目前,我国页岩气逐渐开始由勘探突破向开发建产转变,页岩气产量递减的快慢主要依赖于页岩中吸附气的解吸作用。因此,研究页岩中甲烷的解吸规律对于页岩气的开发有重要意义。为研究川南龙马溪组页岩甲烷等温解吸特征,以川南龙马溪组页岩为研究对象,进行了高压甲烷等温吸附/解吸实验。在此基础上,优选了适用于川南龙马溪组页岩的甲烷解吸模型,计算了页岩中甲烷解吸效率曲线,分析了目标区页岩气解吸规律。研究结果表明：当实验条件为低压（＜12 MPa）时,5个模型拟合效果差别不大;当实验条件为高压时,Weibull模型和D-A模型相较于其他几个模型,能够更好地描述甲烷解吸过程。基于实验测试结果,模型拟合效果为：Weibull模型>D-A模型>解吸式模型>Langmuir模型>Freundlich模型。随着压力的降低,拟合精度最好的Weibull模型得到的页岩甲烷解吸效率先缓慢增大后快速增大。根据特征压力点,将甲烷解吸过程划分为4个阶段,其中快速解吸阶段的甲烷解吸量占全部解吸量的40 %,对页岩气产能贡献最大。

At present, China’s shale gas is gradually began to change from exploration breakthrough to development and production. The rate of decline of shale gas production mainly depends on the desorption of the adsorbed gas in shale. Therefore, it is of great significance to study the rule of methane desorption in shale for the development of shale gas. In order to study the isothermal desorption characteristics of methane in shale from Longmaxi Formation in South Sichuan Basin, the high-pressure isothermal adsorption and desorption experiments have been carried out with the shale of this formation as the research object. On this basis, the optimized model of methane desorption and the calculated desorption efficiency curve of methane in shale has been used to analyze the desorption characteristics of shale from Longmaxi Formation. The results show that the fitting effects of five models have little difference with low experimental pressure（less than 12 MPa）. While under high pressure, Weibull model and D-A model can describe the methane desorption process better than other models. Based on the experimental test results, the model fitting effect is as follows: Weibull model>D-A model>Desorption model>Langmuir model>Freundlich model. With the decrease of pressure, the shale methane desorption efficiency obtained by Weibull model with the best fitting accuracy tends to increase slowly at first and then rapidly. According to the characteristic pressure points, the methane desorption process is divided into four stages. The methane desorption amount in the rapid desorption stage accounted for 40 % of the total desorption amount, which contributes the most to shale gas production capacity.