With the increasing global energy demand, unconventional
oil and
gas, especially shale gas, have become an important natural gas resource.
In the modern petroleum engineering field, CO2 is commonly
used to displace shale gas. CH4 is the main component of
shale gas; therefore, understanding the competitive adsorption behavior
in the shale matrix is of great significance for optimizing shale
gas production. This review explores the competitive adsorption behavior
of CH4 and CO2 on a shale matrix from the perspective
of molecular simulation and emphasizes the latest research progress
in this field. First, several molecular simulation methods for studying
gas adsorption are introduced, including density functional theory
(DFT), grand canonical Monte Carlo (GCMC), molecular dynamics (MD),
coarse-grained molecular dynamics (CGMD), and dissipative particle
dynamics (DPD). The competitive adsorption behavior of CO2/CH4 on organic kerogen models, inorganic mineral models,
and organic–inorganic composite shale models is discussed,
comparing the gas adsorption differences on different shale molecular
models. Additionally, the multi-scale simulation methods for shale
gas combined with molecular simulations and the application of machine
learning (ML) methods are also discussed. Finally, the influence of
factors such as the temperature, pressure, moisture content, and pore
size on competitive adsorption behavior is analyzed. The challenges
and prospects in the current competitive adsorption simulation of
CO2/CH4 are summarized, such as constructing
shale organic–inorganic composite pore models that combine
pore structure and surface chemical heterogeneity and comprehensively
considering the multi-scale migration of shale gas from atomic scale
to mesoscopic scale to macroscopic scale. This research provides important
theoretical support for optimizing the development of natural gas
resources and promoting CO2 sequestration technology.
