Subsurface Carbonate CO2 Storage and Security

Geological CO₂ storage security is determined by the structural integrity of the storage formation and the migratory patterns of the sequestered CO₂. This research proposal focuses on the final step in the CCS (carbon capture and storage) value chain - injection and subsurface storage of CO₂ - with emphasis on carbonate geological systems. Carbonate rocks are extremely reactive, and coupled with their highly heterogeneous pore structure, present a tremendously complicated reactive transport problem. Current lack of understanding in reservoir structural integrity and CO₂ migration cast doubt on estimations of long-term geologic CO₂ storage. For years, reactive transport through carbonate porous media has been modeled as a simple function of reaction and advection. We recently investigated reactive transport in carbonate media and found that the reaction product, CO₂, forms a separate, wetting phase during carbonate dissolution that engulfs the carbonate grain and prevents further local reaction. This mechanism was not described in the literature, and the discovery of the new phenomenon impacts estimation of preferential CO₂ flow path in carbonate storage formations. The project will expand the existing knowledge on this topic to convince the public that subsurface CCS is vital for a transition to a less fossil-fuel dependent society. The proposal has two work packages that emphasize flow and CO₂ trapping mechanisms in a carbonate geological storage site at two different length scales using new, sophisticated experimental tools developed by the research team: 1) pore-scale reactive flow in geochemically representative µ-models; and, 2) reactive flow patterns on core-scale using explicit CO₂ tracking with positron emission tomography. The CCS context of the research project will naturally focus on flow in CO₂ storage sites, but the research will also be highly relevant for groundwater flow, deposit of radioactive waste, oil recovery, and contamination in soils.