Numerical Simulation of Stress-seepage Coupling of Pre-extraction Gas in Surface Well

Abstract

Based on the theory of elastic mechanics, rock mechanics and seepage of porous media, the stress-seepage coupling model of pre-extracted gas through ground wells is established. Combined with the specific engineering examples, the influence of ground stress on the pre-extraction gas effect of the ground well is analyzed. The study results indict that: under the action of surface well extraction, the gas pressure of coal seam decreases continuously, and the larger the ground stress is, the slower the gas pressure decreases; as the extraction continues, the gas pressure decreases and the effective stress of the coal increases, the permeability decreases, and due to gas desorption, the pore and fracture of coal seam become larger and the permeability increases, and the permeability of coal seam generally presents a nonlinear increase trend under the joint action of the two effects. The in-situ stress has a significant influence on the extraction efficiency of surface wells, and the two have a negative correlation, that is, with the increase of in-situ stress, the matrix porosity in coal seam decreases and the cracks tend to close, resulting in the decrease of coal seam permeability, and finally the decrease of gas extraction amount.

Keywords

• ground well
• gas pre-extraction
• ground stress
• permeability
• stress-seepage coupling
• numerical simulation