TECTONIC EVOLUTION OF SANTOS BASIN, BRAZIL AND ITS BEARING ON OIL-GAS EXPLORATION

The Santos Basin, a passive continental margin basin in the South Atlantic Ocean on the east coast of Brazil, is an important target for oil-gas exploration for the time being. Based on the interpretation of seismic data, combined with the evolutionary model of a superimposed basin for the South Atlantic Ocean, the tectonic evolution of the Santos Basin can be subdivided into four stages: pre rifting stage, rifting stage, transitional stage and drifting stage, corresponding to the four prototype basins of craton, rift, depression, and passive continental margin. The well-matched spatiotemporal relationship of the prototype basin provides ideal tectonic conditions for the generation of super large oil-gas systems in the Santos Basin. Based on the previous research results on the "source-reservoir-cap system", the oil-gas distribution patterns are clear, that is, "accumulated under salt in the area with thick salt; and above the salt in the area with thin salt ". The analysis of regional tectonic evolutionary history of the basin with seismic data has revealed that there are thick and high-quality lacustrine source rocks in the neglected eastern depression area under salt, oil and gas generated may migrate following the major basement faults and unconformities. Blocked by the evaporite rocks deposited in the transitional period, oil-gas accumulations are dominantly formed in the composite structural and stratigraphic traps and stratigraphic unconformity blocked traps.