渝东南强变形区断裂对页岩气藏保存条件的控制作用

Controlling effect of faults in strong deformation zone on shale gas reservoir preservation conditions in southeast Chongqing

汪威 张志平 曾春林 王巧丽 余忠樯 2

页岩气勘探开发国家地方联合工程研究中心，重庆 401120 自然资源部页岩气资源勘查重点实验室（重庆地质矿产研究院），重庆 401120

National Joint Engineering Research Center for Shale Gas Exploration and Development, Chongqing 401120, China Key Laboratory of Shale Gas Exploration, Ministry of Natural Resources, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China

渝东南地区五峰组—龙马溪组为一套深水陆棚页岩沉积建造，在区内分布广泛，具有厚度大、总有机碳质量分数高、有机质成熟度适中、脆性矿物体积分数高的特点，具备形成页岩气的良好物质基础。该套富有机质页岩的厚度、总有机碳质量分数、矿物组分等静态指标在平面上展布稳定，但各钻井含气性在区域内差异性较大，整体呈现东西分带的特征，可见构造变形对页岩气的后期保存有重要影响。文中通过野外地质调查、岩心观察、分析测试等手段，综合分析了断裂对研究区页岩气藏保存条件的影响。分析认为，渝东南地区断裂比较发育，断裂按照规模大小可划分为基底逆冲断裂、深大逆冲断裂、层间滑脱断裂3级。其中：层间滑脱断裂，没有切穿上下围岩，增大了页岩储层空间；基底逆冲断裂和深大逆冲断裂连通了上下围岩，使气体发生置换或逸散，最终破坏了页岩气藏。进一步分析发现，区内发育的马喇湖断裂断距大、延伸广，具有远程推覆特征，沿断层上下盘可能发生相变，这是导致研究区内五峰组—龙马溪组页岩含气性东西分带的主要原因。

The Wufeng-Longmaxi Formation in southeast Chongqing is a deep-water shelf shale sedimentary formation. It is widely distributed in this area and has the characteristics of large thickness, high TOC, moderate organic matter maturity and high content of brittle mineral, which has a good basis for shale gas formation. The lateral distributions of the static indicators such as organic-rich shale thickness, organic carbon content, and mineral composition are stable in study area. But obvious differences exist in the gas-bearing property among the wells within the study areas, with the characteristics of east-west zoning, which shows that the structural deformation has an important influence on the later preservation conditions of shale gas. This paper analyzes the effects of faults on the preservation of shale gas reservoirs in the study area by means of field geological surveys, core observations, and analytical tests. According to the analysis, faults in the southeast of Chongqing are relatively developed, and can be divided into three levels according to their size: basement thrust faults, deep and-large thrust faults, and interlayer slip faults. Among them, interlayer slip faults did not cut through the surrounding rocks, which increased shale reservoir space; basement thrust faults and deep-large thrust faults connected the surrounding rocks, causing gas to be replaced or escaped, and eventually the shale gas reservoir was destroyed. Further analysis revealed that the Malahu fault developed in the area has large fault distances and long extensions, and has a long-distance nappe feature. Facies changes may occur along the hanging wall and footwall of the fault, leading to east-west zoning of the gas-bearing property of Wufeng-Longmaxi Formation shale in the study area.

10.6056/dkyqt202006004