Abstract
Data gathered from two geothermal exploration wells in the Acoculco caldera, within the Trans-Mexican Volcanic 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 carried out in the framework of the international research project GEMex. In this manuscript, we present best estimates of the in-situ stress field conditions at the site – an important, yet highly uncertain, parameter for stimulation planning. The study is based on geological data, drilling parameters, geophysical logging, laboratory measurements on collected rock samples, and statistical analyses. The in-situ stress regime of the Acoculco geothermal area 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 the rock permeability and discuss the potential EGS development options for the Acoculco geothermal area.
Highlights
The Acoculco field is located within the Trans-Mexican Volcanic Belt (TMVB) in the Puebla and Hidalgo states
When during Formation Integrity Tests (FIT) no fluid leak-off was observed it was assumed that S3 value is higher than the sum of pressure exerted by the fluid column in the well and the applied differential pressure
The sum of pressure exerted by the fluid column in the well and differential pressure (dP), being maximum pressure at the wellhead applied during a FIT, serves as a lower bound on the S3 magnitude in the Monte Carlo (MC) simulations within the tested depth interval with an assumption of no pre-existing fractures
Summary
The Acoculco field is located within the Trans-Mexican Volcanic Belt (TMVB) in the Puebla and Hidalgo states. This basement was intruded by a late Mesozoic granitic body that caused the limestones to metamorphose into marbles (Canet et al, 2010a, and references therein) Whereas regionally these carbonates are kilometres thick, in the central area of the Acoculco caldera exploration wells were drilled through approximately 800 m of carbonate lithologies and met much younger 180 ka (Avellán et al, 2019) granitoids at depth of about 1600 m (Pulido et al, 2010). We highlight further exploration options and demonstrate the influence of the in-situ stress tensor on the potential EGS site development concepts
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