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.

Anisotropic Damage Mechanism of Coal Seam Water Injection with Multiphase Coupling

“…So, a new physical model is established for coupling water-containing brittle materials (coal and rock) with fluid mechanics to describe plastic deformation and material damage. Numerous scholars have conducted extensive theoretical research on containing water coal and rock, which is mainly divided into the following aspects: (1) numerical study of mechanical properties is used by classical elastic–plastic models for containing water coal and rock, but without considering induced anisotropic damage . (2) The mechanical behavior of unsaturated coal and rock is studied without considering the coupling effect with fluid mechanics. , Therefore, it needs to establish a new model of the coupling effect of the damage mechanics between coal-rock and fluid, and in the new model, several physical characteristics are considered, which are the nonlinear pore elastic behavior of containing water coal, the relative permeability of water and gas variation with water saturation, damage and failure induced by water saturation, and the relationship between inherent permeability and coal damage. , …”

Optimization and Application of Water Injection Process in Gas-Bearing Coal Seam

“…As the most abundant energy source in the world, coal has become the basis for promoting rapid economic development. It is still the main energy source that has been used to support the social and economic development of our country for a long time [1,2]. However, in the process of coal mining, spontaneous coal combustion, gas explosions, and coal mine dust-induced accidents often occur [3][4][5][6][7][8][9][10][11][12][13], which seriously affect the underground green environment, bring serious and fatal damage to the miners, and cause huge economic losses.…”