A study of the hydrochemical characteristics and geothermal water of typical granite geothermal reservoir in the Jiaodong area

Abstract

Zhaoyuan is located in Jiaodong uplift zone. Proterozoic altered granites are widely distributed. The trace elements are enriched in geothermal fields. In order to ascertain the occurrence conditions of the trace components, the granite geothermal reservoir and geothermal resources. We use hydrochemical analysis, reservoir temperature analysis and effective energy conversion methods, establish Gibbs model, PHREEQC model, reservoir estimation, and obtain the occurrence conditions and reservoir environment of trace components of thermal water. The results show that (1) Zhaoyuan geothermal water, similar to seawater, is Cl—Na type. The total dissolved solids (TDS) of geothermal water ranges from 1359.7 mg/L to 5302.0 mg/L, and the mass concentrations of strontium, bromine and metasilicic acid are 26.20, 7.50 and 88.00 mg/L, respectively, which exceed the national medical thermal mineral water quality standards. (2) The Linglong granite in the northeast of the geothermal field has high strontium content, ranging from 334 mg/kg to 1 805 mg/kg, which is an important source of strontium. (3) The reservoir temperature of geothermal field is between 107 °C and 215 °C, and the mixing proportion of cold water is between 33.6% and 58.9% calculated from silicon enthalpy diagram. The calculation results indicate that available energy is 19.73 TJ/a, 5479.57 MW·h and 471.16 toe between 40 and 60 °C. The total available energy is 301.57 TJ/a, 83771.53 MW·h, and 7203.06 toe over 60 °C. The trace components come from lixiviation between strontium-rich granite surrounding rock and groundwater. The enrichment process of trace elements is affected by geothermal reservoir. This study may provide a better understanding of the characteristics of geothermal water in the granite thermal reservoirs, and enrich and promote the theory of geothermal water-rock interactions.

Keywords

• geothermal water
• trace components
• reservoir temperature
• geothermal energy
• water-rock interaction