Injecting external CO₂ into soft and low-permeability coal seams can improve CH₄ extacctinn efficiency, and also benefit in CO₂ sequestration. However, the distribution law of damage zone around borehole in soft coal seam and its effect on the efficiency of CO₂ injection promoted CH₄ extraction are not clear. In this paper, a multi-physics coupling mathematical model considering damage effect is established for simulating the process of CO₂ injection promoted CH₄ extraction in soft and low-permeability coal seam. The distribution of damage zone and permeability around boreholes under different diameters and coal strengths are analyzed. The gas pressure and gas content in coal seam during CO₂ injection promoted CH₄ extraction when the model considered damage effect are compared with that of ignored. The results show that small borehole diameter corresponds to narrow damage zone around the borehole in coal seam. The damage zone expands with the increase of the borehole diameter. The damage zone increases exponentially with the borehole diameter, while decreases exponentially with the compressive strength of coal seam. The highest permeability in the damage zone has increased by nearly 300 times under the condition of simulated case. CH₄ pressure around the extraction borehole reduces, and the reduction area expands with the increase of time. Compared with the result of considering the damage effect, the reduction area of ignoring it is smaller, and the reducing speed is slower. The integrated effect of CO₂ injection and CH₄ extraction leads to rapid decrease of CH₄ content in coal seam near the boreholes. The CO₂ pressure and content increase around the injection borehole, and the increasing area gradually extends to the whole coal seam. In soft coal seams, failure to consider the damage effect will underestimate the efficiency of CH₄ extraction and CO₂ sequestration, resulting conservative layout of boreholes.

将外部CO ₂注入软弱低渗透煤层可以提高CH _{4 的}抽采效率，也有利于CO ₂封存。_{但松软煤层钻孔周围损伤带的分布规律及其对注CO 2}促进CH ₄抽采效率的影响尚不清楚。本文建立了考虑损伤效应的多物理场耦合数学模型来模拟CO ₂注入促进CH _{4的过程。}软弱低渗透煤层抽采。分析了不同直径和煤体强度下钻孔周围损伤区和渗透率的分布情况。将考虑损伤效应的模型与忽略损伤效应的模型进行比较，发现CO ₂注入过程中煤层瓦斯压力和瓦斯含量促进了CH _{4 的抽采。}结果表明，煤层钻孔直径较小，对应的钻孔周围损伤区较窄。破坏区随着钻孔直径的增大而扩大。破坏区随钻孔直径呈指数规律增大，随煤层抗压强度呈指数规律减小。模拟工况条件下，损伤区最高渗透率提高了近300倍。CH_4.抽采钻孔周围压力减小，且随着时间的增加，减小面积扩大。与考虑损伤效应的结果相比，忽略损伤效应的减少面积更小，减少速度更慢。_{CO 2}注入和CH ₄抽采的综合作用导致钻孔附近煤层CH _{4含量迅速下降。}注水钻孔周围CO ₂压力和含量增加，且增加区域逐渐向全煤层延伸。在松软煤层中，不考虑损害效应将低估CH ₄和CO _{2的抽采效率}封存，导致钻孔布局保守。