Evaluation of the Storage Characteristics and Circulation Model of the Low- and Middle-temperature Geothermal Reservoir in Guangzhong Basin by Using the Data of Hydrogen-oxygen Stable Isotopes

Abstract

Guangzhong Basin is the typical geopressured-type low and middle-temperature geothermal field in the west of China. The hydrogen and oxygen isotope characteristics have some implications for the storage characteristics and circulation model of geothermal resources in this basin. This paper divides the study area into six tectonic units and conducts the systematic analysis of 121 sets of hydrogen-oxygen isotope data. The hydrogen-oxygen isotopes throughout Guangzhong Basin show a trend of gradual increase from the basin’s peripheral areas to the basin center. For the recharge of groundwater, with Weihe Fault as a border, the area to the south is the piedmont geothermal system of Qinling Mountains, and the area to the north is the piedmont geothermal system of North Mountains. When the geothermal water is recharged through atmospheric precipitation, the atmospheric temperature is about 0.2-1.8℃. The main factors that affect the geothermal water δ18O drifting in Guangzhong Basin include depth of geothermal reservoir and temperature at well heads, and also lithological characteristics, water-rock interaction, geothermal reservoir environment, and residence time. The δ18O-δD relation shows that the main source of geothermal water in the basin is the atmospheric precipitation, together with some sedimentary water, but there was no deep primary magmatic water and mantle water. If the distribution principle of hydrogen-oxygen isotopes is examined, the groundwater circulation model of this basin can be divided into open circulation type, semi-open type, closed type and sedimentary type, which offers some insights for the rational exploitation of geothermal resources.