Oil & Gas Terms in Category S

Side pocket

An offset heavy-wall sub in the production string for placing gas lift valves, and so on.

Spiral grapple

A helically shaped gripping mechanism that is fitted into an overshot to retrieve fish from the borehole.

See grapple.

Surfactant mud

A drilling mud prepared by adding a surfactant to a water-base mud to change the colloidal state of the clay from that of complete dispersion to one of controlled flocculation.

Such muds were originally designed for use in deep, high-temperature wells, but their many advantages (high chemical and thermal stability, minimum swelling effect on clay-bearing zones, lower plastic viscosity, and so on) extend their applicability.

Settling pit

See shaker tank

Sodium carbonate

Used extensively for treating various types of calcium contamination.

Also called soda ash.

Stock tank barrel

Stb; one barrel of stabilized or dead oil at the surface after the gas has escaped.

See stock tank conditions.

Semi-expendable gun

A perforating gun that consists of a metallic strip on which encapsulated shaped charges are mounted.

After the gun is fire, the strip is retrieved.

See gun-perforate.

Seismic data

Detailed information obtained from earth vibration produced naturally or artificially (as in geophysical prospecting).


Abbreviation: spontaneous potential or self-potential.


The degree to which a substance will dissolve in a particular solvent.

Seal-bore extension

A tube extending the effective packer seal bore; used where excessive tubing expansion or contraction is anticipated.

Slow formation

A formation in which the velocity of the compressional wave traveling through the borehole fluid is greater than the velocity of the shear wave through the surrounding formation.

In such conditions, there is no critical refraction of the shear wave and no shear head wave generated, so that standard techniques based on monopole transducers cannot be used to measure formation shear velocity.

Instead, it is necessary to use dipole sources to excite the flexural mode.

The velocity of the latter is closely related to that of the shear wave.

In very slow formations, such as in high-porosity gas sands, the formation compressional velocity also may be less than the borehole fluid velocity, causing no compressional head wave.

In such cases, it is possible to estimate the formation compressional velocity from the low-frequency end of a leaky mode.

see also fast formation.


A device used to clean deposits of paraffin from tubing or flow lines (see pig or rabbit).


The sodium or potassium salt of a high-molecular weight fatty acid.

Commonly used in drilling fluids to improve lubrication, emulsification, sample size, and defoaming.

Saturated solution

A solution that contains at a given temperature as much of a solute as it can retain.

At 68 degrees f it takes 126.5 lb/bbl salt to saturate 1 bbl of fresh water.

See supersaturation.