We have conducted some field experiments to study CO2 sequestration in solid minerals by injecting CO2 dissolved water into a high temperature borehole, OGC-2, at the Ogachi Hot Dry Rock geothermal site in Japan. OGC-2 was drilled into granitic rock to a depth of 1,100 m and the bottom-hole temperature was measured around 210 degree C.

Ca concentration of the water sampled at 1,030 m depth in OGC-2 increased to a maximum of 85.2 mg/L in a few hours after CO2 dissolved water (3 weight %) injection. Then the Ca concentration decreased in a few days. The Ca concentration increase was considered that Ca was supplied from Ca-feldspar in granitic rock by chemical reaction of the injected CO2 dissolved water with the rock.

Calcite precipitation on calcite crystals was observed when the crystal samples were suspended in CO2 dissolved water at 850 m in OGC-2. Calcite precipitation rate on calcite crystals was measured a maximum of 1 micro meters per an hour in CO2 dissolved water at a temperature of around 210 degree C. This supports the view that injected CO2 might be fixed as carbonate minerals.

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