Gas-based methods
CO2 injection
In miscible conditions (which depends on pressure, temperature and oil composition), CO2 and oil will dissolve in each other to form a single phase. This oil mixture is typically less viscous while also reducing the interfacial tension between oil and water. Oil is re-mobilised and swept towards the production wells. As CO2 injection is continuing, the oil concentration in the mixture will reduce. At the end of production, large parts of the oil in the reservoir will have been replaced by CO2. This forms the basis for CCUS (Carbon capture, utilisation and storage).
Miscible gas injection
This method works in the same way as CO2 injection but uses hydrocarbon gas instead of CO2. The drawback of hydrocarbon gas compared to CO2 is that it is frequently more difficult to achieve miscibility with the oil. Miscibility is achieved by making the gas richer in heavier hydrocarbon compounds, but this means that the gas could have a considerable market value.
FAWAG
FAWAG (foam-assisted water alternating gas injection) is a method to control gas mobility in the reservoir using foam. Foaming compounds can be added to the gas in a WAG process in the event of poor displacement efficiency from the gas phase. Foam restricts how easily gas can move through the reservoir, improving displacement efficiency and increasing oil recovery.
Updated: 27/11/2020