Análise sísmica de cold seeps como zonas de prospecção na porção offshore da Bacia de Barreirinhas, Margem Equatorial Brasileira

Abstract

The Brazilian Equatorial Margin (BEM) is an oblique-transform segment with counterparts in the Gulf of Guinea in West Africa. Both margins are inherited from the Pangea breakup and hence opening of the Equatorial Atlantic Ocean. These areas have been studied as new exploratory frontiers due to petroleum systems found in deep- and ultra-deep waters. The Barreirinhas Basin, located at the central portion of the BEM, has counterparts with the oil and gas producers Ivory Coast and Tano basins. Nevertheless, no relevant reserves were identified in the Barreirinhas Basin yet, moreover due to the poor study in respect to the petroleum systems. This present study aims to identify cold seeps in shallow strata and associated with hydrocarbon migration, indicating possible hydrocarbon accumulations along the offshore Barreirinhas Basin. Investigation was made through conventional 2D seismic reflection in post-stack time migration with additional use of seismic attributes. The results comprise the identification of cold seeps associated with hydrocarbon migration, including leaking faults, gas chimneys, pockmarks, hydrocarbonderived diagenetic zone (HRDZ), bottom simulating reflectors (BSR), and deep-water mounds. Regional morphologic and stratigraphic structures constrain the zones of cold seep occurrences. In the eastern lower continental slope and continental rise, regional normal faults control cold seep formation. On the central to northern sectors of the continental rise and abyssal plain, several deep-water mounds are sourced by gas chimneys and faults. Gravitational gliding systems are dominated by normal faults and negative flower structures that produce cold seeps on proximal regions, defining the extensional domain. These structural controls are related to the compressional domain of the distal portion, where the decollement zones and series of faults and folds are correlated to pockmarks and deep-water mounds. Near to the western compressional domain, igneous intrusions control the development of leaking faults, gas chimneys, bright spots, and pockmarks. These hydrocarbon-derived structures indicate potential petroleum systems in the Albian to Turonian-Oligocene tectono-sedimentary sequences in the central sector of the BEM. However, more refined techniques are needed to confirm the presence of active hydrocarbon seepage and/or storage. Likewise, the Barreirinhas Basin can be a vast field to the petroleum industry and scientific research, with the latter specially focusing in the nature of the deep-water mounds, endowed of great potential for the geobiology.