Seabed Potential Hazards On The Ilha Grande Bay, Rio De Janeiro, Brazil

Based on a quali-quantitative evaluation of high resolution seismic records, bottom samples and a digital bathymetric map, studies of the seabed on the Ilha Grande Bay were carried out in order to investigate the regional seabed potential hazards to the operational oil and gas industry activities. These hazards were divided into two general environmental risk attributes: structural and sedimentary. In these studies, we observed a juxtaposition of environmental risk attributes at three sites: the area of Estrelas sound, the area between Itapinhocanga and Conceição de Jacareí sounds and the central channel. Close to Estrelas sound evidences of fractures (or faulting) were observed, besides bottom texture transitions and sediments with high porosity, susceptible to great packing at superficial level. Between Itapinhocanga and Conceição de Jacareí sounds, sites of strong topographic slope (greater than 30º) were observed, combined to mobile seabed (subjected to bottom flows around 50 cm/s). The coastal depression between the land and Ilha Grande (central channel), showed large basement outcrops. They reach depths of 23 m, in places where depths are around 40 m. These integrated studies revealed a structurally heterogeneous seabed associated to bottom texture transitions and mobile seabed sedimentary sites.