Non-isothermal Diffusion-seepage Model Of Coalbed Methane Based On Modified Channel-flow Term

Coalbed methane extraction is very important for coal mine safety and natural gas resource replenishing,among which the study of coal-bed methane mechanism can provide important guarantee for engineering application.At present,scholars generally believe that the migration process of coalbed methane includes three links:desorption,diffusion and seepage.The desorption process is generally considered to be instantaneous,and the dual-medium model of pore-fissure is mainly used to describe the desorption,diffusion and seepage process of coalbed methane.The existing dual media model is still not perfect,in which the accurate expression of the cross-flow term is particularly important and there are still some problems.Based on this,the main research work of this paper is as follows:(1)Based on the dual media model,the gas-solid-thermal coupling model of coal bed methane desorption-diffusion-seepage process is established.By comparing the experimental data,the correction factor of the channelling term based on the residual rate is introduced to correct the part of the channelling term.(2)The coal particles used in the experiment are assumed to be a dual medium model in the limit form of "the crack concentration is atmospheric pressure";The problem that the channel-to-flow item could not be verified by experiment was solved.The desorption and diffusion experiments of coal particles with different temperatures,pressures,particle sizes and metamorphic degrees were carried out to verify the applicability of the modified channel-to-flow item under different conditions.(3)Gas desorption-diffusion-seepage experiment was carried out on briquet-coal specimens with diameter of 25mm and height of 50mm,and the law of gas desorption-diffusion-seepage flow rate changing with time in briquet-coal specimens under different pressures was obtained.(4)Based on the gas-solid-thermal coupling model established and the modified channel-flow term,the numerical simulation of gas desorption-diffusion-seepage process in briquet-coal specimens was carried out,and the comparison with the experimental results was made to verify the improvement and applicability of the model established in this paper compared with the existing model.(5)The numerical simulation of gas migration process in anisotropic coal seams was carried out,and the influence of permeability anisotropy and other factors on gas migration process was studied.Based on this,the optimization of hole distribution parameters was carried out.