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

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.