3D Electrical Resistivity Distribution in Los Humeros and Acoculco Geothermal Zones, Mexico

Abstract

Summary The Los Humeros geothermal field and the Acoculco geothermal prospect in Mexico are identified as two key locations to advance the understanding of unconventional geothermal resources. In the Los Humeros geothermal field, temperatures higher than 400C have been found, being a suitable case study of a super-hot system. In Acoculco area, there are two exploratory holes with temperature of 300C at 2000m depth with practically null permeability. Hence, representing an interesting case to develop an Enhanced Geothermal System (EGS). Both areas were study subjects in the project “Mexico-Europe Cooperation to investigate improved geothermal systems and super-hot geothermal systems” (GEMex). We conduct magnetotelluric (MT) surveys in both areas to provide information on the electrical resistivity distribution at depth. We measured 123 MT sites in Los Humeros and 68 in Acoculco. The observation sites were distributed with a high spatial density to provide well-constrained resistivity models. The models clearly detect a conductive zone between 500 and 1000m deep associated with a clay zone of hydrothermal alteration. In Los Humeros the clay-cap overlies an intermediate resistivity zone probably related to the reservoir. At Acoculco, the resistivity increases rapidly beneath the clay-cap, in agreement with the presence of impermeable metamorphic rocks.