CO2 sequestration in subsurface geological formations: A review of trapping mechanisms and monitoring techniques

Carbon capture and storage (CCS) in subsurface formations has emerged as a promising strategy to address global warming. In light of this, this review aims to provide a comprehensive understanding of the mechanisms involved in the geological trapping of CO2. Additionally, it aims to identify the techniques used to evaluate the potential for CO2 sequestration before injecting CO2 into subsurface formations and the methods used to monitor the progress of CO2 sequestration after injection. The review also presents future research directions based on current research trends in the field. Four principal trapping mechanisms were identified: structural, capillary (residual), solubility, and mineral trapping. These mechanisms vary in their CO2 trapping capacity over time and the storage security they offer. Structural trapping provides the most significant contribution to CO2 trapping, whereas mineral trapping offers the highest storage security. In terms of monitoring and assessment, three main approaches were identified, including seismic and borehole geophysical methods, atmospheric monitoring methods, and laboratory-scale experiments. One of the novel aspects of this review is that it outlines the various experimental techniques used for investigating CO2 trapping mechanisms, an area that prior reviews have not addressed. At the laboratory level, various tests and experiments are used to study CO2 trapping characteristics. These are categorized into petrophysical characterization, pore-scale experiments, CO2-fluid-rock interaction experiments, and CO2 adsorption evaluation. Another novel contribution of this review is the development of a qualitative assessment approach for the applicability of various monitoring techniques throughout the stages of CO2 sequestration projects. This innovative approach has not been reported in the previous literature. Our review was prepared following a scoping review methodology, ensuring the inclusion of the most recent and relevant studies.