An Analytical Solution to Interpret Active Ion Transport During Chemically-Tuned Waterflooding Process in High-Temperature Carbonate Rocks

Abstract

Recent studies on carbonate reservoirs suggest that modifying the injected brine chemistry leads to a competition amongst ions at the rock surface sites, causing alteration in the rock wettability. As such, the potential increase in oil recovery heavily relies on the relationship between the ion transport and chemical reaction. In this work, we highlighted the three processes that govern this relationship as advection by fluid transport, hydrodynamic dispersion resulting in spreading, and sorption of the ions to the rock. An analytical solution to the mathematical equations describing solute reactive transport was derived based on the advection-reaction-dispersion equation (ARDE). Our model was first used to replicate produced ion histories from single phase experiments to emphasize the impact of the active ions on rock surface sites. We then studied the movement of the active ions by predicting the breakthrough composition of different ions during oil-brine displacement experiments and evaluated the impact of the transport and reaction parameters on the wettability change. The wettability change profile was captured in terms of the sorbed ion concentration, where a high retardation was observed for the active ions. The observed oil recoveries in a data set of two-phase experiments were correlated to the resultant effect of the rock surface chemistry. This study highlights the importance of rock surface chemistry on wettability change and oil production from carbonate rocks.