Geochemical characteristics of thermal fluid from the Xiaotangshang geothermal field, Beijing, China

Abstract

The Xiaotangshan geothermal field is a famous low-temperature geothermal field in China. Its geothermal resources have been utilized for a long time but utilization of hot water from boreholes began 25 years ago. The geothermal system consists basically of three reservoirs, Jx.w and Jx.t made of dolomite and the Cambrian system made of limestone. The present study indicates that the thermal water is of meteoric origin and its age, based on 14C dating, is approximately 24000 to 30000 years. The study shows that the chemical composition of waters from three monitoring wells has change very little during the time of exploitation. It is suggested that as long as the reservoirs are exploited at similar conditions as between 1987 and 1995, only minor chemical changes will occur. Because of relatively low temperature of the geothermal water and mixing with cold groundwater, the thermal fluid seems not to be in equilibrium with any hydrothermal minerals in the reservoirs, except for chalcedony. Geothermometer calculations show that one can expect the highest temperature, of approximately 80 °C, ...