| Abstract |
Avoiding hot spring interference by geothermal power development is strongly required for geothermal developments in Japan to avoid conflict with hot-spring owners and environmentalists. Since many hot springs in Japanese geothermal fields are used for bathing in the tourist industry, their opinions and those of the Environmental Agency cannot be ignored in geothermal power development. For predicting hot spring failures prior to committing to the construction of power plants, a method had been developed which is based on techniques used for geothermal resource exploration and reservoir engineering. In this study, verification of effectiveness of the method was conducted by comparing predicted results and monitoring data in various fields. The prediction method consists of studies in three steps. The first step is performed to assist in understanding the relationship between geothermal reservoirs and hot spring aquifers using a geothermal model which includes both the geological structure and the thermal structure. The purpose of the second step is the construction of a geothermal fluid-flow model which considers the origin of hot spring water. At this step, the connection of the hot spring aquifer with the geothermal reservoir is investigated using mainly chemical and isotopic analyses of fluid. If the models on geological and geothermal structures can be prepared with relatively high precision and the flow model of geothermal fluid is considered reliable, then the prediction of future changes in hot springs caused by geothermal power development is performed as a third step study using a reservoir simulator, based on these models. Changes in temperature and pressure of hot spring aquifers are calculated at this step, and, in some cases, changes in the concentration of non-reactive chemical components such as chloride ion etc. are also calculated. With consideration of the results from the above three steps and their errors, changes to hot springs are predicted all-inclusively and adequate monitoring methods for the hot springs are proposed. The method developed has been applied to several geothermal fields such as Beppu, Kirishima, Wairakei, Palinpinon and so on for the purpose of verifying its effectiveness. The Wairakei and Beppu fields are well-known as typical geothermal fields where significant changes to hot springs near geothermal development have been reported. Predictions using the above method were done using mainly existing data available prior to power plant operation. Predicted results agreed generally with the observed changes of the hot springs after commissioning the power plants in these fields. Consequently, the method was verified to be effective and useful. The method was also applied to the Kirishima field where the operation of geothermal power plant has not influenced the hot springs in and around the power plant. In this field, reasonable agreement between the predicted changes and measured ones were obtained, and the effectiveness of the method was also confirmed. |