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Abandon a well v : to stop producing hydrocarbons when the well becomes unprofitable. A wildcat may be abandoned after poor results from a well test.
Mechanical and cement plugs are placed in the wellbore to prevent fluid migration to surface and between different zones.

Abnormal pressure n : a formation pressure which is greater or less than the "normal" formation fluid hydrostatic pressure. Such pressures may be classified as "subnormal" (lower than normal) or "overpressured" (higher than normal).

Accelerometer n : a surveying instrument which measures components of the Earth's gravitational field.

Acidise v : to apply acids to the walls of oil and gas wells to remove any material which may obstruct flow into the wellbore.

Adjustable choke n : a choke in which the rate of flow is controlled by adjusting a conical needle and seat.

Air drilling n : a method of drilling that uses compressed air as the circulating medium.

Angle unit n : the component of a survey instrument used to measure inclination.

Annular preventer n : a large BOP valve that forms a seal in the annular space between the wellbore and the drillpipe. It is usually installed above the ram type preventers in the BOP stack.

Annulus n : the space between the drillstring and open hole or drillstring and cased hole in the wellbore.

Anticline n : a configuration of folded and stratified rock layers in the shape of an arch.Often associated with a trap.

A.P.I. abbr : American Petroleum Institute. The leading standardising organisation on oilfield drilling and production equipment.

A.P.I. gravity n : a measure of the density of liquid petroleum products, expressed in degrees. It can be derived from the following equation:
API Gravity (degrees) = ( 141.5 )/ Specific Gravity - 131.5

Azimuth n : used in directional drilling as the direction of the trajectory of the wellbore measured in degrees (0-359) clockwise from True North or Magnetic North.

Back off v : to disconnect a section of stuck drillpipe by unscrewing one of the connections above the stuckpoint.

Back up :
1. v - to hold one section of pipe while another is being screwed into or out of it (as
in back up tongs).
2. n - a piece of equipment held in reserve in case another piece fails.

Badger bit n : a specially designed bit with one large nozzle, which can be used as a deflecting tool in soft formations.

Bail n : a rounded steel bar which supports the swivel and connects it to the hook. May also apply to the steel bars which connect the elevators to the hook (links).

Ball up v : buildup of a mass of sticky material (drill cuttings) on components of drillstring (especially bits and stabilisers)

Barge n : a flat decked, shallow draft vessel which may accommodate a drilling rig, or be used to store equipment and materials or for living quarters.

Barite (Baryte) n : Barium Sulphate (BaSO4), a mineral used as a weighting material to increase mud weight (specific gravity = 4.2).

Barrel n : a measure of volume for fluids. One barrel (bbl) = 42 U.S. gallons = 0.15899 cubic metres. The term bbl is derived from the blue barrels in which oil was originally transported.

Bed n : a geological term to specify one particular layer of rock.

Bell nipple n : In marine drilling, the uppermost component of the marine riser attached to the telescopic joint. The top of the nipple is expanded to guide drilling tools into the well.

Bentonite n : a finely powdered clay material (mainly montmorillonite) which swells when mixed with water. Commonly used as a mud additive, and sometimes referred to as "gel".

Bent sub n : a short piece of pipe whose axis is deviated 1 ?-3 ? off vertical. Used in directional drilling as a deflecting tool. Bit n : the cutting element at the bottom of the drillstring, used for boring through the rock.

Bit breaker n : a heavy metal plate which fits into the rotary table and holds the bit while it is being connected to or disconnected from the drillstring.

Bit record n : a report containing information relating to the operating parameters and performance of the bits run in a well.

Bit sub n : a short length of pipe installed immediately above the bit. The threads on the bit sub accept the pin thread on the bit and the pin thread for the drillcollars.

Bit walk n : the tendency for the bit and drillstring to wander off course by following the direction of rotation (usually to the right) in a directionally drilled well.

Blind rams n : one of the valves on the BOP stack. It is designed to close off the wellbore when the drillstring is out of the hole.

Blocks n : an assembly of pulleys on a common framework.

Blooey line n : the discharge pipe from a well being drilled with compressed air.

Blow out n : an uncontrolled flow of formation fluids into the atmosphere at surface.

BOP abbr : Blow Out Preventer. A valve installed on top of the wellhead to control wellbore pressure in the event of a kick.

BOP stack n : an assembly of BOPs consisting of annular preventers and ram type preventers. For land drilling the BOP stack is installed just below the rig floor, while for floating rigs the stack is positioned on the seabed.

Borehole n : the hole made by the drill bit.

Bottom hole assembly (BHA) n : the part of the drillstring which is just above the bit and below the drillpipe. It usually consists of drill collars, stabilisers and various other components.

Bottom hole pressure (bhp) n : the pressure,
1. at the bottom of the borehole, or
2. at a point opposite the producing formation.

Box n : the female section of a tool joint or other connection.

Brake n: the device operated by the driller to stop the downward motion of the travelling block and therefore the drillstring.

Breakout v : to unscrew one section of pipe from another.

Bridge n : an obstruction in the borehole usually caused by the borehole wall caving in.

BRT abbr : Below Rotary Table. Reference point for measuring depth.

Building assembly n : a BHA specially designed to increase the inclination (drift angle) of the wellbore.

Build up rate n : the rate at which drift angle is increasing as the wellbore is being deviated from vertical. Usually measured in degrees per 100 ft drilled.

Build up section n : that part of the wellbore's trajectory where the drift angle is increasing.

Bumper sub n : a drilling tool, placed in the BHA, consisting of a short stroke slip joint which allows a more constant WOB to be applied when drilling from a floating rig.

Cable tool drilling n : an earlier method of drilling used before the introduction of modern rotary methods. The bit was not rotated but reciprocated by means of a strong wire rope.

Caliper log n : a tool run on electric wireline which measures the diameter of the wellbore. It may be used for detecting washouts, calculating cement volumes, or detecting internal corrosion of casing.

Cap rock n : an impermeable layer of rock overlying an oil or gas reservoir and preventing the migration of fluids.

Cased hole n : that part of the hole which is supported by a casing which has been run and cemented in place.

Casing n : large diameter steel pipe which is used to line the hole during drilling operations.

Casing head Housing n : a large recepticle which is installed on top of the surface casing string. It has an upper flanged connection. Once it is installed it provides: a landing shoulder for the next casing string; and a flanged connection for the BOP stack to be connected to the well.

Casing head Spool n : a large recepticle which is installed on top of the casing head housing or a previous spool. It has both an upper and lower flanged connection. Once it is installed it provides: a landing shoulder for the next casing string; access to the annulus between the casing strings and a flanged connection for the BOP stack to be connected to the well.

Casing hanger n : a special component which is made up on top of the casing string to suspend the casing from the previous casing housing or spool.

Casing shoe n : a short section of steel pipe filled with concrete and rounded at the bottom. This is installed on the bottom of the casing string to guide the casing past any ledges or irregularities in the borehole. Sometimes called a guide shoe.

Casing string n : the entire length of all the casing joints run into the borehole.

Cathead n : a spool shaped attachment on a winch, around which rope is wound. This can be used for hoisting operations on the rig floor.

Caving: 1. v: collapse of the walls of the borehole. Also referred to as "sloughing".
2. n: a small part of the borehole wall that has collapsed into the hole.

Centraliser n : a device secured around the casing which is designed to support and centralise the casing in deviated wellbores.

Centrifugal pump n : a pump consisting of an impellor, shaft and casing which discharges fluid by centrifugal force. Often used for mixing mud.

Centrifuge n : a piece of solids control equipment which separates out particles of varying density.

Cement Slurry n: A mixture of cement powder, water and additives which harden to form a cement sheath or cement plug in a well.

Cementing v : the placement of a liquid slurry of cement and water inside or outside of the casing. Primary cementing is carried out immediately after the casing is run. Secondary cementing is carried out when remedial work is required.

Cement channeling v : the irregular displacement of mud by cement, leaving voids in the cement sheath between the casing and the borehole, thereby reducing the effectiveness of the cement sheath.

Cement head n : a manifold system installed on the top of the casing which allows the cement slurry to be pumped from the cement unit down the casing string. The cement head is also used for releasing the top and bottom cement plugs.

Cement plug n :
1. A specific volume of cement placed at some point in the wellbore to seal off the well.
2.A device used during a primary cement job to separate the cement slurry from contaminating fluids in the casing. A wiper plug is pumped ahead of the slurry and a shut off plug behind the slurry.

Chain tongs n : a tool used by roughnecks on the rig floor to tighten or loosen a connection. The tool consists of a long handle and an adjustable chain which will fit a variety of pipe sizes.

Check valve n : a valve which permits flow in one direction only.

Choke n : an orifice installed in a line to restrict and control the flow rate.

Choke line n : a pipe connected to the BOP stack which allows fluids to be circulated out of the annulus and through the choke manifold when a well kiling operation is beimg performed.

Choke manifold n : an arrangement of pipes, valves and chokes which allows fluids to be circulated through a number of routes.

Christmas tree n : an assembly of control valves and fittings installed on top of the wellhead. The Christmas tree is installed after the well has been completed and is used to control the flow of oil and gas.

Circulate v : to pump drilling fluid through the drillstring and wellbore, returning to the mud pits. This operation is carried out during drilling and is also used to improve the condition of the mud while drilling is suspended.

Clay n : a term used to describe the aluminium silicate minerals which are plastic when wet and have no well-developed parting along bedding planes. Such material is commonly encountered while drilling a well.

Clay minerals n : the constituents of a clay which provide its plastic properties. These include kaolinite, illite, montmorillonite and vermiculite.

Closure n : the shortest horizontal distance from a particular survey station back to the reference point.

Combination string n : a casing string which is made up of various different grades or weights of casing (sometimes referred to as a tapered string when different sizes of casing are used).

Company man n : an employee of an operating company whose job is to represent the operator's interests on the drilling rig (sometimes referred to as "drilling supervisor" or "company man").

Compass unit n : the component of a survey instrument used to measure azimuth.

1. v : the activities and methods used to prepare a well for the production of oil or gas.
2. n: the tubing and accessories installed in the production casing and through which the produced fluid flows to surface.

Conductor line n : a small diameter wireline which carries electric current. This is used for logging tools and steering tools.

Conductor pipe n : a short string of casing of large diameter which is normally the first casing string to be run in the hole.
Connection v : the joining of a section of drillpipe to the top of the drillstring as drilling proceeds.

Core n : a cylindrical rock sample taken from the formation for geological analysis.

Core barrel n : a special tool which is installed at the bottom of the drillstring to capture and retain a core sample which is then recovered when the string is pulled out of the hole.

Core Bit (Core Head) n: A donut shaped drilling bit used just below the core barrel to cut a cylindrical sample of rock.

Correction run n : a section of hole which must be directionally drilled to bring the well path back onto the planned course.

Crater n : a large hole which develops at the surface of a wellbore caused by the force of escaping gas, oil or water during a blowout.

Cross-over n : a sub which is used to connect drill string components which have different types or sizes of threads.

Crown block n : an assembly of sheaves or pulleys mounted on beams at the top of the derrick over which the drilling line is reeved.

Cuttings n : the fragments of rock dislodged by the bit and carried back to surface by
the drilling fluid.

Easting n : one of the co-ordinates used to plot a deviated well's position on the horizontal plane (along the x axis).

Electric logging v : the measurement of certain electrical characteristics of formations traversed by the borehole. Electric logs are run on conductor line to identify the type of formations, fluid content and other properties.

Elevators n : a lifting collar connected to the travelling block, which is used to raise or lower pipe into the wellbore. The elevators are connected to the travelling block by links or bails.

Emulsion n : a mixture in which one liquid (dispersed phase) is uniformly distributed in another liquid (continuous phase). Emulsifying agents may be added to stabilize the mixture.

Exploration well n : a well drilled in an unproven area where no oil and gas production exists (sometimes called a "wildcat").

Fastline n : the end of the drilling line which is attached to the drum of the drawworks.

Fault n : a geological term which denotes a break in the subsurface strata. On one side of the fault line the strata has been displaced upwards, downwards or laterally relative to its original position.

Field n : a geographical area in which oil or gas wells are producing from a continuous reservoir.

Filter cake n : the layer of concentrated solids from the drilling mud that forms during natural filtration on the sides of the borehole. Sometimes called "wall cake" or "mud cake".

Filter press n : a device used in the measurement of the mud's filtration properties.

Filtrate n : a fluid which has passed through a filter. In drilling it usually refers to the liquid part of the mud which enters the formation.

Filtration v : the process by which the liquid part of the drilling fluid is able to enter a permeable formation, leaving a deposit of mud solids on the borehole wall to form a filter cake.

Fish n : any object accidentally left in the wellbore during drilling or workover operations, which must be removed before work can proceed.

Fishing v : the process by which a fish is removed from the wellbore. It may also be used for describing the recovery of certain pieces of downhole completion equipment when the well is being reconditioned during a workover.

Fishing tool n : a specially designed tool which is attached to the drill string in order to recover equipment lost in the hole.

Flange up v : to connect various components together (e.g. in wellheads or piping systems).

Flare n : an open discharge of fluid or gas to the atmosphere. The flare is often ignited to dispose of unwanted gas around a completed well.

Flex joint n : a component of the marine riser system which can accommodate some lateral movement when drilling from a floater.

Float collar n : a special device inserted one or two joints above the bottom of a casing string. The float collar contains a check valve which permits fluid flow in a downward direction only. The collar thus prevents the back flow of cement once it has been displaced.

Floater n : general term used for a floating drilling rig.

Float shoe n : a short cylindrical steel component which is attached to the bottom of a casing string. The float shoe has a check valve and functions in the same manner as the float collar. In addition the float shoe has a rounded bottom which acts as a guide shoe for the casing.

Float sub n : a check valve which prevents upward flow through the drill string.

Flocculation v : the coagulation of solids in a drilling fluid produced by special additives or contaminants in the mud.

Fluid loss v : the transfer of the liquid part of the mud to the pores of the formation. Loss of fluid (water plus soluble chemicals) from the mud to the formation can only occur where the permeability is sufficiently high. If the pores are large enough the first effect is a "spurt loss", followed by the buildup of solids (filter cake) as filtration continues.

Formation n : a bed or deposit composed throughout of substantially the same kind of rock to form a lithologic unit.

Formation fluid n : the gas, oil or water which exists in the pores of the formation.

Formation pressure n : the pressure exerted by the formation fluids at a particular point in the formation. Sometimes called "reservoir pressure" or "pore pressure".

Formation testing v : the measurement and gathering of data on a formation to determine its potential productivity.

Fracture n : a break in the rock structure along a particular direction. Fractures may occur naturally or be induced by applying downhole pressure in order to increase permeability.

Fracture gradient n : a measure of how the strength of the rock (i.e. its resistance to break down) varies with depth.

Fulcrum assembly n : a bottom hole assembly which is designed to build hole inclination.

Gas cap n : the free gas phase which is sometimes found overlying an oil zone and occurs within the same formation as the oil.

Gas cut mud n : mud which has been contaminated by formation gas.

Gas show n : the gas that is contained in mud returns, indicating the presence of a gas zone.

Gas injector n : a well through which produced gas is forced back into the reservoir to maintain formation pressure and increase the recovery factor.

Gel n : a semi-solid, jelly-like state assumed by some colloidal dispersions at rest. When agitated the gel converts to a fluid state.

Gel strength n : the shear strength of the mud when at rest. Its ability to hold solids in suspension. Bentonite and other colloidal clays are added to the mud to increase gel strength.

Geostatic pressure n : the pressure exerted by a column of rock. Under normal conditions this pressure is approximately 1 psi per foot. This is also known as"lithostatic pressure" or "overburden pressure".

Guideline tensioner n : a pneumatic or hydraulic device used to provide a constant tension on the wire ropes which run from the subsea guide base back to a floating drilling rig.

Guide shoe n : See Float Shoe.

Gumbo n : clay formations which contaminate the mud as the hole is being drilled. The clay hydrates rapidly to form a thick plug which cannot pass through a marine riser or mud return line.

Gunk n : a term used to describe a mixture of diesel oil, bentonite and sometimes cement which is used to combat lost circulation.

Gusher n : an uncontrolled release of oil from the wellbore at surface.

Gyro multi-shot n : a surveying device which measures and provides a series of photographic images showing the inclination and direction of the wellbore. It measures direction by means of a gyroscopic compass.

Gyro single-shot n : a surveying device which measures the inclination and direction of the borehole at one survey station. It measures direction by means of a gyroscopic compass.

Gyroscope n : a wheel or disc mounted on an axle and free to spinto spin rapidly about one axis, but free to rotate about one or both of the other two axes. The inertia of the wheel keeps the axis aligned with the reference direction (True North in directional survey tools).

Hole opener n : a special drilling tool which can enlarge an existing hole to a larger diameter.

Hook n : the large component attached to the travelling block from which the drill stem is suspended via the swivel.

Hopper n : a large funnel shaped device into which dry material (e.g. cement or powdered clay) can be poured. The purpose of the hopper is to mix the dry material with liquids injected at the bottom of the hopper.

H.W.D.P. abbr : heavy weight drill pipe. Thick walled drill pipe with thick walled sections used in directional drilling and placed between the drill collars and drill pipe.

Hydrostatic pressure n : the load exerted by a column of fluid at rest. Hydrostatic pressure increases uniformly with the density and depth of the fluid.

Inclination n : a measure of the angular deviation of the wellbore from vertical. Sometimes referred to as "drift angle".

Injection n : usually refers to the process whereby gas, water or some other fluid is forced into the formation under pressure.

Impermeable adj : preventing the passage of fluid through the pores of the rock.

Insert bit n : a type of roller cone bit where the cutting structure consists of specially designed tungsten carbide cutters set into the cones.

Intermediate casing n : a string of casing set in the borehole to keep the hole from caving and to seal off troublesome formations.

Invert oil emulsion mud n : a drilling fluid which contains up to 50% by volume of water, which is distributed as droplets in the continuous oil phase. Emulsifying agents and other additives are also present.

Iron roughneck n : an automated piece of rig floor equipment which can be used to make connections.

Jack-up rig n : an offshore drilling structure which is supported on steel legs.

Jet deflection n : a technique used in directional drilling to deviate the wellbore by washing away the formation in one particular direction. A special bit (badger bit) is used which has one enlarged nozzle which must be orientated towards the intended direction.

Jet sub n : a tool used at the bottom of the drill pipe when the conductor pipe is being jetted into position (this method of running the conductor is only suitable where the surface formations can be washed away by the jetting action).

Joint n : a single length of pipe which has threaded connections at either end.

Junk n : debris lost in the hole which must be removed to allow normal operations to continue.

Junk sub n : a tool run with the BHA, which is designed to recover pieces of debris left in the hole.

Kelly n : the heavy square or hexagonal steel pipe which runs through the rotary table and is used to rotate the drillstring.

Kelly bushing n : a device which fits into the rotary table and through which the Kelly passes. The rotation of the table is transmitted via the kelly bushing to the kelly itself. Sometimes called the drive bushing.

Kelly cock n : a valve installed between the kelly and the swivel. It is used to control a backflow of fluid up the drillstring and isolate the swivel and hose from high pressure.

Kelly spinner n : a pneumatically operated device mounted on top of the kelly which, when actuated, causes the kelly to rotate. It may be used to make connections by spinning up the kelly.

Key seat n : a channel or groove cut into the side of the borehole due to the dragging action of the pipe against a sharp bend (or dog leg).

Key seat wiper n : a tool made up in the drillstring to ream out any key seats which may have formed and thus prevent the pipe from becoming stuck.

Kick n : an entry of formation fluids (oil, gas or water) into the wellbore caused by the formation pressure exceeding the pressure exerted by the mud column.

Kill line n : a high pressure line connecting the mud pumps to the BOP stack through which mud can be pumped to control a kick.

Killing a well v : the process by which a well which is threatening to blow out is brought under control. It may also mean circulating water or mud into a completed well prior to workover operations.

KOP abbr : kick-off point. The depth at which the wellbore is deliberately deviated from the vertical.

Latitude n : one of the co-ordinates used in plotting the wellpath on the horizontal plane (along the y axis).

Lead angle n : the direction at which the directional driller aims the well to compensate for bit walk. Lead angle is measured in degrees left or right of the proposed direction.

Liner n :

1. A string of casing which is suspended by a liner hanger from the inside of the previous casing string and does not therefore extend back to surface as other casing strings do.

2. A replaceable sleeve which fits inside the cylinder of a mud pump.

Liner hanger n : a slip type device which suspends the liner inside the previous casing shoe.

Location n : the place at which a well is to be drilled.

Log n : a systematic recording of data (e.g. drillers log, electric log, etc.)

Lost circulation n : the loss of quantities of whole mud to a formation due to caverns, fractures or highly permeable beds. Also referred to as lost returns.

Magnetic declination n : the angle between True North and Magnetic North. This varies with geographical location, and also changes slightly each year.

Magnetic multi-shot n : a surveying instrument which provides a series of photographic discs showing the inclination and direction of the wellbore. It measures direction by means of a magnetic compass and so direction is referenced to Magnetic North.

Magnetic North n : the northerly direction in the earths magnetic field indicated by the needle of a magnetic compass.

Magnetometer n : a surveying device which measures the intensity and direction of the earths magnetic field.

Make up v : to assemble and join components together to complete a unit (e.g. to make up a string of casing).

Make hole v : to drill ahead

Marine riser n : the pipe which connects the subsea BOP stack with the floating drilling rig. The riser allows mud to be circulated back to surface, and provides guidance for tools being lowered into the wellbore.

Mast n : a portable derrick capable of being erected as a unit unlike a standard derrick which has to be built up.

Master bushing n : a sleeve which fits into and protects the rotary table and accommodates the slips and drives the kelly bushing.

Measured depth (MD) n : the distance measured along the path of the wellbore (i.e. the length of the drillstring).

Mill n : a downhole tool with rough, sharp cutting surfaces for removing metal by grinding or cutting.

Milled tooth bit n : a roller cone bit whose cutting surface consists of a number of steel teeth projecting from the surface of the cones.

Monel n : term used for a non-magnetic drill collar made from specially treated steel alloys so that it does not affect magnetic surveying instruments.

Monkey board n : the platform on which the derrickman works when handling stands of pipe.

Moon pool n : the central slot under the drilling floor on a floating rig.

Motion compensator n : a hydraulic or pneumatic device usually installed between the travelling block and hook. Its function is to keep a more constant weight on the drill bit when drilling from a floating vessel. As the rig heaves up and down a piston moves within the device to cancel out this vertical motion.

Mousehole n : a small diameter pipe under the derrick floor in which a joint of drill pipe is temporarily stored for later connection to the drillstring.

M.S.L. abbr : Mean Sea Level.

Mud n : common term for drilling fluid.

Mud balance n : a device used for measuring the density of mud or cement slurry. It consists of a cup and a graduated arm which carries a sliding (counterbalanced) weight and balances on a fulcrum.

Mud conditioning v : the treatment and control of drilling fluid to ensure that it has the correct properties. This may include the use of additives, removing sand or other solids, adding water and other measures. Conditioning may also involve circulating the mud prior to drilling ahead.

Mud engineer n : usually an employee of a mud service company whose main responsibility on the rig is to test and maintain the mud properties specified by the operator.

Mudline n : the seabed.

Mudlogging n : the recording of information derived from the examination and analysis of drill cuttings. This also includes the detection of oil and gas. This work is usually done by a service company which supplies a portable laboratory on the rig.

Mud motor n : a downhole component of the BHA which rotates the bit without having to turn the rotary table. The term is sometimes applied to both positive displacement motors and turbodrills.

Mud pits n : a series of open tanks in which the mud is mixed and conditioned. Modern rigs are provided with three or more pits, usually made of steel plate with built-in piping, valves and agitators.

Mud pump n : a large reciprocating pump used to circulate the drilling fluid down the well. Both duplex and triplex pumps are used with replaceable liners. Mud pumps are also called slush pumps.

Mud return line n : a trough or pipe through which the mud being circulated up the annulus is transferred from the top of the wellbore to the shale shakers. Sometimes called a flowline.

Mud screen n : shale shaker.

Mule shoe n : the guide shoe on the lower end of a survey tool which locates into the key way of the orienting sub. The survey tool can then be properly aligned with the bent sub.

M.W.D. abbr : Measurement While Drilling. A method of measuring petrophysical properties of formations, drilling parameters (WOB, torque etc.) and environmental parameters downhole and sending the results to surface without interrupting routine drilling operations. A special tool containing sensors, power supply and transmitter is installed as part of the BHA. The information is transmitted to surface by a telemetry system using mud pulses or signals through the pipe.

Nipple n : a short length of tubing (generally less than 12") with male threads at both ends.

Nipple up v : to assemble the components of the BOP stack on the wellhead.

Normal pressure n : the formation pressure which is due to a normal deposition process where the pore fluids are allowed to escape under compaction. The normal pressure gradient is usually taken as 0.465 psi per foot of depth from surface.

Northing n : one of the co-ordinates used in plotting the position of the wellbore in the horizontal plane along the y axis.

Offshore drilling n : drilling for oil or gas from a location which may be in an ocean, gulf, sea or lake. The drilling rig may be on a floating vessel (e.g. semi-submersible, drill ship) or mounted on a platform fixed to the seabed (e.g. jack up, steel jacket).

Oil based mud n : a drilling fluid which contains oil as its continuous phase with only a small amount of water dispersed as droplets.

Open hole n : any wellbore or part of the wellbore which is not supported by casing.

Operator n : the company which carries out an exploration or development programme on a particular area for which they hold a license. The operator may hire a drilling contractor and various service companies to drill wells, and will provide a representative (company man) on the rig.

Orientation v : the process by which a deflection tool is correctly positioned to achieve the intended direction and inclination of the wellbore.

Orienting sub n : a special sub which contains a key or slot, which must be aligned with the scribe line of the bent sub. A surveying instrument can then be run into the sub aligning itself with the key to give the orientation of the scribe line, which defines the tool face.

Overburden n : the layers of rock lying above a particular formation.

Overshot n : a fishing tool which is attached to the drill pipe and is lowered over, and engages, the fish externally.

Packed hole assembly n : a BHA which is designed to maintain hole inclination and direction of the wellbore.

Packer n : a downhole tool, run on drillpipe, tubing or casing, which can be set hydraulically or mechanically against the wellbore. Packers are used extensively in DSTs, cement squeezes and completions.

Pay zone n : the producing formation.

Pendulum assembly n : a BHA which is designed to reduce hole inclination by allowing the drill collars to bend towards the low side of the hole.

Perforate v : to pierce the casing wall and cement, allowing formation fluids to enter the wellbore and flow to surface. This is a critical stage in the completion of a well. Perforating may also be carried out during workover operations.

Perforating gun n : a device fitted with shaped charges which is lowered on wireline to the required depth. When fired electrically from the surface the charges shoot holes in the casing and the tool can then be retrieved.

Permeability n : a measure of the fluid conductivity of a porous medium (i.e. the ability of fluid to flow through the interconnected pores of a rock). The units of permeability are darcies or millidarcies.

pH value n : a parameter which is used to measure the acidity or alkalinity of a substance.

Pilot hole n : a small diameter hole which is later opened up to the required diameter. Sometimes used in directional drilling to control wellbore deviation during kick off.

Pin n : the male section of a threaded connection.

Pipe ram n : a sealing device in a blowout preventor which closes off the annulus around the drill pipe. The size of ram must fit the drillpipe which is being used.

Polycrystalline diamond compact bit (PDC bit) n : a PDC bit is a type of drag bit which uses small discs of man-made diamond as the cutting surface.

P.O.H. abbr : Pull Out of Hole.

Pore n : an opening within a rock which is often filled with formation fluids.

Porosity n : a parameter used to express the pore space within a rock (usually given

as a percentage of unit volume).

Positive displacement motor (PDM) n : a drilling tool which is located near the bit and is used to rotate the bit without having to turn the entire drillstring. A spiral rotor is forced to rotate within a rubber sleeved stator by pumping mud through the tool. Sometimes called a Moineau pump or screw drill.

Pressure gradient n : the variation of pressure with depth. Commonly used under hydrostatic conditions (e.g. a hydrostatic column of salt water has a pressure gradient of 0.465 psi/ft)

Primary cementing n : placing cement around the casing immediately after it has been run into the hole.

Prime mover n : an electric motor or internal combination engine which is the source of power on the drilling rig.

Production casing n : the casing string through which the production tubing and accessories are run to complete the well.

Propping agent n : a granular material carried in suspension by the fracturing fluid which helps to keep the cracks open in the formation after fracture treatment.

Protective casing n : an intermediate string of casing which is run to case off any troublesome zones.

p.s.i. abbr : pounds per square inch. Commonly used unit for expressing pressure.

Pup joint n : a short section of pipe used to space out casing or tubing to reach the correct landing depths.

Rathole n :

1. A hole in the rig floor 30'-60' deep and lined with pipe. It is used for storing the kelly while tripping.

2. That part of the wellbore which is below the bottom of the casing or completion zone.

Reactive torque n : the tendency of the drillstring to turn in the opposite direction from that of the bit. This effect must be considered when setting the toolface in directional drilling.

Ream v : to enlarge the wellbore by drilling it again with a special bit.

Reamer n : a tool used in a BHA to stabilise the bit, remove dog legs or enlarge the hole size.

Reeve v : to pass the drilling line through the sheaves of the travelling block and crown block and onto the hoisting drum.

Relief well n : a directionally drilled well whose purpose is to intersect a well which is blowing out, thus enabling the blow out to be controlled.

Reservoir n : a subsurface porous permeable formation in which oil or gas is present.

Reverse circulate v : to pump fluid down the annulus and up the drillstring or tubing back to surface.

Rig n : the derrick, drawworks, rotary table and all associated equipment required to drill a well.

R.I.H. abbr : Run In Hole.

Riser tensioner n : a pneumatic or hydraulic device used to provide a constant strain in the cables which support the marine riser.

R.K.B. abbr : Rotary Kelly Bushing. Term used to indicate the reference point for measuring depths.

Roller cone bit n : a drilling bit with 2 or more cones mounted on bearings. The cutters consist of rows of steel teeth or tungsten carbide inserts. Also called a rock bit.

R.O.P. abbr : rate of penetration, normally measured in feet drilled per hour.

Rotary hose n : a reinforced flexible tube which conducts drilling fluid from the standpipe to the swivel. Also called "kelly hose" or mud hose.

Rotary table n : the main component of the rotating machine which turns the drillstring. It has a bevelled gear mechanism to create the rotation and an opening into which bushings are fitted.

Roughneck n : an employee of a drilling contractor who works on the drill floor under the direction of the driller.

Round trip v : the process by which the entire drillstring is pulled out the hole and run back in again (usually to change the bit or BHA).

Roustabout n : an employee of the drilling contractor who carries out general labouring work on the rig.

R.P.M. abbr : revolutions per minute. Term used to measure the speed at which the drillstring is rotating.

Safety joint n : a tool which is often run just above a fishing tool. If the fishing tool has gripped the fish but cannot pull it free the safety joint will allow the string to disengage by turning it from surface.

Salt dome n : an anticlinal structure which is caused by an intrusion of rock salt into overlying sediments. This structure is often associated with traps for petroleum accumulations.

Sand n : an abrasive material composed of small quartz grains. The particles range in size from 1/16mm to 2mm. The term is also applied to sandstone.

Sandline n : small diameter wire on which light-weight tools can be lowered down the hole (e.g. surveying instruments).

Scratcher n : a device fastened to the outside of the casing which removes mud cake and thus promote a good cement job.

Semi-submersible n : a floating drilling rig which has submerged hulls, but not resting on the seabed.

Shale n : a fine-grained sedimentary rock composed of silt and clay sized particles.

Shale shaker n : a series of trays with vibrating screens which allow the mud to pass through but retain the cuttings. The mesh must be chosen carefully to match the size of the solids in the mud.

Shear ram n : the component of the BOP stack which cuts through the drillpipe and forms a seal across the top of the wellbore.

Sheave n : (pronounced shiv) a grooved pulley.

Sidetrack v : to drill around some permanent obstruction in the hole with some kind of deflecting tool.

Single n : one joint of pipe.

Slips n : wedge-shaped pieces of metal with a gripping element used to suspend the drillstring in the rotary table.

Slug n : a heavy viscous quantity of mud which is pumped into the drillstring prior to pulling out. The slug will cause the level of fluid in the pipe to fall, thus eliminating the loss of mud on the rig floor when connections are broken.

Slurry (cement) n : a pumpable mixture of cement and water. Once in position the slurry hardens and provides an impermeable seal in the annulus and supports the casing.

Spear n : a fishing tool which engages the fish internally and is used to recover stuck pipe.

Specific gravity n : the ratio of the weight of a substance to the weight of the same

volume of water.

S.P.M. abbr : Strokes Per Minute. Rate of reciprocation of a Mud Pump.

Spool n : a wellhead component which is used for suspending a string of casing. The spool also has side outlets for allowing access to the annulus between casing strings.

Spud v : to commence drilling operations.

Squeeze cementing v : the process by which cement slurry is forced into place in order to carry out remedial work (e.g. shut off water producing zones, repair casing leaks).

Stab v : to guide the pin end of a pipe into the tool joint or coupling before making up the connection.

Stabbing board n : a temporary platform erected in the derrick 20'-40' above the drill floor. While running casing one man stands on this board to guide the joints into the string suspended on the rig floor.

Stabiliser n : a component placed in the BHA to control the deviation of the wellbore. One or more stabilisers may be used to achieve the intended well path.

Stage collar n : a tool made up in the casing string which is used in the second stage of a primary cement job. The collar has side ports which are opened by dropping a dart from surface. Cement can then be displaced from the casing into the annulus. Also called a DV collar.

Stand n : three joints of pipe connected together, usually racked in the derrick.

Standpipe n : a heavy wall pipe attached to one of the legs of the derrick. It conducts high pressure mud from the pumps to the rotary hose.

Standpipe manifold n : a series of lines, gauges and valves used for routing mud from the pumps to the standpipe.

Steering tool n : surveying instrument used in conjunction with a mud motor to continuously monitor azimuth, inclination and toolface. - These measurements are relayed to surface via conductor line, and shown on a rig floor display.

Stimulation n : a process undertaken to improve the productivity of a formation by fracturing or acidising.

Stripping v : movement of pipe through closed BOPs.

Stuck pipe n : drillpipe, collars, casing or tubing which cannot be pulled free from the


Sub n : a short threaded piece of pipe used as a crossover between pipes of different

thread or size. Subs may also have special uses (e.g. bent subs, lifting subs, kelly saver


Subsea wellhead n : the equipment installed on the seabed for suspending casing strings when drilling from a floater.

Suction pit n : the mud pit from which mud is drawn into the mud pumps for circulating down the hole.

Surface casing n : a string of casing set in a wellbore to case off any fresh water sands at shallow depths. Surface casing is run below the conductor pipe to depth of 1000'- 4000' depending on particular requirements).

Surge pressures n : excess pressure exerted against the formation due to rapid downward movement of the drillstring when tripping.

Survey v : to measure the inclination and direction of the wellbore at a particular depth.

Survey interval n : the measured depth between survey stations.

Survey station n : the point at which a survey is taken.

Swabbing n : a temporary lowering of the hydrostatic head due to pulling pipe out of the hole.

Swivel n : a component which is suspended from the hook. It allows mud to flow from the rotary hose through the swivel to the kelly while the drillstring is rotating.

Syncline n : a trough-shaped, folded structure of stratified rock.

Target n : the objective defined by the geologist which the well must reach.

Target area n : a specified zone around the target which the well must intersect.

Target bearing n : the direction of the straight line passing through the target and the reference point on the rig. This is used as the reference direction for calculating vertical section.

T.D. abbr : Total Depth.

Telescopic joint n : a component installed at the top of the marine riser to accommodate vertical movement of the floating drilling rig.

Thread protectors n : a device made of metal or plastic which is screwed onto pipe threads to prevent damage during transport or movement around the rig.

Tight formation n : a formation which has low porosity and permeability.

Tongs n : the large wrenches used to connect and disconnect sections of pipe. The tongs have jaws which grip the pipe and torque is applied by pulling manually or mechanically using the cathead. Power tongs are pneumatically or hydraulically operated tools which spin the pipe.

Tool face n : the part of the deflection tool which determines the direction in which deflection will take place. When using a bent sub the tool face is defined by the scribe line.

Tool joint n : a heavy coupling device welded onto the ends of drill pipe. Tool joints have coarse tapered threads to withstand the strain of making and breaking connections and to provide a seal. They also have seating shoulders designed to suspend the weight of the drillstring when the slips are set. On the lower end the pin connection is stabbed into the box of the previous joint. Hardfacing is often applied in a band on the outside of the tool joint to resist abrasion.

Toolpusher n : an employee of the drilling contractor who is responsible for the drilling rig and the crew. Also called rig superintendent.

Torque n : the turning force which is applied to the drillstring causing it to rotate Torque is usually measured in ft-lbs.

Tour n : (pronounced tower) an 8 hour or 12 hour shift worked by the drilling crew.

Trajectory n : the path of the wellbore.

Trap n : the geological structure in which petroleum reserves may have accumulated.

Travelling block n : an arrangement of pulleys through which the drilling line is reeved, thereby allowing the drillstring to be raised or lowered.

Trip v : to pull the drillstring out of the hole, or to run in back in.

Trip gas n : a volume of gas (usually a small amount) which enters the wellbore while making a trip.

Triplex pump n : a reciprocating mud pump with three pistons which are single


True North n : the direction of a line joining any point with the geographical North pole. Corresponds with an azimuth of 000.

Tugger line n : a small diameter cable wound on an air operated winch which can be used to pick up small loads around the rig floor.

Turbodrill n : a drilling tool located just above the bit which rotatesd the bit without turning the drillstring. The tool consists of a series of steel bladed rotors which are turned by the flow of drilling fluid through the tool.

T.V.D. abbr : True Vertical Depth. One of the co-ordinates used to plot the wellpath on the vertical plane.

Twist off v : to sever the drillstring due to excessive force being applied at the rotary table.

Underground blow out v : this situation arises when lost circulation and a kick occur simultaneously. Formation fluids are therefore able to enter the wellbore at the active zone and escape through an upper zone which has been broken down. (Sometimes called an internal blow out")

Under ream v : to enlarge the size of the wellbore below casing.

Upset n : the section at the ends of tubular goods where the OD is increased to give better strength.

Valve n : a device used to control or shut off completely, the rate of fluid flow along a pipe. Various types of valve are used in drilling equipment.

V door n : an opening in one side of the derrick opposite the drawworks. This opening is used to bring in pipe and other equipment onto the drill floor.

Vertical section n : the horizontal distance obtained by projecting the closure onto the target bearing. This is one of the co-ordinates used in plotting the wellpath on the vertical plane of the proposed wellpath.

Viscometer n : a device used to measure the viscosity of the drilling fluid.

Viscosity n : a measure of a fluids resistance to flow. The resistance is due to internal friction from the combined effects of cohesion and adhesion.

Vug n : geological term for a cavity in a rock (especially limestone).

Washout n :

1. Wellbore enlargement due to solvent or erosion action of the drilling fluid.

2. A leak in the drillstring due to abrasive mud or mechanical failure.

Water back v : to reduce the weight and solids content of the mud by adding water. This is usually carried out prior to mud treatment.

Water based mud n : a drilling fluid in which the continuous phase is water. Various additives will also be present.

Water injector n : a well which is used to pump water into the reservoir to promote better recovery of hydrocarbons.

Wear bushing n : a piece of equipment installed in the wellhead which is designed to act as a bit guide, casing seat protector and prevent damage to the casing hanger already in place. The wear bushing must be removed before the next casing string is run.

Weight indicator n : an instrument mounted on the drillers console which gives both the weight on bit and the hook load.

Wellbore n : a general term to describe both cased hole and open hole.

Wellhead n : the equipment installed at the top of the wellbore from which casing and tubing strings are suspended.

Whipstock n : a long wedge-shaped pipe that uses an inclined plane to cause the bit to deflect away from its original position.

Wildcat n : an exploration well drilled in an area where no oil or gas has been produced.

Wiper trip n : the process by which the drill bit is pulled back inside the previous casing shoe and then run back to bottom. This may be necessary to improve the condition of the wellbore (e.g. smooth out any irregularities or dog legs which could cause stuck pipe later).

Wireline n : small diameter steel wire which is used to run certain tools down into the wellbore. Also called slick line. Logging tools and perforating guns require conductor line.

W.O.B. abbr : Weight On Bit. The load put on the bit by the drill collars to improve penetration rate.

W.O.C. abbr : Waiting On Cement. The time during which drilling operations are suspended to allow the cement to harden before drilling out the casing shoe.

W.O.W. abbr : Waiting On Weather. The time during which drilling operations must stop due to rough weather conditions. Usually applied to offshore drilling.

Workover n : the carrying out of maintenance and remedial work on the wellbore to increase production.