Oil & Gas Terms in Category B

Bleed into

To cause a gas or liquid to mingle slowly with another gas or liquid usually by pressure.



An obstruction in the borehole, usually caused by the caving in of the well or the borehole or by the intrusion of a large boulder.


A tool place in the hole to retain cement or other material; it may later be removed, drilled out, or left permanently.

Breaking down

Unscrewing the drill stem into single joints and placing them on the pipe rack.

The operation takes place on completion of the well, or in changing from one size of pipe to another.

Bow spring centralizer

A low to moderate strength centralizer formed by arched spring-like straps of metal.

Beam pumping unit

A machine designed specifically for sucker rod pumping.

An engine or motor (prime mover) is mounted on the unit to power a rotating crank.

The crank moves a horizontal member (walking beam) up and down to produce reciprocating motion.

This reciprocating motion operates the pump.

Compare pump jack



The apparent loss of weight of an object immersed in a fluid.

If the object is floating, the immersed portion displaces a volume of fluid the weight of which is equal to the weight of the object.


The upward force acting on an object placed in a fluid.

The buoyancy force is equal to the weight of fluid displaced by the object.

Buoyancy can have significant effects in cases in which the wellbore and tubing string contain liquid and gas.

Any change in the relative volumes or fluid levels will change the buoyancy forces.


To supervise another too closely or continuously

Bleed line

A pipe through which pressure is bled, as from a pressurized tank, vessel, or other pipe.



An installation of identical or nearly identical pieces of equipment (such as a tank battery or a battery of meters).


An electricity storage device.

Bourdon tube

A pressure-sensing element consisting of a twisted or curved rube of non-circular cross section, which tends to straighten when pressure is applied internally.

By the movements of an indicator over a circular scale, a bourdon tube indicates the pressure applied.


A special threaded connection

Bit record

A historical record of how a bit performed in a particular wellbore.

The bit record includes such data as the depth the bit was put into the well, the distance the bit drilled, the hours the bit was being used “on bottom” or “rotating,” the mud type and weight, the nozzle sizes, the weight placed on the bit, the rotating speed and hydraulic flow information.

The data are usually updated daily.

When the bit is pulled at the end of its use, the condition of the bit and the reason it was pulled out of the hole are also recorded.

Bit records are often shared among operators and bit companies and are one of many valuable sources of data from offset wells for well design engineers.

Bullet perforator

A tubular device that, when lowered to a selected depth within a well, fires bullets through the casing to provide holes through which the formation fluids may enter the wellbore.

Break circulation


To start the mud pump for restoring circulation of the mud column.

Because the stagnant drilling fluid has thickened or gelled during the period of no circulation, high pump pressure is usually required to break circulation.


To establish circulation of drilling fluids after a period of static conditions.

Circulation may resume after a short break, such as taking a survey or making a mousehole connection, or after a prolonged interruption, such as after a round trip.

The operation is of more concern to drillers and well planners with longer static intervals, since immobile drilling mud tends to become less fluid and more gelatinous or semisolid with time.

Bent sub

A short cylindrical device installed in the drill stem between the bottom-most drill collar and a downhole motor.

Its purpose is to deflect the downhole motor off vertical to drill a directional hole.

See drill stem.