The contact between magma flows as a conditioning of the occurrence and productivity of fractured aquifers
Abstract
The Serra Geral Aquifer System, fractured and of intensely varied water potential, represents the main underground reservoir in the northeast of the state of Rio Grande do Sul, and is mainly controlled by the structural system of the rocks, through the occurrence of fractures and fracture zones. For this, the objective of this work is to evaluate the contact between magma flow as possible conditioning of fractured aquifers and its influence on the productivity of wells. The research stems from an initial data collection, supplied by information provided by CORSAN, SIAGAS, and data collected in the field. With this information, and thorough descriptions, statistical analysis, and graphics, the geology and hydrogeology of the study polygon were characterized. The results allowed us to describe the Gramado Formation as predominantly in the region, composed of basaltic rocks, with contact structures that do not exhibit accentuated erosion, keeping the top preserved. The Palmas/Caxias Formation is distinguished by being composed of acidic rocks, with irregular surface contacts caused by an erosive structure and located at higher altitudes, generally above 539 m. The productivity evaluation was carried out based on the analysis of the specific capacity and flow parameters. The contact between the formations is marked by the overlapping of acidic rocks through an erosive and well-defined structure, preferably located between 500 and 550 m. The hydrogeological assessment identified that wells with water inflows at altitudes lower than 550 m, possibly crossing the contact zone between formations, had a higher average than wells associated exclusively with the rocks of the Palmas/Caxias Formation, located above 550 m. As for productivity, the parameters indicated classes that are more productive when the water inlets are located between 550 and 650 m of altitude. Likewise, water inflows into high flow wells (greater than 25 m³/h) occur between 600 and 650 m, and wells that do not reach contact zones between spills have lower flow rates or are unproductive. Finally, the evaluation of the most productive areas, through the analysis of geological sections, indicated that the contact structures are associated with water inflows into the wells, influencing the water circulation and productivity of the wells.
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