Page 344 - Shale Shakers Drilling Fluid Systems

326 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Stroke The distance between the extremities of motion or total displacement
normal to the screen (i.e., the diameter of a circular motion or twice the
amplitude). See.- Amplitude.

Stuck A condition whereby the drill pipe, casing, or any other device inserted
into the wellbore inadvertently becomes lodged in the hole. Sticking may
occur while drilling is in progress, while casing is being run in the hole,
or while the drill pipe is being tripped.

Stuck Pipe See.- Differential Pressure Sticking, Stuck.

Suction Compartment (1) The area of the check/suction section from which drilling fluid is
picked up by the suction of the mud pumps. (2) Any compartment from
which a pump moves fluids.

Sump (1) A disposal compartment or earthen pit for holding discarded liquids
and solids. (2)The pan or compartment below the lowest shale shaker
screen.

Super-Saturation If a solution contains a higher concentration of a solute in a solvent than
would normally correspond to its solubility at a given temperature, a state
of super-saturation exists. This is an unstable condition because the ex-
cess solute separates when the solution is seeded by introducing a crys-
tal of the solute. The term "super-saturation" is frequently used errone-
ously for hot salt drilling fluids.

Support Screen A heavy, wire mesh—either plain or calendered—that supports a finer
mesh(s) screen for use in filtering or screen separation. See.- Back-up
Screen.

Surface Active Materials See. Surfactant.

Surface Tension Generally, the cohesive forces acting on surface molecules at the inter-
face between a liquid and its own vapor. This force appears as a tensile
force per unit length along the interface surface and is usually expressed
in units of dynes per centimeter. Since the surface tension is between
the liquid and air, values measured against air are commonly referred to
as "surface tension," and measurements at an interface between two liq-
uids or a liquid and a solid are termed "interfacial tension." See.- Interfa-
cial Tension, Emulsion.
Surfactant Material that tends to concentrate at an interface of an emulsion or a
solid liquid. Used in drilling fluids to control the degree of emulsifica-
tion, aggregation, dispersion, interfacial tension, foaming, defoaming, wet-
ting and the like.

Surfactant Drilling Fluid A drilling fluid that contains a surfactant. Usually refers to a drilling fluid
containing surfactant material to effect control over the degree of aggre-
gation and dispersion or emulsification.

Surge The pressure increase in a wellbore caused by lowering tubulars. Viscous
drilling fluid flowing up the annulus, displaced by drill pipe, tubing, or
casing, creates the pressure surge.

Surge Loss This is a colloquial term used to describe a spurt of filtrate and solids,
which occurs in the initial stages of any filtration before pore openings
are bridged and a filter cake is formed. The preferred term is "spurt loss."
See.- Spurt Loss.