Yale University and partners are investigating basic questions about the chemical and mechanical processes that must occur underground (Figure 1) for carbonation (the process by which CO2 reacts with minerals in the reservoir to form solid carbonates) of basaltic (mafic) and ultramafic rocks to be practical for large–scale geologic storage of CO2. Mafic and ultramafic rocks contain low levels of silica and high levels of calcium-rich minerals that react with CO2 to form solid carbonate minerals (Figure 2), thus permanently isolating it from the atmosphere. The research is determining whether in situ carbonate reactions generate fractures within the target reservoir (increasing overall formation permeability) or if the presence of CO2 and subsequent mineralization reduces injectivity by constricting the available pore space (reducing overall formation permeability).
This project is a multi-scale, interdisciplinary laboratory study with two main focus areas: (1) geochemical experiments related to carbonate mineralization reaction rates, with systematic research emphasis on the influence of variables including pressure, temperature, ionic activity, reaction surface area pH, and the extent of reaction; and (2) geomechanical experiments integrated with numerical modeling to study how the available pore space within the basaltic reservoir rocks evolves as the carbonation reaction proceeds. Geochemical testing is being conducted on a multi-scale level with initial micro-scale level testing of powdered minerals typically found in basaltic rocks followed by a macro-scale testing using rock samples. Macroscale geomechanical testing is focusing on interactions caused by CO2 injection into the pore-space available within the rock.
The overall goal of the Department of Energy’s (DOE) Carbon Storage Program is to develop and advance technologies that will significantly improve the effectiveness of geologic carbon storage, reduce the cost of implementation, and prepare for widespread commercial deployment between 2020 and 2030. Research conducted to develop these technologies will ensure safe and permanent storage of carbon dioxide (CO2) to reduce greenhouse gas (GHG) emissions without adversely affecting energy use or hindering economic growth.
Geologic carbon storage involves the injection of CO2 into underground formations that have the ability to securely contain the CO2 permanently. Technologies being developed for geologic carbon storage are focused on five storage types: oil and gas reservoirs, saline formations, unmineable coal seams, basalts, and organic-rich shales. Technologies being developed will work towards meeting carbon storage programmatic goals of (1) estimating CO2 storage capacity +/- 30 percent in geologic formations; (2) ensuring 99 percent storage permanence; (3) improving efficiency of storage operations; and (4) developing Best Practices Manuals. These technologies will lead to future CO2 management for coal-based electric power generating facilities and other industrial CO2 emitters by enabling the storage and utilization of CO2 in all storage types.
The DOE Carbon Storage Program encompasses five Technology Areas: (1) Geologic Storage and Simulation and Risk Assessment (GSRA), (2) Monitoring, Verification, Accounting (MVA) and Assessment, (3) CO2 Use and Re-Use, (4) Regional Carbon Sequestration Partnerships (RCSP), and (5) Focus Area for Sequestration Science. The first three Technology Areas comprise the Core Research and Development (R&D) that includes studies ranging from applied laboratory to pilot-scale research focused on developing new technologies and systems for GHG mitigation through carbon storage. This project is part of the Core R&D GSRA Technology Area and works to develop technologies and simulation tools to ensure secure geologic storage of CO2. It is critical that these technologies are available to aid in characterizing geologic formations before CO2- injection takes place in order to predict the CO2 storage resource and develop CO2 injection techniques that achieve optimal use of the pore space in the reservoir and avoid fracturing the confining zone (caprock). The program’s R&D strategy includes adapting and applying existing technologies that can be utilized in the next five years, while concurrently developing innovative and advanced technologies that will be deployed in the decade beyond. This study explores the effects of injecting CO2 into basaltic reservoir rock.
This research could lead to a greater understanding of the effects of CO2 injection into mafic/ultramafic rock reservoirs and allow for multi-phase modeling of multiple geomechanical parameters, which could lead to larger scale injectivity testing in the future. Mafic/ultramafic rocks are considered promising potential geologic CO2 storage formations due to their unique chemical makeup, which could potentially convert all of the CO2 injected into them to a solid mineral form and permanently isolate it from the atmosphere.
The ultimate benefit of this type of research is a better understanding of CO2 interactions within mafic and ultramafic rocks, in particular how carbonate formation affects CO2 injectivity and permeability within the rock reservoir. This research is contributing to the Carbon Storage Programmatic goals of estimating CO2 storage capacity +/- 30 percent in geologic formations and improving the efficiency of storage operation in basaltic formations. Successful storage of CO2 in these rocks would reduce its contribution to global warming by permanently removing it from the atmosphere.
The primary goal of this project is to determine the carbon storage potential of mafic and ultramafic rocks via in situ carbonate mineralization as described above. The specific goals include:
Conduct geomechanical experiments to determine how pore space of basalts and other mafic/ultramafic rocks evolves during carbonation reactions, especially in the competition between cracking and pore constriction and collapse (Figure 3).
Developing a multi-dimensional model using data gathered during the geochemical and geomechanical testing phases to achieve greater understanding of CO2 injectivity and pore space availability for larger scale field testing.
Supply data on the carbonation capacity of several important basaltic rock types in Hawaii to provide ground-truth constraints for a DOE-funded assessment of carbon dioxide sinks in Hawaii as part of Hawaii’s inclusion in the West Coast Regional Carbon Sequestration Partnership (WESTCARB).
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