Page 381 - Petrophysics 2E

VERTICAL SATURATION PROFILE IN A RESERVOIR 349

\

-
-4
-I 6-
2
0 4- CI
c
.-
W
2-
0 I FWL
0 0.2 t 0.4 0.6 0.8 1.0
t
Slw Swor
WATER SATUR All 0 N
Figure 5.22. Vertfcal Saturation profile of a reservoir calculated from a capillaq?
pressure curve.

the free water level. The position of the maximum value of the residual oil
saturation can be located; this is important because no mobile oil exists
at depths below this point. A transition zone exists between S,,, and
Si, where water is always produced along with the oil. If the reservoir
thickness is large enough to exceed the value at Si, (135 ft, Figure 5.22),
only oil will be produced at heights above the point were Si, occurs.
Mixed wettability and oil-wet reservoirs will not have a threshold
pressure because the cores, when saturated 100% with water and
contacted with oil, will imbibe oil at zero capillary pressure. The oil-water
contact and the free water level, therefore, are synonymous (occurring
at the same point).
When the core data from a reservoir indicate variability of permeability
and porosity throughout the sand, or as a trend increasing or decreasing
with respect to depth, the capillary pressure data for each core can be
reduced to a single J-function curve, which is a function of saturation:

(5.64)