Solid-gas coupling model for coalseams based on dynamic diffusion and its application

LIN Baiquan; LIU Ting; YANG Wei

Abstract：Based on the assumption of dual-porous media,a solid-gas coupling model was developed with the consideration of effective stress,matrix shrinkage effect and Klinkenberg effect.A dynamic diffusion coefficient was introduced into the model,which makes the simulation results closer to the actual situation.The results show that with the decrease of the distance to the borehole,the coal permeability decreases first and then increases.The attenuation coefficient has little effect on the permeability distribution at the initial stage,but at the later stage,the difference between the permeability distributions is significant.When λ≤1 × 10-7,the permeability deceases first and then increases with the drainage time and while λ≥2 × 10-7,the variation trend is complicated.In addition,the attenuation coefficient has a marked influence on the gas pressure distribution.A higher value of attenuation coefficient will lead to a rapid attenuation of the fracture gas pressure and a slow decay of the matrix pore pressure.The effective drainage radius determined by the fracture pressure increases faster and faster with the time,while that determined by the pore pressure increases fast with time at first,but later gradually trends gently.The pore pressure is the reasonable index for the determination of the effective gas drainage radius of the borehole.