Coupling Mechanism of Coal Body Stress–Seepage around a Water Injection Borehole

Abstract

In China, coal seam water injection technology is widely used in the prevention and control of mine gas and dust disasters. The evolution law of stress–seepage field in the range of hydraulic influence in the process of coal seam water injection is the most basic theoretical problem in coal seam water injection technology. Therefore, this paper first uses the radial seepage experimental system to test the permeability of raw coal samples, and then numerically inverts the stress–seepage evolution law of the coal body around the water injection hole. The results show that the coal seam permeability decreases exponentially with the increase in the experimental overburden pressure. The dynamic water intrusion causes the pressure relief area and the stress concentration area to transfer to the deep part of the coal body, and abnormal stress occurs near the water injection hole wall. The composite stress area formed by the superposition of stress and pore water pressure reduces the permeability of the hole wall. During the radial development of water injection, the pore water pressure dropped sharply and eventually tended to zero, while Darcy’s velocity decreased significantly (within the pressure relief zone, it rapidly decreased from 7.26 × 10−3 m s−1 to 2.5 × 10−3 m s−1 (by 65.56%)). Near the initiation point, the maximum step-down height of Darcy’s velocity decreased from 6.73 × 10−3 m s−1 to 5.27 × 10−3 m s−1 (by 22.73%). This can make it clear that the seepage velocity presents a non-Darcy seepage phenomenon under the influence of pore pressure.