Numerical Simulation of Cerro Pabellon Geothermal Field (Chile) with TOUGH-2

Abstract

The Apacheta concession is located in the II Region of Chile, about 1300 km north of Santiago, in correspondence of the Aguilucho-Apacheta volcanic complex, with elevation variable between 4000 and 5500 m above mean sea level. The area is carachterized by a structure known in the literature as Pabelloncito or Apacheta graben. In 2009-2010, after a phase of shallow exploration surveys, four deep exploratory wells were drilled confirming the presence of a geothermal reservoir with temperatures of about 250°C at depths over 1500 m. In 2017, according to these positive results, a development program was implemented, including the drilling of additional wells for production and reinjection, and the construction of a power plant. Currently the Cerro Pabellon project consists of two ORC units (24 MW gross each) utilizing 5 production wells and 3 as reinjection wells. A sustainability analysis of the geothermal development project of Cerro Pabellon was carried out by means of a numerical modelling based on the geological-geothermal model , using a geothermal reservoir simulator namely Tough-2. The simulated area is 225 km2, abundantly covering the concession area of Apacheta, in order to avoid boundary conditions. The depth of the domain was set to 1000 m a.s.l., corresponding to roughly 500 meter deeper than the deepest well. The reservoir bottom, or heat plate, is considered to be the heat source for the geothermal field. The natural state was successfully simulated assuming different permeability of the rocks to match the initial pressures and temperatures distribution in the reservoir. In particular small permeability adjustment were done to fit the temperature profiles for each well. The history of the industrial exploitation was then introduced in terms of injection and production flow rates in each well, and thus a sustainability evaluation for pressures distribution, cold front location and flowing enthalpy was produced. The field production results to be sustainable at least for the next 40 years. The same model constitutes the base for evaluating the sustainability of the planned further development of the field.