Controle de porosidade secundária em depósitos da formação Barra Velha no polo pré-sal da Bacia de Santos (idade Aptiano) com uso de afloramento análogo da formação Salitre na Bacia do Irecê (idade Neoproterozoico)

Abstract

This paper presents a novel approach to predicte cyclostratigraphy control in the occurrence of secondary porosity in fine-grained carbonate rocks (laminites and mudstones) of a brazilian Pre-salt tight carbonate reservoir (Aptian age) controlled by a basin-scale accommodation zone in Santos External High (SEH) based on analogous outcrops. The aim is shows the predictability of fractures and dissolution feutures by facies tracts and that cyclicity can be used to guide the style and scale of secondary porosity features that develop in carbonatic sedimentary successions with smooth variations (predominance of laminate (Lmt) facies). The Pre-salt studied area is seated in the central portion of the SEH, where the regional NE-trending faults system that prevails in the Santos Basin bends to NNW and becomes diffuse into several low displacement normal faults. These faults control a series of segmented structural highs, with some of them holding significant amounts of oil within lower permeability facies. In this context, secondary porosity can constitute an alternative scenario to make production feasible. The Pre-salt field is a NW horst, segmented in three domains by 290° Az and 245° Az trending relay ramp systems. The tectono-sedimentary time and space evolution based on the interpretation of 3D multi-azimuthal high-resolution seismic data and a regional transect through the central portion of the Santos Basin (SE Brazilian margin) allowed us to address the following points: (i) The geometry and kinematics of the structures developed at the transfer zone and (ii) Tectonosedimentary evolution of the syn-rift and post-rift phases that controlled the main stratigraphic sequences observed in wells and extrapolated along the sections with the seismic interpretation. We interpret multi-stage fault growth along the NW structural trend as a mechanism for the distribution of reservoir rocks, promoting localized syn-rift footwall uplift of isolated normal faults. Data from analogous outcrops of the Salitre Formation (Neoproterozoic age), located in the Irecê Basin, were used to resolve the lack of data in predicting secondary porosity. Despite the differences in terms of depositional environment (marine/continental) and degree of recrystallization (diagenesis), the deposits of the Salitre formation can help to predict secondary porosity features in the Pre-Salt field. The scale of medium frequency cycles is the same used in the geological models of the pre-salt reservoir, around ~5 (m). Therefore, the vertical compatibility in cycle scale allows transporting the secondary porosity control model established in the outcrops of the Irecê Basin to the pre-salt parameterization.