Study on borehole layout of coalbed gas extraction based on multi-field coupling simulation

Sun Liuyong; Tian Jiakuo; Zhang Ran; Kang Jianhong

doi:10.19896/j.cnki.mtkj.2025.01.012

Abstract：The borehole layout method is an important factor affecting the efficiency of coalbed gas extraction.In response to the current lack of consideration for the multi-row borehole layout method in coal seams in existing research,single row and multi-row borehole gas extraction models were constructed based on the multi field coupling model of coal seam gas flow.COMSOL software was used to numer-ically simulate the gas pressure distribution around the boreholes,the area of the extraction standard zone,and the gas extraction effi-ciency.Optimization research was conducted on the spacing between single row boreholes,the shape and method of multi-row borehole layout.The results show that with the increasing borehole spacing,the gas pressure drop gradient between boreholes decreases,and the extraction standard area increases first and then decreases.When the spacing is 3.5 m,the maximum of extraction standard area is 31.9 m2.The optimal spacing of single row borehole layout is 3-4 m.For the multi-row borehole method,the standard extraction area and standard range of diamond shaped borehole method are 53.66 m2 and 10.9 m,respectively,which are larger than those of rectangular borehole method at 48.32 m2 and 9.8 m;within the same gas extraction period,the diamond shaped borehole method is superior to the rectangular borehole in terms of gas concentration,extraction rate and cumulative extraction amount.The preferred borehole method is the diamond borehole.