四川盆地外围常压页岩气勘探开发进展与攻关方向

首先简要介绍了美国常压页岩气的基本地质情况和生产特征,以及造成页岩气常压或低压的原因,再以四川盆地外围武隆、彭水、道真等残留向斜上奥陶统五峰组-下志留统龙马溪组页岩气藏的勘探开发为例,通过对比,指出美国常压、低压页岩气藏与四川盆地外围常压页岩气的最大差别有3点:一是美国页岩气藏的厚层富有机质页岩连续分布面积大;二是绝大多数有机质热演化程度不高、吸附气含量高,多采用直井生产;三是页岩沉积后期经历的构造运动期次少、强度低。采用超轻支撑剂的氮气泡沫水平井压裂在美国Big Sandy地区Ohio低压页岩气开发中取得了成功。通过对3个残留向斜勘探开发进展的分析,提出改造期次、强度、埋深、分布面积等是盆外残留向斜保存条件差异的主要因素,也是导致地层压力系数和产量差异的主要原因;基于此,提出了下步盆地外围常压页岩气勘探开发与技术攻关建议。

Progress and direction of exploration and development of normally-pressured shale gas from the periphery of Sichuan Basin

This study firstly introduces the geology and production characteristics of the typical normally-pressured shale gas plays in the U.S. and analyzes the origins of normal pressure and under-pressure. The normally-pressured shale gas reservoirs from the periphery of Sichuan Basin are then characterized using the E & P cases of the Upper Ordovician Wufeng to Lower Silurian Longmaxi formations in the Wulong, Pengshui and Daozhen areas. The comparison between normally- and under-pressured shale gas reservoirs in the U.S. and China reveals that: (a) U.S. shales with large thickness are widely distributed; (b) U.S. shales have relatively lower maturity compared to Chinese marine shales; and (c) U.S. shales experienced fewer tectonic events after deposition. Nitrogen foam and ultra-light proppant have been successfully used for the hydraulic fracturing of the under-pressured Ohio shale in the Big Sandy area. Based on the analysis of the exploration and development progress of three residual synclines, it is apparent that the tectonic period and strength, burial depth and distribution area are the main factors for the difference of preservation conditions of residual synclines outside the basin, and are also the main reasons for the difference of formation pressure coefficient and production. Based on this, the paper puts forward some suggestions for further theoretical and technical research on normally-pressured shale gas from the periphery of the basin.