Dynamic Gas Diffusion Model of Capillary Pores in a Coal Particle Based on Pore Fractal Characteristics

摘要

Gas diffusion in a porous medium is a very complex process. Aiming at accurately describing the whole process of gas diffusion in a coal particle, a dynamic diffusion model of capillary pores in a coal particle (hereafter referred to as CPCPDD model) which is dependent on both the pore size and the pore pressure and based on the fractal characteristics of these capillary pores was established according to the characteristics of gas diffusion in different-sized pores. Next, parameters of the CPCPDD model were obtained through gas desorption, low-temperature nitrogen adsorption and mercury injection experiments on a coal particle. Furthermore, a comparative analysis was made between the solution results of the CPCPDD model and the data obtained from the gas desorption experiment. The results suggest that the CPCPDD model proposed in this study can accurately describe the whole process of gas diffusion in a coal particle. The diffusion coefficient obtained by the CPCPDD model is a variable related to the pore diameter and the pore pressure, and the classical uni-pore diffusion model, bi-disperse diffusion model and the multi-pore diffusion model are specific manifestations of the CPCPDD model in different pore size ranges. The research results boast crucial theoretical significance for in-depth understanding and interpretation of gas migration in coal reservoirs.