CO₂驱煤层气封存（CO₂-ECBM）是重要的CO₂地质利用与地质封存方式，有望破解以淮南煤田为代表的松软、低渗、难抽采煤层煤层气开发效果差、产量衰减快等难题，提高煤层气产量和采收率。CO₂注入煤层与煤中无机矿物的地球化学作用可导致煤层孔裂隙结构和渗透性的变化，对煤层CO₂封存能力和煤层气增产效果具有显著影响。为此，考虑有效应力、温度及地球化学效应影响下的CO₂与CH₄竞争吸附、扩散与渗流作用、CO₂−水−煤地球化学作用及其影响的煤层孔隙率与渗透率动态演化特征，建立了CO₂注入煤储层渗流场−应力场−温度场−化学场全耦合数学模型，开展了淮南煤田CO₂-ECBM工程数值模拟研究，分析了地球化学作用条件下，CO₂注入煤层增产CH₄效果，以及CO₂注入压力、初始渗透率和含水饱和度等对CH₄增产、CO₂封存的影响。结果表明：数学模型与试验结果吻合度较高，CH₄、CO₂混合气体体积分数及产出速率平均误差为1%～10%；相较于未考虑地球化学作用的情况，模拟周期内CH₄累计产量降低11%，CO₂累计封存量提升19.8%，表明忽略CO₂−水−煤地球化学作用会高估CH₄增产效果和低估CO₂封存量；注入压力和煤储层初始渗透率越大，CH₄增产效果越显著，CO₂封存量越大；而高含水饱和度对CH₄增产和CO₂封存产生不利影响，指示了CO₂驱煤层气封存应结合储层性质，优选目标层位，并通过合理设计注入工艺最大化CH₄增产和CO₂封存效果；CO₂−水−煤地球化学作用能够缓解CO₂注入导致的储层压力升高，降低裂隙中自由态CO₂含量，进而抑制应力−应变效应造成的煤储层渗透率下降，促进渗透率的回升，渗透率回升幅度达2.4%～3.3%，而渗透率回升进一步促进了储层压力传导和CO₂吸附、CH₄解吸与扩散，从而提升CH₄增产和CO₂封存效果。

CO₂-enhanced coalbed methane recovery (CO₂-ECBM) is a key method for CO₂ geological utilization and sequestration. It holds promise for addressing challenges such as soft, low-permeability coal seams with difficult gas extraction, poor development performance, rapid production decline, and low recovery rates, as exemplified by the Huainan coalfield. The geochemical interactions of CO₂ injection into coal seams and inorganic minerals in coal can alter the pore-fracture structure and permeability of the coal, significantly influencing CO₂ sequestration capacity and methane production enhancement. Therefore, considering the effects of effective stress, temperature, and geochemical interactions—including competitive adsorption, diffusion, seepage of CO₂ and CH₄, and CO₂-water-coal geochemical interactions, as well as their impact on the dynamic evolution of coal seam porosity and permeability—a fully coupled Thermo-Hydro-Mechanical-Chemical mathematical model was developed for the seepage-stress-temperature-chemical interactions in CO₂-injected coal reservoirs. Numerical simulation studies on CO₂-ECBM were conducted for the Huainan coalfield to analyze the effect of geochemical interactions on CH₄ production enhancement during CO₂ injection, as well as the influence of injection pressure, initial permeability, and water saturation on CH₄ production and CO₂ sequestration. The results showed a high degree of consistency between the mathematical model and experimental outcomes, with the average error range for CH₄ and CO₂ mixture volumetric fractions and production rates falling within 1%−10%. Compared to scenarios ignoring CO₂-water-coal geochemical interactions, the cumulative CH₄ production decreased by 11%, while cumulative CO₂ storage increased by 19.8%, indicating that neglecting geochemical interactions could lead to an overestimation of CH₄ production and underestimation of CO₂ storage capacity. Higher injection pressures and initial permeability of coal reservoirs resulted in more significant CH₄ production enhancement and CO₂ sequestration, whereas high water saturation adversely affected both processes. These findings suggest that CO₂-ECBM should be tailored to reservoir properties, optimizing target layers and injection strategies to maximize CH₄ production and CO₂ storage. Geochemical interactions were found to alleviate the reservoir pressure increase caused by CO₂ injection, reduce the free-state CO₂ content in fractures. This, in turn, mitigated permeability decline due to stress-strain effects, promoting permeability recovery by 2.4%−3.3%. The permeability recovery further facilitated pressure transmission, CO₂ adsorption, and CH₄ desorption/diffusion, ultimately enhancing CH₄ production and CO₂ sequestration efficiency.