| Title | Field Experiments for Studying CO2 Mineral Trap at High Temperature at Ogachi, Japan |
|---|---|
| Authors | Hideshi Kaieda, Akira Ueda, Kenji Kubota, Hiroshi Wakahama, Saeko Mito, Kazunori Sugiyama, Akiko Ozawa, Yoshihiro Kuroda, Yoshikazu Kaji, Heigo Suzuki, Hisao Sato |
| Year | 2009 |
| Conference | Australian Geothermal Energy Conference |
| Keywords | CO2, Mineral trap, Geothermal, Calcite, Ogachi |
| Abstract | Previous experiments at Ogachi, up until 2007, generated two important results obtained by injecting CO2 dissolved water into a 1,100 m deep well, OGC-2 at Ogachi in Japan, for which the bottom-hole temperature was measured at about 210 degree C. One result was that Ca concentration of the CO2 dissolved (3 weight %) water, at a depth of 1,030 m in OGC-2, increased to a maximum of 85.2 mg/L in a few hours. The Ca was considered to be dissolved from rock. The second result was that calcite precipitation on calcite crystal samples was observed when the samples were held at depths of 850 m and 950 m for an hour in the CO2 dissolved water in OGC-2. In 2008, we reconfirmed that calcite precipitation occurred on calcite crystal samples at a depth of 950 m in OGC-2. From these results, we constructed a model for describing a CO2 mineral trap mechanism at high temperature. When CO2 is injected underground at high temperature four zones are created, one is a super critical CO2 zone, second is a dense CO2 dissolved water zone, third is a thin CO2 dissolved water zone, and fourth is a formation water zone. The CO2 dissolved water zones react with rock. Ca dissolves from rock in the dense CO2 dissolved water zone by high CO2 concentration (low pH) but in the thin CO2 dissolved zone (nearly neutral pH), by mixing with formation water, Ca precipitates as calcite minerals. |