Experimental and Numerical Analysis of Gas Transport in Shale Including the Role of Sorption

Abstract

Abstract This study adds to the knowledge base of carbon dioxide sequestration and methane recovery enhancement from gas shale. If gas shale is desired to be used as a storage medium for CO2, then knowledge of how to maintain gas permeability while enhancing storage via sorption is mandatory. In this work, physical and numerical pressure-transient, pulse-decay experiments are conducted on Eagle Ford shale cores. The experiments are conducted isothermally at various pore and confining pressures that maintain a constant net effective stress. The gases investigated are helium, methane, and carbon dioxide. Porosity and permeability measurements are conducted using various techniques including numerical simulation that incorporates detailed measurements of the in-situ, core-scale porosity distribution. The research simulator is fully implicit, finite volume, unconditionally stable, and incorporates gas sorption in ultra-small pore networks. Langmuir sorption parameters are determined after matching the upstream and downstream pressure profiles simultaneously. Experiments are also interpreted using available analytical models and compared to the high-resolution simulations matched to experimental observations. Results highlight the interplay of gas slip and sorption of pure gases at core-level. Results also quantify the role of CO2 sorption in various shale fabrics and thus promote the potential for sequestration. While the gas molecular kinematic diameter plays a role in dictating the pore accessibility, and thus governs slip flow, gas sorption is more influential in determining permeability. Gas transport in wide channels, however, undermines the influence of sorption on measured permeability. While He is a non-sorptive gas, CH4 sorption isotherms are described by a Langmuir model and CO2 isotherms are similar to an n-BET model. The experiments demonstrate that He and CH4 have a similar measured permeability while carbon dioxide has a lower permeability. These differences are attributed to the strong sorption of carbon dioxide.