BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Figure 5-16
Semi-Permeable Membranes
Emulsifiers
Surfactants
Surfactants lower surface energy/tension, as discussed earlier, and are required to emulsify the
water/aqueous phase and “oil-wet” the mineral solids. They are amphiphilic compounds with both
hydrophilic “heads” and organophilic “tails,” partially soluble in both water and oil.
Surfactants are conveniently classified according to the charge on the hydrophilic “head.” The main
classes are anionic (negatively charged), cationic (positively charged), and non-ionic (uncharged).
The surfactants used in CARBO-DRILL SM , ISO-TEQ TM , SYN-TEQ, and SYN-TEQ CF systems
include CARBO-TEC ® , CARBO-MUL ® HT, OMNI-MIX TM , OMNI-MUL and OMNI-TEC TM .
Because most modern invert emulsion fluids now contain more than one emulsifier with different
chemical structures but similar functions, they will be discussed separately.
Soaps
The most common anionics are soaps. Soaps were the first surfactants known and are common. They
are usually considered in a separate class. Soaps are formed from an alkaline material such as lime
[Ca(OH) 2 ] and “long-chain” organic acids, such as stearic acid which is derived from tallow. The lime
saponifies the stearic acid and supplies a cation (Ca ++ in this case), also referred to as a counter ion,
which balances the negatively charged hydrophilic head (see Figure 5-17).
Calcium soaps are the most commonly encountered soaps in oil-base fluids, or inverts, although
magnesium, ammonium, and amine soaps have been used. Long-chain organic acid sources include
tall oil, asphaltic, naphthalenic, and blown-wax acids. Soaps can be pre-formed and used, or can be
formed in the drilling fluid using lime.
Soaps are the cheapest surfactants. Some, such as asphaltics and naphthalenic, occur naturally in some
oils. Soaps are good emulsifiers in high pH or water-base drilling fluid systems, but less useful at
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 5-21