Numerical simulation study and application of coal seepage evolution law around water injection borehole in the stope “dynamic-static” pressure zone

Abstract

A pressure relief anti-reflection model of a borehole along a coal seam goaf was constructed to analyze the stress-plastic spatiotemporal evolution characteristics of a borehole, and the implementation process of pressure relief anti-outbursts from the underground mine of the Huaibei Qingdong Coal Mine was used as the research background. A simulation of the mathematical relationship between the permeability of the coal seam sample and the overburden-gas pressure was performed, incorporating the dynamic balance parameters of the stress after the borehole was constructed along the coal seam; in addition, the water injection pressure relief process and the plastic deformation mechanism of the boreholes in the “dynamic-static” pressure zone were simulated. These simulations were performed to explore the evolution of stress permeability of the coal body before and after water injection. The results showed that after water injection, the stress unloading in the stress relief region was 12.8 ∼ 31.1%, and the permeability was increased by 23.5 ∼ 42.9%; the stress unloading in the stress concentration region was 26.7 ∼ 58.4%, and the permeability was increased by 263.7 ∼ 563.5%. With the application of water injection technology in the drilling zone of a bedding layer at the 726 working face of the Qingdong Coal Mine, the average cutting volume in the water injection area decreased by 17.19%, the K1 and Δh2 values decreased by 40.3% and 12.2%, respectively, and the return gas concentration decreased by 31%. Thus, pressure relief had an outstanding anti-outburst effect.