Influence of the Pore Geometry Structure on the Evolution of Gas Permeability

Abstract

In order to investigate the effect of pore geometry structure on the gas permeability, 3 permeability models with different pore shapes were constructed, considering the sorption-induced deformation, adsorption molecular layer and variable Klinkenberg’s effect. The effect of pore geometry structure on the effective pore radius, Klinkenberg’s factor and permeability was analyzed under 3 different conditions, including constant effective stress conditions, constant pore pressure conditions and constant mean stress conditions. Results showed that, under constant effective stress conditions, the spherical pores show a greater effect on the effective radius, followed by the cylindrical pores and the slit pores. Under the constant pore pressure conditions and the constant mean stress conditions, the effective pore radius is more sensitive to the slit pores, followed by the cylindrical pores and the spherical pores. Under 3 different conditions, Klinkenberg’s factor is more sensitive to the slit pores, followed by the cylindrical pores and the spherical pores. Moreover, the permeability evolution with different pore geometry structures shows similar characteristics with effective pore radius, indicating that the effective radius dominates the permeability difference in different pore geometry structures. Furthermore, a numerical model was proposed to investigate the permeability evolution in the reservoir conditions. In the initial extraction stage, the permeability is increased with the rising slit pores. However, in the later stage, the spherical pores show more notable improvement effect on the permeability. Then, the effective pore radius and Klinkenberg’s factor were analyzed to reveal the influence mechanism of different pore geometry structures, indicating that the effective pore radius dominates the permeability difference, while Klinkenberg’s effect plays more significant role for the permeability trends and shows notable improvement effect on the permeability.