The Rio Grande Rise and Associated Mechanisms for Distribution of CO2 in Brazil Pre-Salt Reservoirs

Recent exploration in the Santos and Campos basins focused on the Aptian Pre-Salt carbonate play. Early drilling in the Santos Basin resulted in discovery of multiple giant oil fields containing variable amounts of CO2. Recent exploration wells outboard of the Santos Basin outer high report CO2 as the primary reservoir fluid. In contrast, Pre-Salt penetrations in the outboard Campos basin consistently report CO2 concentrations lower than 20 mol percent. The mechanism that is often attributed with the introduction of CO2 into the system has been linked with the rifting and magmatism associated with the opening of the present-day Atlantic Ocean. However, an alternative source for CO2 in these basins is the magmatism of calc-alkaline melts associated with the Western Rio Grande Rise (WRGR) and the Jean Charcot Seamount Chain (JCSC). A lineament from the west of Alto Cabo Frio to the JCSC highlights a zone of intense magmatism through this time period that is adjacent to the highest concentrations of CO2. Using Moho as a proxy for lithospheric base, the favored route of flow is towards the eastern Santos basin, and higher amounts of CO2 will be expected in this area juxtaposed to the JCSC.