Drilling Oildfield Glossary A-C

Front 1

A subsurface condition in which the pore pressure of a geologic formation exceeds or is less than the expected, or normal, formation pressure.

Back 1

Abnormal pressure

Front 2

A valve usually used in well control operations to reduce the pressure of a fluid from high pressure in the closed wellbore to atmospheric pressure

Back 2

Adjustable choke

Front 3

A drilling fluid (or mud) that has gas (air or natural gas) bubbles in it, resulting in a lower bulk, unpressurized density compared with a mud not cut by gas.

Back 3

Air cut mud

Front 4

To drill using gases (typically compressed air or nitrogen) to cool the drill bit and lift cuttings out of the wellbore, instead of the more conventional use of liquids.

Back 4

Air drill

Front 5

A large valve used to control wellbore fluids. In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collar, drillpipe, casing, or tubing) or the openhole.

Back 5

Annular blowout preventer

Front 6

A flow of formation gas in the annulus between a casing string and the borehole wall. Annular gas flows occur when there is insufficient hydrostatic pressure to restrain the gas. They can occur in uncemented intervals and even in cemented sections if the cement bond is poor.

Back 6

Annular gas flow

Front 7

The speed at which drilling fluid or cement moves in the annulus.

Back 7

Annular velocity

Front 8

Plural form of annulus.

Back 8

Annuli

Front 9

The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow.

Back 9

Annulus

Front 10

A drill bit, usually polycrystalline diamond compact bit (PDC) type, designed such that the individual cutting elements on the bit create a net imbalance force.

Back 10

Antiwhril bit

Front 11

The angle between the vertical projection of a line of interest onto a horizontal surface and true north or magnetic north measured in a horizontal plane, typically measured clockwise from north.

Back 11

Azimuth

Front 12

To unscrew drillstring components downhole. The drillstring, including drillpipe and the bottomhole assembly, are coupled by various threadforms known as connections, or tool joints. Often when a drillstring becomes stuck it is necessary to "back off" the string as deep as possible to recover as much of the string as possible.

Back 12

Back of

Front 13

Another term for reverse circulation, the intentional pumping of wellbore fluids down the annulus and back up through the drillpipe. This is the opposite of the normal direction of fluid circulation in a wellbore.

Back 13

Back wash

Front 14

An average or baseline measure of gas entrained in circulating mud. This baseline trend pertains to gas that is liberated downhole while drilling through a uniform lithologic interval at a constant rate of penetration.

Back 14

Background gas (BGG)

Front 15

Referring to openhole or without casing, as in barefoot completion or barefoot drillstem test.

Back 15

Barefoot

Front 16

A tool run into the wellbore to retrieve junk from the bottom of the hole.

Back 16

Basket sup

Front 17

An enlarged pipe at the top of a casing string that serves as a funnel to guide drilling tools into the top of a well.

Back 17

Bell nipple

Front 18

The lower portion of the drillstring, consisting of (from the bottom up in a vertical well) the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collar, heavy-weight drillpipe, jarring devices ("jars") and crossovers for various threadforms.

Back 18

Bottomhole assembly (BHA)

Front 19

The temperature of the circulating fluid (air, mud, cement or water) at the bottom of the wellbore after several hours of circulation. This temperature is lower than the bottomhole static temperature.

Back 19

BHCT

Front 20

The pressure, usually measured in pounds per square inch (psi), at the bottom of the hole.

Back 20

Bottomhole pressure (BHP)

Front 21

The temperature of the undisturbed formation at the final depth in a well. The formation cools during drilling and most of the cooling dissipates after about 24 hours of static conditions, although it is theoretically impossible for the temperature to return to undisturbed conditions.

Back 21

BHST

Front 22

An integral bit and eccentric reamer used to simultaneously drill and underream the hole.

Back 22

Bicenter bit

Front 23

The tool used to crush or cut rock. Everything on a drilling rig directly or indirectly assists the bit in crushing or cutting the rock

Back 23

Bit

Front 24

A container, usually made of steel and fitted with a sturdy lock, to store drill bits, especially higher cost PDC and diamond bits.

Back 24

Bit box

Front 25

A special tool used by the rig crew to prevent the drill bit from turning while the bit sub on top of it is tightened or loosened.

Back 25

Bit breaker

Front 26

The part of the bit that includes a hole or opening for drilling fluid to exit. The hole is usually small (around 0.25 in. in diameter)

Back 26

Bit nozzle

Front 27

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

Back 27

Bit record

Front 28

The process of pulling the drillstring out of the wellbore for the purpose of changing a worn or underperforming drill bit.

Back 28

Bit trip

Front 29

A thick, heavy steel component of a conventional ram blowout preventer. In a normal pipe ram, the two blocks of steel that meet in the center of the wellbore to seal the well have a hole (one-half of the hole on each piece) through which the pipe fits.

Back 29

Blind ram

Front 30

A blowout preventer (BOP) closing element fitted with hardened tool steel blades designed to cut the drillpipe or tubing when the BOP is closed, and then fully close to provide isolation or sealing of the wellbore. A shear ram is normally used as a last resort to regain pressure control of a well that is flowing.

Back 30

Blind shear ram

Front 31

A set of pulleys used to gain mechanical advantage in lifting or dragging heavy objects. There are two large blocks on a drilling rig, the crown block and the traveling block.

Back 31

Block

Front 32

An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface

Back 32

Blow out

Front 33

A set of two or more BOPs used to ensure pressure control of a well.

Back 33

BOP Stack

Front 34

The wellbore itself, including the openhole or uncased portion of the well.

Back 34

Borehole

Front 35

Borehole direction. Borehole orientation may be described in terms of inclination and azimuth.

Back 35

Borehole orientation

Front 36

The sample obtained at the bottoms-up time or a volume of fluid to pump, as in "pump bottoms-up before drilling ahead."

Back 36

Bottoms up

Front 37

A metal strip shaped like a hunting bow and attached to a tool or to the outside of casing. Bow-spring centralizers are used to keep casing in the center of a wellbore or casing ("centralized") prior to and during a cement job.

Back 37

Bow spring centralizer

Front 38

A female threadform (internally threaded) for tubular goods and drillstring components.

Back 38

Box

Front 39

The mechanism on the drawworks that permits the driller to control the speed and motion of the drilling line and the drillstring, or the brake handle that the driller operates to control the brake mechanism.

Back 39

Brake

Front 40

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

Back 40

Brake circulation

Front 41

To unscrew drillstring components, which are coupled by various threadforms known as connections, including tool joints and other threaded connections.

Back 41

Break out

Front 42

A clutching mechanism that permits the driller to apply high torque to a connection using the power of the drawworks motor.

Back 42

Breakout cathead

Front 43

Large capacity self-locking wrenches used to grip drillstring components and apply torque. The breakout tongs are the active tongs during breakout operations.

Back 43

Breakout tongs

Front 44

The gangplank or stairway connecting a jackup rig to a fixed platform."

Back 44

Bridge

Front 45

Water containing more dissolved inorganic salt than typical seawater.

Back 45

Brine

Front 46

To forcibly pump fluids into a formation, usually formation fluids that have entered the wellbore during a well control event.

Back 46

bullhead

Front 47

An electromechanical device used to connect an electrical tool string to a logging cable, electrical wireline or coiled tubing string equipped with an electrical conductor.

Back 47

Cable head

Front 48

A method of drilling whereby an impact tool or bit, suspended in the well from a steel cable, is dropped repeatedly on the bottom of the hole to crush the rock.

Back 48

Cable-tool drilling

Front 49

A representation of the measured diameter of a borehole along its depth.

Back 49

Caliper log

Front 50

A test performed by the mudlogger or wellsite geologist, used to calculate sample lag.

Back 50

Carbide lag test

Front 51

The portion of the wellbore that has had metal casing placed and cemented to protect the openhole from fluids, pressures, wellbore stability problems or a combination of these.

Back 51

Cased hole

Front 52

Large-diameter pipe lowered into an openhole and cemented in place.

Back 52

Casing

Front 53

A mechanical device that keeps casing from contacting the wellbore wall. A continuous 360-degree annular space around casing allows cement to completely seal the casing to the borehole wall. There are two distinct classes of centralizers. The older and more common is a simple, low-cost bow-spring design.

Back 53

Casing centralizers

Front 54

The threaded collar used to connect two joints of casing.

Back 54

casing collar

Front 55

A short length of pipe used to connect two joints of casing.

Back 55

Casing coupling

Front 56

A system of identifying and categorizing the strength of casing materials.

Back 56

Casing grade

Front 57

The adapter between the first casing string and either the BOP stack (during drilling) or the wellhead (after completion).

Back 57

Casing head

Front 58

The location, or depth, at which drilling an interval of a particular diameter hole ceases, so that casing of a given size can be run and cemented.

Back 58

Casing point

Front 59

The bottom of the casing string, including the cement around it, or the equipment run at the bottom of the casing string.

Back 59

Casing shoe

Front 60

An assembled length of steel pipe configured to suit a specific wellbore. The sections of pipe are connected and lowered into a wellbore, then cemented in place.

Back 60

Casing string

Front 61

A relatively thin cable used with other equipment to move small rig and drillstring components and to provide tension on the tongs for tightening or loosening threaded connections.

Back 61

Cat line

Front 62

A clutched spool connected to the drawworks power system used to tension chains, cables and softline rope.

Back 62

Cathead

Front 63

A long, rectangular platform about 3 ft [0.9 m] high, usually made of steel and located perpendicular to the vee-door at the bottom of the slide. This platform is used as a staging area for rig and drillstring tools, components that are about to be picked up and run, or components that have been run and are being laid down.

Back 63

Catwalk

Front 64

A dug-out area, possibly lined with wood, cement or very large diameter (6 ft [1.8 m]) thin-wall pipe, located below the rig.

Back 64

Cellar

Front 65

The binding material in sedimentary rocks that precipitates between grains from pore fluids. Calcite and quartz are common cement-forming minerals.

Back 65

Cement

Front 66

A representation of the integrity of the cement job, especially whether the cement is adhering solidly to the outside of the casing. The log is typically obtained from one of a variety of sonic-type tools.

Back 66

Cement bond log

Front 67

A device fitted to the top joint of a casing string to hold a cement plug before it is pumped down the casing during the cementing operation. In most operations, a bottom plug is launched before the spacer or cement slurry.

Back 67

Cement head

Front 68

The colloquial term for the crew member in charge of a specialized cementing crew and trucks.

Back 68

Cementer

Front 69

To prepare and pump cement into place in a wellbore.

Back 69

Cementing

Front 70

The colloquial term for the crew member in charge of a specialized cementing crew and trucks.

Back 70

Cementing engineer

Front 71

A rubber plug used to separate the cement slurry from other fluids, reducing contamination and maintaining predictable slurry performance.

Back 71

Cementing plug

Front 72

A type of pipe wrench used for hand-tightening various threaded connections around the rigsite.

Back 72

Chain tongs

Front 73

A high-pressure pipe leading from an outlet on the BOP stack to the backpressure choke and associated manifold.

Back 73

Choke line

Front 74

A set of high-pressure valves and associated piping that usually includes at least two adjustable chokes, arranged such that one adjustable choke may be isolated and taken out of service for repair and refurbishment while well flow is directed through the other one.

Back 74

Choke manifold

Front 75

The set of valves, spools and fittings connected to the top of a well to direct and control the flow of formation fluids from the well.

Back 75

Christmas tree

Front 76

To pump fluid through the whole active fluid system, including the borehole and all the surface tanks that constitute the primary system.

Back 76

Circulate

Front 77

To pump the drilling fluid until a sample from the bottom of the hole reaches the surface.

Back 77

Circulate out

Front 78

The loss of drilling fluid to a formation, usually caused when the hydrostatic head pressure of the column of drilling fluid exceeds the formation pressure.

Back 78

Circulation loss

Front 79

The complete, circuitous path that the drilling fluid travels. Starting at the main rig pumps, major components include surface piping, the standpipe, the kelly hose (rotary), the kelly, the drillpipe, drill collars, bit nozzles, the various annular geometries of the openhole and casing strings, the bell nipple, the flowline, the mud-cleaning equipment, the mud tanks, the centrifugal precharge pumps and, finally, the positive displacement main rig pumps.

Back 79

Circulation system

Front 80

Water containing more dissolved inorganic salt than typical seawater.

Back 80

Clear brine

Front 81

A long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool.

Back 81

Coiled tubing (CT)

Front 82

The use of coiled tubing with downhole mud motors to turn the bit to deepen a wellbore

Back 82

Coiled tubing drilling

Front 83

Another term for a tapered string: a string of drillpipe or casing that consists of two or more sizes or weights.

Back 83

Combination string

Front 84

To remove the drillstring from the wellbore.

Back 84

Come out of the hole

Front 85

The representative of the oil company or operator on a drilling location.

Back 85

Company man

Front 86

The hardware used to optimize the production of hydrocarbons from the well.

Back 86

Completion

Front 87

Having the same center, such as when the casing and the wellbore have a common center point and, therefore, a uniform annular dimension.

Back 87

Concentric

Front 88

The casing string that is usually put into the well first, particularly on land wells, to prevent the sides of the hole from caving into the wellbore. This casing, sometimes called drive pipe, is generally a short length and is sometimes driven into the ground.

Back 88

Conductor casing

Front 89

Any threaded or nonthreaded union or joint that connects two tubular components.

Back 89

Connection

Front 90

A brief influx of gas that is introduced into the drilling fluid when a pipe connection is made.

Back 90

Connection gas

Front 91

Gas that is introduced into the drilling mud from a source other than the formation.

Back 91

Contamination gas

Front 92

The depth in a drilling well at which the drilling contractor receives a lump-sum payment for reaching a particular milestone.

Back 92

Contract depth

Front 93

To deepen the wellbore by way of collecting a cylindrical sample of rock. A core bit is used to accomplish this, in conjunction with a core barrel and core catcher.

Back 93

Core

Front 94

Antiquated term for a deviated wellbore, usually used to describe a well deviated accidentally during the drilling process.

Back 94

Crooked hole

Front 95

The flow of fluid across the bottom of the bit after it exits the bit nozzles, strikes the bottom or sides of the hole and turns upwards to the annulus.

Back 95

Crossflow

Front 96

The fixed set of pulleys (called sheaves) located at the top of the derrick or mast, over which the drilling line is threaded.

Back 96

Crown block

Front 97

The rubblized rock just below the tooth of a rock bit. Rock in the crushed zone fails due to the high compressive stress placed on it by the bit tooth (in the case of a roller-cone bit)

Back 97

Crushed zone

Front 98

A method for recovering wireline stuck in a wellbore. In cut-and-thread operations, the wireline is gripped securely with a special tool and cut at the surface. The cut end is threaded through a stand of drillpipe. While the pipe hangs in the wellbore, the wireline is threaded through another stand of drillpipe, which is screwed onto the stand in the wellbore. The process is repeated until the stuck wireline is recovered. This technique, while dangerous and time-consuming, is known to improve greatly the chances of full recovery of the wireline and the tool at its end in the shortest overall time compared with trying to grab the wireline in the openhole with fishing tools.

Back 98

Cut and thread fishing technique

Front 99

Small pieces of rock that break away due to the action of the bit teeth.

Back 99

Cuttings