Multilayer drainage is one of the important technologies for coalbed methane (CBM) production in China. In this study, a multi-field fully coupled mathematical model for CBM production was established to analyze the multilayer drainage of CBM well group in southern Qinshui basin. Based on the numerical simulation results, the characteristics of CBM well production under different drainage rates and key factors influencing the CBM production were further discussed. The results show that the effect of an increased drainage rate on gas production of CBM wells and CBM recovery of No.3 coal seam is not significant. However, it significantly improved the gas production of CBM wells and CBM recovery of No.15 coal seam. After a long period of production, the CBM content in No.3 coal seam has reduced to a low level and the pressure drop potential of No.3 coal seam is insignificant, which are important reasons for the insignificant increase of CBM production even under a drainage rate of 2 to 7 times. Conversely, No.15 coal seam has larger residual CBM content and increasing the drainage rate can significantly improve the pressure drop and superimposed well interference of No.15 coal seam, which means No.15 coal seam has greater production potential than No.3 coal seam. Therefore, it is recommended to improve the gas production and CBM recovery in No.15 coal seam by increasing the drainage rate, and the average hydraulic pressure drop should be 0.018–0.031 MPa/day. The influence of effective stress is weak in No.3 and No.15 coal seam, and the coal seam permeability is largely influenced by the shrinkage of coal matrix caused by CBM desorption. This indicates the feasibility of increase in gas production from CBM wells by increasing the drainage rate.

中文翻译：

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沁水盆地南部多层排采煤层气井组排采速率数值分析

多层抽采是我国煤层气生产的重要技术之一。本研究建立了煤层气生产多场全耦合数学模型，对沁水盆地南部煤层气井群多层排采进行了分析。基于数值模拟结果，进一步探讨了不同排采速率下煤层气井产量的特点及影响煤层气产量的关键因素。结果表明，提高排采速度对煤层气井产气量和3号煤层煤层气采收率的影响不显着。但显着提高了煤层气井的产气量和15号煤层的煤层气采收率。经过长时间的生产，3号煤层煤层气含量已降至较低水平，3号煤层压降潜力较大。3 煤层微不足道，这是即使在 2 至 7 倍的排水率下煤层气产量仍不显着增加的重要原因。反之，15号煤层残余煤层气含量较大，提高抽采率可显着改善15号煤层压降和叠加井干扰，意味着15号煤层比3号煤具有更大的生产潜力接缝。因此，建议通过提高排采速度来提高15号煤层的产气量和煤层气采收率，平均水压降为0.018～0.031 MPa/d。3号和15号煤层有效应力的影响较弱，煤层渗透率受煤层气解吸引起的煤基质收缩影响较大。