Page 350 - Petrophysics 2E

3 18 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

Figure 5.4. Three-phase water-wet system at equilibrium showing the radii of
interfacial curvature.

fluid saturation, and surface tension. The angle of contact (e) between
the liquid interface and the solid, measured through the denser phase,
is a function of the relative wetting characteristics of the two fluids
with respect to the solid. Figure 5.4 illustrates the typical shapes of the
interface and contact angle when the preferential wetting phase located
between the solid grains is at a low saturation. When the radii of curvature
have their centers of rotation on the same side of the interface they are
positive, but when the radii are on opposite sides, as shown in Figure 5.4,
R1 is positive and R2 is negative [3, 41. The radius of curvature on the
side of the interface occupied by the preferential wetting fluid is given a
negative sign [ 5 -81.
CAPILLARY RISE

When a capillary tube is inserted below the interface of a two-phase
system, the meniscus of the immiscible fluids in the capillary will be
either:

(1) concave with respect to the denser phase, which will rise above the
interface between the two liquids outside the capillary;
(2) straight across the capillary and level with the bulk fluids interface; or
(3) convex with respect to the denser phase and below the bulk fluids
interface as illustrated in Figure 5.5.