An overview of isotherm models for gas adsorption on shale for enhanced gas recovery

Adsorption of carbon dioxide (CO 2 ) on shale formations is a viable strategy for improving methane (CH 4 ) recovery, crucial for maximising natural gas production and resolving environmental concerns about greenhouse gas emissions. Shale’s fine-grained sedimentary structure and high organic content make it ideal for CO 2 adsorption. This interaction can potentially boost methane extraction while contributing to carbon sequestration efforts. For the successful exploration of shale gas recovery, the gas adsorption mechanisms must be well understood. This article discusses the recent works on shale gas adsorption and their merits and demerits. The study of desorption behaviour is also critical to understanding the gas release behaviour, desorption hysteresis, influence of TOC, clay minerals, and presence of water on gas adsorption-desorption behaviour. For small-sized particle samples, the gravimetric method could be the best choice; however, the volumetric method is widely used for heterogeneous materials like shale rock. Adsorption processes are commonly analysed using a variety of isotherm models, including Langmuir, Freundlich, Brunauer–Emmett–Teller (BET), Dubinin–Radushkevich (DR), Temkin, Sips, Redlich–Peterson, Simplified Local Density (SLD) theory, and the Ono–Kondo model. These models have been developed through advanced theoretical approaches and empirical routes, enabling them to describe both generalised and specific gas adsorption phenomena. A powerful technique, molecular simulation – including Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) – has recently emerged for investigating gas adsorption on shale at the microscopic level, offering deeper and more detailed insights into gas–shale interactions at the atomic scale.