CONSTRAINING MULTICOMPONENT EQUILIBRIUM GEOTHERMOMETER TEMPERATURE ESTIMATES USING LABORATORY EXPERIMENTS: PRELIMINARY RESULTS

More accurate chemical geothermometers can potentially decrease economic risk associated with geothermal prospecting by providing more reliable temperature estimates. However, when applying the suite of traditional geothermometers, diverse temperature estimates result because 1) each geothermometer utilize only a subset of the available water chemical composition data, and 2) they do not explicitly account for many composition altering physicochemical processes along its flow path. Multicomponent equilibrium geothermometry (MEG) has an advantage over traditional geothermometers in its ability to use a complete chemical analysis of a water sample for temperature prediction. Nevertheless, the uncertainty associated with MEG estimated temperature relies in part on a correct understanding of mineral-water interactions occurring at depth in reservoir and proper quantification of composition altering processes along its flow path. Laboratory experiments simulating reservoir conditions (e.g., T and P) is one approach for understanding mineral-water interactions and quantifying composition altering processes occurring during fluid migration. As part of project to develop approaches for MEG, we are conducting a series of water-rock interaction experiments at 200-250 ºC using 1-liter stirred Parr bench-top reactors. Representative reservoir rock samples from Raft River Geothermal area in Idaho were crushed to different grain-sized fractions and reacted separately with synthetic geothermal fluids for > 2 months. Fluid samples were extracted at different times to evaluate the chemical evolution of system and to test the accuracy and uncertainty in temperature estimates with MEG. Preliminary results based on water compositions in association with likely mineral assemblage in these experiments demonstrate that with the increasing extent of reaction over time, the temperatures estimated with MEG approach the experimental temperature with decreasing uncertainty. Additional experiments with the goal of simulating some of the composition altering chemical and physical processes are planned. We expect that these water-rock interaction experiments simulating reservoir and flow path processes will allow us to constrain MEG temperature estimates with reduced and quantifiable uncertainty.