Investigating Suitable Geochemical Tracers for Monitoring CO2 Sequestration in Offshore Deep-Sea Basalt in the Cascadia Basin




Louis, Emma

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Carbon dioxide concentrations in the atmosphere have drastically increased due to human activities, causing accelerating climate change. Carbon dioxide (CO2) removal technologies are now deemed essential to aid in reaching international climate goals to limit further global surface temperature increase. As deep-sea basalt has significant potential to permanently sequester enormous quantities of CO2 but has never been tested, an investigation into monitoring this process was carried out with an emphasis on the use of geochemical tracers to verify the success of CO2 sequestration into deep-sea basalt as part of the Solid Carbon feasibility study. In basalt, CO2 that would otherwise be released into the atmosphere is sequestered through chemically binding the injected CO2 to form carbonate minerals in the pore spaces of the basalt. This research investigates geochemical tracers typically used in hydrogeologic and carbon capture and storage studies to determine their suitability at the temperature and pressure conditions within the basaltic crust in the Cascadia Basin. The most suitable conservative tracer for the planned CO2 injection experiment is SF5CF3, for verifying CO2-rich fluid breakthrough and determining fluid velocities and rates of dilution. The most suitable reactive tracer is concluded to be stable carbon isotopes, for confirming carbon has been removed from formation fluids through precipitation of carbonate minerals. Fluid samples collected before, during, and after injection with long-term osmotically pumped fluid sampling systems and mobile pumping systems could be used to analyze tracer concentrations, in addition to analyzing alkalinity, pH, dissolved inorganic carbon, and major ion and trace element concentrations to inform geochemical changes occurring in-situ in the deep-sea basaltic aquifer. A variety of measurements from sensors connected to the NEPTUNE cabled observatory were also evaluated to collect geochemical data in real time. Finding suitable tracers and geochemical monitoring parameters for the in-situ conditions in deep-sea basaltic crust is necessary for interpreting geochemical changes due to CO2 injection. The monitoring parameters outlined in this research may be useful in future offshore deep-sea basalt CO2 injection scenarios with more understanding of tracer behavior in supercritical CO2/water systems under high pressures and temperatures.



Geochemical Tracers, Cascadia Basin, Geologic CO2 Sequestration, Monitoring CO2 Sequestration, CO2 Sequestration in Basalt