Abstract: To make clear the influences of different factors on enhancing methane extraction by hydraulic fracturing in coal seam, and ensure the safe mining of coal mine, a unified mathematical model was built for hydraulic fracturing and gas drainage based on the multiphysics coupling theory, involving a hydraulic field, a mechanical field and a damage field. The processes of hydraulic fracturing and gas drainage were simulated by Comsol with Matlab software. The effectiveness of the model was verified by the data obtained in the field test. The influences of borehole-to-borehole spacing, water injection pressure, coal elasticity modulus and in-situ stress on fracturing were quantitatively analyzed. Results show that the fracture breakthrough time of numerical simulation is in good agreement with that obtained in the field test, that the key to effective gas drainage is that the fracturing damage zone can be connected at the drainage borehole, that the fracture breakthrough time increases linearly with elastic modulus and homogeneity of coal seam, increases exponentially with vertical stress and borehole-to-borehole spacing, and decreases exponentially with injected water pressure.

Key words: hydraulic fracturing, gas drainage, coal permeability enhancement, influence factors, numerical simulation