Water-based methods

Low-salinity water flooding

Wetting properties of the reservoir rock can be changed by altering the chemical composition of the injected water by reducing salinity, or in the case of smart-water, just optimizing the ion composition more generally.

This can contribute toward mobilisation and production of parts of the immobile oil. Other benefits from using low salinity water can be the reduced risk of reservoir acidification. This can prevent precipitation of chemicals that can cause scaling in wells.

Polymer flooding

Adding polymer to the injection water increases the viscosity of the water. Depending on the properties of the oil, this will result in a more stable and effective displacement of the oil.

Surfactant flooding

Surfactant is added to the injection water to change the wetting properties of the reservoir rock and reduce interfacial tension between oil and water, mobilising parts of the immobile oil.

Gel

If the reservoir is heterogeneous with highly permeable zones set amongst lower quality rock, this can result in water preferentially flowing in these good zones. This will result in poor vertical sweep of the oil, resulting in low recovery factor, especially if these zones connect between injectors and producers. The highly permeable zone can be "plugged" by setting a gel plug, which forces the water into undrained surrounding areas.

Alkaline flooding

Alkaline substances are added to the injection water. These substances will react with the oil, resulting in reduced interfacial tension between oil and water, changing the wetting properties of the rock. This can mobilise parts of the residual oil, resulting in increased production.