Columbia University researchers are performing field studies at the CarbFix CO2 geologic storage site in Iceland (Figure 1). This site is home to a pilot study where CO2 is being injected into a storage formation of basaltic rock. A field study is being used to test and evaluate the efficacy of using carbon-14 (14C) as a reactive tracer (a substance that is used to monitor chemical reactions) to monitor the CO2 transport and characterize CO2 geochemical reactions in the basalt formation. Furthermore, subsurface CO2 transport is being monitored with trifluormethylsulphur pentafluoride (SF5CF3) and sulfurhexafluoride (SF6) tracers. To date, water injection tests verified the injectivity of the formation, and small quantities of CO2 dissolved in water (on the order of several hundred tons) and tracers have been injected. The overall goal is to inject between 1500 and 2000 tons of CO2 dissolved in water.
Researchers are obtaining fluid and rock samples from the CarbFix site where the injected CO2 has been labeled with the 14C tracer. These samples will be analyzed to determine the extent of mineral carbonation (the process by which CO2 reacts with minerals in the reservoir to form solid carbonates) that occurs when CO2 is injected into a basaltic storage reservoir. To monitor the CO2 movement in the target injection reservoir, Columbia University is monitoring SF5CF3 and SF6 tracer concentrations in the storage reservoir by collecting fluid samples in the injection and monitoring wells. Fluid samples are being analyzed and the results are being used to characterize the CO2 dispersion in the basalt. Results are being integrated to assess the use of the tracers for determining reservoir flow and geochemical reactivity, and to assess in situ mineral carbonation in basalt storage formations.
Mineral carbonation is the most permanent storage mechanism as it locks CO2 into the solid structure of a mineral. Basalts are a promising reservoir rock because they have the potential for permanent storage through carbonation. However, mineral carbonation can affect the permeability of reservoir rock, reducing the amount of CO2 that can be injected and stored. It is therefore vital to characterize the relevant geochemical reactions that occur in a reservoir after the injection of CO2 and to improve our understanding of the rate at which these reactions occur. Little is known about geochemical reactions caused by CO2 injection and in situ mineral carbonation rates in basaltic storage reservoirs. The results of this research should increase our understanding of migration and carbonation processes in these potential reservoirs.
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 is exploring ways to monitor the fate of CO2 after it has been injected into a geologic formation to assure permanent trapping.
This research project is developing and testing the feasibility of 14C, SF5CF3, and SF6 as a reactive tracer for quantitative monitoring and accounting of geological CO2 storage. In particular, this project is helping to characterize the relevant geochemical reactions that occur in basalt storage reservoirs after the injection of CO2 as well as determining the rate at which these reactions occur. None of the currently applied CO2 monitoring approaches are able to provide a surveying tool for dissolved or chemically transformed CO2. The technology, when successfully demonstrated, will provide an improvement over current monitoring practices. This technology contributes to the Carbon Storage Programmatic goal of demonstrating 99 percent storage permanence.
The goal of this project is to demonstrate that 14C can be used as a reactive tracer to monitor geochemical reactions in a CO2 reservoir and to evaluate the extent of mineral trapping in basaltic rocks. 14C is being used in combination with SF5CF3 and SF6 as conservative tracers to monitor the CO2 transport in a storage reservoir and to verify in situ mineral carbonation using retrieved fluid and rock samples. This research is increasing confidence in geologic storage by providing actual validation that mineral carbonation is occurring in these types of reservoirs and by providing real world rate estimates for this process.
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