BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
potassium chloride in sea water before the potassium ion became the dominant ion as apposed to
magnesium, calcium, and the other cations indigenous to naturally occurring seawater.
Potassium
KCl is most often used to supply the major source of potassium. Most data to date indicates that
a 3% to 5% concentration (10.7 to 18.1 lbm/bbl) is sufficient to provide inhibition of clay
swelling and hydration. Attempts have been made to increase the inhibitive effect by increasing
the KCl concentration up to 15% (57.6 lbm/bbl), but improved clay stability has not always been
achieved.
A secondary source of potassium is potassium hydroxide (KOH) which is sometimes used as an
alkalinity agent, similar to caustic soda (NaOH). Generally, it is used in such low concentrations
that the K + ion contribution is insignificant. Approximately 1.6 lb of KOH is required to get the
same pH effect as one pound of caustic soda. KOH provides approximately 2000 ppm of K + ion
for each pound per barrel added.
Viscosifiers
Materials used as viscosifiers in potassium-based systems include,
• XAN-PLEX ® (xanthan gum)
• MILGEL ® (Wyoming bentonite)
• Colloidally protected bentonite
• Guar gum (modified)
• Hydroxyethylcellulose (HEC).
PERMA-LOSE HT (Modified starch - functions as both viscosifier and filtration additive)
The combination of 6 to 10 lbm/bbl pre-hydrated bentonite plus 1.0 lbm/bbl XAN-PLEX has
been a commonly used viscosifying treatment. In some cases, because of shortages, guar gum
and HEC have been used as viscosifiers. Though these products do increase viscosity, they do
not increase carrying capacity satisfactorily; accordingly they are considered unsatisfactory
substitutes and require higher bentonite concentrations to provide adequate hole cleaning.
Note:
Colloidally protected bentonite will yield higher Fann low rpm viscosities in a potassium
chloride environment and retain this viscosity longer when compared to unprotected prehydrated
bentonite.
This base fluid typically exhibits an extremely high yield point, plastic viscosity ratio, and a
relatively high filtration rate. For example,
• PV = 5 cP
• YP = 35 lb f / 100 ft 2
• Filtrate (API) = 25 to 35 mL/30 min
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-49