Abstract
The Qingshui Basin in China is a hotspot for coalbed methane exploration, and the selection and arrangement of the surface well are crucial engineering issues for the drainage process. To address this, the present study establishes several novel coal permeability models based on the strain relationship of representative elementary volumes (REV) and discusses the evolution mechanism of permeability. Moreover, the spatiotemporal evolution patterns of permeability during the drainage process are analyzed, and a methodology is presented for the selection and arrangement of a surface well based on the predrainage time at the working face. The results indicate that in the permeability model, the volumetric strain of REV is linearly correlated with the volumetric strain of their respective fractures, with the correlation coefficient representing the initial fracture porosity. The variation pattern of coal permeability near surface wells during the drainage process is closely aligned with the trend of the adsorption strain. Additionally, the selection and arrangement of surface wells are correlated with the predrainage time at the working face, including the minimum number and location of vertical wells, as well as the optimal length of horizontal wells. The research findings provide valuable insights into enhancing the efficiency of coalbed methane drainage.