In my previous features, I discussed the challenges facing carbon dioxide (CO2), both technical and economic. By far the biggest use of CO2 is in enhanced oil recovery (EOR). In this feature, the focus is on overcoming the biggest challenges facing CO2 EOR—gravity override and mobility. When CO2 is injected into a reservoir, it has a tendency to rise and segregate to the top of the reservoir, thereby bypassing some of the remaining oil. This is primarily because of the density difference between CO2 and reservoir fluids.
Review of Potential IOR Methods The ultratight matrix and high conductivity of natural fractures might be the two most important factors that impair success of conventional IOR methods. The authors conducted a critical review of more than 70 studies aiming to find applicability of different IOR methods in unconventional reservoirs. Generally, this category includes three methods: surfactant, polymer, and alkaline injection. Surfactant injection has the most-promising potential to improve oil recovery in North American unconventional reservoirs. These reservoirs are well-known as intermediate-wet to oil-wet; this type of rock affinity would prevent the aqueous phase from invading the matrix to displace the oil in place.