| Abstract |
The Los Humeros (LH) geothermal system is steam dominated and has been exploited since the 1990’s with 65 wellbores (23 still producing). With temperatures above 380 °C, the system is characterized as a super-hot geothermal system. The geothermal system in Acoculco (AC, presently consisting of two exploration wells) is characterized by temperatures of approximately 300 °C at a depth of about 2 km. It contains almost no fluids, even though a fracture network exists. Therefore the system serves as a demonstration site for the development of an enhanced geothermal system. For better reservoir understanding and prospective modeling, extensive geological, geochemical, geophysical and technical investigations are performed within the scope of the GEMex project (EU-H2020, GA Nr. 727550). Relatively little is known about the petro- and thermophysical rock properties in the study area. However, this data is critical for i) processing and interpreting geophysical data and ii) parameterizing reservoir models. Therefore, outcrop analogue and reservoir sample studies have been carried out in order to define and characterize all key units from the basement to the cap rock. Thus to identify geological heterogeneities on different scales (outcrop analysis, representative rock samples, thin sections and chemical analysis) enabling reservoir property prediction. More than 300 rock samples were taken from representative outcrops inside of the LH and AC calderas, the surrounding areas and from exhumed ‘fossil systems’ in Las Minas and Zacatlán. Additionally, 66 core samples from 16 wells of the LH geothermal field were obtained. Samples were analyzed for density, porosity, permeability, thermal conductivity, thermal diffusivity, heat capacity, as well as ultra-sonic wave velocities and magnetic susceptibility. Detailed complementary thin section analysis combined with XRD and XRF measurements provide information about the mineral assemblage, geochemistry and the intensity of hydrothermal alteration. Based on the outcrops and petrological analysis, the unit’s geological heterogeneity, which controls the rock properties, can be addressed. An extensive rock property database was created comprising more than 34 parameters analyzed on more than 2160 plugs altogether. Based on statistical analysis (geostatistical analysis and stochastic modeling approaches) different thermofacies-units were identified to define geothermal model units of future TH(M) 3D models. |