Glossary

jet	(1) A high-speed stream of fluid exiting a nozzle. (2) A high-pressure, high-velocity, vapor stream exhibiting mass which is produced by the detonation of high explosives with shaped, lined cavities. Used in gun perforating and salvage operations. See shaped charge.

jet charge	See shaped charge.

joint	A length of pipe, casing, or tubing usually from 20 to 30 feet long. On drilling rigs, drill pipe and tubing are run the first time (lowered into the hole) one joint at a time. When pulled out of the hole and stacked in the rig, they are usually pulled two, three, or four at a time depending upon the height of the derrick. These multiple-joint sections are called stands.

joule	A unit for all forms of energy or work. The joule is equal to 10⁷ ergs which is on the order of 1 watt-second. It is approximately equal to 0.738 foot-pound of 0.239 calorie.

Joule-Thomson effect	A thermal phenomenon produced by passing a gas at a higher pressure through an aperture or porous material to an environment at lower pressure. Hydrogen and helium gain heat (become warmer) in the process of expansion, whereas all other gases (nonperfect) lose heat (become cooler).

junk	Any kind of debris, extraneous to the formation, and that has become detached from some part of equipment used in an operation on a well and has become lodged or lost in some part of the borehole or borehole wall. Junk may be a lost bit, pieces of a bit, milled pieces of pipe, wrenches, or any relatively small object that impedes drilling. It often obstructs casing, tubing. or open hole and must be fished out. See also fish.

junk basket	(1) A device made up on the bottom of the drill stem to cut a core into the bottom of the hole on which junk rests. As the core is cut, the junk enters a barrel in the tool and is held by metal projections, or catchers. When the basket is brought back to the surface, the junk is removed with the core. (2) A basket-like device which can be run on a wireline survey cable for the purpose of removing small debris from inside a cased well bore.

juvenile water	Water that is derived from the interior of the earth and has not previously existed as atmospheric or surface water.