Influência do paleorelevo na segmentação da Plataforma Carbonática Albiana, localizada no Alto de Badejo ao sul da Bacia de Campos

Abstract

The shallow water carbonate rocks lying above the Badejo Basement High have over 30 years of successful oil production. Well known in terms of stratigraphic arrangement and permo-porosity, these accumulations are problematic when the subject is its structural control. One relevant point regarging these accumulations is whether or not the paleorelief below these carbonate platform controlled the fragmentation and downslope gravity movements and how much of these processes influenced the internal compartments of producing oil fields. In detail, the oil fields at the Badejo High are above salt pillows and welds, overlying a buried basement step that, in map view, bends from N-S to NE-SW. Gravitational structures in the sedimentary sequences above the salt layer are mostly collinear with the paleorelief architecture of the basement beneath. Such alignment motivated the investigation of a possible passive influence of the substrate after cessation of the fragmentation and basinward gliding processes. Evidences supporting this idea came from an integrated approach that included analysis of well-logs, seismic interpretation, section restoration and generation of palinspastic maps. These techniques revealed a clear association of the buried basement step and the salt-related fault patterns. Two distinct fault arrangements were identified: one of NW-SE subparallel planar normal faults, strongly conditioned by a frontal backstop, located at the southern portion of the studied area; and another with radial divergent map view, dominated by non-planar N-S to NNW-SSE listric faults, following with the buried bend of the basement high. Cross-section restorations revealed that greater extensions of 7% were accumulated in the listric fault domain, whereas in the planar fault systems, away from the bent paleorelief, the lateral displacements were inexpressive. Such behaviour suggests different coupling degrees between substrate beneath the salt layer and the carbonate platform above it. The tracking of lateral movements through time deduced from the sequential restoration indicates that the apices of deformation occurred in the Eoalbian-Cenomanian and it was likely associated to the ESE tilting of the basin. The progressive deceleration of the basinward gliding started in the Late Cretaceous till its complete cessation in the Paleogene