| dc.description.abstract |
Seventeen samples from the Waesano geothermal area, Indonesia, have been interpreted to study the chemical characteristics, determine the type and origin of the waters, and estimate the reservoir temperature. In this study, Cl-SO4-CHO3, Li-ClB, and Na-K-Mg ternary diagrams, stable isotope ratios, geothermometers, and mixing models have been used to evaluate the results of the analysis of the samples. The results show that most of the samples plot as mature waters in the Cl-SO4-HCO3 ternary diagram, the samples appear to be in a partial equilibrium with the rock and apparently, they are associated with volcanism. Some samples show a δ18O isotope shift in a δD – δ18O diagram, meaning there is water-rock interaction. One sample, APWS-01, plots with a large δ18O shift. The Waesano geothermal water shows several characteristics of deep reservoir water such as a near-neutral pH, high salinity, high chloride, boron-rich composition, and a large δ18O isotopic shift of up to 5‰ from the meteoric water line in a δD – δ18O diagram. The Na-K geothermometer results give temperatures of 124-252°C. The temperatures obtained from log (Q/K) are 125-200°C, similar to the average for the Na-K geothermometer which is then interpreted as the reservoir temperature. The Na-K-Mg ternary diagram suggests a temperature in the range 160-265°C. Two types of mixing models have been applied to evaluate the temperature of the hot water component in the geothermal reservoir, the chloride-enthalpy model and the silica-enthalpy model. Together they indicate a reservoir temperature of 140-213°C. Based on four methods that have been used, a temperature in the range 200±70°C has been obtained, suggesting that the Waesano geothermal system is a medium temperature system. |
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