Integrated Stress Field Estimation and Implications for Enhanced Geothermal System Development in Acoculco, Mexico

Data gathered from two geothermal exploration wells in the Acoculco caldera, within the Trans-MexicanVolcanic Belt, indicated that temperature is high enough for economic utilization, but permeability is insufficient.Hence, heat exploitation at this location may only be possible by Enhanced Geothermal System (EGS)technologies. To evaluate the potential for EGS development, a wide range of exploration work has been carriedout in the framework of the international research project GEMex. In this manuscript, we present best estimatesof the in-situ stress field conditions at the site - an important, yet highly uncertain, parameter for stimulationplanning. The study is based on geological data, drilling parameters, geophysical logging, laboratory measurementson collected rock samples, and statistical analyses. The in-situ stress regime of the Acoculco geothermalarea can be described as transtensional with a maximum horizontal stress striking in the NE-SW direction,a pore pressure gradient of 8.73 MPa·km-1, a minimum horizontal stress gradient of 22.8 ± 3.3 MPa·km-1, a vertical stress gradient of 24.3 ± 1.5 MPa·km-1, and a maximum horizontal stress gradient of 42.9 ±28.5 MPa·km-1. Based on the predicted stress tensor, we estimate the maximum pressure required to enhance therock permeability and discuss the potential EGS development options for the Acoculco geothermal area.