Hydrothermal Mineralogy as a Tool to Define the Thermal Aquifer of Los Humeros Geothermal Field, Mexico

Abstract

An interpretation of the hydrothermal mineralogy in the Los Humeros geothermal field has provided information on water-rock ratios prevailing in the reservoir before the start of commercial exploitation. It was found that the intensity of the hydrothermal alteration varies according to the liquid fraction present in the reservoir, which depends mainly on fluid recharge, temperature and the rock permeability. Rock samples collected from deep from wells drilled in the Colapso Central area show low alteration intensity. This part of the field is close to the local basement where the highest temperatures have been measured. Little or no deep fluid recharge is the cause of the low intensity of rock alteration in this area. The intensity of hydrothermal alteration indicates that in some parts of Los Humeros there is a single geothermal reservoir hosted in andesitic rocks; while in the Colapso Central area the degree of alteration distinguishes two producing zones in the andesites, one with high liquid saturation and one with low liquid saturation. Based on mineralogical data the existence of an acid reservoir in the geothermal field is rejected.