In-situ Temperature Determination at the Villarrica Geothermal System, Southern Chile: Implications from Laboratory Experiments for Geothermometry

Abstract

Exploring a geothermal system the determination of reservoir temperatures is a major task. Unfavorably, the uncertainties of classical solute geothermometry are still large preventing reliable reservoir temperature estimations. In this study results of laboratory experiments are presented, equilibrating two reservoir rock analogues from the Villarrica area at 140 °C. These experiments clearly show the impact of reservoir rock composition on the fluid chemistry. In order to quantify and reduce the uncertainties of geothermometric methods, we assess the performance of classical geothermometers and multicomponent geothermometry with regard to different rock compositions, by applying them to the fluids derived from the alteration experiments as well as to fluids from natural geothermal springs in the Villarrica area. It is shown that differing rock mineralogy strongly affects calculated temperatures from classical solute geothermometry. Multicomponent geothermometry is obviously more robust leading to significantly smaller temperature spreads. The here presented data are first results of ongoing research of establishing an easy-to-use modification of the multicomponent geothermometric method on basis of limited fluid analysis. Although, calculated temperatures for the Villarrica area subsurface are therefore preliminary, the approach is apparently a step into the right direction.