TABLE OF CONTENTS The vertical sweep efficiency, EV, is defined as the fraction of the vertical section of the pay zone that is the injection fluid. This particular sweep efficiency depends primarily on (1) the mobility ratio and (2) total volume injected. As a consequence of the nonuniform permeabilities, any injected fluid will tend to move through the reservoir with an irregular front. In the more permeable portions, the injected water will travel more rapidly than in the less permeable zone.
Perhaps the area of the greatest uncertainty in designing a waterflood is the quantitative knowledge of the permeability variation within the reservoir. The degree of permeability variation is considered by far the most significant parameter influencing the vertical sweep efficiency.
To calculate the vertical sweep efficiency, the engineer must be able to address the following three problems:
How to describe and define the permeability variation in mathematical terms
How to determine the minimum number of layers that are sufficient to model the performance of the fluid
How to assign the proper average rock properties for each layer (called the zonation problem)
A complete discussion of the above three problems is given below.
As pointed out in Chapter 4, one of the first problems encountered by the reservoir engineer is that of organizing and utilizing the large amount of data available from core and well logging analyses. Although porosity and connate water saturation may vary aerially and vertically within a reservoir, the most important rock...
