Apparent gas permeability in an organic-rich shale reservoir

Abstract

Accurate models of gas transport in shale gas reservoirs must consider complex gas transport mechanisms and phase behavior in nanopores, as well as different pore types. The gas transport mechanisms in shale gas reservoirs include viscous flow, Knudsen diffusion, surface diffusion, adsorption and desorption. In this study, a unified model of nanopore gas transport in shale gas reservoirs is presented. Gas storage patterns are different in organic pores and inorganic pores. Therefore, we develop two fully coupled apparent permeability models to describe gas transport in organic pores and inorganic pores separately. The apparent permeability model of organic pores considers the gas transport mechanisms of viscous flow, Knudsen diffusion, surface diffusion, adsorption and desorption. The apparent permeability model of inorganic pores considers the gas transport mechanisms of viscous flow and Knudsen diffusion. In both models, stress dependence, real gas effects and phase behavior are taken into account. Then, the influences of pore pressure, effective stress, real gas effects, pore radius, phase behaviors and transport properties on apparent gas permeabilities in organic pores and inorganic pores are analyzed based on the proposed models.