Study on abnormal distribution characteristics of coal gas in fault zone under tunneling disturbance

Abstract

The structural heterogeneity of fault zone can lead to the heterogeneity and anisotropy of medium permeability, which has an important influence on the gas seepage process in coal. The coal permeability model and transverse isotropic fault permeability model under the influence of tunneling stress are established, and the COMSOL numerical simulation software is used to calculate and analyze it. The evolution characteristics of stress field and permeability in front of tunneling affected by faults are obtained. Theoretical and numerical simulation results show that: affected by tunneling stress, obvious stress zoning appeared in front of exposure surface, plastic deformation continued to 5 m away from exposure surface, and plastic zone step phenomenon appeared. The fracture and coal matrix gas pressure gradients considering heterogeneous faults are 0.043 MPa/m and 0.042 MPa/m, respectively, which are significantly higher than those considering homogeneous faults. In the fault core area, the permeability decreases to a minimum of 6.438 3×10-18 m2, which is 1/7 of the initial permeability of coal seam. The large gas pressure gradient and low permeability in the fault-affected area verify the rationality of high risk of coal accumulation and gas outburst in the fault area.

Keywords

• heterogeneity of fault zone structure
• gas abnormal
• heterogeneity
• coal road driving
• laterally isotropic permeability model
• fluid-solid coupling