Reservoir Mechanisms of Polymer Flooding


The value of adding polymer to a conventional waterflood can be explained by considering the mobility ratio which is defined by the following formula:
 

 
where λ, µ and k are the mobility, viscosity and effective permeability respectively and where the subscripts w and o refer to water and oil.
 
 
A mobility ratio equal to 10 means that water is ten times more mobile than oil. To decrease this value and bring it close to 1, a possibility is to increase the viscosity of water, referred as µw.
Polymers will increase the water viscosity and thus the mobility ratio and the displacement efficiency in the reservoir. It can be achieved with concentration ranges from a few hundred ppm to as high as 2000 ppm for typical polymer flood projects. It depends on the water characteristics and especially salinity. High salinity waters require fine-tuned products and stability tests to ensure that no degradation occurs. It is also valid for high temperature reservoirs.