Hydrodynamic model of Los Humeros geothermal field, Mexico, based on geochemical, mineralogical and isotopic data

Abstract

The local basement of Los Humeros geothermal field is a Paleozoic metamorphic complex, a Mesozoic folded sedimentary sequence formed by chlorite-muscovite shales, lower Tertiary syenitic and granodioritic intrusions and Pliocene andesites. Based on pressure test logs in the central collapse area two geothermal reservoirs were recognized: A reservoir of low liquid saturation located at depth and a shallow (two phase) reservoir dominated by liquid clearly related to the hydrothermal mineralogy. Geochemical data confirm the presence of two aquifers: An upper, neutral pH aquifer with temperature around 280oC, and a deeper one with higher temperature. The chemical classification shows that waters are bicarbonate and chloride types. Mineralogical studies identified a zone of typical hydrothermal alteration, considered as high-rank low-intensity, and another zone where deep wells located in the central collapse zone show no alteration but high temperatures. The mineralogical evidence confirms the boundaries of the two reservoirs in the system. Isotopic results of C, H and O in fluids from producing wells and related natural springs were used to study the dynamics of the system. The data allowed a preliminary model to be postulated.