Review and Update of the Main Features of the Los Humeros Geothermal Field, Mexico

Abstract

Los Humeros is one of the four geothermal fields currently producing electricity in Mexico. This paper presents a review on the main geologic, geochemical and production characteristics of the field and updates them, considering the imminent construction of new production wells for installing an additional power unit. Those characteristics can be summarized as follows. At the subsurface there are four lithologic units, the third of which, composed of Tertiary andesites 1,200 m thick in average, contains the geothermal fluids. These fluids are mainly composed of steam with minor amount of low-salinity water of sodium-chloride to bicarbonate-sulfated type and oversaturated in silica and calcite. Instead of two different reservoirs, as previously proposed, the geothermal system seems to be a single reservoir with several feeding zones and subject to recurrent processes of self-sealing and hydro micro-fracturing. The hydrothermal mineralogy found in the subsurface seems to form three distinct zones: zeolites, epidote and amphiboles with respectively increasing temperatures. The most profitable areas are the Colapso Central and the corridor between the Antigua and Maztaloya faults. Production from deep zones in wells at the Colapso Central has provoked problems of corrosion and scaling in the past, and so these zones have been avoided in the last 15 years. For the new wells it is recommendable, however, try to exploit these deep zones, taking measures to prevent those problems, in order to get a better production of steam.