Hydrogeochemical characteristics of Gaoyang geothermal field in central Hebei Depression and its constraint on geothermal genesis

This paper is the result of geothermal exploration engineering.

Objective Gaoyang geothermal field rich in low−medium temperature geothermal resources. Hydrogeochemical research of geothermal fluids is an effective method to understand the processes of deep geothermal water circulation and to reveal the genesis mechanism of geothermal systems.

Methods Through analyzing hydrochemical and isotopic data of geothermal water samples in Gaoyang field, we can explore the formation and development process of deep geothermal water.

Results The hydrochemical type of carbonate reservoirs is Cl–Na type, and that of sandstones reservoirs is HCO₃·Cl–Na and Cl·HCO₃–Na type. The ionic components in geothermal water are mainly controlled by the dissolution of salt rock and carbonate rock and the alternating adsorption of cations. Geothermal water is recharged from precipitation in the Taihang and Yanshan mountains, The recharge elevation of geothermal water is 759.12~1092.33 m. The geothermal reservoirs temperature of Jxw is 102~154℃, and the depth of thermal cycle is 2524~4020 m; the geothermal reservoirs temperature of Ng is 61~84℃, and the depth of thermal cycle is 1357~2024 m.

Conclusions In Gaoyang geothermal field, the γNa⁺/γCl^– of samples from the Jxw reservoirs is smaller than that Ng reservoirs, and the γSO₄^2–/γCl^– and γCl^–/(γHCO₃^–+CO₃^2–) are larger than that of the Ng reservoirs. This indicates that Jxw reservoirs has a higher degree of metamorphism, better confinement, slower geothermal water circulation and higher degree of salinization than the Ng reservoirs. The heat from the deep thermal storage is partly transferred upward by thermal convection through hot water along the fault channels, and partly transferred upward by thermal conduction through rocks, forming a convection−conduction type geothermal system.