Page 39 - Petroleum and Gas Field Processing

known as the chemical recovery methods. The two most common chemical
recovery methods are as follows:
1. Surfactant Flooding: In this method, a slug of water–surfactant
solution is first injected through the injection well into the
formation. This is followed by injection of ordinary water as in
regular water-flooding operations. The surfactant ahead of the
floodwater causes changes in the interfacial tension and
mobilizes the oil that would otherwise adhere to the surface of
the rock. Thus, the displacement of the oil by the floodwater
becomes possible. Again, adding polymers to the water to create
favorable mobility conditions could increase the flooding
effectiveness. In this case, the method can be called surfactant–
polymer flooding.
2. Caustic Flooding: This method is essentially a surfactant
flooding, with the surfactant being generated within the reservoir
rather than being injected. The method is applicable in situations
where the reservoir oil contains high concentrations of natural
acids, which can react with alkaline to produce surfactants. The
most common approach is to inject a slug of caustic soda
(NaOH) solution ahead of the floodwater. The alkaline reacts
with the acids in the oil to in situ produce surfactants. Then, the
process is converted into a surfactant-flooding process. This
method is less expensive than the regular surfactant-flooding
process.

Miscible Recovery
In this method, a slug of a substance that is miscible in the reservoir oil is
injected into the reservoir at pressures high enough to achieve good
miscibility. This is then followed by water injection. The process has been
used with carbon dioxide, rich natural gas, nitrogen, flue gases, and light
hydrocarbon liquids as the miscible fluid. Miscible flooding could achieve
very high recovery factors.

Thermal Recovery

Heavy oil reservoirs present a unique production problem. The high
viscosity of the oil makes it difficult, and in some cases impossible, to
produce the oil, even with the above-discussed improved recovery
methods. The best method to mobilize the oil is to heat the formation
in order to reduce the oil viscosity. When heating is used in recovering the

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