Permeability enhancement simulation of hydraulic fracturing in underlying coal seams in goaf

• Published in: Geomechanics and Geophysics for Geo-Energy and Geo-Resources
• Main Authors: Kaikai Zhao, Chenxi Liu, Ye Hua, Yanjun Feng, Xiaodong Sun, Cun Zhang
• Format: Article
• Language: English
• Published: Springer 2025-07-01
• Subjects: Hydraulic fracturing; Underlying coal seams; Permeability model; Stress disturbance; Numerical simulation
• Online Access: https://doi.org/10.1007/s40948-025-01016-3
• ISSN: 2363-8419; 2363-8427

Abstract The mining of No.3 coal at Sihe Mine has created a large area of goaf, which has led to a large-scale pressure relief of No.15 coal. It has the advantageous conditions for the development of coalbed methane (CBM). To better achieve the efficient development of CBM, the hydraulic fracturing effect and permeability enhancement mechanism of underlying coal seams in Goaf (UCSG) were studied. This study takes the No. 15 coal of Sihe Mine as the research object. Through experiments, the seepage characteristics of coal samples in different areas after hydraulic fracturing along with gas pressure decline were obtained, and a gas pressure decline permeability model was established. A numerical simulation method for hydraulic fracturing of UCSG has been constructed. A large-scale three-dimensional numerical model was established to obtain the stress distribution law of UCSG. Based on this, a small-scale hydrostatic fracturing fluid–structure coupling numerical model of the No.15 coal was constructed. After conducting the hydraulic fracturing simulation, three areas with different degrees of permeability enhancement were delineated: the strongly disturbed area, the weakly disturbed area, and the undisturbed area. Finally, the permeability is updated based on the gas pressure decline permeability model to achieve the simulation of gas extraction. According to the simulation results, the stronger the stress concentration effect of the UCSG, the worse the hydraulic fracturing effect is. The research provides guidance for the hydraulic fracturing and gas extraction of UCSG.