渝西大安地区五峰组-龙马溪组深层页岩微观孔隙结构与含气性控制因素

Pore microstructure and its controlling effects on gas content of deep shale reservoirs in the Wufeng-Longmaxi formations， Da'an area， western Chongqing

王馨佩 刘成林 蒋立伟 冯德浩 邹辰 刘飞 李君军 贺昱搏 董明祥 焦鹏飞

Xinpei WANG Chenglin LIU Liwei JIANG Dehao FENG Chen ZOU Fei LIU Junjun LI Yubo HE Mingxiang DONG Pengfei JIAO

四川盆地渝西大安地区是五峰组-龙马溪组深层页岩气的勘探新区，具有良好的勘探前景，但页岩储层微观孔隙结构特征及其对含气性的控制作用仍不清楚，制约了页岩气勘探进程。基于扫描电镜、低温气体吸附及核磁共振实验分析测试资料，研究了五峰组-龙马溪组不同岩相深层页岩的孔隙结构特征及其对含气性差异的控制作用。研究结果表明：①大安地区深层页岩主要发育硅质页岩相、混合硅质页岩相、含黏土硅质页岩相和黏土质/硅质混合质页岩相，孔隙类型以有机质孔为主，发育晶间孔、溶蚀孔和黏土矿物层间孔，可见有机质充填缝、黏土矿物层间缝和构造应力缝。②深层页岩孔隙结构主要为介孔（2 ~ 50 nm）和宏孔（>50 nm）。含量增加有利于微孔（<2 nm）和宏孔发育，硅质矿物含量增加促进宏孔发育，黏土矿物含量增加促进介孔发育。③深层页岩含气性与、硅质矿物含量成正相关，宏孔体积增大页岩气含气量增加；高硅质含量的页岩相含气性最好，是深层页岩气富集的有利岩相。④中浅层页岩主要发育微孔和介孔，以吸附气为主。深层页岩主要发育介孔和宏孔，以游离气为主。深层页岩中宏孔的发育有利于游离气的储集，增加了深层页岩的含气量。

The Da’an area， located in western Chongqing within the Sichuan Basin， serves as a promising new target for deep shale gas exploration in the Wufeng-Longmaxi formations. However， the pore microstructure characteristics of shale reservoirs in this area and their controlling effects on gas content are yet to be clarified， posing a challenge for shale gas exploration in depth. Using the analytical and test data from scanning electron microscopy （SEM）， low-temperature gas adsorption， and nuclear magnetic resonance （NMR） experiments， we investigate the features of pore microstructures of various lithofacies in deep shales in the Wufeng-Longmaxi formations， as well as their controlling effects on the differences in gas content. The results indicate the presence of four lithofacies in deep-seated shales in the Da’an area： siliceous shales， mixed siliceous shales， clayey siliceous shales， and mixed clayey-siliceous shales. Pores in the shales are dominated by organic pores， followed by intercrystalline pores， dissolution pores， and interlayer pores in clay minerals. Meanwhile， fractures also observed in the shales consist of organic matter-filled fractures， interlayer fractures in clay minerals， and tectonic stress-induced fractures. Primary pore structures in the deep-seated shales include mesopores （pore size ranging from 2 to 50 nm） and macropores （pore size greater than 50 nm）. An increased total organic carbon （） content is conducive to the development of micropores （pore size less than 2 nm） and macropores. In contrast， the elevated content of siliceous and clay minerals foster the formation of macropores and mesopores， respectively. The gas content of the deep shales is positively correlated with the content and the siliceous mineral content， so does the macropore volume to gas content. Shales with a high siliceous content manifest the optimal gas-bearing properties， establishing them as the favorable lithofacies for the enrichment of deep shale gas. Moderately shallow shales in the Da’an area primarily contain micropores and mesopores， with adsorbed gas predominating. In contrast， deep-seated shales in the area principally exhibit mesopores and macropores and the predominance of free gas. The well-developed macropores create favorable conditions for free gas preservation， thus increasing the gas content in the deep-seated shales.

10.11743/ogg20250116