BAKER HUGHES - Drilling Fluids Reference Manual

GLOSSARY OF TERMS
Buffer - Any substance or combination of substances which, when dissolved in water, produces a
solution which resists a change in its hydrogen ion concentration upon the addition of acid or base.
Cable-Tool Drilling - A method of drilling a well by allowing a weighted bit at the bottom of a cable
to fall against the formation being penetrated. See Rotary Drilling.
Cake Consistency - According to APIRP 13B. such notations as "hard." "soft." "tough." "rubbery ...
"firm." etc.. may be used to convey some idea of cake consistency.
Cake Thickness – The thickness measurement of filter cake deposition by a drilling fluid against a
porous medium, most often following the standard API filtration test. Cake thickness is usually
measured in 1/32 of an inch. See-Filter Cake and Wall Cake.
Calcium - An alkaline earth element with a positive valence of 2 and an atomic weight of about 40.
Calcium compounds are indigenous to the hardness of water. It is also a component of lime, gypsum,
limestone, etc.
Calcium Carbonate - CaCO 3 . A water insoluble, yet acid soluble calcium salt sometimes used as a
weighting material (limestone, oyster shell, etc.), in specialized drilling fluids. It is also used as a unit
and/or standard to report hardness.
Calcium Chloride - CaCI 2 . A hydroscopic salt used in both oil and water based drilling fluids for
inhibition control. Used in completion fluids for inhibition and to increase the density of clear brines.
Calcium Contamination - Dissolved calcium ions in sufficient concentration to impact undesirable
properties in a drilling fluid, such as flocculation, reduction in yield of bentonite, increase in fluid
loss, etc. See also Calcium Carbonate.
Calcium Hydroxide - Ca(OH) 2 . The active ingredient of slaked lime. It is also the main constituent
in cement (when wet). This material is referred to as "lime" in field terminology.
Calcium-Treated Fluid - Calcium-treated fluids are drilling fluids to which quantities of soluble
calcium compounds have been added or allowed to remain from the formation drilled in order to
impart special rheological and inhibition properties.
Calcium Sulfate - (Anhydrite: CaSO 4 ; plaster of paris: CaSO 4 x ½H 2 O and gypsum: CaSO 4 x 2H 2 0).
Calcium sulfate occurs in fluids as a contaminant from the formation drilled or may be added to
certain fluids to impart special properties of inhibition and/or rheology.
Carrying Capacity - The ability of a circulating drilling fluid to transport cuttings out of the
wellbore. Carrying capacity is an essential function of a drilling fluid, synonymous with
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 15-8