Abstract
A sandstone unit of the Sergi Formation in the region of Cocorobo - Bahia was selected as an experimental area for an appraisal of the feasibility of artificial injection of water in sedimentary underground reservoirs of the semiarid region of the Brasilian Northeast. Geological mapping of the region showed that these sandstones occur intercalated with argillaceous lithologies in a block-faulted structure, a quite common framework in that region. Some fault zones are impervious due to silicification along the planes of rupture. The threedimensional geometrical configuration of the formation were delineated using AFMAG (audio-frequency magnetic), electrical and seismic refraction methods. The AFMAG measurements yielded a very good delineation of the fault systems of the area. Electrical soundings and seismic profilings defined the geometry of the reservoir,and gave qualitative informations about its boundaries and the hydrological properties of the sandstones at depth. Direct observations, in a well drilled through the formation, showed that the reservoir is undersatured under the conditions prevailing in that semiarid environment.
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