Effect of Salts on Interfacial Tension and CO2 Mass Transfer in Carbonated Water Injection

Carbonated water injection (CWI) is a promising enhanced oil recovery (EOR) and CO2 sequestration method, which overcomes the problems associated with CO2 EOR. CO2 mass transfer and interfacial tension (IFT) are important parameters that influence oil recovery efficiency. This study addresses the impact of MgCl2 and Na2SO4 in carbonated water (CW) on CW/hydrocarbon IFT and CO2 mass transfer. An axisymmetric drop shape analysis was used to estimate the IFT and the CO2 diffusion coefficient. It was found that CW+MgCl2 reduced both the CW/n-decane IFT (36.5%) and CO2 mass transfer, while CW+Na2SO4 increased both the IFT and CO2 mass transfer (57%). It is suggested that reduction in IFT for CW+MgCl2 brine is mainly due to the higher hydration energy of Mg2+. The Mg2+ ion forms a tight bond to the first hydration shell [Mg(H2O)(6)](2+), this increases the effective size at the interface, hence reduce IFT. Meanwhile, the SO42- outer hydration shell has free OH groups, which may locally promote CO2 mass transfer. The study illustrates the potential of combining salts and CW in enhancing CO2 mass transfer that can be the base for further investigations. Furthermore, the contribution and proposed mechanisms of the different ions (SO42- and Mg2+) to the physical process in carbonated water/hydrocarbon have been addressed, which forms one of primary bases of EOR.