Characterization of adsorption isotherm and density profile in cylindrical nanopores: Modeling and measurement

Abstract

Gas adsorption behavior in shale kerogen may not be fully described using the Simplified Local-Density (SLD) model with a slit-shaped pore. In this study, an extension of the SLD model is proposed to characterize the adsorption isotherm and density profile in shale nanopores with a circular pore geometry. Such an extension enables the pore structure associated with the SLD model to be comparable with the cylindrical micro- and mesopores in shale kerogen. To examine the accuracy and reliability of the extended SLD model, adsorption isotherms and density profiles of methane and carbon dioxide in single-walled carbon nanotubes (SWCNTs) calculated by the extended SLD model were compared with the corresponding quantities determined via the grand canonical Monte Carlo (GCMC) simulations. In addition, the extended SLD model was used to evaluate the measured adsorption of methane on the Marcellus shale core sample to demonstrate its practicability. The results of this study indicate that the adsorption isotherm and density profile calculated by the extended SLD model are in reasonably good agreement with those determined via the GCMC simulation. Moreover, the extended SLD model can properly characterize the measured adsorption isotherm of methane on shale. These findings illustrate that the extended SLD model is a robust engineering model, which is capable of predicting the adsorption isotherm and density profile in cylindrical nanopores. More significantly, the extended SLD model serves as a link to convey the microscopic details from the GCMC simulations to the interpretation of experimental measurements through rapid computations.