四川盆地东南部南川地区煤层气地质特征及富集主控因素

Geological characteristics and main enrichment controlling factors of coalbed methane in Nanchuan area, southeastern Sichuan Basin

何希鹏 汪凯明 罗薇 高玉巧 刘娜娜 郭涛 周亚彤 武迪迪

HE Xipeng WANG Kaiming LUO Wei GAO Yuqiao LIU Nana GUO Tao ZHOU Yatong WU Didi

1. 中国石化 深层煤层气勘探开发重点实验室, 南京 210019; 2. 中国石化 华东油气分公司, 南京 210019; 3. 中国石化 华东油气分公司 勘探开发研究院, 南京 210019

1. SINOPEC Key Laboratory of Deep Coalbed Methane Exploration and Development, Nanjing, Jiangsu 210019, China; 2. SINOPEC East China Oil & Gas Company, Nanjing, Jiangsu 210019, China; 3. Research Institute of Exploration and Development, SINOPEC East China Oil & Gas Company, Nanjing, Jiangsu 210019, China

四川盆地东南部南川地区上二叠统龙潭组深层煤层气勘探取得重要战略突破，展现出该区煤层气良好的勘探潜力。为揭示其富集主控地质因素，利用钻井、岩心、测井及实验分析等资料，从龙潭组煤层分布、煤岩煤质、物性、含气性以及可压裂性特征等方面入手，开展了煤层气地质特征与富集主控地质因素研究。研究表明：(1)龙潭组主力煤层具有分布稳定(厚度2.8～5.7 m)、煤体结构好(主要为原生结构煤)、镜质组含量高(平均含量79.7%)、热演化程度较高(Ro平均为1.9%)和灰分产率较低(平均14.3%)的特点，具备形成煤层气藏的基本条件；(2)煤储层为孔隙—裂隙型储层，微孔占比78%，其比表面积占比达99.6%，有利于煤层气的吸附及压裂后渗流；(3)煤层总含气量为14.0～46.7 m3/t，游离气占比为39%～44%，具有“高含气、富含游离气、过饱和”及含气量随埋深增加而增大的特征；(4)研究区地应力适中(35～60 MPa)，两向水平应力差异系数小(＜0.1)，顶底板条件好，可形成良好的应力隔挡，有利于压裂改造；(5)南川地区煤层气富集主控地质因素为沉积环境控制含煤建造、演化程度控制生烃强度、保存条件控制富集程度。

A significant strategic breakthrough has been achieved in the exploration of deep coalbed methane (CBM) in the Upper Permian Longtan Formation in the Nanchuan area, southeastern Sichuan Basin, showing promising exploration potential for CBM in this area. To identify the main geological factors controlling its enrichment, this study used data from drilling, cores, well logging, and experimental analyses to investigate the geological characteristics and main controlling factors for CBM enrichment, focusing on coal seam distribution, coal quality, physical properties, gas content, and fracturability characteristics of the Longtan Formation. The results show that: (1) The main coal seams of the Longtan Formation exhibit stable distribution (thickness of 2.8 to 5.7 m), good coal body structure (mainly primary structural coal), high vitrinite content (average content of 79.7%), high degree of thermal evolution (average Ro of 1.9%), and low ash yield rate (average of 14.3 %). These characteristics provide the basic conditions for the formation of CBM reservoirs. (2) The coal reservoir has a pore-fracture structure, with micropores accounting for 78% of the total pore volume and contributing 99.6% of the total specific surface area, which is favorable for CBM adsorption and post-fracturing seepage. (3) The total gas content of the coal seam is 14.0 to 46.7 m3/t, with free gas accounting for 39% to 44%. It is characterized by “high gas content, abundant free gas, and oversaturation”, and its gas content increases with burial depth. (4) The in-situ stress in the study area is moderate (35 to 60 MPa), with a small two-way horizontal stress difference coefficient (＜0.1) and good roof and floor plates, forming effective stress shielding favorable for fracturing transformation. (5) The main controlling factors for CBM methane enrichment in the Nanchuan area include the sedimentary environment, which determines coal-bearing formations; the degree of coal evolution, which determines the intensity of hydrocarbon generation; and the preservation conditions, which govern CBM enrichment.

中国石化科技部项目“渝东南地区煤层气富集规律及勘探关键技术”(P24118)资助。

https://doi.org/10.11781/sysydz2025010064