El pozo termal Villaguay-1, provincia de Entre Ríos, Argentina.

STÖCKLI, FERNANDO; DAPEÑA, CRISTINA; STÖCKLI, MARTINA

ASUNCIÓN, PARAGUAY

Congreso; VIII Congreso Latinoamericano de Hidrología Subterránea. ALHSUD; 2006

ASOCIACIÓN LATINOAMERICANA DE HIDROLOGÍA SUBTERRANEA PARA EL DESARROLO (ALHSUD)

In recent years, several undertakings have been carried out in the Entre Ríos province, Argentina, in order to exploit geothermal deep aquifers for different purposes, such as recreation and balneotheraphy. During 2003, the Villaguay Municipality began to drill an exploration well, similar to those recently done in Colón, Villa Elisa, Federación, and Gualeguaychú, searching for thermal groundwater. The sounding is located in the Villaguay periurban area, near the Municipal Hospital and within the campus of the Faculty of Kinesiology, which will use the well with therapeutic objectives. The telescopic well reached a depth of 1356.5 m. It is a non-artesian well with a static level of 0.80m below ground surface. A suitable and maximum exploitation discharge was fixed at 26.5m3/h, which causes an acceptable drawdown of 20 meters. The first 446 m have a cemented casing in order to protect the aquifer that supplies fresh water to the community. From cutting analysis three sections were defined: suprabasaltic, interbasaltic and infrabasaltic Three sections were defined on the basis of the cutting analysis: suprabasaltic, interbasaltic and infrabasaltic. Several lithologies can be described within the suprabasaltic section: a) between 0.80-155 m, there is a sequence consisting of brown silty clay, medium to fine well-sorted silty sand, brow sandy-clayey silt, and silty sand with intercalations of green and grey clays. This sequence holds fresh water with a conductivity of 300ms/cm. b) between 155-270 m, a series of brown clayey silt, plastic clay with lenses of green arcillites and grey silty sandstones, bearing water with a conductivity of 1.900 ms/cm occur. c) between 270-444 m, there are grey sandy silts, brown clays with lenses of blue clay, sandy silts with lenses of bluish-green arcillites, and brown clays containing lenses of calcareous material, pebbles, sands, and silts. This sequence holds salty water with a conductivity of 4000ms/cm. An induction profiling was performed along the suprabasaltic section, determining spontaneous potential, short and long resistivity, conductivity, etc. Beneath the suprabasaltic section, we can find the interbasaltic section ranging from 444 to 1294 m deep. It consists of a sequence of 22 basaltic lava flows with intercalations of clay and sand layers, bearing water with high salinity, over 20600 ms/cm. Finally, between 1294-1354 m deep, there is a succession of pink sands with water with high salinity, over 49.000 ms/cm, underlain by a brown arcillite located between 1354 and 1356.5 meters deep. This thermal resource is related to a large transboundary groundwater reservoir shared by Brazil, Paraguay, Uruguay and Argentina and known as the Guaraní Aquifer System (GAS). It forms part of the Paraná and Chacoparanense sedimentary basins. The geological units related to this system are the Triassic-Jurassic eolian and fluvial sandstones of the Piramboia and Botucatu Formations, and the Serra Geral Basalts that present clastic intercalations. This effusive Cretaceous complex covers the sandstones and provides a high-confinement degree. The geological, hydrogeological, hydraulic, hydrochemical and thermal characteristics of the GAS vary throughout the whole basin and are controlled by variations in the depositional environment, in the structural evolution and in the residence time of water within the formations.  The management of the Villaguay well has to take into account the pollution risk involved in thermal exploitation due to the high salinity and temperature of the thermal effluents and should proceed to carry out an effluent treatment according to the Entre Ríos laws.