川东南地区不同埋深五峰组—龙马溪组页岩储层微观结构特征与对比

Microstructure characteristics of Wufeng-Longmaxi shale gas reservoirs with different depth, southeastern Sichuan Basin

刘伟新 卢龙飞 魏志红 俞凌杰 张文涛 徐陈杰 叶德燎 申宝剑 范明

LIU Weixin LU Longfei WEI Zhihong YU Lingjie ZHANG Wentao XU Chenjie YE Deliao SHEN Baojian FAN Ming

中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 中国石油化工集团公司 油气成藏重点实验室, 江苏 无锡 214126 中国石化 勘探分公司, 成都 610041 中国地质大学 构造与油气资源教育部重点实验室, 武汉 430074

Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi, Jiangsu 214126, China SINOPEC Exploration Branch Company, Chengdu, Sichuan 610041, China Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China

采用薄片、X衍射、常规扫描电镜、高分辨率氩离子抛光扫描电镜及压汞、氮气吸附等方法，结合有机碳含量（TOC）与孔隙度的分析，对川东南不同深度上奥陶统五峰组-下志留统龙马溪组页岩储层的矿物组成、微观结构和微孔体积进行了研究。该区深层D1井和浅层J1井页岩储层硅质、黏土、碳酸盐等矿物除含量上略有差异，纵向变化规律相近，仅硅质含量大于40%的优质页岩层厚度不同。深、浅层五峰组-龙马溪组页岩储层微孔隙都以有机质内微孔为主，常见粒缘缝（隙）、微层（页）理缝，粒间微孔因有机质充填而不发育；底部优质页岩储层表现为结构各向同性，向上纵横向结构各向异性变强，单一微纹层厚度变薄，微层理缝密度增加；底部优质页岩层段TOC高，向上明显降低；底部储层孔隙度高，向上降低，表明有机孔隙的贡献大，但孔隙度降幅明显小于TOC，应与页岩中存在较多的无机孔隙有关。深、浅层五峰组-龙马溪组页岩纵向上矿物组成、微观结构、TOC、孔隙度随深度具有相似的变化规律。与浅层J1井相比，深层D1井底部优质储层具有微孔、介孔、大孔与总孔体积数量更大的特点，这与深层D1井储层存在较多的粒缘缝等无机孔有关。川东南五峰组-龙马溪组页岩储层在深埋条件下孔隙保持较好，具有良好的储集空间。

Thin section analysis, X-ray diffraction, conventional scanning electron microscopy (SEM), high-resolution Ar+ ion polishing SEM, mercury intrusion, nitrogen adsorption, total organic carbon (TOC) content and porosity analyses were used to determine the mineral composition, microstructure and micro-pore volume of shale reservoirs from different depths in the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation in southeastern Sichuan Basin. There are slight differences in the content of siliceous, clay, carbonate and other minerals in shale reservoirs of well D1 in the deep layer and well J1 in the shallow layer, and the longitudinal changes are similar. Only high-quality shale layers with a silica content greater than 40% have different thicknesses. The shale reservoirs of the Wufeng-Longmaxi formations in the deep and shallow layers are dominated by micro-pores in organic matter disseminated in the shale matrix, and the microfractures around the boundaries of silt particles or organic grains and micro-foliation seams parallel to bedding plane are also common, while and intergranular pores are not developed. The high quality shale reservoir at the bottom is structurally isotropic, and the vertical and horizontal structural anisotropy becomes stronger upwards, with thinner micro-lamina and more foliation seams. The TOC content is high at the bottom, and diminishes upwards. The porosity at the bottom shows the same changing trend, indicating a large contribution of organic pores; however, the decrease in porosity is significantly smaller than that of TOC, which is inferred to be related to the existence of more inorganic pores in the shale. The mineral composition, microstructure, TOC and porosity of the Wufeng-Longmaxi shales in the deep and shallow layers have similar changes with depth. Compared with well J1 in the shallow layer, the high-quality reservoir in well D1 in the deep layer has a larger number of micro-pores, meso-pores, macro-pores and total pore volume, which might be explained by more inorganic pores such as grain boundary pores.The shale reservoirs of the Wufeng-Longmaxi formations in the southeastern Sichuan Basin maintain a good porosity under deep burial conditions and have good storage space.

国家油气重大专项 2016ZX05036002;国家油气重大专项 20162X05036003;国家自然科学基金项目 U1663202;国家自然科学基金项目 41972163;国家自然科学基金项目 41972164;国家自然科学基金项目 U19B6003-02

https://doi.org/10.11781/sysydz202003378