Petroleum geology characteristics and exploration targets of pre-salt formations in Santos Basin, Brazil

The Santos Basin in Brazil has experienced three tectonic evolution stages (rifting, transitional and passive continental) with three sequences deposited (pre-salt, salt and post-salt). Source rocks in the pre-salt formations in the lower rift were the most effective source rocks in the basin. Microbial limestones in the upper rift and depression, and coquina limestones in upper rift served as the main reservoirs for the pre-salt source rocks. The salt formations had strong capping capacity thanks to great thickness and continuous distribution in the deep water area. The basement horst belt helped the formation of various structural traps. All these advantageous geologic conditions provided a good basis for the generation of giant oil and gas pools in the pre-salt formations in the basin. The basement horst belt in the deep water area in the north of the basin was a favorable location for the pre-salt hydrocarbon accumulation, where the source rocks were moderately mature, and the thick, continuously distributed salt formations provided a good preservation environment. In the shallow water area formed by a basement horst, carbonate reservoirs were well-developed, and traps such as horsts, tilted fault blocks and drape anticlines were very common. Hydrocarbons generated in the surrounding grabens migrated to and accumulated in the horsts. The other pre-salt formations had poor accumulation conditions.