2D geological processes modeling of Aptian Pre-salt carbonate reservoirs: Assessing a conceptual depositional model in the Sapinhoá Field, Santos Basin, Brazil

Abstract

Recently discovered Pre-salt reservoirs along the Brazilian Eastern margin are among the industry's most challenging oil fields due to their high heterogeneity. Recent studies indicate that the deposition of facies was primarily governed by chemical and physical processes within lakes formed by thermal subsidence, which developed prior to the breakup of Gondwana during the Lower Cretaceous. However, debate persists regarding whether these lakes were shallow or deep, the extent to which the structures observed today in seismic data were prominent at the time of deposition, and the nature of the lateral connectivity of the deposits in relation to the vertically stacked sedimentation cycles observed in well data. The aim of this study is to develop a quantitative 2D model for the upper Barra Velha Formation (BVF) based on a conceptual framework, providing new constraints within the boundaries of the available data and the physical laws implemented in the model. This model simulates sediment deposition in the upper BVF of the Sapinhoá Field over time. The topography used for the simulation was constructed from a reconstructed, flattened seismic horizon, allowing for the simulation of a shallow lake with no major paleo-relief variations. Well data were used to interpret flooding and evaporation cycles that controlled sediment deposition and stacking patterns. Following this method, a seismic forward model was created, enabling comparisons between the features observed in seismic data and those produced by the shallow lake simulation model. This quantitative approach reproduces the expected stacking pattern and offers insights into the lateral connectivity of the deposits in line with the chosen conceptual depositional model, while maintaining strong correlation with well data and lake fluctuation cycles interpreted through a high-resolution stratigraphic analysis. The simulation results support the hypothesis of a shallow lake within the study area for the deposition of the upper BVF, thus prompting further discussion on the depositional settings of the Pre-salt interval, especially regarding the updip portions of the Santos Basin.