EOR methods
Miscible water alternating gas (WAG) injection with CO₂ or hydrocarbon (HC) gas: Under miscible conditions (which depend in part on pressure, temperature and oil composition), gas and oil will dissolve in each other to create a common phase. These processes make it easier to push oil towards the production wells.
Low-salinity/smart water. Changing the injection water’s chemical composition so that its salinity alters can amend wettability in the reservoir. That can help to mobilise part of the immobile oil for production. This method is being assessed, for example, on the carbonate fields in the Ekofisk area.
Low salinity with polymers. This involves a combination of injecting low-salinity water and polymers. Adding the latter increases the injection water’s viscosity and makes oil displacement more stable and even.
Combining surfactants with polymers. Adding polymers increases the injection water’s viscosity and makes oil displacement more stable and even. Surfactants are added to the injection water to change wettability in the reservoir and reduce surface tension between oil and water. That can mobilise part of the immobile oil.
Gels. The highly permeable zone where the oil has already been produced can be “sealed” by setting a gel plug which forces the water into surrounding undrained areas.
Alkalines. Alkaline substances are added to the injection water and react with the oil, reducing the surface tension between oil and water and altering wettability in the reservoir. This can mobilise part of the immobile oil.
Figure 3.11 A scientist at work in Stavanger's IOR centre. Photo: Jan Inge Haga.