Page 356 - Petrophysics 2E

324 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

Prsssure Regulators
Transducers & Dlgital Voltmeters

Cyllnder Alr Compressor
Figure 5.8. Porous disk method for measurement of capillary pressure using a
pressure transducer [331.

The pressure of the displacing fluid is increased in small increments
(Figure 5.8). After each increase of pressure, the amount of water
displaced is monitored until it reaches static equilibrium. The capillary
pressure is plotted as a function of water saturation as shown in
Figures 5.9 and 5.10. If the pore surfaces are preferentially wet by water,
a finite pressure (the threshold pressure, Pet) will be required before
any of the water is displaced from the core (Figure 5.9). If the core is
preferentially oil wet, and oil is the displacing fluid, oil will imbibe into
the core, displacing water at zero capillary pressure (Figure 5.10).
The displacement may be reversed by placing the core on another
porous disk, which is saturated with oil, and the core is covered with
water. If the core is preferentially wet by water, water will imbibe into the
core and displace the oil toward residual oil saturation (Sor = 1 - Swor),
following a path such as curve 2 in Figure 5.9. If the core is preferentially
wet by oil, a path similar to curve 2 in Figure 5.10 will be followed.

MEASUREMENT CAPILLARY PRESSURE
BY
OF
ERCURY INJECTION

CapilIary pressure curves for rocks have been determined by mercury
injection and withdrawal because the method is simple to conduct