Overview of the main oil displacement mechanisms

When waterflooding a reservoir proves to be inefficient, in the sense that there is early water production and low oil recovery at breakthrough, polymer flooding may be considered as a possible remedy. However, exactly how the polymer flooding process is applied and how the design of the flood is determined depends on the nature of the recovery mechanism that is in operation. 

Central to all polymer oil recovery mechanisms, however, is the idea of mobility ratio, M, defined as  

Even in reservoirs where the water-oil mobility ratio is close to unity, there may be a very inefficient sweep by waterflooding because of reservoir 

In order to evaluate projects using the usual type of project economic analysis, it is important to have predicted recovery profiles for the continued waterflood and for a range of polymer flooding strategies. The only way of obtaining these data is to perform reservoir simulation calculations of the proposed projects. Although these calculations may be subject to many uncertainties and difficulties, they are currently the only available means of assessing projects of this type in a rational and consistent manner for a specific reservoir. For this reason, polymer flood simulation is discussed in some detail in this and other chapters. 

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