Fracture Modeling applied to the geothermal system potential reservoir of Rosario de La Frontera (La Candelaria Ridge, NW Argentina).

MAFFUCCI ROBERTA; BIGI SABINA; CORRADO SVEVA; DI PAOLO LEA; CHIODI AGOSTINA

Congreso; 86° Convegno Società Geologica Italiana; 2012

Fracture Modeling consists of three-dimensional deterministic or combined stochastic/deterministic representation of fractures network that characterizes natural fracture systems. DFN (discrete fracture network) reconstruction is widely applied in geothermal exploration, since it provides input parameters for static and dynamic reservoir modeling. This fractures characterization represents, in fact, an important tool to predict the anisotropy of the permeability in a geothermal reservoir and its effects on fluid flow. Fracture modeling approach is applied to the geothermal system of Rosario de La Frontera, in the Salta province, with the aim to assess the effective permeability of the reservoir and the effectiveness of its cap-rock. The study area lies within the structural province of the Santa Barbara System, in the Sub-Andean foreland thrust belt, and is characterized by several hot springs with temperatures at surface ranging between 50°C and 99°C. These manifestations are located close the town of Rosario de la Frontera, to the north of La Candelaria Ridge that consists of a broad anticline uplifted by faults dipping to the west with a top-to-the-east sense of transport. It exposes low grade metasedimentary Precambrian rocks that are unconformably overlain by a thick sequence of predominantly continental Cretaceous to Paleogene strata (Salta Group) related to the Cretaceous rift stage (SALFITY AND MARQUILLAS, 1981, 1994). The permeable levels of the syn-rift strata belonging to the Salta Group (Pirgua subgroup) has been interpreted as the reservoir of the active geothermal system (MORENO ESPELTA et al, 1975). The post-rift (Balbuena and Santa Barbara subgroups) and syn-orogenic impermeable levels (Metán subgroup), that are related to an inversion tectonic phase, provide the cap rock to the geothermal system (BIANUCCI et al, 1981, COMINGUEZ AND RAMOS, 1995, GEBHARD et al, 1974). Structural field study concerned a qualitative (orientation, dimension, spatial distributions and surface texture) and quantitative (fractures frequency) analysis of discontinuities observed in the analogue rocks of both potential reservoir and seal. The characterization was performed in different structural positions of the studied anticline, along the forelimb, backlimb and northern plunging nose. This work allowed to relate the fractures system features to the folding process. These data will be used in the next future as input values to generate a DFN model in a 3D volume of the buried geothermal reservoir. The purpose of this modeling will be to reconstruct the fracture properties distribution (such as porosity, permeability, connectivity) in order to evaluate the potential of the geothermal reservoir.