Page 34 - Principles of Applied Reservoir Simulation 2E

Chapter 3

Multiphase Flow Concepts

This chapter summarizes the basic concepts of multiphase flow including
interfacial tension, wettability, and contact angle. These concepts lead naturally
to a discussion of capillary pressure, mobility, and fractional flow.

3.1 Basic Concepts

Some basic concepts must be introduced as prerequisites for understanding
capillary pressure. The concepts are interfacial tension, wettability, and contact
angle. They are defined here.

Interfacial Tension
On all interfaces between solids and fluids, and between immiscible fluids,
there is a surface free energy resulting from electrical forces. These forces cause
the surface of a liquid to occupy the smallest possible area and act like a
membrane. Interfacial tension (IFT) refers to the tension between liquids at a
liquid/liquid interface. Surface tension refers to the tension between fluids at
a gas/liquid interface.
Interfacial tension is energy per unit of surface area, or force per unit
length. Interfacial tension is often abbreviated as IFT. The units of IFT are
typically expressed in milli-Newtons/meter or the equivalent dynes/cm. The
value of IFT depends on the composition of the two fluids at the interface
between phases. Table 3-1 lists a few examples:

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