2nd GEMex Side-event

GEMex researchers will present their results during the European Geothermal Workshop on 9-10 October 2019 in Karlsruhe, Germany.

GEMex researchers are invited to present their results during the EGW on:

  • Results from geological, geochemical and geophysical investigations in Los Humeros and Acoculco, Mexico

  • Results from geological, temperature and reservoir modelling

  • Results from technology development for super hot geothermal reservoirs

More info on this event here

Characterising the influence of pre-existing structures on caldera evolution by analogue modelling

Marco Bonini, Giacomo Corti, Daniele Maestrelli, Domenico Montanari, Giovanna Moratti

GEMex researchers investigate the interplay between tectonics and magmatic processes in shaping volcanic edifices, focusing on specific volcano-tectonic issues that may be relevant for the exploration of the Los Humeros geothermal field. This study is been carried out through analogue modelling, which is an experimental technique that allows to study geological processes in the laboratory by analysing scaled physical models, built and deformed at reduced geometrical and temporal scales. Given the structural setting of the study area, scientists initially focused their activity on the collapse of calderas and volcanic edifices, and the associated surface and subsurface deformation pattern. Based on GEMex geologists’ observations that the pre-volcanic basement is affected by regional NE-ENE and NW trending fault systems, the researchers developed a series of analogue models exploring the role of pre-existing structures on caldera collapse.

The analogue models have shown that pre-existing discontinuities could strongly control caldera evolution. Various combinations among one or two fault-controlled straight sides in the magma chamber and discontinuities in the overlying brittle overburden have been considered in the modelling. The resulting structural patterns are complicated and differ significantly from a ‘standard’ evolutionary model of collapse over a symmetric (i.e., circular) reservoir. For example, a vertical discontinuity in the overburden forces the caldera to develop a straight side (Figure). This is similar to what is observed in several calderas worldwide including in Los Humeros. Deformation of models has been monitored through laser scanning and photographs, which have been used to implement PIV (Particle Image Velocimetry) analysis of model surface.

Figure: Analogue model investigating the effect of a magmatic chamber with a rectilinear side, mimicking a pre-existing fault. (a) 3D view and (b) top view of a collapsed caldera model. In this specific case, the discontinuity is also present in the brittle overburden above the rectilinear side of the analogue magmatic chamber. (c) Cross section AB of the model (trace of cross section AB is shown in “b”).

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Acoculco

The site at Acoculco, foreseen for EGS development, has been explored by two deep wells drilled by the CFE (Comisión Federal de Electricidad). These wells found hardly any fluids but temperatures around 300°C at a depth of 2 km. The lack of fluids at depth is surprising, as this area of Mexico is subject to abundant precipitation. Nonetheless, the high temperature gradient makes it an interesting target for exploitation and the lack of a clear resource makes it an ideal region for testing our knowledge on how to constrain an area where EGS can be performed.

Los Humeros

The geothermal system at Los Humeros is currently exploited. The northern part of the area, however, is much hotter (>380°C) than the wells used for production today. The development of this part of the reservoir presents a challenge, both because of the high temperature and because of the water chemistry. In addition, the area has only been poorly characterised by geophysical and geological surveys. Therefore our understanding required for the development and exploitation of this super-hot resource is limited. The uncertainty about the potential of this resource and the technical challenges involved with the development of such a super-hot geothermal system currently prevent its economic development.