| Title | Geochemical Reservoir Exploration and Temperature Determination at the Mt. Villarrica Geothermal System, Chile. |
|---|---|
| Authors | Nitschke, F; Held, S; Villalon, I; Mundhenk, N; Kohl, T; Neumann, T |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | water-rock interaction, geothermometer, batch experiments, geochemical exploration |
| Abstract | Chile has a huge potential for the utilization of geothermal energy that is mostly associated with active volcanism. This resource has remained largely untapped so far but efforts on geothermal exploration have been increased recently. In the vicinity of Mt. Villarrica a variety of hot natural springs occur which manifest a complex geothermal system, which is rather poorly described. Identifying the reservoir rock and its associated thermal and hydraulic properties is a main task in the early stage of geothermal exploration. By having no reliable knowledge about in-situ conditions (i.e. borehole data etc.), the approach of this study is the indirect reservoir rock identification from the chemical composition of hot springs. The rock alteration processes should leave a ubiquitous footprint within the fluid, which should enable a source rock deduction. Therefore batch experiments at 140 °C, which is the assumed reservoir temperature indicated by HSO4 -- H2O oxygen isotope geothermometry on field data, were performed leaching two analogues which were presumed to be most likely the source rocks. Evolving chemical water composition was analyzed in dependence from elapsed reaction time. After reaching a chemical steady state, which is also assumed in terms of on-site reservoir conditions, water compositions were compared to natural geothermal waters to deduce the reservoir rock for each spring. Furthermore on the basis of this definite temperature laboratory data geothermometer estimations for natural springs were revaluated. It is shown that the validity of derived temperatures has to be assessed very cautiously. An extensive knowledge about mineral assemblage and associated rock-water interaction processes is a prerequisite for a valid application of geothermometers. |