BAKER HUGHES - Drilling Fluids Reference Manual

GLOSSARY OF TERMS
Silt - Materials that exhibit little or no swelling whose particle size generally falls between 2 microns
and API sand size, or 74 microns (200-mesh). A certain portion of dispersed clays and barite for the
most part also fall into this same particle-size range.
Skid - Moving a rig from one location to another, usually on tracks where little dismantling is
required.
Slide - To drill with a mud motor rotating the bit downhole without rotating the drillstring from the
surface. This operation is conducted when the bottomhole assembly has been fitted with a bent sub
or bent housing mud motor, or both, for directional drilling. Sliding is the predominant method to
build and control or correct hole angle in modern directional drilling operations. By controlling the
amount of hole drilled in the sliding versus the rotating mode, the wellbore trajectory can be
controlled precisely.
Slip Velocity - The difference between the annular velocity of the fluid and the rate at which a
cutting is removed from the hole.
Sloughing - The partial or complete collapse of the walls of a hole resulting from incompetent,
unconsolidated formations, high angle or repose, and wetting along internal bedding planes. See
Heaving and Cave-In.
Slug the Pipe - A procedure before pulling the drillpipe whereby a small quantity of heavy fluid is
pumped into the top section of the drillstring to cause an unbalanced column. As the pipe is pulled,
the heavier column in the drillpipe will fall, thus keeping the inside of the drillpipe dry at the surface
when the connection is unscrewed.
Smectite Clay - A category of clay minerals that have a three-layer crystalline structure (one
alumina and two silica layers) and that exhibit a common characteristic of hydrational swelling when
exposed to water. Montmorillonite is a well-known smectite clay mineral. Its sodium form,
bentonite, is a widely-used water mud additive. It is also used as an oil-mud additive when made
oil-dispersible by surface treatment.
Soap - The sodium or potassium salt of a high molecular-weight fatty acid. When containing some
metal other than sodium or potassium, they are called "metallic" soaps. Soaps are commonly used in
drilling fluids to improve lubrication, emulsification, sample size, defoaming, etc.
Soda Ash - See Sodium Carbonate.
Sodium - One of the alkali metal elements with a valence of -1 and an atomic weight of about 23.
Numerous sodium compounds are used as additives to drilling fluids.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 15-42