Comprehensive Review of CO₂ Adsorption on Shale Formations: Exploring Widely Adopted Isothermal Models and Calculation Techniques

The continuous use of fossil fuels has a huge impact on climate change because they release CO₂, which is a major greenhouse gas that causes 70-75% of global warming. Shale reserves could be used to store CO₂ to lower greenhouse gas emissions. This could happen mostly through adsorbed gas, which can make up about 85% of all shale gas. It is important to fully understand the CO₂ adsorption processes in shale, especially when using isothermal models, to get accurate estimates of storage capacity and predictions of how shale will behave. This work examines the application of several isothermal models, including Langmuir, Freundlich, Brunauer-Emmett-Teller, Dubinin-Radushkevich, Dubinin-Astakhov, Sips, Toth, and Ono-Kondo lattice models, to explore the adsorption of CO₂ on shale formations. The aim of this research work is to assess the efficiency of these models in forecasting CO₂ adsorption in different shale samples with specific mineral compositions, total organic content (TOC), surface areas, and pore geometry at 298 K and up to 2 MPa. This review provides a state-of-the-art knowledge on the constraints of existing models and proposes adaptations, such as integrating density-dependent correction factors and hybrid modeling techniques, to enhance precision during numerical simulation work. Furthermore, the possible incorporation of molecular dynamic (MD) simulations with experimental data is suggested to improve the understanding of the CO₂ adsorption in the geological rock at the molecular scale. The results emphasize the need for future studies to concentrate on the improvement of models and empirical validation to more accurately forecast the storage behavior of CO₂ in shale formations at resevoir conditions.