Thermodynamic Modeling of Brine Dilution-Dependent Recovery in Carbonate Rocks with Different Mineralogical Content

Extensive experimental studies during the last two decades have demonstrated improved oil recoveries through the injection of diluted brine in both sandstone and carbonate rocks. However, the mechanisms that lead to improved oil recovery in carbonate rocks are not well established, though wettability alteration has been widely cited as a primary mechanism. It is also important to understand the role of carbonate mineralogical composition during diluted brine injection on the geochemical interactions taken place. In this study, we have formulated a theory for the anticipated chemical interactions between oil, brine, and rock, and linked the geochemical interactions to multicomponent transport within the porous rock. In so doing, we investigated different hypotheses on the viable link between geochemical interactions and wettability modifications. Our simulation results could capture the trend in the experimental oil recovery and pressure differential results, together with the effluent ions and pH under varying mineralogical content. On the basis of our model, we infer that mineral alteration alone could not describe the observed behavior and that one has also to consider the interplay between surface charge and mineral alteration. We then followed with simulation of a quarter of a five-spot pattern to demonstrate that incremental recovery varied with different rock mineralogy. The outcomes of our study clearly highlight the need to establish the relationship between appropriate process mechanism(s) and impact of mineralogical content when implementing brine dilution-dependent oil recovery in carbonate reservoirs.