| Title | Multivariate Analysis for Chemical Evolution of Reservoir Water for 35-year Operation of the Onikobe Geothermal Plant, Japan |
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| Authors | Shuji Ajima, Norifumi Todaka and Chitoshi Akasaka |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Multivariate analysis, Mixing processes, Reinjection water, Onikobe geothermal power station |
| Abstract | The Onikobe geothermal power station located in northern part of Japan has been operating for 35 years since 1975. The chemical characteristics of the Onikobe geothermal fluids are classified into two distinct types; neutral fluid with low concentration of chloride and acid fluid with high concentration of chloride. Complex chemical changes of production waters have been caused by 35 years operation of the Onikobe geothermal power station. Multivariate analysis was performed to understand mixing of reinjection water with original reservoir water and influence of reinjection water during the plant operation. Seven components of Na, K, Ca, Mg, Cl, SO4 and pH of 370 fluid samples were used for the analysis. As a result, change of the principal component score of production water has some relationship to the reinjection history. It means that the changes in mixing ratios of reinjection and reservoir waters and the connectivity between reinjection and production wells. It applied that the analysis could be used as tracer test. Multivariate analysis is useful to understand mixing processes in the Onikobe reservoir due to disturbances of production and reinjection. |