| Abstract |
The Xiaotangshan geothermal field in Beijing, as one of the earliest explored low-temperature geothermal field in China, has been exploited for about 30 years and the reservoir pressure has declined with the increasing production rate. For the sustainable development of geothermal field, it is necessary to analyze its long-term exploitation stability. The changes of isotopic and chemical compositions in geothermal water have been employed to analyze the exploitation condition. By comparing the changes of chemical compositions in geothermal water between the natural state and the production period, it was found that the concentration of Ca2+, Mg2+ and HCO3 - were increasing while K+, Na+, Cl-, SO4 2- and TDS were decreasing after geothermal field development began. The concentration of chemical compositions in geothermal water monitored at wells throughout 3 years shows a linear relation with the monthly production rate. Also, the content of deuterium, oxygen-18 and tritium in geothermal water changes with the reservoir pressure and well production. It suggested that the recharge process of geothermal field had been changed and the cold groundwater entered the reservoir. The reservoir temperature given by geothermometer decreased due to intense production although there was no monitored temperature change at wellhead. The geothermal field seems to have been depleting. For the long-term exploitation, the present production rate should be reduced for geothermal recover. |