Study on the effects of multi-factor coupling and cycling confining pressure on the permeability of CH4 in coal rock

Abstract

The permeability of coal reservoirs is affected by its inherent properties, temperature, stress state, etc. Taking the 13-1 coal seam of Huainan Liuzhuang Coal Mine as the research object, the variation of CH4 permeability under the coupling of volume stress, temperature and gas pressure, and under cyclic confining pressure were studied based on the CH4 permeability test. The results show that the CH4 permeability of coal affected by the coupling of volume stress and gas pressure mainly controlled by the effective stress, and the greater the effective stress is, the lower the permeability is. The effect of gas pressure on CH4 permeability is limited by volume stress, but gas pressure has a greater effect on CH4 permeability than volume stress. The influence of temperature and gas pressure coupling on CH4 permeability is dominated by gas pressure. Permeability decreases with the increase of gas pressure showing a type of “U slide”, and the “slide” change is more obvious than the “U” change. The influence of gas pressure on CH4 permeability is greater than that of temperature, and the increasing gas pressure will reduce the influence of temperature on permeability. The cyclic confining pressure will cause irreversible plastic deformation of the pore fractures, which reduces effective seepage channels in the coal and decreases CH4 permeability. The plastic deformation produced by the first cyclic confining pressure is the largest, and the amount of plastic deformation gradually decreases with the increase of the number of cycles.

Keywords

• permeability of ch4
• coupling
• volume stress
• temperature
• gas pressure
• cyclic confining pressure