Molecular simulation and experimental characterization of the nanoporous structures of coal and gas shale

• Characterization of coal and shale rock to obtain pore size distribution (PSD).
• Nuclear magnetic resonance cryoporometry experiments to determine the PSD.
• Low-pressure gas adsorption isothermal experiments to determine the PSD.
• Creating 3D pore network model using Voronoi tessellation method.

Characterization of coal and shale is required to obtain pore size distribution (PSD) in order to create realistic models to design efficient strategies for carbon capture and sequestration (CCS) at full scale. Proton nuclear magnetic resonance (NMR) cryoporometry and low-pressure gas adsorption isothermal experiments, conducted with N2 at 77 K over a P/P0 range of 10− 7 to 0.995, were carried out to determine the PSD and total pore volumes to provide insight into the development of realistic simulation models for the organic matter comprising coal and gas shale rock. The PSDs determined on the reference materials (SiliaFlash F60 and Vycor 7930) show a reasonable agreement between low-pressure gas adsorption and NMR cryoporometry showing complementarity of the two independent techniques. The PSDs of coal and shale samples were determined with low-pressure gas adsorption isothermal experiments, but were unable to be measured by NMR cryoporometry. This is likely due to a combined size and pore surface chemistry effect that prevents the water from condensing in the pores, such that when the sample is heated there is no distinction based upon melting or phase change. Molecular modeling is carried out to create the pore structure network in which the transport and adsorption predictions are based. The three-dimensional (3D) pore network, representative of porous carbon-based materials, has been generated atomistically using the Voronoi tessellation method. A comparison of the computed PSD using this method was made to the measured PSD using isothermal low-pressure gas adsorption isothermal experiments on coal and gas shale samples. Applications of this work will lead to the development of more realistic 3-D models from which enhanced understanding of gas adsorption and transport for enhanced methane recovery and CO2 storage applications can be developed.