Abstract: Exploration practice indicates that the reservoir sedimentary characteristics are key factors affecting oil and gas production in subsalt lacustrine carbonate rocks in Santos Basin. The high-quality reservoirs are mainly composed of microbial reefs and shoal carbonate rocks deposited in paleo uplifts. Based on seismic structural interpretation and gravity data, the sub-salt structural units and distribution of paleo uplifts in Santos Basin have been redefined. The study results indicate that the basin was divided into five primary structural units, in which the outer uplift zone was originated from the abandoned Ocean Ridge after transition during breakup of the South Atlantic, which was very conducive to the development of microbial reefs. The drilling and seismic data have been used to analyze the core facies, logging facies, seismic facies, and sedimentary facies, identifying the distribution of sedimentary facies of sub-salt strata in the core depression zone. In addition, combined with the structural characteristics and paleogeography during rift period, four types of sedimentary modes of high-quality carbonate reservoirs have been established, including the large gentle slope, isolated high basement, intra-platform highland, and steep slope types. Among them, the large gentle slope and steep slope sedimentary modes were controlled by monoclinal fault blocks, and the intraplatform highland sedimentary mode was controlled by fault-uplift structure, and they are mainly distributed in the outer uplift zone. The isolated high basement sedimentary mode was controlled by fault horst, which was mainly distributed in the western depression zone and outer depression zone.

Key words: Santos Basin, lacustrine carbonate rocks, large gentle slope type sedimentary mode, isolated high basement type sedimentary mode, intraplatform highland type sedimentary mode, steep slope type sedimentary mode