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The Role of Salt Tectonics on the Distribution of Hydrocarbon Accumulations in the Santos Basin, Southeast of Brazil


Chang, Hung Kiang1, Fernando Santos Correa1, Flavio Luis Fernandes1, Mario Luis Assine1, Joel Carneiro Castro1, Eduardo de Mio1, Julio Setsuo Tinen1, Milton Romeu Franke2, Sandro Mércio2 (1) São Paulo State University, Rio Claro, Brazil (2) Petroleum National Agency, Rio de Janeiro, Brazil


Extending from the southmost Santos Basin to the Sergipe-Alagoas basin, a large Aptian evaporitic basin has developed along the Atlantic Brazilian margin during the opening of South Atlantic Ocean. Carbonates, anhydrite, halite and complex magnesium and potassium chlorides are present, arranged in several evaporitic sequences. The salty section is overlain by a widespread and thick succession of Albian carbonate rocks, important because many of its intervals contain rocks of high porosity. The original evaporite thickness was variable, reaching up to 2000m. However, with the rapid progradation of siliciclastic wedges from the late Cretaceous to the present, the evaporitic beds has been moving downslope in the Santos Basin, given rise to diapiric structures and enhancing enormously the present thick­ness of salt in some areas. Halokinetic movements and salt detachments are responsible for hydrocarbon traps, such as turtle-peel and rollovers. Moreover, Turonian turbidites and Albian limestones reservoir rocks were detached and moved to deeper portions of the basin. Due to this raft salt tectonics, the gap in the evaporite beds has created windows for hydro­carbon migration from the underlying rift sequences, which contain the richest source-rocks of the entire basin. The understanding of the salt tectonic dynamics is crucial in oil and gas exploration in the Santos Basin because the most important structural traps are associated with the salt movements, as well as the creation of pathways to migration of hydrocarbons generated in rich source-rocks of the lower Cretaceous rift sequences.