Molecular Simulation of CH4 Nanoscale Behavior and Enhanced Gas Recovery in Organic-Rich Shale

Abstract

Occurrence and transport are two important nanoscale behaviors in the exploitation of shale gas. Nanopores in a realistic shale organic matrix are composed of kerogen molecules, which will have a great impact on surface-gas interactions and gas nanoconfined behavior. Although there are previous studies, the physics of gas transport through shale systems remains ambiguous. In this work, cylindrical nanopore models representing different pore sizes and organic-rich shale were constructed. By applying the molecular dynamics simulation method, the occurrence characteristics and transport characteristics of CH4 in the nanopores of organic-rich shale were studied. At last, the process of the adsorbed CH4 displaced by CO2 and N2 in shale nanopores at the subsurface condition was explored. This work can provide a better understanding of gas nanoscale behavior in shale systems and assist the future design of the CO2 sequestration and enhanced gas recovery technique.

Shale Gas Nanofluid in the Curved Carbon Nanotube: A Molecular Dynamics Simulation Study

“…After gaining sufficient knowledge about the impact of curvature on methane transportation, we can gradually add more complexities to model the nanochannel. These complexities could include adding functional groups or roughness to the surface of the walls, altering the shape of the cross-section, or even constructing the curved nanochannel by compressing multiple individual kerogen molecules. ,, This progressive approach will allow us to build a more comprehensive and accurate model of the nanochannels in kerogen, enhancing our understanding of methane behavior in these environments.…”

Development of Atomistic Kerogen Models and Their Applications for Gas Adsorption and Diffusion: A Mini-Review

“…Using a simple model of kerogen in gas shale, in agreement with experimental observations, these authors found that replacing methane by CO 2 is favorable from a thermodynamic viewpoint owing to the strong interactions between CO 2 and kerogen. Since then, by investigating methane/carbon dioxide coadsorption in molecular models of kerogen, many simulation studies have shown that injection of carbon dioxide indeed shifts the adsorption isotherm conditions by favoring the depletion of methane. − While the thermodynamic view derived from these works should be complemented by transport coefficients (to fully grasp the complexity of enhanced gas recovery), they already provide a comprehensive view of the problem. Using similar molecular modeling approaches, other authors also considered simple available thermodynamic models to describe methane/carbon dioxide coadsorption in kerogen. , Finally, as an important development beyond thermodynamic modeling, Xu et al have proposed a kinetic model of enhanced gas recovery.…”

Molecular Dynamics Simulation of Adsorption and Absorption Behavior of Shale Oil in Realistic Kerogen Slits

“…With further development of experimental methods, techniques such as elemental analysis, X-ray photoelectron spectroscopy (XPS), and 13 C NMR were used to characterize the elemental composition and functional groups of kerogen to construct a molecular monomer. − A dense matrix can be obtained by several kerogen monomers through a series of annealing procedures. Researchers have modified the matrix according to different research purposes: (1) dummy particles were added in the compression process to build a matrix model with a specific porosity , and (2) cutter atoms were introduced to construct different pore shapes in matrix models. − Numerous kerogen matrices have been used in gas adsorption isotherm simulations and adsorption-induced kerogen swelling effects. − Yu et al used GCMC-MD to compare the volumetric strain caused by the adsorption of CH 4 , C 2 H 6 , and CO 2 . The author suggested that the maximum absolute adsorption capacity of C 2 H 6 was smaller than that of CH 4 and CO 2 , which was attributed to the molecular size.…”