Reconstruction of different original water chemical compositions and estimation of reservoir temperature from mixed geothermal water using the method of integrated multicomponent geothermometry: A case study of the Gonghe Basin, northeastern Tibetan Plateau, China

The Gonghe geothermal field, northeastern Tibetan Plateau, China, is considered to be a potential target development area for Hot Dry Rock (HDR) resources, where the first Chinese Enhanced Geothermal System (EGS) research project is likely to be located. This area has formed typical layered geothermal reservoirs in a sedimentary basin with an anomalously high geothermal gradient (more than 55 degrees C/km), and the hydrothermal systems at different depths are connected by hidden faults. To investigate the geothermal structure and geo-chemical characteristics, water samples from the Gonghe geothermal field were collected and measured. The method of Integrated Multicomponent Geothermometry (IMG) was used to analyse the mixing processes and to estimate the reservoir temperatures. Due to significant differences in the Al and Mg concentrations between shallow and deep reservoirs, the IMG method, which uses measured and optimized values to reconstruct the composition of shallow and deep geothermal water, was successfully applied to constrain the mixing processes. This study predicted three typical geothermal reservoirs at different depths, and it quite accurately estimated the reservoir temperatures. The methodology of the present work can also be used in other geothermal fields with similar geological and geothermal conditions, to reconstruct the original deep and shallow water compositions from mixing processes, estimate reservoir temperatures, and build conceptual geothermal reservoir models.