Caracterização estrutural da seção Pré-Sal na porção central do Alto Externo da Bacia de Santos, através da análise estrutural de dados sísmicos

Abstract

This study uses techniques of structural geology to characterize a key area within the central portion of the Outer High of the Santos Basin (AEBS), a regional feature which is considered to be a landmark in the oil industry as it contains many of the largest discoveries of pre-salt reserves of the southeastern Brazilian margin. The main objective of this study is to understand which structures control the changes in the structural patterns observed across the two sub-highs of the AEBS. The tridimensional structural framework of the area was constructed through seismic interpretation of horizons and faults, aided by the seismic attributes extraction (Variance). The study area is dominated by NNE-striking faults, and this direction (N27E) is persistent across all stratigraphic levels suggesting a strong basement control on faulting within this portion of the basin. The area was subdivided in two domains separated by a north-south oriented accommodation zone. Domino-style faulting with northwestward dipping faults prevails in the western domain, while the eastern domain presents a symmetrical structural architecture characterized by horsts and grabens. As expected, strain evaluations of the fault displacement for each horizon indicates a substantial decrease in the intensity of faulting intensity within the post-rift section in comparison with the underlying syn-rift section. The fault properties maximum displacement (dmax) and fault length (L) can be related to each other by the equation dmax = cLn. We observed that the n coefficient of this equation gradually increases from the upper to lower stratigraphic horizons, indicating a greater connectivity between the fault segments in the older lithostratigraphic units. This information helps describe the evolution of faulting in the basin, and the tridimensional characterization of the geometry and interaction between fault planes revealed different stages of development and destruction of the relay ramps. Such features are frequently observed in the area and range in size from hundreds to thousands of meters in length, displaying an aspect ratio compatible with relay ramps described within other basins. The interpretation of the results of this study agrees with the sinistral transtensive kinematics of the Helmut lineament that defines the south-eastern limit of the AEBS and forms an angle of approximately 45° with the direction of the majority of the normal faults described in the study area.