Sub- and Supercritical Geothermal Fluids Revealed by Hydrothermal Experiments

Abstract

Several kinds of hydrothermal experiments were carried out to understand water-rock interaction under sub- and supercritical conditions. Chemical reaction diversity was examined using batch and flow through type autoclaves. The supercritical region up to the critical point for water has been inferred to be a homogeneous state, which neither conforms to a true liquid phase nor a true vapor phase. In terms of dissolution of granite and quartz, the supercritical state, being artificially defined as higher pressures and temperatures of the critical point, can be subdivided into two apparent phases, comprising a ëliquid-likeí region and a ëvapor-likeí region.

The critical points of various kinds of geofluids, which were composed from solution in the H2O-CO2-X (NaCl) system, were experimentally determined in a visible-type autoclave with transparent sapphire windows. Chemical reaction diversity, depending on location of the critical point for a given solution and apparent phase boundary with respect to chemical reaction within the supercritical state, was recognized by hydrothermal experiments.

It was possible to measure IR spectra under supercritical condition by using high temperature-pressure cell, and characteristics of molecular structure of interfacial water revealed by IR spectra was changed by environmental conditions such as temperature, pressure and substrate.