Multicomponent geothermometry

Person in charge: Lars Yström

For successful geothermal exploration, the temperature estimation of the reservoir is important. The use of conventional solute geothermometers (SiO2, Na-K, Mg-K, etc.) often leads to large variation in reservoir temperature estimation. Therefore, a statistical approach in multicomponent geothermometry is developed to optimise the estimated temperatures. The method is based on the solubility of multiple mineral phases utilised as geothermometers. The multicomponent geothermometer is validated by comparing its results to measured borehole temperatures. Reservoir-specific mineral sets are developed for main geothermal sites. The reservoir temperatures can be inferred from the state of equilibrium (saturation index) of the mineral phases of the site-specific mineral assemblage. Thus, an automated tool called “MulT_predict” was programed. The tool is coupling MATLAB with IPHREEQC. During the calculation of the saturation indices, sensitive parameters are optimised (redox potential, pH value, aluminium concentration, and dilution factor). The result is a minimisation of the range of the temperature estimation. The modelled reservoir temperatures are in agreement with the in-situ temperature measurements. The application of "MulT_predict" provides a precise reservoir temperature estimation while being quick and easy‑to‑handle.

Output-data of MulT_predict. Saturation curves of mineral phases (upper left), the global minimum (upper right), statistical evaluation of the spread in temperature distribution (down left), and the temperature estimation box plot (down right).

Results of geothermal wells in Krafla, Iceland. Comparison of an unspecific mineral set to a basaltic set and its optimisation.