多套烃源岩，其中渝东南地区五峰组—龙马溪组具有有机质页岩厚度大、TOC丰度高、有机质成熟度适中等特点，整体具备页岩气发育的气源条件；但各钻井含气性差异显著，可见区域构造对页岩气的后期保存存在重要影响。以渝东南地区为例，通过野外地质调查、岩心观测、含气性分析等手段，研究区域构造分布对页岩气赋存条件的影响，并认为：渝东南地区主要断裂均为逆断裂，且靠近褶皱核部的断裂盘地层变形更为明显，属于相对受伤盘；濯河坝向斜西翼的主控断裂——王家湾—大河口逆冲断裂两盘差异明显：向斜核部、断裂下盘构造缝高度发育，整体含气性较差，是页岩气保存条件的欠佳区域，不利于页岩气成藏。通过分析发现，区域应力背景控制褶皱体系，褶皱变形程度决定断裂分布和组合样式，断裂形态决定地层变形和裂缝发育，从而进一步控制页岩气的保存和富集。因此，全面分析构造匹配模式，是研究不同地区页岩气保存能力的先决条件。

Controlling mechanism of faults on the preservation conditions of shale gas:A case study of Wufeng-Longmaxi Formations in Southeast Chongqing

Several sets of source rocks are widely developed in the Upper Yangtze Platform,which provide solid material sources for the shale-gas exploration in recent years.Although the Wufeng-Longmaxi Formations have some advantages of shale-gas development,such as thick organic-rich shales,high TOC and moderate organic matter maturity,obvious differences exist in the gas content among the wells within the study areas,which demonstrates that the tectonics has an important influence on the preservation conditions of shale gas.Based on the southeast Chongqing area,distribution of folds and faults and its impact on the preservation conditions of shale gas is discussed in this paper through field work,core observation and gas content/component analysis,which shows that the majority of the faults in southeast Chongqing area are reverse faults,and the layers along the cores of folds are deformed more seriously.Furthermore,while considering the Wangjiawan-Dahekou reverse faults,which are the main controlling faults of the western limb of the Zhuoheba Syncline,the structural fractures are highly developed and the gas content is relatively lower in the foot walls and cores of folds,so that it becomes the unfavorable zone in the shale-gas reservoirs.In a word,the regional stress conditions determine the fold systems,the deformation degrees of fold systems determine the distributions of the faults,and the shape of faults determines the layer distortion and fracture development,which further has a significant effect on the reservation of shale gas.Therefore,a comprehensive analysis on the tectonic framework is necessary for the accurate study on the preservation capacity of shale gas in different areas.