Unlocking Pandora - Insights from Pre-salt Reservoirs in Campos and Santos Basins (Offshore Brazil)

Abstract

Pre-salt carbonate reservoirs in the offshore Campos and Santos basins have played a crucial role over the last years with giant discoveries being made every year. The overall pre-salt discoveries account for 28.8 BBls RR with twelve fields currently producing 648,000 b/d from pre-salt carbonates. The pre-salt carbonate reservoirs present an heterogeneous variation that can range from thick packages of microbial carbonate sections, interbedded sequences of carbonates and volcanics or complete absence of reservoir facies. Moreover, diagenetic processes, such as hydrothermalism, have also significantly obliterated the initial rock matrix. Described as a world class reservoir, the pre-salt microbial reservoir presents average porosities of 11%, NG of 55%, SW of 20% and net reservoir thicknesses of 125 m. Widespread magmatism, has impacted the reservoir presence and predictability. Although pre-salt reservoirs present a normal pressure regime, overpressures were observed in the westernmost part of Santos basin. Differential compaction together with hydrocarbon cracking could play a major role. CO2 origin is related to mantle contribution. Its distribution suggests that Santos basin presents higher concentrations than in Campos basin. Locally, there is a correlation between the presence of high CO2 values and regional NW-SE transfer faults.