Fundamentals of Fluid Flow in Porous Media

 

Chapter 2

Multi-phase Saturated Rock Properties:

Effect of Pore Geometry on Capillary Pressure

Capillary pressure is affected by the geometry of a given porous medium.  The following section discusses the effects of flow into and out of a constriction.

In the case of fluid flowing into a constriction (Figure 2‑53), pressure is needed to force the non-wetting phase into the constriction and the wetting phase out of the constriction. According to the figure:

The equation for capillary pressure then becomes:

Where, R decreases from left to right (in the direction of flow) resulting in an increased Pc, allowing the meniscus to move from left to right into the constriction.

Figure 2-53: Flow Into a Constriction (Cone)

Figure 2‑54 shows an example of a fluid flowing out of a constriction, Pc decreases with position as meniscus moves from left to right in the direction shown in this figure. According to the figure:

The equation for capillary pressure becomes:

In order to change the position of the meniscus P_nw, P_w or R may be altered (all other parameters are fixed).

Figure 2-54: Flow Out of a Constriction