BAKER HUGHES - Drilling Fluids Reference Manual

Oil / Synthetic Fluids
Surface energies/tensions, as a result, are even higher in ionic solids such as glass, quartz, clays, barite,
and most mineral solids. High-surface energy/tension liquids, such as water, will interact strongly
with high-surface energy (hydrophilic) solids, such as glass, and the attractive forces are sufficient to
overcome gravity causing water to rise in glass capillary tubes as shown in Figure 5-7.
Figure 5-7
Surface Tension Causing the Capillary Rise of Water in a Small Glass Tube
Nonpolar molecules (such as hydrocarbon oils, waxes, and many plastics) show only weak attractive
forces between molecules, small imbalances of force at the surface, and have low surface
energies/tensions. High surface energy liquids, such as water, will not interact with low-energy
surfaces, such as plastic, and will not rise in plastic capillaries. Low-surface energy liquids, such as
hydrocarbon oils, will interact only weakly with any surface and show only minimal capillary rise
regardless of the capillary material used.
Emulsions
Liquids which are soluble in one another are said to be miscible. An example of soluble liquids is
water and alcohol. Liquids which are not soluble in each other are immiscible. An example would be
water and oil.
When immiscible liquids are mixed vigorously, one liquid will be suspended or dispersed as droplets
in the other liquid. Such two-phase systems are called emulsions (see Figure 5-8). The dispersed or
suspended liquid is called the internal, or dispersed, phase. The other liquid is called the external, or
continuous, phase.
Baker Hughes Drilling Fluids
Reference Manual
5-12 Revised 2006