Methodology for 4D Petro-Elastic Modeling including Rock-Fluid Interaction in pre-salt Carbonate Reservoir

Brazilian pre-salt carbonates represent more than 70% of the produced hydrocarbons in Brazil, which makes them of great interest for 4D seismic studies. 4D seismic modeling is crucial to understand how production impacts the 4D seismic response. We propose including rock-fluid interaction on the traditional methodology for 4D petro-elastic modeling (generally considering only variations of pressure and fluid saturation) given the presence of CO2 in the injected fluid. To model the rock-fluid interaction, we consider expressing the dry rock bulk and shear moduli as a function of the porosity for the monitor data. In the modeling, we focus in observing changes in the rock due to dissolution of CaCO3 by the CO2-rich injected fluid. We perform the analysis in the region around the injector wells and the results show that rock-fluid interaction favors the 4D anomalies, considering the reservoir conditions in this study. The higher ∆AI values obtained in petro-elastic modeling with rock-fluid interaction present an optimistic scenario compared to a traditional petro-elastic modeling in 4D feasibility studies and as another hypothesis that supports the interpretation of 4D anomalies.