SEDIMENTARY CHARACTERISTICS AND EVOLUTION OF POST-SALT CLASTIC DEPOSITS OF SANTOS BASIN, EASTERN MARGIN OF BRAZIL

The Santos Basin on the eastern margin of Brazil is one of the hot spots for oil and gas exploration in recent years. Hydrocarbon discoveries in the post salt clastic series are mainly distributed in the Late Cretaceous Cenomanian-Turonian period, Late Cretaceous Coniacian-Maastrichtian period and Paleocene period. Based on the analysis of regional depositional settings, provenance characteristics of the surrounding drainages with the drilling, seismic, logging data, this paper makes a systematic study on the main depositional characteristics and the evolution of the three post salt sandstone reservoirs. The results suggest that the south part of the Santos Basin is dominated by shallow-bathyal argillaceous sediments in the Cenomanian-Turonian period, while the small deltas and turbidite channels dominate the middle and northern part of the basin. In the Coniacian-Maastrichtian period, sufficient sediment supply made larger scale deltas continuously prograded seaward into the shallow water shelf area, leaving submarine fans developed on the slope, forming a pattern of "channels dominating the early stage, lobes dominating the later stage". During the period of Paleogene, due to the migration of regional drainage system, sediment supply was reduced, and argillaceous sediments increased. As the results, the scale of delta was obviously reduced, and small channels or channelized lobes dominate the deep-water areas.