Estimation of Waterflood Recovery Efficiency

Equation (11.1) is an expression for the overall recovery efficiency for any fluid displacement process:

where

E = overall recovery efficiency

E_v = volumetric displacement efficiency

E_d = microscopic displacement efficiency

The volumetric displacement efficiency is made up of the areal displacement efficiency, E_s, and the vertical displacement efficiency, E_i. To estimate the overall recovery efficiency, values for E_s, E_i, and E_d must be estimated. Methods of estimating these terms are discussed in waterflood textbooks and are too lengthy to present in detail here.^3–7 However, some brief, general comments concerning each of the displacement efficiencies can be made.

There are several methods of obtaining estimates for the microscopic displacement efficiency. The basis for one method was presented. The areal displacement, or sweep, efficiency is largely a function of pattern type and mobility ratio. The vertical displacement efficiency is primarily a function of reservoir heterogeneities and thickness of the reservoir formation.

Waterflooding is an important process for the reservoir engineer to understand. A successful waterflood in a typical reservoir results in oil recoveries increasing from 25% after primary recovery to 30% to 33% overall. It has made and will continue to make large contributions to the recovery of reservoir oil.