| Authors |
Francesco BACCARIN, Gianni VOLPI, Germain RIVERA, Nadia GIORGI, Alessia ARIAS, Geoffrey GIUDETTI, Maurizio CEI, Marco CECIONI, Lisandro ROJAS and Carlos RAMIREZ |
| Abstract |
Cerro Pabellón (formerly called Apacheta) geothermal field is mainly hosted inside the so-called Pabelloncito or Apacheta Graben, a main NW-SE structural feature, about 120 km north-east of Calama city (Antofagasta region, Chile) at an elevation around 4,500 m a.s.l. The project was entirely managed by Geotérmica del Norte (GDN), a joint venture between Enel Green Power (EGP) and Empresa Nacional del Petróleo (Enap). The project started with a thorough surface exploration phase, inclusive of different geophysical surveys and a slim-hole, and prosecuted with a deep exploration phase (4 commercial diameter wells) and a following development phase (9 commercial diameter wells and the construction of a 48 MW power plant in parallel). The geothermal resource found is a liquid dominated reservoir, Na-Cl type, showing a temperature of about 250-260°C in the wells drilled inside the Apacheta graben, while outside the latter, the wells measured about 30-40°C less at the same depth, even if still associated with a convective thermal gradient. The 13 geothermal wells drilled so far provided a lot of direct subsurface data, such as lithology and hydrothermal alteration minerals from cuttings and core analyses. Also thermodynamic data from both injection and static T&P logs, performed during and after drilling respectively and physical-chemical data from fluid sampled during production tests are available. All of these data allowed performing spatial reconstructions of the main features of the geothermal system, like the geological setting, the hydrothermal mineralogical alteration facies distribution, temperature, pressure, and permeability distributions according to depth. Moreover, it was also done a comparison between the new data and the resistivity features coming from a magnetotelluric survey executed during the shallow exploration phase. The merging of all these geoscientific data was uploaded into the 3D modeling Petrel® software: this allowed having a 3D view for correlating data deriving both from surface surveys and deep drillings. Based on the 3D Petrel® model, a geothermal model of the area is here proposed, in which the main elements of the system, as cover, reservoir and fluid circulation pattern, are defined and geometrically described as input for a numerical modelling. |