Fluid-Rock Reactions Within Geothermal Systems of the Eastern Trans-Mexico Volcanic Belt

Abstract

A vast amount of the presently-accessible geothermal resource cannot be exploited with conventional technologies. Such unconventional resources include enhanced geothermal systems in very hot environments (hot-EGS), and super-hot geothermal systems (SHGS), where deep geothermal fluids exceed temperatures of 350°C. To address the challenges associated with these, two sites in Mexico with unconventional geothermal characteristics have been selected for detailed study as part of the collaborative European-Mexico GEMex project: Acoculco (hot-EGS) and Los Humeros (super-hot). As well as these two sites, there is also study of more ancient, exhumed analogous (analogue) geothermal systems at Las Minas, where erosion has exposed fluid flow zones showing evidence for several generations of different fluid-rock reactions as the systems evolved along a decreasing temperature gradient. Both currently active and analogue systems have igneous intrusions (heat source) into Jurassic-Cretaceous carbonates, with fractures controlling upward flow of hot fluids into overlying andesitic reservoir rocks, which are in turn overlain by ignimbrite caprocks. Fluid movement between these will result in fluid-rock reactions, and we have analysed samples of borehole materials, outcrop samples, and material from high temperature laboratory experiments to better understand them. We will describe the nature and extent of the fluid-rock reactions that result as a consequence of geothermal fluid circulation.