Page 384 - Fundamentals of Reservoir Engineering

NATURAL WATER INFLUX 319

F/E (MMstb)
o
600

3 3
4 4 5
5 6
6 7
550 8 7 8 9
9,10 10
2 2

500

1
450 1

400

1,2,3...etc. Time (years)
r=5
eD
350 r=10
eD

N =312
p
300
100 200 300 400

W/E (MMstb)
o
e
Fig. 9.15 Aquifer fitting using the interpretation technique of Havlena and Odeh

9.4 THE APPROXIMATE WATER INFLUX THEORY OF FETKOVITCH FOR FINITE
AQUIFERS

The unsteady state influx theory of Hurst and van Everdingen provides the correct
method for calculating the cumulative water influx, under practically all circumstances,
for radial and linear aquifers. Unfortunately, it has the disadvantage that calculations
performed using the method are rather tedious, due to the complexity of superposing
solutions for each time step. This drawback is exaggerated by the fact that influx
calculations, when history matching, usually require a trial and error approach.
Because of this, many attempts have been made in the past to find a more direct
computational method of performing water influx calculations which would duplicate
results obtained with the Hurst and van Everdingen method and remove the necessity
of superposition.

2
The most successful of the methods is that proposed by Fetkovitch in 1971 . In this
approach the flow of aquifer water into a hydrocarbon reservoir is modelled in precisely