An Integrated Model for the Syn-Rift Structural Evolution of the Santos and the Campos Basins

Abstract

The pre-salt hydrocarbon play in the Santos Basin has been the focus of several major exploration activities since past ten years. Recent oil discovery by Petrobras in the pre-salt of the Marlim Sul area has gained the attention of major players towards the pre-salt prospectivites of the Campos Basin as well. Most of the pre-salt discoveries in south Brazil involve different forms of carbonate reservoirs (travertine, microbialite, coquina) that are located on gigantic basement uplifts towards the outboard areas of the basins ( eg. the 12000sq.km Outer High in the Santos basin). The reservoir rocks were deposited during a time of thermal subsidence (referred to as the ‘sag’ sequence) in Aptian preceded by the major south Atlantic rifting event that started during Barremian. A sound idea about the structural style and evolution of this area is necessary to conceptualize a framework for sedimentation, petroleum migration and trap timing.

The current study uses geologic interpretation of regional 2D seismic lines and prospect scale 3D seismic volumes and integration of structural data from published tectonic maps to investigate the different stages of rifting in the Brazilian south Atlantic. The results of the study show the presence of at least two major rifting events in the Santos and Campos area: 1) Phase1 that initiated during Hauterivian and 2) Phase 2 that initiated during mid-late Barremian. Phase 1 is referred to as the Abimael Spreading Centre in literature (Sandwell, 2014). It is an aulacogen that extends from the south Santos (near Florianopolis High) all the way towards the western boundary of the Campos basin. Rifting activity failed to create a spreading centre during Phase 1 probably due to greater mechanical competence of the continental crust. The focus of extension shifted further east leaving an outboard piece of isolated crustal high in the shape of a continental ribbon that was connected from Santos to Campos during mid-late Barremian to Aptian. From early to mid-Albian the transfer faults that accommodated the extension within the outboard crustal high developed into major transform faults as breakup of the continental crust ensued. The right lateral motion of these transform faults eventually rendered the presently separated geometry of the Santos and Campos outer highs.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018