煤层气解吸阶段划分方法及其意义

Division of coalbed methane desorption stages and its significance

为了定量分析煤层气解吸特征对产能的影响,基于兰格缪尔等温吸附理论,建立了煤层气解吸阶段划分方法,并通过煤层气开发实例分析了方法的指示意义。引入解吸效率定量表征不同压力下的煤层气解吸速率。根据数学曲线上的关键节点,定义了启动压力、转折压力与敏感压力;不同煤样3个关键压力点的解吸效率为定值,据此将煤层气解吸过程划分为低效解吸、缓慢解吸、快速解吸与敏感解吸4个阶段。研究表明:快速与敏感解吸阶段对煤层气井产能贡献很大,低效与缓慢解吸阶段则很小;煤层吸附能力、含气性和储集层压力是影响煤层气解吸特征的关键因素。沁南和柳林地区煤层气开发现状表明建立的解吸阶段划分方法可以有效指导煤层气开发。

To quantitatively analyze the effect of desorption characteristics on productivity, a division method of coalbed methane （CBM） desorption stages was established based on the Langmuir adsorption isothermal theory, and the indicating significance of the method was analyzed with cases of CBM production. The desorbed efficiency was used to quantitatively characterize the CBM desorbed rate under different reservoir pressures. On the basis of key nodes on mathematical curves, the starting pressure, turning pressure and sensitive pressure were defined. For different coal samples, the corresponding desorbed efficiencies of the three nodes were always constants, therefore the CBM desorption process was divided into four stages, i.e., inefficient, slow, fast and sensitive desorption stages. Studies reveal that, fast and sensitive desorption stages contribute a lot to CBM productivity, while inefficient and slow desorption stages have very little contribution; absorption capacity, gas-bearing property and reservoir pressure are the key factors for the desorption characteristics. The production status of southern Qinshui Basin and Liulin area in Ordos Basin in Northwest China demonstrates that the method can guide the CBM development effectively.