Evaluation Of Deep Water Submarine Hazards At Campos Basin, Brazil

Abstract

Abstract Based upon an interpretation of long range side scan sonar mosaics and of associated multi-beam bathymetry together with all available geological and geophysical data of the deeper part of the Campos Basin in Rio de Janeiro, Brazil, areas of geologic hazards of offshore engineering structures were discriminated. Submarine canyons, ground motion through creep, submarine slumps and slides, movements along growth faults, and sand movements down gradient mapped by their areas of influence were the mainly considered hazards. Introduction Campos Basin, in the Southeastern Brazilian Continental Margin (Figure I), is the primary producing Brazilian basin, accounting for 70% of the oil and 37% of the gas produced in Brazil. In the last decade, the exploration within the basin has moved to increasingly greater depths, where PETROBRÁS is presently leading the world in offshore production, recovering oil from water depths greater than 1,700 m. In order to have an assessment of the submarine hazards associated with the location and construction of offshore engineering, structures for hydrocarbon production PETROBRÁS has been developing new concepts and generatmg new knowledge regarding the submarine sedimentary processes and seafloor stability conditions at Campos Basin. G.G.G. Consultoria is participating in thiseffort for more than 10 years with PETROBRÁS. As a part of such effort, a complete side scan sonar and swath bathymetry survey of the entire Continental Slope and a portIon of the Sao Paulo Plateau at Campos Basin was performed by Seafloor Surveys International Inc. (SSI). Sonographic mosaics were generated, which were interpreted by G. G. G. staff in conjunction with PETROBRÁS personnel producing a series of maps describing the bottom stability conditions. This data was integrated with other relevant geophysical and geological information derived from previous surveys, allowing the definition of various sectors within the Continental Slope and São Paulo Plateau at Campos Basin. Each of these sectors depicts its own morphology, structures and dominant sedimentary processes. After this integration, submarine hazards were discriminated on the basis of the geological × geophysical evidences: areas of bottom instability by ground movement (creep), areas of slump and debris flows, areas of turbidity currents such as in canyon thalwegs, areas of intensive flow of sands from the continental shelf (ravines and sheet flows), areas of growth faults, areas of the flanks of the canyons (steep gradients), areas of steep gradients where halokinesis is notorious or suggested where pointed out. The present day activity of all the associated processes needs to be further investigated. This paper discusses the regional geology of the Campos Basin area that led to the present day phisiography. It also discusses the database that was used to elaborate a comprehensive knowledge about the regional morphology structures and the sediment processes. Finally, submarine hazards are pointed out on basis of all the knowledge acquired so far. Regional Geology Overview Campos Basin, off of Rio de Janeiro State, has an approximate area of 100.000 Km2, mostly situated offshore, extending to water depths of 3.400 m. Its northern and southern limits are defined respectively by the Vitória and the Cabo Frio structural highs.