Study on deformation characteristics and permeability response of coal under hydro-mechanical coupling

Abstract

During the process of coal seam water injection, the coupling effect of stress and water pressure causes deformation of the coal, which affects the seepage. To explore the evolution law of the volume strain and permeability characteristics of coal during the seepage process of water injection, rock mechanics testing machine is used to carry out hydraulic coupling seepage test of coal. The influence law of stress on the permeability and volume strain characteristics of coal is obtained. On this basis, the evolution law of volumetric strain and permeability characteristics of coal under the influence of water pressure is studied. The experimental results show that there is a significant response law of permeability to volumetric strain, and the exponential function relationship between the permeability and volumetric strain of coal is obtained through data fitting. In the constant water pressure test, the permeability of coal shows a trend of decrease and then increase. During this process, the coal sample undergoes a transition from compression to expansion, and the permeability reaches its maximum value after the coal fractures are interconnected. During the alternating water pressure test, the coal fractures were observed to be compacted under lower water pressure cycles, leading to a decrease in permeability fluctuation. However, with the increase of the number of cycles and the expansion of fractures, the permeability of coal and rock begins to increase under the action of hydraulic coupling. Under the same stress condition, high pore water pressure promotes crack propagation, volume strain and permeability.

Keywords

• coal seam water injection；fluid-solid coupling
• surrounding rock stress
• pore water pressure
• volume strain
• permeability