Multiphysics responses of coal seam gas extraction with borehole sealed by active support sealing method and its applications
Journal of Natural Gas Science and Engineering
School of Engineering / Centre for Sustainable Energy and Resources
China Postdoctoral Science Foundation (No. 2021M701101),
Science and Technology Project of Henan province (No. 222102320295),
National Natural Science Foundation of China (No. 41872188).
Air-leakage is one of the main reasons leading to poor coal seam gas (CSG) extraction performance, and needs to be mitigated urgently. Despite the active support sealing method for air-leakage prevention previously proposed, the multiphysics responses around a CSG borehole has not been systematically studied, hindering further applications of the method. This research first studied the coal damage, porosity, permeability, and air partial pressure around boreholes sealed by different active supports numerically by a coupled model of coal/rock continuous damage and binary flow. Moreover, a delayed swelling (DS) material providing active support on hole-wall was introduced. For boreholes sealed by DS and foam cement (FC) materials, the stress, fractures, pores and air-leakage around boreholes were characterized comparatively in the laboratory study. Finally, the CSG extraction performance of boreholes sealed by DS and FC materials were evaluated in field scale. The results demonstrate that: (1) With the increasing of active support, coal stability around the borehole sealing section is improved, porosity and permeability variations are restrained, and the air-leakage extension along the borehole is remarkably restrained. (2) Compared with the FC material, there are much less meso- and micropores and fractures formed around the borehole sealed by DS material because of the active support imposed on the hole-wall. The maximum air-leakage of the borehole sealed by DS material is 0.93 L/min, which is much lower than 1.34 L/min sealed by FC material. (3) The average methane concentrations and fluxes of the boreholes sealed by the DS material are higher than those sealed by the FC material in field scale. This study illuminates the multiphysics responses of CSG extraction with boreholes sealed by active support sealing method and demonstrates the successful application cases, which provide a guidance for applying the method in reducing air-leakage and improving CSG extraction performance.