| Title | CO2 Sequestration into Hydrothermal System at Ogachi HDR Site |
|---|---|
| Authors | A.Ueda, Y.Kuroda, K.Sugiyama, A.Ozawa, H.Kaieda, Y.Kaji, S.Mito and H.Wakahama |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | CO2 georeactor sequestration calcite |
| Abstract | Field experiments of CO2 sequestration in the Ogachi hot dry rock (HDR) site with a temperature of 200°C were performed to investigate the mineralization of CO2 as carbonates through interaction with rocks (Georeactor  Ca extraction from rocks and carbonate fixation). In 2007, carbonated water (1 wt% CO2  river water with dry ice) was directly injected into well OGC-2 during Test #1 (September 2-9) and Test #2 (September 11-16). Several tracers were also injected simultaneously. Water samples were collected at the depth of about 850m by a sampler (500ml in volume) and monitored for their chemical and isotopic compositions. During Test #2, river water was injected into OGC-1 2 days after the injection of CO2 water into OGC-2. The CO2 concentrations in fluids collected decreased with duration time and were almost 2/3 of the expected concentration from the behavior of tracers. This provided evidence that CO2 injected into well OGC-2 can be removed from fluid by carbonate fixation. During the field experiments, the dissolution and precipitation rates of calcite were determined using a technique of “in site analyses.” Calcite crystals covered with Au film were held in a crystal cell and set in a crystal sonde. The crystal sonde was then put into well OGC-2, and water samples were introduced into the sonde at the specified depth. After 1 hour, the sonde was recovered and the calcite crystals were observed using a newly developed phase shift interferometer to analyze the dissolution and precipitation rates of calcite in relation to the reservoir fluids. The “in situ analyses” show that calcite precipitation was observed within 2 days of the injection. This supports the view that a majority of injected CO2 might be fixed as carbonate. |