Enhanced coalbed methane (ECBM) recovery by gas injection is regarded as a feasible method for ECBM recovery. To investigate the mechanism of CH4 displacement by N2 injection, a series of physical experiments were conducted in the laboratory under different N2 injection pressures. The experimental results showed a continuous increase in the N2 volume fraction and a decrease in the CH4 volume fraction with the N2 injection pressure. The CH4 displacement efficiency increases rapidly in the initial stage and then gradually stabilizes. Given the effect of matrix shrinkage and effective stress on coal permeability, a dynamic multi‐field coupling model of ECBM recovery by N2 injection (N2‐ECBM) was proposed in this work. Then, numerical simulations were implemented by the coupling model to analyze the key factors affecting coal permeability, N2 injection pressure and CH4 pressure during the N2–ECBM process. Furthermore, the Response Surface Methodology (RSM) was used to investigate the interactions of multiple factors, the results reveal that an increase in one factor would weaken the influence of another factor. In addition, a RSM regression model was obtained and verified by the experimental data, with a well‐fitting outcomes. Therefore, the RSM model can be used in practical engineering applications to optimize specific extraction parameters for ECBM recovery at minimum cost in a limited extraction period.

中文翻译：

---

注气提高煤层气采收率建模与耦合分析

注气强化煤层气（ECBM）采收率被认为是一种可行的煤层气采收方法。研究CH的机制4位移 N2注射后，在实验室在不同N条件下进行了一系列物理实验2注射压力。实验结果表明N持续增加2体积分数和 CH 的减少4体积分数与 N2注射压力。CH4驱替效率在初始阶段迅速增加，然后逐渐稳定。考虑基质收缩和有效应力对煤渗透率的影响，建立了 N 采煤 ECBM 动态多场耦合模型。2注射（N2‐ECBM）是在这项工作中提出的。然后，通过耦合模型进行数值模拟，分析影响煤体渗透率、N2注射压力和CH4N期间的压力2–ECBM 过程。此外，采用响应面法（RSM）来研究多个因素的相互作用，结果表明一个因素的增加会削弱另一因素的影响。此外，还得到了RSM回归模型，并通过实验数据进行了验证，结果拟合良好。因此，RSM模型可以在实际工程应用中，在有限的开采周期内，以最小的成本优化ECBM回收的具体开采参数。