Geotechnology Applied to Analysis of Outcrop

Abstract

The Cabaços Formation is a margo-calcareous unit dated from the Upper Jurassic of the Lusitanian Basin, which shows deposits of lagoon to shallow marine conditions sometimes bituminous and it has a source rock potential. When in shallow marine conditions, they are associated with algal laminites areas, constituing microbialites, which is the focus of multiscale facies characterization performed in this work. Microbialites gained importance after the pre-salt discoveries of reservoirs in Brazil's eastern shore. This work focuses on the use of meso-scale tools, including Scintilometer and Terrestrial Laser Scanner (LST) as support for interpretation on analogous reservoirs models from outcrop data. Logging with Scintilometer allowed building GR profiles totaling 37 m in Pedrógão beach outcrop and 50 m in Cabo Mondego. The acquisition with LST totaled 18 stations and more than 40 GB of points clouds data. From collected data it was found that the total radioactive signature in both outcrops is related to the presence of the element K, present in argillaceous litologies, which dominate the margous sedimentation in these outcrops. In Cabo Mondego outcrop, the predominance of shales described in field log was proven. In Pedrógão outcrop there is a reduction of gamma radiation to the top, as evidenced by the outcrop log that shows essentially carbonate litologies to the top, as biocontructions, bioclastic limestone and microbialites. The lateral continuity of Pedrógão beach deposits was evidenced by the generated point clouds, which reaches parts of the outcrop where access was not possible for description. From the cloud was also possible to measure precisely the thickness of the layers in locations where no access was possible. In Pedrógão, the layers have about 75 m of lateral continuity and 50 cm in thicker and 10 cm in thinner, suggesting deposition in low-energy depositional environment. In Cabo Mondego, layers have an average lateral continuity of 25m and average thickness of 15 cm. It was also possible to prove the cyclicity of the layers through reflection that they presented which was measured in the LST, where thinner layers showed lower reflection with dark tonality while the thicker layers had good reflection showing in the image the cyclicity observed in lithological profiles. Another application was the delimitation of Callovian/Oxfordian contact in Pedrógão where in point cloud a surface is generated and it can be exported for use in virtual models. The use of the various tools was essential to the complete characterization of studied outcrops. The approach is part of the multiscale characterization of reservoir analogue outcrops contributing to the analysis in macro and meso-scale. Integrating these data and results with micro scale analysis is essential to generate oil reservoir virtual models.

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015