Page 299 - Petrophysics 2E
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270 PETROPHYSICS: RESERVOIR ROCK PROPERTIES
(1) Select cores that have not been dehydrated by excessive heat or
cleaned excessively with solvents.
(2) Remove hydrocarbons from the core by flushing it with propane and
then with water.
(3) Measure core electrical conductivity Co vs. water conductivity Cw
for at least three different salinities.
(4) Plot Co, against C,.
(5) Repeat Steps 3 and 4 until the points form a straight line as shown
in Figure 4.34.
(6) If the term CesQv/C&, evaluated at formation water salinity, is greater
than 0.1, the shaliness effect is significant.
EXAMPLE
Estimate the water saturation of a sandstone formation which displays
the following characteristics:
Porosity = 25%
Shaly-sand formation resistivity factor, F * = 12.43
CEC = 0.08 meq/g
Formation temperature = 230°F
Rw = 0.04 ohm-m
Rt = 4 ohm-m
pma = 2.65 g/cm3
Shaly-sand saturation exponent n* = 2
SOLUTION
Similar to Equation 4.92, the quadratic form of the Waxman and Smith
model in terms of resistivity is:
(RJ s$ + (R~R,BQ,) s, - F*R~ = o (4.140a)
The effective volume concentration of clay-exchange cation, Qv,
can be estimated as follows (Equation 4.141):
0.08(1 - 0.25)2.65
Qv = 0.636 meq/cm3
(0.25)
