Abstract In this work we develop a multiscale model for flow and transport problem in CO2-enhanced coalbed methane recovery. The coalbed methane reservoir is characterized by two levels of porosity associated with nanopores in the matrix and cleat network. Mass conservation equations for fluid mixture (CH4 and CO2) in the matrix at the microscale are rigorously derived by using the formal homogenization technique taking into account the gas mixture adsorption in the nanopores. The Density Functional Theory (DFT) is used to compute the gas adsorption isotherms and the solvation force acting on the nanopore wall, showing a much more pronounced adsorption capacity of CO2 compared to CH4. The average transport equations in the matrix together with the multiphase flow problem in fracture network (gas mixture and water) are homogenized giving rise to a macroscopic model ruled by the effective conductivities, partition and transfer coefficients. The cleat permeability evolution due to deformation is taken into account through a three-scale poromechanical model reported in a previous work. Computational simulations illustrate the macroscopic laws underlying the gas pressure distributions, cleat closure phenomena and CH4 production curve enhanced by CO2 injection.

中文翻译：

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结合气体混合物吸附效应的 CO2 强化煤层气采收中流动和输运的多尺度模型

摘要 在这项工作中，我们为 CO2 强化煤层气回收中的流动和传输问题开发了一个多尺度模型。煤层气储层的特征在于与基质和割理网络中的纳米孔相关的两个级别的孔隙度。通过使用正式的均质化技术，考虑到纳米孔中的气体混合物吸附，可以严格推导出微尺度基质中流体混合物（CH4 和 CO2）的质量守恒方程。密度泛函理论 (DFT) 用于计算气体吸附等温线和作用在纳米孔壁上的溶剂化力，表明与 CH4 相比，CO2 的吸附能力要明显得多。矩阵中的平均输运方程与裂缝网络（气体混合物和水）中的多相流动问题一起被均质化，从而产生由有效电导率、分配和传递系数控制的宏观模型。通过先前工作中报道的三尺度多孔力学模型考虑了由于变形引起的割理渗透率演化。计算模拟说明了气体压力分布、割理闭合现象和 CO2 注入增强的 CH4 生产曲线背后的宏观规律。