INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Structural Study of the Mariposa Geothermal system
PAMELA ALVARES; LAURA GIAMBIAGI; ESTANISLAO GODOY
Naturaleza de la
producción energía geotermal
Campo de Aplicación:
This report was prepared by Pamela Alvarez and Laura Giambiagi as required by ENERCO SpA, using a pseudo three-dimensional modeling for the Mariposa Geothermal system. To this aim Tehema Consultores Geológicos assessed the available information and then carried out a field program, both in the Project area, as well as south and north of it. This report describes the activities performed and presents both the data, as well as the main results.MetodologyStep 1The following activities were carried out:Compilation of existing bibliographic information in the areaSynthetic view of the available dataGeneration of a mapping project in ArcGIS platform, where the maps provided by Enerco Spa (images, digital topography, geological map, etc) were used.Participation in a meeting where Enerco Spa professionals presented the results obtained in the area in previous studies, both the available geological and geophysical and drilling results.Preliminary mapping based on previous data and interpretation of satellite imagesAnalysis of the previous structural study in the area.Identification of areas where the structural mapping was focused, based on the previous analysis.Step 2. Collection of field dataA thorough understanding of a deformed region requires the characterization of the main structures, secondary and fractures at outcrop scale, both those generated during the last event of deformation as those previously developed during different structuring stages. To do this we modeled the study area geometric, kinematic and mechanically during various stages of deformation identified. The geometric modeling determined the position, size and geometry of the primary and secondary structures. The kinematic modeling was performed to identify displacement structures and constraining its age, so as to determine the strain field at the time these structures were formed.The structural mapping was integrated with the field data: (i) the location and spatial arrangement of faults and folds; (ii) characterization of fractures, and (iii) kinematic data structures. From the integration of these outcrop data with the data collected at regional scale, an evolutionary model of the kinematics of the area was prepered.The Mariposa Project area was covered in the field with Carolina Rodríguez, who introduced us to the state of the knowledge regarding the geology of the area.Step 33D structural modelling of the area.The structural study involved 24 days field work done by: Laura Giambiagi, Estanislao Godoy and Pamela Álvarez. The structural model presented here was generated with the structural data obtained in close to 200 control points (Figure 1.3). During the field work, together with the acquisition of structural data, contacts between different units were checked. Three Jurassic-Cretaceous formations were distinguished: Nacientes del Teno (Early to Middle Jurassic), Río Damas (Late Jurassic) and Baños del Flaco (Late Jurassic ? Neocomian). We propose that limestones of the Nacientes del Teno Formation crop out at the headwaters of Estero del Valle, underlying the Rio Damas Formation. The succession is assigned based only on its stratigraphic position. Further mapping is nedeed to prove this proposal.Seven detailed balanced structural sections were constructed in the study area, using which a pseudo 3D model was developed. The model allows us to observe in three dimensions the main structures related to deformation of the project area.A regional profile was also constructed, in order to understand better the large-scale characteristics of the deformation in the study area.We evaluated the slip tendency (the ratio between the effective shear stress and the effective normal stress, Morris et al., 1996) of the main faults affecting the reservoir. The value of the slip tendency for a fault segment is a measure for its likelihood to fail under the given stress field, and depends only upon the ratios of the principal stresses and the orientation of the fault segments. Higher slip tendency values for a given fault segment imply higher probability of slip.A morphometric analysis of volcanic centers in surrounding areas was also carried out.Structural Database (attitudes and kinematic indicators of faults, lineaments and fractures) was formed.A predictive model of the behavior of structural and possible spatial distribution of the units constituting underground geothermal reservoir was proposed.