Natural open fractures are present in sidewall cores and in whole core samples from pre-salt reservoirs in the license BM-C-33 in the Campos Basin, Brazil. Open fractures are also observed in borehole image logs, and fracture densities are in general high. The highest density of open fractures is seen in the damage zones above and below larger cavities (Amalgamated Cavern Damage Zones - ACDZs). Outside the ACDZs the fracture density is high in silicified carbonates, where it tends to increase with decreasing porosity. Clean dolomites are less fractured than the silicified interval while the less brittle argillaceous dolomites have the lowest fracture density. Some fractures appear vuggy on borehole image logs and fracture densities are high close to vugs and larger cavities. The positive correlation between fractures and vugs is caused by flow of dissolving fluids through open fractures, and fracturing at stress concentrations around vugs, Two major fault zones have been interpreted from borehole image logs which have damage zones with very high fracture density. The well test permeability is much greater than the matrix permeability estimated from sidewall core and log measurements. This excess permeability is attributed to fractures, in combination with caverns and intervals with frequent vugs.

Seismic velocity models have significant importance in subsurface studies, notably when applied in structurally challenging areas. In some parts of the Campos Basin, offshore Brazil, the pre-salt reservoir's overburden shows complex structures, mainly due to raft tectonism that positions laterally resulting in interspersed salt domes, carbonate rafts, and siliciclastic sediments. This work used an extensive well database in the Marlim Complex to analyze the raft seismic velocities and their related impacts on pre-salt reservoir models. Based on well data, in combination with detailed seismic interpretation, it was proposed seven alternative velocity scenarios for the rafts. The geological motivations for each scenario are discussed aiming to develop constrained depth models for pre-salt reservoirs. The depth forecast results could be tested by the drilled wells and resulting models are quantitatively compared in terms of depth predictions and gross-rock volumes. The results show that the topography of the target pre-salt reservoirs can vary considerably, even in scenarios where well and geological constraints are considered. This can impact pre-salt geological characterization and field development.

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