Page 339 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

306 Reservoir Engineering

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-0 500 IO00 1500 2000 2500
PERMEA 81 L ITY , md

Figure 5-173. Critical capillary number as a function of permeability [194].
cases, as the core is raised, gases will come out of solution and can cause residual
oil to bleed from the core. The loss of gas causes the oil to shrink.

Corrections for Shrinkage and Bleeding. Shrinkage of residual oil can be esti-
mated from laboratory measurements of shrinkage when the pressure of bottom-
hole oil samples is lowered. Reduction of temperature will also contribute to
shrinkage. The following corrections have been proposed for the effects of
shrinkage and bleeding [125].
(SJR = (SJC B.E (5-247)

where (S0JR = average post-waterflood residual oil saturation in the flooded
region of the reservoir
(SJ, = average oil saturation from cores
Bo = oil formation volume factor at the time of coring
E = bleeding factor (in the absence of specific bleeding measure-
ments, a value of 1.11 is assumed)

A modification to this calculation has been suggested [325] to compensate
for waterflood displacement efficiency by dividing the reservoir residual oil
saturation by the conformance factor. In the absence of a reservoir simulator
that accounts for reservoir heterogeneity, capillary effects, mobility of oil,
and mobility of water, it was suggested the conformance factor be estimated by
(1 - W/M
where M = mobility ratio or the ratio of the mobility of water at the average
water saturation in the reservoir at breakthrough to the mobility of
oil in the oil bank ahead of the displacing hnt
V = the Dykstra-Parsons permeability variation