Petrophysical characterization of the Los Humeros geothermal field (Mexico): from outcrop to parametrization of a 3D geological model

Abstract

The Los Humeros Volcanic Complex has been characterized as a suitable target for developing a super-hot geothermal system (> 350 °C). For the interpretation of geophysical data, the development and parametrization of numerical geological models, an extensive outcrop analogue study was performed to characterize all relevant key units from the basement to the cap rock regarding their petrophysical properties, mineralogy, and geochemistry. In total, 226 samples were collected and analyzed for petrophysical and thermophysical properties as well as sonic wave velocities and magnetic susceptibility. An extensive rock property database was created and more than 20 lithostratigraphic units and subunits with distinct properties were defined. Thereby, the basement rocks feature low matrix porosities (< 5%) and permeabilities (< 10–17 m2), but high thermal conductivities (2–5 W m−1 K−1) and diffusivities (≤ 4·10–6 m2s−1) as well as high sonic wave velocities (≥ 5800 m s−1). Basaltic to dacitic lavas feature matrix porosities and permeabilities in the range of < 2–30% and 10–18–10–14 m2, respectively, as well as intermediate to low thermal properties and sonic wave velocities. The pyroclastic rocks show the highest variability with respect to bulk density, matrix porosity (~ 4– > 60%) and permeability (10–18–10–13 m2), but feature overall very low thermal conductivities (< 0.5 W m−1 K−1) and sonic wave velocities (~ 1500–2400 m s−1). Specific heat capacity shows comparatively small variations throughout the dataset (~ 700–880 J kg−1 K−1), while magnetic susceptibility varies over more than four orders of magnitude showing formation-related trends (10–6–10–1 SI). By applying empirical correction functions, this study provides a full physiochemical characterization of the Los Humeros geothermal field and improves the understanding of the hydraulic and thermomechanical behavior of target formations in super-hot geothermal systems related to volcanic settings, the relationships between different rock properties, and their probability, whose understanding is crucial for the parametrization of 3D geological models.

The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)

“…In contrast to the outcrop samples, the reservoir samples show a higher parameter range and scattering (e.g., porosity: < 2% to > 30%, permeability: 10 -18 m 2 to 10 -14 m 2 , and thermal conductivity: 0.7 W m −1 K −1 to 2.7 W m −1 K −1 ). Results of the marbles and ignimbrites are well in line with measurements performed on outcrop samples collected from the Xáltipan ignimbrite and marbles from Las Minas (Weydt et al 2022). However, the ignimbrite core samples investigated in this study only represent the unwelded to partially welded upper section of the Xáltipan ignimbrite.…”

“…According to Cavazos-Álvarez et al (2020), the Xáltipan ignimbrite shows an increased degree of welding with reservoir depth alongside a porosity reduction. Therefore, porosity of the highly welded basal sections can be smaller than < 5% (Weydt et al 2022;Cavazos-Álvarez et al 2020).…”

“…However, even after more than 40 years of exploration, information on rock properties of the different geological units in the study area were scarce or not available. To overcome the lack of suitable data for economic assessments, numerical reservoir simulations, and the interpretation of geophysical surveys, an extensive outcrop analog study has been performed to characterize all relevant key units regarding their geochemistry, mineralogy, petrophysical, and mechanical rock properties (Weydt et al 2021a(Weydt et al , 2022.…”

Valgarður: a database of the petrophysical, mineralogical, and chemical properties of Icelandic rocks

“…Although the database is restricted to Iceland, we believe that the data contained in this database provide useful constraints on the petrophysical properties of basaltic rocks outside of Iceland. Similar relationships between alteration S. W. Scott et al: Valgarður: a database of the properties of Icelandic rocks type/extent and petrophysical properties have been observed in previous studies performed using altered volcanic rocks obtained from geothermal systems in New Zealand (Heap et al, 2017a;Mordensky et al, 2018;Villeneuve et al, 2019) and Mexico (Weydt et al, 2022). However, the limitations of the database should also be acknowledged.…”

“…Rock properties such as porosity and permeability reflect magmatic degassing, eruptive conditions, and environmental conditions related to tectonics, alteration, exhumation, and weathering (Petford, 2003;Ceryan et al, 2008;Pola et al, 2012Pola et al, , 2014Schön, 2015;Colombier et al, 2017;Villeneuve et al, 2019). Variability in the distribution of pore space, fractures, and minerals strongly influences the susceptibility of rock to hydrothermal alteration, which can produce strong changes in mechanical and physical properties (Browne, 1978;Thompson, 1997;Saripalli et al, 2001;Dobson et al, 2003;Cox, 2005;Franzson et al, 2008;Frolova et al, 2014;Siratovich et al, 2014;Wyering et al, 2014;Sanchez-Alfaro et al, 2016;Heap et al, 2017a;Mordensky et al, 2018;Cant et al, 2018;Navelot et al, 2018;Heap et al, 2020aHeap et al, , 2022aNicolas et al, 2020;Weydt et al, 2022). Due to the natural heterogeneity in rock properties, constraining the quantitative relationships between different petrophysical properties and inferring the underlying causes of variability may require extensive petrophysical and mineralogical databases amenable to statistical analysis (Aladejare and Wang, 2017;Asem and Gardoni, 2021).…”