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利用不可开采煤层处置二氧化碳可以有效控制温室气体的排放量并可驱动和增加煤层气资源的开采量. 二氧化碳注入煤层处置后引入一个复杂的 CH4-CO2 二元气体与煤体的气固耦合问题, 耦合了二元气体竞争吸附, 竞争扩散, 气体渗流以及煤体变形过程. 基于 COMSOL Multiphysics 建立了二元气固耦合的有限元数值模型, 并应用数值模拟实验对二元气固耦合进行了机理分析. 模拟结果表明, CO2 注入煤层后不断驱替 CH4, CH4 组分明显减少; 气体吸附引起的煤层膨胀量可以抵消部分有效应力引起的压缩变形, 由于 CH4-CO2 二元气体较单一 CH4 引起的煤层吸附膨胀量大, 二氧化碳注入煤层后可以缓解煤层的压缩变形; 不同孔隙压力条件下, 吸附膨胀与孔隙压力两者竞争作用引起的煤层净变形不同, 而净变形也控制着煤层孔隙压力和渗流率的变化, 煤层渗透整体呈现先降后升, 模拟进行到 4.66× 107 s 时煤层渗透率发生反弹.

Abstract: The prospect of geological sequestration and storage of CO2 as a means of reducing global emission of this greenhouse gas and enhancing coalbed methane recovery (ECBM) has recently attracted worldwide interest due to the global warming and the resource shortage. Complicated coupled binary gas-solid interaction arises during carbon dioxide sequestration in a coal seam, which combines effects of CO2-CH4 counter adsorption, CO2-CH4 counter diffusion, binary gas flow and coal bed deformation. Through solving a set of coupled field governing equations, a novel full coupled Finite Element (FE) model was established by COMSOL Multiphysics. The new FE model was applied to the quantification of coal porous pressure, coal permeability, gas composition fraction and coal displacement when CO2 was injected in a CH4 saturated …