An Improved Gas Permeability Evolution Model of Coal Containing Gas with Klinkenberg Effect

Most of coal fields in China have low permeability, which is a key parameter to reflect the possibility of gas migration in coal seams, coal and gas outburst. Permeability is also a important factor for expectation and mine of coal-bed methane. Low permeability coal seams have significant Klinkenberg effect, and that with decreasing permeability of coal the Klinkenberg effect increases. However, most of previous permeability models do not consider Klinkenberg effect. It is known that when mean free path of gas molecules is close to the pore size of porous materials Klinkenberg effect appears, which is the essence of Klinkenberg effect. In this study, we build relationships between mean free path of gas molecules and Klinkenberg factor b. By using the relationships and the formula of effective permeability and absolute permeability, we establish a gas permeability evolution model of coal containing gas with Klinkenberg effect. Then we make a compare between our permeability model and other permeability models, such as Levine model, P-M model, S-D model, and the results show that the model considering Klinkenberg effect best accords with the experimental data under condition of fixed confining stress. We think that model considering Klinkenberg effect has important significance for expectation and mine coal-bed methane when it comes to low permeability coal seams.