Analysis of Experimental Variables during Water-Rock Interaction Experiments for Solute Geothermometer Calibration

Abstract

An extensive world-wide compilation of geothermal fluid compositions demonstrated an important lack of hydrogeochemical data below 200ºC. These data revealed to be essential for a correct statistical evaluation of the linear regression between temperature and elemental concentrations when proposing new solute geothermometers. In order to shed some light on the fluid composition in this temperature range, water-rock interaction studies are being performed using batch reactors at 25, 90, and 150ºC. However, we have considered necessary to analyze with detail the variables involved in water-rock interaction in different experimental system conditions in order to obtain the best control in the experiment. In this work we present an analysis of the most important experimental variables to take into account during water-rock interaction experiments. These variables are: (1) temperature, (2) experimental system; (3) water/rock ratio, (4) rock grain size, (5) fluid and rock initial compositions, (6) sampling techniques and (7) reaction time. Among these, temperature and reaction time seem to be the most important ones. Reaction times longer than 4000 hours are needed to perform water/rock interaction experiments at temperatures < 200°C.