Calculation of Geothermal Reservoir Temperatures and Steam Fractions from Gas Compositions

Abstract

This paper deals with the chemical equilibria and physical characteristics of the fluid in the reservoir (temperature, steam fraction with respect to total water, gas/steam ratio, redox conditions), which seem to be responsible for the observed concentrations of some reactive species found in the geothermal fluids (CO2, H2, H2S, and CH4). Gas geochemistry is of particular interest in vapor dominated fields where the fluid discharged consists of almost pure steam containing a limited number of volatile chemical species. Considering several geothermal systems, a good correlation has been obtained among the temperatures calculated from the gas geothermometers and the temperature measured in the reservoir or evaluated by other physical or chemical methods.