Isotopic Study of Well Fluids from the Los Humeros Geothermal Field, Mexico

Abstract

Isotopic data of well fluids from the Los Humeros geothermal field were interpreted. Twenty wells were monitored during 1994-1996 in order to study the reservoir behavior as a result of exploitation. Isotope composition ranges between -8 and -1 ë for oxygen-18, and -75 and -55 ë for deuterium. Isotopic patterns suggest the occurrence of a mixing process between reservoir and reinjection fluids since a linear (deuterium vs oxygen-18) tendency with positive slope was found. The reservoir fluid for well H-7 (sampled June 1996) was found to be the lightest extreme of the relationship, while the reinjection fluid composition constituted the most enriched component. The relationship between geothermal fluids and "andesitic waters" suggests that reservoir fluids contain more than 40% of this component.