Testing some Common Concepts in CO2 Storage

AbstractTwo concepts have been very influential in aiding the evolving understanding of CO2 storage systems. The first of these was the trapping diagram that first appeared in the IPCC Special Report on CCS (2007). This shows the evolution of the balance of trapping processes – physical seals, capillary trapping, dissolution and reactive trapping - over time. This clearly demonstrated the need to move beyond simplistic estimates of storage capacity to understanding the interplay between the trapping processes. The second was a conceptual model of the evolution of risk through the life of a CO2 storage site presented by Benson at GHGT-8. This showed risk rising to a peak during injection and then declining back to a low level as the site stabilised post injection.Both of these concepts were presented in diagrammatic form and have been the subject of considerable discussion ever since. As an illustration, opinion remains divided as to whether storage risk peaks and declines or whether it continues to rise as buoyant migration causes the plume to contact an ever increasing area of seal. In this study we use a simplified model based upon vertical equilibrium concepts to develop analytically derived versions of both the IPCC trapping diagram and to explore the risk of seal failure in the post-closure period