However, in the tertiary processes injected fluids interact with the reservoir rock/oil system thereby creating oil swelling, lower interfacial tensions, oil viscosity reduction, or favorable phase behavior. In some situations, the tertiary process might be applied as a secondary operation.
In brief, all these efficient oil recovery methods tend to recover more oil from reservoirs by various mechanisms such as IFT reduction, wettability alteration, mobility control, change of physical properties and gravity drainage.
However, it also can be seen from that all these traditional Enhanced Oil Recovery (EOR) processes face some important challenges. For example, if gas is injected into the well it deeply penetrates leaving behind large uncovered residual. Hence proper understanding is required on flow through porous media and its characteristics in depletion of oil using EOR techniques.