Page 520 - Practical Well Planning and Drilling Manual

Appendix NEW! revised 11/00/bc 1/30/01 3:30 PM Page 496

[ ]
Glossary

Shear Rate. This is the relative velocity of the fluid layers, divided by
their normal separation distance. See also Viscosity.

Shear Strength. A measure of the shear value of the fluid. The mini-
mum shearing stress that will produce permanent deformation. See
Gel Strength.

Shear Stress. This is an expression used in muds to describe the
force required to overcome a fluid’s resistance to flow, divided by the
area that the force acts on. See also Viscosity.

Shoulder Effect. An anomaly on resistivity logs where a low resis-
tance formation and a high resistance formation meet. The change in
resistivity “channels” the current causing characteristic horn-shaped
signal responses in uncorrected logs. The effects can be corrected by
tool design and signal processing.

Side Wall Coring. The taking of geological samples of the formation
which constitutes the wall of the well bore. Another term in general
use for this operation is “side wall sampling.”

Skid. Moving a rig from one location to another, usually on tracks,
where little dismantling is required.

Slim-Hole drilling. Slim hole, by current Industry definition, is one
where the well is TD’d in 41/2” or smaller hole size. Slim-Hole
drilling brings significant cost and environmental benefits but
makes well control more difficult due to the high ECDs and small
annular capacities.

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 also Heaving
and Cave-in.

496