Residual trapping capacity of subsurface systems for geological storage of CO2: Measurement techniques, meta-analysis of influencing factors, and future outlook

Geological storage of CO2 is a promising technique to mitigate anthropogenic CO2 emissions. The effectiveness of CO2 storage in the subsurface formations relies on various trapping mechanisms that immobilize the injected CO2. Among these mechanisms, residual trapping has been identified as a critical factor, closely associated with residual CO2 saturation. The extent of residual CO2 saturation is strongly influenced by the petrophysical physicochemical and hydrodynamic properties of CO2/fluid/rock systems and operational conditions, thereby governing the overall residual trapping efficiency. This article reviews the published experimental datasets on the initial and residual CO2 saturation and analyzes the corresponding trapping efficiency for a range of in-situ CO2/fluid/rock systems. We explore the factors that influence trapping efficiency, including wettability, rock type, rock properties, and flow rate. The gas saturations and trapping efficiencies of different gas types (i.e., CO2, N2, and H2) are also discussed. Finally, we present the knowledge gaps and outline prospects for future research. This review establishes a state-of-art data repository of gas saturations in different conditions, enhancing our understanding of residual trapping in subsurface gas storage.