Integrated 3D forward stratigraphic and basin modeling of the Santos Basin, offshore Brazil: Implications of sedimentary depositional facies and CO2 migration for silicification of continental carbonate reservoirs

Silicification plays an important role in the quality of pre-salt reservoirs, resulting in significant heterogeneities that are difficult to predict. A better understanding of the distribution of silicified pre-salt reservoirs at the basin scale helps in mapping such heterogeneities and further optimizing responsible hydrocarbon exploration and production. Here we investigate a scenario involving the interaction of an internal silica source from Mg-rich clay (sedimentary depositional facies) and CO2-rich fluid upwelling along deep-rooted faults. These are some of the main controlling factors of silicification, as confirmed with conceptual and numerical geochemical modeling. We present a new modeling workflow integrating forward stratigraphic modeling (FSM), basin/thermal modeling, quantitative chemical modeling, and map-based analysis to derive silicification probability maps of the Barra Velha Formation in the Santos Basin (Brazil). FSM simulates, with a process-based approach, the sediment distribution in the Barra Velha Formation including Mg-rich clay. Basin/thermal modeling simulates the rock-fluid systems evolution, CO2 migration, accumulation, and concentration in the formation. Geochemical modeling provides Mg-clay transformation ratios depending on Mg-clay content of rock matrix and CO2 concentration. Combining all elements together enables calculation of basin scale silicification probability maps across the study area. Highest probability of silicification is found above uplifted areas known to include Mg-rich clay, intense faulting, and trapping structures.