Oil & Gas Glossary 1.0

The force exerted by a column of liquid expressed by the height of the liquid above the point at which the pressure is measured. Although "head" refers to distance or height, it is used to express pressure, since the force of the liquid column is directly proportional to its height. Also called head or hydrostatic head. Compare hydrostatic pressure.

See hydrostatic pressure

An accessory attached o the top of the drill pipe or tubing to form a connection with the mud system to permit circulation of the drilling mud. In some cases, it is also a rotating head.

A sealing device used to close off the annular space around the kelly in drilling with pressure at the surface, usually installed above the main blowout preventers. A rotating head makes it possible to drill ahead even when there is pressure in the annulus that the weight of the drilling fluid is not overcoming; the head prevents the well from blowing out. It is used mainly in the drilling of formations that have low permeability. The rate of penetration through such formations is usually rapid.

The force exerted by a body of fluid at rest. It increases directly with the density and the depth of the fluid and is expressed in pounds per square inch or kilopascals. The hydrostatic pressure of fresh water is 0.433 pounds per square inch per foot of depth (9.792 kilopascals per meter). In drilling, the term refers to the pressure exerted by the drilling fluid in the wellbore. In a water drive field, the term refers to the pressure that may furnish the primary energy for production.

2. to pull formation fluids into a wellbore by raising the drill stem at a rate that reduces the hydrostatic pressure of the drilling mud below the bit.

The extent to which the hydrostatic pressure of the mud column exceeds formation pressure.

Weight per unit volume of drilling fluid usually expressed in pounds per gallon or pounds per cubic foot. See hydrostatic pressure.

1. to force pipe or tools into a high-pressure well that has not been killed (i.e., to run pipe or tools into the well against pressure when the weight of pipe is not great enough to force the pipe through the BOPs). Snubbing usually requires an array of wireline bocks and wire rope that forces the pipe or tools into the well through a stripper head or blowout preventer until the weight of the string is sufficient to overcome the lifting effect of the well pressure on the pipe in the preventer. In workover operations, snubbing is usually accomplished by using hydraulic power to force the pipe through the stripping head or blowout preventer.

See cementing head.

Prevention of formation fluid flow by maintaining a hydrostatic pressure equal to or greater than formation pressure

In drilling, the entrance of formation fluids into the wellbore because hydrostatic pressure is less than formation pressure.

Commonly called casinghead gas; gas that is produced with oil or from the casing head of an oil well.

A sudden, usually short-duration, increase in pressure. When pipe or casing is run into a hole too rapidly, an increase in the hydrostatic pressure results, which may be great enough to create lost circulation

The driller or head well puller in charge of operations on a well servicing rig that is used to pull sucker rods or tubing

A blowout prevention device consisting of a gland and packing arrangement bolted to the wellhead. It is often used to seal the annular space between tubing and casing.

Distance between well head and point to which fluid rises in the well.

A plug in the flow line at the well head which has a small hole drilled through it through which oil flows, and which keeps a well from flowing at too high a rate.

4. in hydrostatic testing of a pipeline, a scraper used inside the line to push air out ahead of the test water and to push water out after the test. v: to force a device called a pig through a pipeline or a flow line for the purpose of cleaning the interior walls of the pipe, separating different products, or displacing fluids.

A complete break in pipe caused by metal fatigue. v: to break something in two or to break apart, such as the head of a bolt or the drill stem.

2. the pressure-sealing element of a stripper blowout preventer See stripper head.

An arrangement of slips and packing rings used to suspend tubing from a tubing head.

2. a large pipe connected to a process tank to provide a statis head that can absorb surges of fluid from the process tank.

An extension of a retrievable tool, i.e., a retrievable bridge plug, used to set and release the tool.

A specialized fixture on a downhole tool that will allow the tool to be fished out after it's used downhole. See fish.

A flanged fitting that supports the tubing string, seals off pressure between the casing and the outside of the tubing, and provides a connection that supports the Christmas tree.

An accessory attached to the top of the casing to facilitate cementing of the casing. It has passages for cement slurry and retain chambers for cementing wiper plugs.

The equipment installed at the surface of the wellbore. A wellhead includes such equipment as the casinghead and tubing head. adj: pertaining to the wellhead (e.g., wellhead pressure).

A worker on an offshore rig who handles the equipment and supplies that are sent to the rig form the shore base. The head roustabout is very often the crane operator. a worker who assists the foreman in the general work around a producing oilwell, usually on the property of the oil company. A helper on a well servicing unit.

2. a stripper head.

The pressure lost in a pipeline or annulus due to the velocity of the liquid in the pipeline, the properties of the fluid, the condition of the pipe wall, and the alignment of the pipe. In certain mud-mixing systems, the loss of head can be substantial

A workover performed with a continuous steel tube, normally 3/4 inch to 1 inch outside diameter, which is run into the well in one piece inside the normal tubing. Lengths of the tubing up to 16,000 feet are stored on the surface on a reel in a manner similar to that used for wireline. The unit is rigged up over the wellhead. The tubing is injected through a control head that seals off the tubing and makes a pressure-tight connection. A unique feature of the unit is that it allows continuous circulation while it is being lowered into the hole.