BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
UNI-CAL ® Systems
Lignosulfonates were introduced in the late 1950s as deflocculants for calcium-base systems. In
the early 1960s, Milchem Drilling Fluids (Baker Hughes Drilling Fluids) introduced
lignosulfonate to the industry as a deflocculant in drilling fluids without the presence of gypsum
or lime. The petroleum industry has since used the material regularly in this manner.
UNI-CAL ® , a chrome lignosulfonate product, is extremely effective in the presence of salt and
calcium contamination and has performed well in wells with bottom hole temperatures
approaching 400°F.
Flocculation is the clustering of suspended colloidal particles. The two forces of attraction usually
considered are: (1) partial valence forces, and (2) London Van der Waals forces. The two
mechanisms generally credited with deflocculation or thinning are: (1) electro kinetic
stabilization, which is a rather delicate form of control achieved with materials such as
phosphates, silicates and tannins, and (2) mechanical stabilization, which is fairly rugged in
nature.
The latter type of stabilization is achieved through the formation of a viscous physical barrier. It
is the result of the adsorption of an organic polyelectrolyte on the clay particles. This type of
stabilization requires higher UNI-CAL concentrations in the system on the order of 6 to 8
lbm/bbl. One of the unique properties of UNI-CAL is its ability to deflocculate effectively at
relatively low pH values. This is most helpful when drilling hydroxyl-sensitive clays and shale
formations.
With any fluid conditioning agent, preparing a “recipe” to accurately predict the quantities of
materials required is difficult. Therefore, the following recommendations should be viewed only
as guidelines.
• For top-hole drilling with freshwater fluids, 0.5 to 1.0 lbm/bbl of UNI-CAL is usually
sufficient to establish rheological and filtration control.
• As a deflocculant for seawater fluids, 3 to 6 lbm/bbl is usually adequate. The pH is normally
maintained in the 10.0 to 10.5 range to suppress calcium and magnesium solubility and to
minimize corrosion problems.
• To obtain inhibition with UNI-CAL systems, concentrations of 6 to 8 lbm/bbl are necessary.
Inhibition is derived from the adsorbed layers of UNI-CAL and offers a significant degree of
protection against dispersion and swelling of clay solids.
• For rheological stability in the presence of high bottom hole temperatures ( 350°F+),
supplementary additions of ALL-TEMP ® are beneficial. Field test data indicates that this
material effectively extends the thermal stability of UNI-CAL systems. ALL-TEMP
treatment ranges between 0.5 and 3 lbm/bbl.
• Maintenance requirements for UNI-CAL systems vary with penetration rate, hole size, fluid
density, temperature, solids control program, and the formation being drilled. With good
solids control, maintenance additions can range between 0.5 and 1 lbm/bbl with an average
daily penetration rate of 100 to 200 ft.
• Supplementary filtration control can be maintained with treatments of MILGEL
(approximately 20 lbm/bbl in freshwater and 30 to 35 lbm/bbl in seawater) and a lignite
material such as LIGCO or LIGCON. For temperatures above 300°F or severe salt and
calcium contamination, CHEMTROL X would be a more effective additive.
Reference Manual
Baker Hughes Drilling Fluids
3-66 Revised 2006