Imageamento com GPR de geometrias internas de dunas eólicas, no litoral Oriental do RN

Abstract

The present work addresses imaging techniques of the subsoil, by using geophysical tools, applied on the dunes of Pitangui beach, RN. A considerable amount from the worldwide petroleum reserves are found in siliciclastic reservoir rocks. Important siliciclastic reservoirs of aeolian origin can be found in the Amazon Basin, Solimões Basin, and Recôncavo-Tucano Basin. The Ground Penetrating Radar (GPR) was the method proposed for this work with the aim of obtaining indirect data for representing the internal geometry and deposition, as well as conception of chronostratigraphic framework from the studied dunes field. McMechan et al. (1998), Van Dam & Schlager (2000), Loucks et al. (2004), and Guidry et al. (2007) point out the GPR applications as useful method for imaging and 3D geometric characterization for analogous petroleum reservoirs. It was possible to do the imaging of 30 meters depth by using the following parameters: a 200 MHZ antenna, through acquisition in continuing mode with scan emission every 2 centimetres, range of 400 ns, sample of 2048, and 3,5 dielectric constant. Besides the dunes, at this depth of investigation, it was also possible to observe the Potengi Formation. The dunes are presented with maximum thickness of 10 meters, containing a limiting surface of 1ª order connected to the boundary between the dunes and the Potengi Formation. The 2ª order surfaces demarcate dunes overlapping between different generations, which indicate at least five distinct periods of sedimentation. The periods of no-deposition and erosion are represented by 3ª order limiting surfaces, being evident by the great change of the cross-sections angles. It is possible to observe the presence of these limiting surfaces in the Potengi Formation, as 1ª order, 2ª order, and 3ª order, where the 2ª order surfaces indicates three distinct periods of sedimentation. The maximum thickness is 12 meters.