Effect of Poroelasticity, Pore Confinement, Molecular-to-Inertial Transport, and Threshold Pressure on Flow of Gas through Hydraulically-Fractured Shale-Gas Reservoirs

Abstract

Abstract Transport of gas in nano-permeability shale-gas reservoirs involves complex processes of absorption, adsorption, poroelasticity, alterations of gas properties by pore-confinement, and significant deviations from Darcy-type flow. While recent modifications of Darcy’s law can account for molecular transport in shale depending on the Knudsen conditions, they nevertheless omit the corrections due to convective acceleration and inertial flow occurring through natural fractures and induced fractures formed by hydraulic fracturing and the threshold pressure gradient below which reservoir fluids cannot flow. This paper presents a physically rigorous modeling of shale-gas transport by considering the relevant effects in nanopores and fractures to derive a proper gas storage and transport model. This provides an improved model accounting for complex transport processes in organic and inorganic materials intersected by natural and induced fractures. A non-Darcy equation, comprehensive gas storage model, and quantification of relevant parameters are developed. The model is used to simulate gas transport in laboratory shale-core tests conducted under near-real shale-gas reservoir conditions.