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注入非烃气体提高煤层气采收率(ECBM)既能够节能减排又有助于气体能源开发。此文采用广义Langmuir等温吸附方程,建立了二元ECBM驱替过程的数学模型,并运用特征线理论进行解析求解,通过引入气体分离因子,定量分析了气体吸附特性对驱替过程的影响。研究表明,ECBM驱替模式取决于气体分离因子的大小:当分离因子大于1时,形成活塞式驱替;当分离因子小于1时,形成非活塞式驱替。数学模拟数据与室内N2-CH4和CO2-CH4的驱替实验结果对比具有一致性,其中N2-CH4过程形成非活塞式驱替,N2突破较早,两元过渡带较宽,突破后长时间采出N2和CH4两种气体,而CO2-CH4过程形成活塞式驱替,CO2突破较晚,几乎没有两元过渡带。研究表明CO2-CH4的驱替效果要优于N2-CH4。
The injection of non-hydrocarbon gas to improve the recovery of coal bed methane (ECBM) can not only save energy and reduce emissions, but also contribute to the development of gas energy. In this paper, a generalized Langmuir isothermal adsorption equation is used to establish the mathematical model of binary ECBM displacement process. The characteristic equation is used to solve the problem. The gas separation factor is introduced to quantitatively analyze the influence of gas adsorption on the displacement process. The results show that the ECBM displacement mode depends on the size of the gas separation factor. When the separation factor is greater than 1, the piston displacement is formed. When the separation factor is less than 1, a non-piston displacement is formed. The mathematical simulation data are consistent with the displacement experiment results of N2-CH4 and CO2-CH4 indoors. The N2-CH4 process forms a non-piston displacement, the N2 breakthrough is earlier and the transition band of the binary is wider. After a long break N2 and CH4 two kinds of gas production, and the formation of CO2-CH4 piston displacement, CO2 breakthrough later, almost no binary transition zone. Studies have shown that CO2-CH4 displacement effect is better than N2-CH4.