Page 76 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 61

production well. A reduction in well spacing requires an increase in the density
of production wells. The density of production wells is the number of production
wells in a specified area. Well density can be increased by drilling additional
wells in the space between wells in a process called infill drilling. Infill drilling
is an effective means of altering flow patterns and improving recovery efficiency,
but can be more expensive than a fluid displacement process. The selection of
a development plan depends on a comparison of the economics of alternative
development concepts. Reservoir models are especially useful tools for
performing these studies.

7.3 Pattern Recovery

Optimum performance may be achieved with the patterns defined in the
previous section by controlling the rates of injectors and producers. These
calculations can be performed analytically if we assume the displacing and
displaced fluids are incompressible, the mobility ratio is one, and the reservoir
has uniform properties. Values of injection rates for the three patterns shown
in Figure 7-1 are presented in Table 7-2 [ Wilhite, 1986]. Units and nomenclature
for the rate equations in Table 7-2 are barrels per day for rate q; darcies for
permeability k; feet for thickness h; well separations a and d, and wellbore radius
3
r w; pounds per square inch for pressure change A/ ; and centipoise for viscosity
|i. The well separations are defined in Figure 7-1.

Table 7-2
Analytical Injection Rates for Selected Well Patterns
Pattern Rate
3.541 khbP d
q = — -,-> 1
Direct Line Drive a
H In — + 1.571- -1.838
\r w) a

3541 kh^P
Staggered Line Drive
M In — + 1.571- -1.838
\r wj a