渝东南南川地区深层煤层特征与煤层气赋存状态研究

Characteristics of Deep Coal Seam and Occurrence State of Coalbed Methane in Nanchuan,Southeast Chongqing

基于煤田钻孔资料、煤岩岩心及镜下观察,开展了重庆南川地区煤系储层岩心数字化、液氮吸附、CO_(2)吸附、高压压汞、气相色谱、等温吸附等一系列分析检测测试,分析并讨论了深层煤储层特征、煤层气赋存状态及影响因素。研究表明:①南川区块深部煤层发育,奠定煤层气形成的良好基础。②微裂缝是煤储层的主要储集空间,控制了气体的渗流作用。微孔隙的存在是气体吸附的主要原因,喉道控制了煤层气的微观渗流。③煤的吸附能力随变质程度增加而增大,与压力正相关,与温度负相关。浅层及中深层(1500 m以浅)煤层气吸附量对压力较为敏感,深层(1500 m以深)煤层气吸附量对温度更为敏感。④深层煤层具有“中高演化、微裂隙发育、高含气、富含游离气”的特征,游离气为煤岩解吸提供了大量气源。

This study,based on coalfield drilling data,coal-rock core samples,and microscopic observations,conducts a series of tests,including digital analysis of coal-seam reservoir cores,Liquid N2 adsorption,CO_(2) adsorption,high-pressure mercury intrusion tests,gas chromatography and isothermal adsorption experiments in Nanchuan,Chongqing.The study analyzes and discusses the characteristics of deep coal beds,the occurrence state of coalbed methane and its influencing factors.The research indicates:①The deep coal seam development in Nanchuan block provides good foundation for the formation of coalbed methane.②Micro-fractures serve as the primary reservoir space in coal reservoirs,controlling the permeability of gas.The existence of micropores is the main reason for gas adsorption,while throats control the microscopic flow of natural gas.③The adsorption capacity of coal increases with the degree of metamorphism,positively correlated with pressure,and negatively correlated with temperature.In shallow and mid-deep layers(buried depth less than 1500 m),adsorption is pressure-sensitive,while in deep layers(buried depth more than 1500 m),adsorption is temperature-sensitive.④Deep coal beds exhibit the characteristic of being“Meso-high evolution,micro fissure well developed,highly gas-bearing and rich in free gas”,providing a substantial source of gas for coal rock desorption.