Subsurface Carbonate CO2 Storage and Security

The laboratory-based project focused on carbon sequestration in subsurface porous reservoirs. Most planned CCS project will use sandstone reservoirs to store the injected carbon dioxide, but sandstone only is one of several available rock types capable of storing CO2. Our project study CO2 injection in carbonate reservoirs, know to be reactive and susceptible to dissolution in the presence of CO2-acidified brines. Storage reservoir rock dissolution may undermine subsurface CO2 storage security, and more detailed knowledge of dissolution mechanisms and their impact of CO2 storage potential is needed. We report a range of laboratory-based findings by establishing a new pore-scale system to study fundamental pore-scale reactive transport dynamics. We identified new dissolution mechanisms and their influence on CO2 storage in carbonate systems, and study technologies to seal subsurface leakage pathways. An important development was to benchmark emerging imaging modalities for Darcy-scale porous media CCS research.

Prosjektet har utviklet nye eksperimentelle metoder for eksperimentelle studier på oppløsningsmekanisker under CO2 flyt i karbonatreservoarer, både på pore-skala og på kjerne-skala. Vi tror dette er viktige bidrag for tilsvarende fremtidig forskning.

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.