Usually EOR processes could be classified into several types :
1. Mobility Control Processes
2. Chemical Processes
3. Miscible Processes
4. Thermal Processes
Mobility control processes objective is to maintain favorable mobility ratio to improve the macroscopic efficiency, Ev by means of adding polymers to increase water viscosity. This condition can avoid ” fingering” between water and oil in reservoir.
From this picture we can see that by adding polymers front of displacement is better than waterflooding. This method will increase the macroscopic efficiency and sweept out all of oil as much as possible.
Why we want to improve waterflooding method by adding polymers ?
1. Natural fractures or high permeability region in the reservoir sometimes will cause injected water to channel or flow around much of the oil in place by taking the path of least resistance.
2. The heavier oil or more viscous oil also cause problems for a waterflooding method
3. To help prevent injected water from bypassing oil (fingering). by adding polymers, the water can be made more viscous. This condition will allow the water to move through more of the reservoir rock, resulting in a larger percentage of oil recovery
Chemical processes objective is to improve the microscopic efficiency, Ed by means of using chemical substances such as surfactants. Some times mobility ratio is used in combination with chemical method to improve the macroscopic efficiency (Ev) and microscopic efficiency (Ed) simultaneously.
Source : Green D.W, Willhite G.P, , Enhanced Oil Recovery SPE Textbook series, Texas, 1998
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