Environmental Engineering Reference
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100%
Oil
Water
0
Water Content
Oil Content
0
100%
0
S
wir
100%
S
or
Figure 3.1
Generic relative permeability curves, for preferentially water wet reservoirs
(ater Cohen and Mercer, 1992)
what conditions. Laboratory relative permeability measurements are uti-
lized by reservoir engineers to aid in depletion planning.
The oil/water (k
o/w
) relative permeability curves are complex functions of:
• The pressure gradient within the reservoir
• The relative viscosities of the oil and water phases
• The interfacial tension, between the two immiscible phases
• The matrix wettability
• The capillary forces at the pore throat restrictions, within the
matrix
• The amounts of oil and water (
S
o
and
S
w
) in the reservoir
rock
At irreducible water saturation (
S
wir
), only oil will be produced. At resid-
ual oil saturation (
S
or
), only water can be produced. Comparing the relative
permeability values at intermediate
S
w
and
S
o
values provides estimates of
the oil production and water cut.
For depletion management, the goal is to keep as high on the oil sat-
uration (S
o
) curve as (economically) possible, by managing what can be
managed (usually field balanced production rates) for primary recovery. In
this fashion, oil production is maximized and the water cut is minimized,
increasing income and reducing disposal costs.
During primary production, the reservoir drive declines and secondary
measures, such as gas lift, gas flood, miscible gas injection, and water flood
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