Page 436 - Petrophysics

404 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

(b) If a sandstone is saturated with a brine containing multivalent
cations, will the surface adsorb acetic polar organic compounds
from an oil? Explain your answer using chemical formulas.
4. (a) Explain three methods that can be used to artificially render a
water-wet sandstone surface oil-wet.
(b) What is the difference between the terms mixed wettability and
fractional wettability?
(c) If the Amott wettability index is negative, does this mean that the
rock is water-wet or oil-wet?
(d) If the USBM wettability index is positive, does this mean that the
rock is water-wet or oil-wet?
(e) Draw two hypothetical (negative) water-displacing-oil capillary
pressure curves, one for a water-wet system and the other for
an oil-wet system. Why is the displacement energy less for the
displacement of oil from the water-wet sand?
5. What is the principal reason why fluid/flow experiments should
be conducted at reservoir conditions of temperature, pressure, and
salinity? What is the influence of salinity?
6. If two water-oil-rock systems are tested and one is found to be
water-wet while the other is oil-wet, will the Archie saturation index
(n) be greater for one of the systems? Which one? Justify your answer.
7. If the formation resistivity factor (FR) for a core is measured at ambient
conditions (25"C, 100 kPa) and again at reservoir conditions (62OC,
28 MPa):

(a) Would you expect FR to be greater at ambient conditions or lower?
Give a sample calculation to prove your answer.
(b) What took place to produce the change of FR, if any?
8. Draw two hypothetical oil recovery versus water injected curves, one
for a water-wet system and the other for an oil-wet system.

(a) Which one has the greater rate of oil recovery?
(b) Which one exhibits water breakthrough first?
(c) Which one shows greater recovery after 1.5 pore-volumes of water
have been injected?
(d) Explain, theoretically, why the systems are different.

NOMENCLATURE

A = area; constant (as defined in text)
B =constant
C =constant
C,, = spreading coefficient
F =force(mN)
FE = free energy