Interpretation of chemical composition of geothermal fluids from Árskógsströnd, Dalvík, and Hrísey, N-Iceland and in the Khangai area, Mongolia

Abstract

Data from four production wells in three low-temperature geothermal fields, Árskógsströnd, Dalvík and Hrísey in N-Iceland and 7 hot springs in the Khangai low-temperature geothermal area in Mongolia are presented. The chemical composition of these fluids was analysed by standard methods. The ternary Cl-SO4-HCO3 scheme was used to classify the geothermal fluids with respect to major anion composition and the ternary Na-K-Mg diagram was used to classify waters according to the state of equilibrium at given temperatures. The geothermal fluids of Árskógsströnd and Dalvík are of bicarbonate-sodium water type and the geothermal fluid of Hrísey is of sodium-chloride water type. The hot springs in the Khangai area are of bicarbonate-sodium water type except the Shivert hot spring, which is of sulfate-sodium type. Chemical geothermometers were used to estimate reservoir temperatures. Values for chalcedony geothermometer and Na/K geothermometer values are quite different. Mixing models were used to try to define the source temperature of the geothermal fluid component. The Ryznar stability index (RSI) and WATCH programs were used to interpret the equilibrium state of the reservoirs and to predict calcite scaling tendencies. The Hrísey geothermal fluid (HR-10) has a slight tendency for scaling, but this is not the case for the other geothermal fluids considered here.