A COMSOL simulation of fracture-stress-seepage coupling during extremely thick coal seam mining

Abstract

The law of seepage field evolution of mining overlying rock is complicated, and it plays a key role in controlling the migration and storage of pressure relief gas. To explore the evolution law of the seepage field under the conditions of extremely thick coal seam (ETCS) comprehensive mining, the Liuhuanggou coal mine in Xinjiang Province was selected for study. A similar simulation experiment was carried out for the collapse of the overlying rock at ETCS. The development of “cooling tower” distribution characteristics of mining cracks is elucidated. We used the mining fissure network, qualitative analyses, and COMSOL Multiphysics numerical simulation software to investigate the evolution characteristics of the pressure relief gas migration and storage area, as well as the evolution law of gas seepage in the ETCS. We also conducted a three-dimensional gas extraction field test to verify the results. The results indicate that the distribution pattern of the seepage field in the extraction zone exhibits a “cooling tower” pattern, characterized by a wide bottom and a narrow middle. And pressure relief gas is mainly distributed on both sides of the mining area. In addition, the gas pressure in the quarry increases and then decreases with an increase in height. Based on the relationship between the evolution characteristics of the seepage field in the mining fissure and gas migration and storage, the asymmetric evolution mechanism of the gas-high seepage zone is revealed, and the permeability zoning control equation is established. The magnificent effect of gas extraction in the field ensures the green, safe, and efficient mining of the working face. The study’s results establish a theoretical basis for precise gas extraction in ETCS and offer a fresh outlook on GHG management, with the goal of enhancing gas extraction and achieving safe and efficient mining in ETCS.