Carbon capture and storage (CCS) provides a solution towards decarbonization of the 21global economy. The success of this solution depends on the ability to safely and 22 2 permanently store CO 2 . This study demonstrates for the first time the permanent 23 disposal of CO 2 as environmentally benign carbonate minerals in basaltic rocks. We 24 find that over 95% of the CO 2 injected into the CarbFix site in Iceland was mineralized 25 to carbonate minerals in less than two years. This result contrasts with the common 26 view that the immobilization of CO 2 as carbonate minerals within geologic reservoirs 27 takes several hundreds to thousands of years. Our results, therefore, demonstrate 28 that the safe long-term storage of anthropogenic CO 2 emissions through 29 mineralization can be far faster than previously postulated. 30 31The success of geologic CO 2 storage depends on its long-term security and public 32 acceptance in addition to regulatory, policy, and economical factors (1). CO 2 and brine 33 leakage through a confining system above the storage reservoir or through abandoned 34 wells is considered as one of the major challenges associated with geologic CO 2 storage 35 [e.g. (2, 3, 4)]. Leakage rates into the atmosphere of ≤0.1% are required to ensure 36 effective climate change mitigation [e.g. (5, 6)]. To avoid CO 2 leakage, caprock integrity 37 needs to be evaluated and monitored (7). Leakage risk is further enhanced by induced 38 seismicity, which may open fluid flow pathways in the caprock (8). Mineral 39 carbonatization (i.e. the conversion of CO 2 to carbonate minerals) via CO 2 -fluid-rock 40 reactions in the reservoir minimizes the risk of leakage and thus facilitates long-term 41 and safe carbon storage and public acceptance (9). The potential for carbonatization is, 42 however, limited in conventional CO 2 storage reservoirs such as deep saline aquifers, 43 and depleted oil and gas reservoirs in sedimentary basins due to the lack of calcium, 44 3 magnesium and iron rich silicate minerals required to form carbonate minerals (10, 11). 45An alternative is to inject CO 2 into basaltic rocks, which contain up to 25% by weight of 46 calcium, magnesium and iron. Basaltic rocks are highly reactive, and one of the most 47 common rock types on Earth, covering ~10% of continental surface area and most of the 48 ocean floor [e.g. (12, 13)]. 49 50The CarbFix pilot project was designed to promote and verify in situ CO 2 mineralization 51 in basaltic rocks for the permanent disposal of anthropogenic CO 2 emissions (14). Two 52 injection tests were performed at the CarbFix injection site near the Hellisheidi 53 geothermal power plant: Phase I: 175 tons of pure CO 2 from January to March 2012, and 54Phase II: 73 tons of a CO 2 -H 2 S gas mixture in June to August 2012, of which 55 tons were 55 CO 2 . Note that H 2 S is not only a major constituent of geothermal gases but also of CO 2 -56 rich sour gas. Since the cost of CCS is dominated by capture and gas separation, the 57 overall cost could be lowered substan...
Long-term security is critical to the success and public acceptance of geologic carbon storage.Much of the security risk associated with geologic carbon storage stems from CO 2 buoyancy.Gaseous and supercritical CO 2 are less dense than formation waters providing a driving force for it to escape back to the surface via fractures, or abandoned wells. This buoyancy can be eradicated by the dissolution of CO 2 into water prior to, or during its injection into the subsurface. Here we demonstrate the dissolution of CO 2 into water during its injection into basalts leading directly to its geologic solubility storage. This process was verified via the successful injection of over 175 tons of CO 2 dissolved in 5000 tons of water into porous rocks located 400-800 m below the surface at the Hellisheidi, Iceland CarbFix injection site.Although larger volumes are required for CO 2 storage via this method, because the dissolved CO 2 is no longer buoyant, the storage formation does not have to be as deep as for supercritical CO 2 and the cap rock integrity is less important. This increases the potential storage resource substantially compared to the current estimated storage potential of supercritical CO 2 .
CarbFix, a combined industrial‐academic pilot program, was developed in order to assess the feasibility of in situ CO2 mineral sequestration in basaltic rocks. Unique to CarbFix is its connection to the Hellisheidi geothermal power plant, allowing for capture of otherwise emitted CO2 in addition to CO2 transport and mineral sequestration.Extensive research has been conducted in order to characterize physical properties of the pilot injection site in Hellisheidi. Tracer tests have been carried out and continuous well‐logging confirmed separation of the target formation from shallower groundwater systems. Alteration mineralogy in natural analogs has been mapped out in order to predict which minerals are likely to precipitate upon CO2 injection. In addition to carbonates, these include clays, zeolites, and poorly crystalline hydroxides. Some of the secondary minerals will compete with carbonates for cations dissolved from the rock matrix.Numerical modeling plays an important role in the CarbFix project as it provides tools to predict and optimize long‐term management of the injection site as well as to quantify the amount of CO2 that can be mineralized. A reactive transport model has been developed and numerical simulations of the pilot CO2 injection are ongoing. Extensive monitoring provides the basis for testing, validating, and calibrating reactive transport models.It is anticipated that the results of CarbFix will be used to optimize the in situ carbon mineralization process, enabling it in basalt and ultramafic rock formations throughout the world. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd
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