Abstract Enhanced and efficient recovery of coalbed methane (CBM) is essential to prevent mine disasters and utilize unconventional gas resources. In this study, hydraulic slotting (HS) combined with liquid CO2 (LCO2) injection was employed to enhance coalbed permeability and the efficiency of methane recovery from a high-gas and low-permeability coalbed. First, mercury intrusion porosimetry and scanning electron microscopy experiments were conducted to analyze the variations in the coal microstructure and the permeability after HS combined and LCO2 freezing–thawing was conducted under laboratory conditions. The results indicated that the basic parameters of pore structures increased significantly for the treated coal; for instance, porosity and permeability increased by 47.65 % and 65.31 %, respectively. This indicated that coal permeability increased significantly under multiple stresses induced via HS and LCO2 freezing–thawing. Subsequently, a simulated experiment of LCO2 injection to enhance CH4 recovery from coal was performed; the results thus obtained revealed that LCO2 injection into a high-gas-content coalbed can enhance CBM recovery with an average efficiency of >90 %. Furthermore, an in-situ test indicated that the effective radii for HS and LCO2 injection were 2.5 m and 10 m, respectively. The results of a 90-d-long methane extraction revealed that the efficiency of CBM recovery increased by a factor of >2.2 and that the residual gas content in the test coalbed was

中文翻译：

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通过水力开槽结合液态 CO2 注入提高煤层渗透率和甲烷采收率

摘要 煤层气（CBM）的强化高效回收对于预防矿山灾害和利用非常规天然气资源至关重要。在这项研究中，采用水力开槽 (HS) 结合液态 CO2 (LCO2) 注入来提高煤层渗透率和从高瓦斯低渗透煤层中回收甲烷的效率。首先，通过压汞孔隙率测定法和扫描电子显微镜实验，分析了在实验室条件下进行 HS 结合和 LCO2 冻融后煤微观结构和渗透率的变化。结果表明，处理后的煤的孔隙结构基本参数显着增加；例如，孔隙度和渗透率分别增加了 47.65% 和 65.31%。这表明煤渗透率在 H2S 和 LCO2 冻融引起的多重应力下显着增加。随后，进行了LCO2注入提高煤CH4回收的模拟实验；由此获得的结果表明，将 LCO2 注入高含气煤层可以提高煤层气采收率，平均效率 >90%。此外，原位测试表明，HS 和 LCO2 注入的有效半径分别为 2.5 m 和 10 m。一次 90 天长的甲烷抽采结果表明，煤层气回收效率提高了 2.2 倍以上，并且测试煤层中的残余气含量为 进行了LCO2注入提高煤CH4回收的模拟实验；由此获得的结果表明，将 LCO2 注入高含气煤层可以提高煤层气采收率，平均效率 >90%。此外，原位测试表明，HS 和 LCO2 注入的有效半径分别为 2.5 m 和 10 m。一次 90 天长的甲烷抽采结果表明，煤层气回收效率提高了 2.2 倍以上，并且测试煤层中的残余气含量为 进行了LCO2注入提高煤CH4回收的模拟实验；由此获得的结果表明，将 LCO2 注入高含气煤层可以提高煤层气采收率，平均效率 >90%。此外，原位测试表明，HS 和 LCO2 注入的有效半径分别为 2.5 m 和 10 m。一次 90 天长的甲烷抽采结果表明，煤层气回收效率提高了 2.2 倍以上，并且测试煤层中的残余气含量为