Evaluation of Gas Adsorption in Nanoporous Shale by Simplified Local Density Model Integrated with Pore Structure and Pore Size Distribution

Abstract

Simplified local density (SLD) model has been widely used to describe the gas adsorption behaviors in porous media. However, the slit pore geometry and constant pore width associated with the SLD model may fail to represent the heterogeneous pore network structure in shale. In this study, a new method to integrate the SLD model with the slit and cylindrical pore structures as well as the pore size distribution (PSD) is proposed and validated by the grand canonical Monte Carlo (GCMC) simulations and the experimentally measured adsorption of methane on shale with complex pore network. Comparison results show that reasonably good agreement is achieved between the SLD model and GCMC simulations for both the gas adsorption isotherms and discrete-density profiles in multiwalled carbon nanoslit and nanotube. The corresponding average absolute percentage deviations (% AADs) are below 0.3 and 9.3 for gas adsorption isotherm and discrete-density profile, respectively. In addition, the SLD model coupled with the PSD of slit and cylindrical pores ranging from micro- to macropores properly characterizes the measured excess adsorption of methane on Wolfcamp shale core sample with % AADs between 1.7 and 3.6. It is found that when the pore volume is fixed, the gas adsorption isotherm and gas density profile are heavily dependent on the pore geometry and pore size. Furthermore, integrating the PSD into the SLD model can guarantee the valid identification of the adsorbed- and free-gas regions in flow channels with different sizes based on the gas density profiles. The findings of this study shed light on the effects of pore structure on gas adsorption in nanopores and enable us to precisely evaluate and predict the gas adsorption behaviors in slit and cylindrical pores over a wide range of pore sizes.

Hydraulic Fracturing and Enhanced Recovery in Shale Reservoirs: Theoretical Analysis to Engineering Applications

“…When CO 2 enters the pores of the matrix, CH 4 –CO 2 competitive adsorption will occur (Figure b). CH 4 –CO 2 competitive adsorption is influenced by matrix microporous structure, organic matter content, kerogen maturity, mineral species, water content, and other factors. , The Ono–Kondo lattice model developed by Huo et al found the volume of the micropores, the organic carbon content of the matrix, and the interaction energy have a significant effect on CH 4 –CO 2 competitive adsorption. The CO 2 injection rate affects competitive adsorption by affecting the residence time of the gas in the matrix pores.…”

Surface-Molecule Interaction Strength on CO2 Adsorption Capacity in Nanopores: Implications to Advance CO2 Sequestration Performance

“…In a nanopore with pore width L , when a CO 2 molecule has the distance z away from the left pore surface, then its distance away from the right-side pore surface is L – z . Thus, as described in eq , there exists a term representing the intermolecular interactions and two terms that represent the surface-molecule interactions μ c o n f i n e d = μ f f false( z false) + μ f w false( z false) + μ f w false( L − z false) where μ ff and μ fw are the CO 2 chemical potential caused by intermolecular interactions and surface-molecule interactions respectively, both of which are functions of molecular distance away from the surface as provided below. , μ f f false( z false) = μ o false( T false) + R T ln true( f f f ( z ) f o true) μ f w false( z false) = 4 π N A ρ w ε f w σ f w 2…”

Review on Pore-Scale Physics of Shale Gas Recovery Dynamics: Insights from Molecular Dynamics Simulations

“…Further, the length scale relevant to shale gas storage and recovery can be comfortably explored using modern MD techniques and computing facilities. For these reasons, MD simulations have seen considerable applications in shale gas research or, more broadly, in unconventional hydrocarbon research. − From published works and our own experience, MD simulations are especially useful in three areas: (1) to furnish the thermodynamic and transport properties of nanoconfined fluids for continuum models, (2) to explore, discover, and understand new pore-scale phenomena, and (3) to guide the development of new pore-scale continuum models and validate them. MD works in these areas help better understand and predict shale gas storage and recovery at the pore scale, thus benefiting field-scale simulations.…”