Reconstruction of a “Discrete Fracture Network” in the geothermal reservoir of Rosario de La Frontera (La Candelaria Ridge, Salta province, NW Argentina).

""\\"Discrete fracture network (DFN) models are three-dimensional stochastic or combined . stochastic\\\\\\\/deterministic representations of fractures network that characterizes natural fracture systems. . They represent an important tool to investigate pathways for fluid flow in geothermal reservoirs in order to . predict their behavior in prospect evaluation and reservoir management. . In this project a DFN model is applied to the geothermal system of Rosario de La Frontera, in the Salta . province, with the aim to assess the effective permeability of its reservoir and to obtain input parameters for . dynamic reservoir modeling.. This active geothermal system is marked by several hot springs, with surface temperatures ranging . between 50°C and 99°C, in the surroundings of the town of Rosario de la Frontera, to the north of La . Candelaria Ridge (Fig. 1a). Fractured sandstones strata belonging to the syn-rift deposits of the Salta . Group (Pirgua subgroup) provide the reservoir rocks of this geothermal fluids (Moreno Espelta et alii, . 1975).. With the aid of dedicated software, a 3-D geological model of the La Candelaria anticline was built in order. to extract a 3-D geocellular volume of the deep reservoir to constrain the fracture network model. The reconstruction of the structure model of the La Candelaria Ridge shows a broad N-S east-verging . anticline uplifted by high-angle thrust faults.. Stuctural study on outcrops of the reservoir rocks allowed us to elaborate a deterministic fractures network . model and to calculate the input parameters for the generation of the DFN. Field work was dedicated to a . quantitative and qualitative analysis of the fractures and faults defining diagnostic parameters such as . orientation, dimension, spatial distributions, surface texture, and to calculate their density distribution within . the regional fold. The acquisition of these parameters was performed along scan-lines and on scan-areas . of the outcropping reservoir rocks. . According to orientation, the observed discontinuities were classified as longitudinal, transverse and . oblique with respect to the fold axis trend (e.g. Stearns, 1968; Hancock, 1985; Cooper, 1992), and in turn. grouped into six sets. They show different frequency values across the anticline. In particular NNW-SSE . and NE-SW trending fractures are predominant along the eastern and western limbs of the anticline, . respectively. . In conclusion, DFN models were generated for each fractures set in order to evaluate their influence on the . permeability anisotropy in different portions of the studied anticline. \\"""