Investigating Calcium and Magnesium Ion Effects on Improving Oil Recovery during Smart Water Injection in Carbonate Oil Reservoirs

It is widely accepted that different brines with various compositions can increase the oil recovery during water flooding in carbonate reservoirs. The concept of preparing a kind of smart water for these cases is an interesting subject whose underlying mechanisms have not been fully understood yet. It is still required to consider the crude oil/rock/brine interactions. To understand a typical smart water flooding process, it was decided to evaluate the effect of the two most important ions in a water flooding process. Calcium and magnesium, known as the hard ions, can be very effective, especially in the case of changing the reservoir rock surface behaviour and the fluids interactions. To understand these parameters, some solutions and carbonate rock samples were prepared; the fluids interfacial tensions (IFT) and the rock wettabilities were monitored by changing the ions concentration in aqueous phase. Contact angle measurement results showed that increasing the concentration of each of these ions can improve the water-wet tendency of the initially near oil-wet rock surfaces. This impact was more dominant for the case of having calcium ions. Interfacial tensions also reduced up to 20% while the concentration of these ions approached to that of typical carbonate formation water. The order of change for the case of calcium ion was more dominant (around 3%) than the other ion. The results of these experiments can be applied for real water flooding in carbonate reservoirs which are subject to the injection process, especially while the produced water is going to be used as the re-injecting agent.