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a b s t r a c t CO 2 injection for storage in subsurface geologic medium is one of the techniques developed in the past years to mitigate anthropological CO 2 . Prior to CO 2 injection, it is essential to predict the feasibility of medium in terms of storage capacity, injectivity, trapping mechanisms, and containment. There have been many studies regarding techniques which can be applied to ensure the safety of CO 2 injection. However, there are few studies indicating the importance of capillary trapping during and after CO 2 injection. The aim of this study is to review the fundamentals of injectivity and its relationship with capillary trapping for CO 2 storage in depleted oil and gas reservoirs. Considering the number of effective parameters which are associated with the injectivity and capillary trapping, it is recommended to perform a comprehensive analysis to determine the optimum injection rate and safe storage medium before operation.

Carbon dioxide released into the atmosphere due to anthropogenic activities has raised the alarm of global warming in the near future. CO 2 storage in suitable subsurface geologic media has, therefore, been triggered in recent years. However, identification of suitable sites to store a large quantity of CO 2 for a long period of time is not an easy and straightforward task. Although, a general criterion has already been presented based on local-scale projects in which depth, permeability, porosity, density and containment factors were considered for selection of an appropriate geologic medium, there are many other preliminary factors linked to the storage capacity, injectivity, trapping mechanisms, and containment which should not be neglected during a CO 2 storage site selection. The aim of this paper is to propose a new screening criterion for the CO 2 storage site selection based on a group of key parameters including reservoir and well types, classes of minerals, residual gas saturations, subsurface conditions, rock types, wettability, properties of CO 2 , and sealing potentials. These parameters were combined with those factors presented earlier by other scholars to provide a good insight into the suitable selection of storage sites. Although attempts were made to consider the whole parameters linked to a site selection, more studies are still required to get a final conclusion about the effective parameters which should be a part of the analysis.

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