Page 73 - Principles of Applied Reservoir Simulation 2E

58 Principles of Applied Reservoir Simulation

„ _ swept thickness
(7,4)
total thickness

Reservoir flow models are useful tools for quantifying both swept area and swept
thickness. The product of areal and vertical sweep efficiency is the volumetric
sweep efficiency E vol:

E
vor^E F (7.5)
where

E A areal sweep efficiency
vertical sweep efficiency
E y
Overall recovery efficiency must account for both volumetric and
displacement effects. It is therefore defined as the product of volumetric sweep
efficiency and displacement efficiency:

^-E D^E vorE D^E AxE y (7,6)
where
RE recovery efficiency

Notice that each of the efficiency factors in recovery efficiency can be relatively
large,, and yet recovery efficiency will be relatively small. For example, suppose
the areal and vertical efficiencies are each 70% and displacement efficiency is
80%, the product of these efficiencies is approximately 39%. This means that
even the reservoirs with the best recovery efficiency often have a substantial
volume of unrecovered hydrocarbon remaining in the ground. The most
important goal of improved recovery techniques is to recover this remaining
resource.

7.2 Patterns and Spacing
The displacement processes discussed in Chapters 5 and 6 study fluid
displacement between one injection well and one production well. The alignment
of the injector-producer pair represents a linear displacement process. It is the
simplest pattern involving injection and production wells. A variety of other