Comparison of the effects of wettability alteration and IFT reduction on oil recovery in carbonate reservoirs

Injection of chemicals in a carbonate reservoir may change wettability and reduce interfacial tension (IFT). The question is how much each mechanism contributes to the increase in oil recovery. There is lack of such information in the literature. The information is very important because it will guide us to select which chemicals to use, as some chemicals can effectively reduce IFT, whereas others can change wettability. This paper aims to compare the effects of different mechanisms in oil recovery related to chemical enhanced oil recovery (EOR) . Particularly, we compare the effects of wettability alteration and IFT reduction. Numerical simulation models are used. Our results show that wettability alteration plays important roles when IFT is high, and it is effective in the early time. IFT plays very important roles with or without wettability alteration and is effective during the entire process. Note that the matrix permeability is reasonably high so that the fluids can be redistributed. The implication is that anionic surfactants are preferred to cationic surfactants in chemical EOR, as the former are generally used to reduce IFT, whereas the latter are used to change wettability. Other observations are that in surfactant-induced wettability alteration with low IFT, gravity drive is a very important mechanism. Molecular diffusion of chemicals affects oil recovery rate in the early time, but not ultimate oil recovery. (c) 2012 Curtin University of Technology and John Wiley & Sons, Ltd.