Optimal injection timing and gas mixture proportion have great influence on CO₂ geological sequestration and improvement of recovery. The refined Thermo-hydro-mechanical (THM) coupling model including an improved permeability model was first validated by matching with historical data, and then applied to the simulation of gas mixture enhanced coalbed methane recovery (GM-ECBM). Results show that higher internal expansion coefficients and elastic modulus reduction ratios can weaken the large-scale matrix strain swelling and improve optimal CO₂ composition, as do the effect of smaller matrix diffusivity. The trend of CH₄ production in dehydration period was controlled by the diffusion ability of matrix, which was used to account for the different gas production trends using THM coupling model for the first time. The key of GM-ECBM was to produce and utilize the peak value of initial gas production rate while controlling the production rate of N₂+CO₂. For the constant-composition injection, the optimal CO₂ composition and cumulative recovery rate dropped with the injection delay. Starting with a lower CO₂ concentration input, an increase-composition scheme with 1000 days delay witnessed high recovery rate (65.7%) and high CO₂ storage (8.21 mega cubic meters), in which CO₂ composition was gradually injected at a high-to-low rate.

最佳注入时机和混合气体比例对CO ₂地质封存和提高采收率有很大影响。首先，通过与历史数据进行匹配，验证了包括改进的渗透率模型在内的改进的热-水-机械（THM）耦合模型，然后将其应用于模拟天然气混合物提高了煤层气的采收率（GM-ECBM）。结果表明，较高的内部膨胀系数和弹性模量减少率可以减弱大型基体应变膨胀并改善最佳CO ₂组成，较小的基体扩散系数也可以。CH ₄的趋势脱水期的产量由基质的扩散能力控制，这是首次使用THM耦合模型来解释不同的天然气生产趋势。GM-ECBM的关键是要在控制N ₂ + CO ₂产生率的同时产生并利用初始气体产生率的峰值。对于恒定组成的注入，最佳CO ₂组成和累积回收率随注入延迟而下降。从较低的CO ₂浓度输入开始，延迟1000天的增加组成方案具有较高的回收率（65.7％）和较高的CO ₂储存量（8.21兆立方米），其中CO ₂ 以高至低的速率逐渐注入组合物。