Experimental investigation and Grand Canonical Monte Carlo simulation of gas shale adsorption from the macro to the nano scale

This paper sheds light on the potential of carbon storage and gas recovery from shale using pure and multicomponent sorption studies. A multi scale approach was adopted where experimental characterization at the core level was linked with a digital laboratory through molecular modeling to simulate and predict pure and multicomponent adsorption conditions that were hard to achieve in the lab. The sensitivity of shale physical properties to the gas mixture saturating the pore space was examined for possible carbon storage and enhanced gas shale recovery applications.& para;& para;A novel high precision volumetric gas adsorption apparatus was constructed in house to investigate multi-component gas sorption at the core level. The thermodynamically closed system allowed for simultaneous measurements of three fundamental rock properties at the core level including porosity, permeability and excess adsorption. Experiments were carried out to measure the preferential adsorption of different components in a gas mixture on intact core samples from the Haynesville and Barnett shale plays. Based on the pore size distribution (PSD) of the sample, the experimental observations were confirmed using a grand canonical Monte Carlo (GCMC) simulation employing a slit pore model composed of parallel planar graphitic surfaces.& para;& para;Experimental results revealed multi-layer adsorption coverage with CO2 in comparison to a mono- layer coverage with N-2 and CH4. Mixed gas sorption measurements showed preferential adsorption of CO2 over CH4 as indicated by a selectivity coefficient greater than 1 . GCMC simulations on pore sizes ranging from 1 nm to 50 nm were consistent with the core-scale experimental results and revealed an increasing selectivity for CO2 over CH4 in model shale pores. N-2 injection, however, proved to be an unsuccessful enhanced gas recovery technique due to a preferential adsorption of CH4 over N-2. (C) 2016 Elsevier B.V. All rights reserved.