Assessing the role of dolomite in oil trapping in <i>in situ</i> Brazilian pre-salt carbonate reservoirs by pore-scale modelling and simulation

The main Aptian pre-salt in situ facies were modelled in 3D pore scale to evaluate the impact of diagenetic textures; specifically, the influence of matrix-replacive dolomite on the pore-system development. Our objective is to evaluate how these textures affect residual oil saturation ( S or ) under water- and oil-wet conditions through pore-scale simulations. We developed 12 models with varying proportions of dolomite and calcite spherulites, three models with calcite shrubs, 21 models with shrubs and regularly spaced dolomite, and nine models with shrubs and heterogeneously arranged dolomites. The methodology involved evaluating the tortuosity, surface area and size distribution of pores and throats. Additionally, the quasi-static morphology method was used to estimate the S or . The results indicated that dolomite significantly affects the pore system, leading to a more uniform medium, a decrease in the throat/pore size ratio and an increase in surface area. An increase of dolomite decreases S or in water-wet conditions. Conversely, in oil-wet simulations, increasing dolomite leads to an increase in oil entrapment. Previous research on waterflood experiments concluded that in situ facies with a high content of replacive dolomite tend to show low S or . Hence, it is probable that much of the oil trapped in these rocks is a result of the snap-off under water- or mixed-wet conditions.