CarbFix I: Rapid CO2 mineralization in basalt for permanent carbon storage

Thursday, 17 December 2015
Poster Hall (Moscone South)
Juerg Matter1,2, Martin Stute3, Sandra Snæbjörnsdóttir4, Sigurður R Gíslason4, Eric H Oelkers5, Bergur Sigfússon6, Ingvi Gunnarsson6, Edda S Aradottir6, Einar Gunnlaugsson6 and Wallace S Broecker2, (1)University of Southampton, Southampton, United Kingdom, (2)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (3)Barnard College, New York, NY, United States, (4)University of Iceland, Reykjavik, Iceland, (5)CNRS, Toulouse, France, (6)Reykjavik Energy, Reykjavik, Iceland
Carbon dioxide mineralization via CO2-fluid-rock reactions provides the most permanent solution for geologic CO2 storage. Basalts, onshore or offshore, have the potential to store million metric tons of CO2 as (Ca, Mg, Fe) carbonates [1, 2]. However, as of today it was unclear how fast CO2 is converted to carbonate minerals in-situ in a basalt storage reservoir. The CarbFix I project in Iceland was designed to verify in-situ CO2 mineralization in basaltic rocks. Two injection tests were performed at the CarbFix I pilot injection site near the Hellisheidi geothermal power plant in 2012. 175 tons of pure CO2 and 73 tons of a CO2+H2S mixture were injection from January to March 2012 and in June 2013, respectively. The gases were injected fully dissolved in groundwater into a permeable basalt formation between 400 and 800 m depth using a novel CO2 injection system. Using conservative (SF6, SF5CF3) and reactive (14C) tracers, we quantitatively monitor and detect dissolved and chemically transformed CO2. Tracer breakthrough curves obtained from the first monitoring well indicate that the injected solution arrived in a fast short pulse and a late broad peak. Ratios of 14C/SF6, 14C/SF5CF3 or DIC/SF6 and DIC/SF5CF3 are significantly lower in the monitoring well compared to the injection well, indicating that the injected dissolved CO2 reacted. Mass balance calculations using the tracer data reveal that >95% of the injected CO2 has been mineralized over a period of two years. Evidence of carbonate precipitation has been found in core samples that were collected from the storage reservoir using wireline core drilling as well as in and on the submersible pump in the monitoring well. Results from the core analysis will be presented with emphasis on the CO2 mineralization.

[1] McGrail et al. (2006) JGR 111, B12201; [2] Goldberg et al. (2008) PNAS 105(29), 9920-9925.