四川盆地东南缘页岩气富集模式——以丁山地区上奥陶统五峰组—下志留统龙马溪组页岩为例

Enrichment model of shale gas in southeastern Sichuan Basin: a case study of Upper Ordovician Wufeng and Lower Silurian Longmaxi formations in Dingshan area

倪楷 王明筏 李响

NI Kai WANG Mingfa LI Xiang

中国石化 勘探分公司, 成都 610041

SINOPEC Exploration Company, Chengdu, Sichuan 610041, China

在川东南丁山地区上奥陶统五峰组—下志留统龙马溪组页岩气基本地质条件认识的基础上，利用钻井、测井、压裂测试、分析化验及构造解释等资料，通过天然气在页岩气系统内的赋存形式、运移方式及运移强度的分析，探讨了适用于研究区的页岩气富集模式。页岩气系统中高角度裂缝延伸距离短，页岩储层顺层滑脱缝、页理缝等顺层缝延伸较远，顺层方向渗透率远大于垂直层面方向，这些特征共同决定了天然气在页岩气系统中是以横向运移为主导、垂向—横向联合运移的方式运移。齐岳山断裂带、页岩储层埋深和距齐岳山断裂带的距离是丁山地区五峰组—龙马溪组页岩气富集成藏关键因素。齐岳山断裂带为控盆断裂带，断裂及伴生裂缝发育，为页岩气逸散区；东南部浅埋区页岩气系统中高角度缝较发育，顺层缝开启，游离气占比低于60%，表现为正常压力系统，是页岩气半滞留区；西北部中深埋藏区页岩气系统中高角度缝相对不发育，顺层缝闭合，垂向—横向联合运移受阻，大部分页岩气滞留在页岩储层中，游离气占比超过60%，表现为高压—超高压压力系统，是页岩气滞留富集区。

Based on the understanding of the basic geological conditions of shale gas from the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation in Dingshan area of the southeastern Sichuan Basin, the occurrence, migration mode and intensity of natural gas in the shale gas system were discussed according to the results of drilling, logging, fracturing test, laboratory test and structural interpretation, moreover, a shale gas enrichment mode suitable for the study area was proposed. In shale gas systems, high-angle fractures extend for a short distance, while horizontal fractures such as bedding-parallel detachment and interlayer bedding fractures extend for a long distance. As a result, the permeability in the bedding direction is much greater than that in the vertical direction. These characteristics together determined that natural gas in shale gas system was usually transported horizontally, and sometimes both horizontally and vertically. For the Qiyueshan fault zone, the burial depth of shale reservoir and the distance to Qiyueshan fault zone are the major constrains for shale gas enrichment in the Wufeng-Longmaxi formations in the study area. The Qiyueshan fault zone is a basin-controlling fault zone with fractures and associated fractures developed, and is a shale gas escaping area. In the shallow-buried area in the southeastern part, high-angle fractures were relatively developed, by which horizontal fractures were opened. The proportion of free gas was less than 60%. A normal pressure system indicates a semi-retention area for shale gas. In the middle-to deep-buried area in the northwest, high-angle fractures were relatively undeveloped, and horizontal fractures were closed. The vertical and horizontal migrations were blocked, and most of shale gas was trapped in shale reservoirs. The proportion of free gas is more than 60%. A high-to ultra-high pressure system indicates a shale gas accumulation area.

国家科技重大专项 2017ZX05036-003

https://doi.org/10.11781/sysydz202104580