Oil & Gas Terms in Category T

Thief formation

A formation that absorbs drilling fluid as it is circulated in the well.

Lost circulation is caused by a thief formation.

Also called a thief sand or a thief zone.

Tool joint

A heavy coupling element for drill pipe.

It is made of special ahoy steel and has coarse, tapered threads and seating shoulders designed to sustain the weight of the drill stem, withstand the strain of frequent coupling and uncoupling, and provide a leakproof seal.

The male section of the joint, or the pin, is attached to one end of a length of drill pipe, and the female section, or box, is attached to the other end.

The tool joint may be welded to the end of the pipe, screwed on, or both.

A hard-metal facing is often applied in a band around the outside of the tool joint to enable it to resist abrasion from the walls of the borehole.

Tour (pronounced “tower”)

A working shift for drilling crew or other oilfield workers.

The most common tour is 8 hours; the three daily tours are called daylight, evening (or afternoon), and graveyard (or morning).

Sometimes 12-hour tours are used, especially on offshore rigs; they are called simply day tour and night tour.

Tubing tester

A mechanically operated (tubing rotation) valve u used to shut off formation pressure above a packer, thus testing all connections form the packer to the tree.

Telescoping swivel sub

A sub with a telescoping joint used in dual or triple completions for running additional tail pipe.

Top drill

A drillable tool configuration allowing the opening of formation pressure, during drillout, prior to cutting through the tools slips.

Temporarily abandoned

Temporarily shut in but not plugged.

Tail pipe


A pipe run in a well blow a packer.


A pipe used to exhaust gases from the muffler of an engine to the outside atmosphere.

Torque converter

A hydraulic device connected between an engine and a mechanical load such as a compound.

Torque converters are characterized by an ability to increase output torque as the load causes a reduction in speed.

Torque converters are used on mechanical rigs that have compounds.


A downhole motor that rotates a bit by the action of the drilling mud on turbine blades b built into the tool.

When a turbodrill is used, rotary motion is imparted only at the bit; therefore, it is unnecessary to rotate the drill stem.

Although straight holes can be drilled with the tool, it is used most often in directional drilling.


Pertaining to the transmission of signals over long distances, such as by telegraph, radio, or television.

Tailing in

Guiding a downhole tool into the wellbore or up onto the rig floor.


A vessel in which oil is treated for the removal of s&w or other objectionable substances by the addition of chemicals, heat, electricity, or all three.

Thinning agent

A chemical or combination of chemicals that, when added to a drilling mud, reduces its viscosity.

Trip tank

A small mud tank with a capacity of 10 to 15 barrels, usually with 1-barrel or h-barrel divisions, used to ascertain the amount of mud necessary to keep the wellbore full with the exact amount of mud that is displaced by drill pipe.

When the bit comes out of the hole, a volume of mud equal to that which the drill pipe occupied while in the hole must be pumped into the hole to replace the pipe.

When the bit goes back in the hole, the drill pipe displaces a certain amount of mud, and a trip tank can be used again to keep track of this volume.