Oil and Gas Industry Glossary of Terms

Glossary of Oil and Gas Industry Terms

Abandon to cease producing oil and gas from a well with it becomes unprofitable or to cease further work on a newly drilled well when it proves not to contain profitable quantities of oil or gas.Accumulator see blowout preventer control unit.

Acid Fracture to part or open fractures in productive hard limestone formations by using a combination of oil and acid or water and acid under high pressure.

Acidize to treat oil-bearing limestone or other formations with acid for the purpose of increasing production.

Adjustable choke a choke in which the position of a conical needle, sleeve, or plate may be changed with respect their seat to vary the rate of flow; may be manual or automatic.

Afternoon tour on rigs that employ three 8-hour shifts, the work period that covers the afternoon and evening hours, such as from 300pm to 1100 pm. Also called evening tour.

Air-actuated equipment activated by compressed air, as are the clutch and the brake system in drilling equipment.

Air drilling a method of rotary drilling that uses compressed air as the circulation method.

Air hoist a hoist operated by compressed air; a pneumatic hoist. Air hoists are often mounted on the rig floor and are used to lift joints of pipe and other heavy objects.

Air tugger see air hoist

American Petroleum Institute (API) oil trade organization (founded in 1920) that is the leading standard-setting organization for all types of oilfield equipment. It maintains departments of production, transportation, refining and marketing in WAshington D.C. It offers publications regarding standards, recommended practices, and bulletins.

Angle of deflection in directional drilling, the angle at which a well diverts from vertical; usually expressed in degrees, with vertical being 0 degrees.

Annular blowout preventer a large valve, usually installed above the ram preventers, that forms a seal in the annular space between the pipe and the wellbore or, if no pipe is present, in the wellbore itself. Compare ram blowout preventer.

Annular preventer see annular blowout preventer.

Annular space the space between two concentric circles. In the petroleum industry, it is usually the space surrounding a pipe in the wellbore, or the space between tubing and casing, or the space between tubing and the wellbore; sometimes termed annulus.

Annulus see annular space

Anticline rock layers folded in the shape of an arch. Anticlines sometimes trap oil and gas.

Area drilling superintendent and employee of a drilling contractor whose job it is to coordinate and oversee the contractor’s drilling projects in a particular region or area.

Assistant driller is a member of a drilling rigs’s crew whose job it is to aid and assist the driller during rig operations. This person not only controls the drilling operations at certain times, but also keeps records, handles technical details, and in general, keeps track of all phases of operation. See driller

Assistant rig superintendent an employee of a drilling contractor whose job includes aiding the the rig superintendent; in some cases, the assistant rig superintendent takes over for the rig superintendent during nighttime hours. Consequently, the assistant rig superintendent is sometimes called the night toolpusher. See rig superintendent.

Automatic pipe racker a device used on a drilling rig to automatically remove and insert drill stem components from and into the hole. It replaces the need for a person to be in the derrick or mast when tripping pipe into or out of the hole.


Back-in unit a portable servicing or workover rig that is self-propelled, using the hoisting engines for motive power. Because the driver’s cab is mounted on the end opposite the mast support, the unit must be backed up to the wellhead. See carrier rig, drive in unit

Back off to unscrew on threaded piece (such as a section of pipe) from another.

Back up to hold one section of an object such as pipe while another section is being screwed into or out of it.

Bail a curved steel rod on top of the swivel that resembles the handle, or bail, of an ordinary bucket, but is much larger. Sometimes the two steel rods (the links) that attach the elevator to the hook are also called bails. To recover the bottomhole fluids, samples, mud, sand or drill cuttings by lowering a cylindrical vessel called a bailer to the bottom of a well, filling it, and retrieving it.

Bailer a long cylindrical container fitted with a valve at its lower end, used to remove water, sand, mud, drilling cuttings, or oil from a well in cable-tool drilling.

Ball up to collect a mass of sticky consolidated material, usually drill cuttings, on drill pipe, drill collars, bits, and so forth.

Barge a flat-decked, shallow-drift vessel, usually towed by a boat. A complete drilling rig may be assembled on a barge and the vessel used for drilling wells in lakes and in inland waters and marshes.

Barge control operator an employee on a semi-submersible rig whose main duty is to monitor and control the stability of the rig. From a special work station on board the rig, this person controls the placement of ballast water inside the rig’s pontoons to maintain the rig on even keel during all operations.

Barge engineer see barge control operator

Barge Master see barge control operator

Barite barium sulfate BaSO4; a mineral frequently usedto increase the weight or density of drilling mud.

Barium sulfate a chemical compound of barium, sulfur, and Oxygen. Also called barite.

Barrels per day (bpd) in the United States, a measure of the rate of flow of a well; the total amount of oil and fluids produced or processed per day.

Barrel (bbl) a measure of volume for petroleum products in the United States. One barrel ifs the equivalent of 42 US gallons or 0.15899 cubic meters. One cubic meter equals 6.2897 barrels.

Bed a specific layer of earth or rock that presents a contrast to other layers of different material lying above, below, or adjacent to it.

Bedrock solid rock just beneath the soil

Belt a flexible band or cord connection and wrapping around each of two or more pulleys to transmit power or impart motion.

Belt guard a protective grill or cover for a belt and pulleys.

Bent sub a short cylindrical device installed in the drill stem between the bottommost drill collar and a downhole motor. Its purpose is to deflect the downhole motor off vertical to drill a directional hole.

Bit the cutting or boring element used in drilling oil and gas wells. The bit consists of a cutting element and a circulation element. The cutting element is steel teeth, tungsten carbide cottons, industrial diamonds, or polycrystalline diamond compacts (PDCs)

Bit breaker a heavy plate that fits in the rotary table and holds the drill bit while it is being make up in or broken out of the drill stem. See bit.

Bit cutter the teeth of a bit

Bit pin the threaded element at the top of a bit that allows it to be made up in a drill collar or other component of the drill stem.

Bit record a report that lists each bit used during a drilling operation, giving the type, the footage it drilled, the formation it penetrated, its condition, and so on.

Bit suba sub inserted between the drill collar and the bit. See sub.

Blind ram an integral part of a blowout preventer, which serves as the closing element on an open hole. Its ends do not fit around the drill pipe but seal against each other and shut off the space below completely. See ram.

Blind ram preventer a blowout preventer in which blind rams are the closing elements. See blind ram.

Block any assembly of pulleys on a common framework; in mechanics, one or more pulleys, or sheaves, mounted to rotate on a common axis. The crown block is an assembly of sheaves mounted on beams at the top of the derrick or mast. The drilling line is reeved over the sheaves of the crown block alternately with the shaves of the traveling block, which is raised and lowered in the derrick or mast by the drilling line.

Blowout an uncontrolled flow of gas, oil, or other well fluids into the atmosphere or into and underground formation. A blowout, or gusher, can occur when formation pressure exceeds the pressure applied to it by the column of drilling fluid.

Blowout preventer (BOP) one of several valves installed at the wellhead to prevent the escape of pressure either in the annular space between the casing and the drill pipe or in open hole (i.e., hole with no drill pipe) during drilling or completion operations. See annular blowout preventer, ram blowout preventer.

Blowout preventer control panel controls, usually located near the driller’s position on the rig floor, that are manipulated to open and close the blowout preventers. See blowout preventer

Blowout preventer control unit a device that stores hydraulic fluid under pressure in special containers and provides a method to open and close the blowout preventers quickly and reliably. Usually, compressed air and hydraulic pressure provide the opening and closing force in the unit. See blowout preventer. Also called an accumulator.

BOP blowout preventer.

BOP stack the assembly of blowout preventers installed on a well.

Bore the inside diameter of a pipe or a drilled hole. to penetrate or pierce with a rotary tool.

Borehole a hole made by drilling or boring; a wellbore.

Bottomhole the lowest or deepest part of a well. pertaining to the bottom of the wellbore.

Bottomhole assembly the portion of the drilling assembly below the drill pipe. It can be very simple-composed of only the bit and drill collars-or it can be very complex and make up of several drilling tools.

Bottomhole pressure the pressure at the bottom of a borehole caused by the hydrostatic pressure of the wellbore fluid and, sometimes, by any back-pressure held at the surface, as when the well is shut in with blowout preventers.

Bottom plug a cement plug that precedes cement slurry down the casing. The plug wipes drilling mud off the walls of the casing and prevents it from contaminating the cement. See cementing, wiper plug.

Box the female section of a connection. See also tool joint.

Box and pin see tool joint.

Box threads threads on the female section, or box, of a tool joint. See tool joint.

Brake a device for arresting the motion of a mechanism, usually by means of friction, as in the drawworks brake.

Brake band a part of the brake mechanism consisting of a flexible steel band lined with a material that grips a drum when tightened. On a drilling rig, the brake band acts on the flanges of the drawworks drum to control the lowering of the traveling block and its load of drill pipe, casing or tubing.

Break to begin or start (e.g., break circulation or to break tour).

Break circulation to start the mud pump for restoring circulation of the mud column.

Break it see break out.

Break it out see break out.

Break out to unscrew one section of pipe from another section, especially drill pipe while it is being withdrawn from the wellbore.

Breakout block a bit breaker; a heavy plate that fits in the rotary table and holds the drill bit while it is being unscrewed from the drill collar.

Breakout cathead a device attached to the catshaft of the drawworks that is used as a power source for unscrewing drill pipe; usually located opposite the driller’s side of the drawworks. See cathead. Compare makeup cathead.

Breakout tongs tongs that are used to start unscrewing once section of pipe from another section, especially drill pipe coming out of the hole. See lead tongs, tongs.

Break tour to begin operation 24 hours a day.

Bring in a well to complete a well and put it on producing status.

Buck up to tighten up a threaded connection (such as two joints of drill pipe).

Bulk tank on a drilling rig, a large metal bin that usually holds a large amount of certain mud additive, such as bentonite, that is used in large quantities in the makeup of the drilling fluid. Also call a P-tank.

Bullwheel one of the two large wheels joined by and axle and used to hole the drilling line on a cable-tool rig.

Bumped in cementing operations, pertaining to a cement plug that comes to rest on the float collar. A cementing operator may say, “I have a bumped plug” when the plug strikes the float collar.

Bumps see bumped.

Bushing 1. a pipe fitting on which he external thread is larger than the internal thread to allow two pipes of different sizes to be connected. 2. a removable lining or sleeve inserted or screwed into an opening to limit its size, resist wear or corrosion, or serve as a guide.


Cable a rope of wire, hemp, or other strong fibers. See wire rope.

Cable tool-drilling a drilling method in which the hole is drilled by dripping a sharply pointed bit on bottom. The bit is attached to a cable, and the cable is repeatedly dropped as the hole is drilled.

Caisson one of several columns made of steel or concrete that serve as the foundation for a rigid offshore platform rig, such as the concrete gravity platform rig.

Cap to control a well that is flowing out of control; often accomplished by attaching a valve in the open position on top of the well and then closing it to seal off the flow.

Carrier rig a large, specially designed, self-propelled workover rig that is driven directly to the well site. Power from a rig’s hoist engine or engines also propels the rig on the road. While a carrier rig is primarily intended to perform workovers, it can also be used to drill relatively shallow wells. A carrier rig may be a back-in type or a drive-in type. Compare back-in unit, drive-in unit.

Case the outer cylinder of a concentric cylinder centrifuge. See concentric cylinder centrifuge.

Cased pertaining to a wellbore in which casing has been run and cemented. See casing.

Cased hole a wellbore in which casing has been run.

Casing steel pope placed in an oil or gas well to prevent the wall of the hole from caving in, to prevent movement of fluids from one formation to another, and to improve the efficiency of extracting petroleum if the well is productive.

Casing centralizer a device secured around the casing at regular intervals to center it in the hole. Casing that is centralized allows a more uniform cement sheath to form around the pipe.

Casing coupling a tubular section of pipe that is threaded inside and used to connect tow joins of casing.

Casing elevator see elevators.

Casing float collar see float collar.

Casing float shoe see float shoe.

Casing hanger a circular device with a frictional gripping arrangement of slips and packing rings used to suspend casing from a casinghead in a well.

Casinghead heavy, flanged steel fitting connected to the first string of casing. It provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off. Also called a spool.

Casing point 1. the depth in a well at which casing is se, generally the depth at which the casing shoe rests. 2. the objective depth in a drilling contract, either a specified depth or the depth at which a specific zone is penetrated.

Casing pressure the pressure in a well that exists between the casing and the drill pipe.

Casing seat the location of the bottom of a string of casing that is cemented in a well.

Casing shoe see guide shoe.

Casing string the entire length of all the joins of casing run in a well.

Casing tongs large wrench used for turning when making up or breaking out casing. See tongs.

Casing-tubing annulus in a wellbore, the space between the inside of the casing and the outside of the tubing.

Catch samples to obtain cuttings for geological information as formations are penetrated by the bit.

Cathead a spool-shaped attachment on the end of the catshaft, around which rope for hoisting and moving heavy equipment on or near the rig floor is wound. See breakout cathead, makeup cathead.

Cathead spool see cathead.

Catline a hoisting or pulling live powered by the cathead and used to lift heavy equipment on the rig. See cathead.

Catshaft an axle that crosses through the drawworks and contains a revolving spool called a cathead at either end. See cathead.

Catwalk the ramp at the side of the drilling rig where pipe is laid to be lifted to the derrick floor by the catline or by an air hoist.

Caving collapsing of the walls of the wellbore. Also called sloughing.

Cellar a pot in the ground, usually lined with concrete or wood, that provides additional height between the rig floor and the wellhead to accommodate the installation of blowout preventers, rathole, mousehole and so fourth.

Cement a powder consisting of alumina, silica, lime, and other substances that hardens with mixed with water. Extensively used in the oil industry to bond casing to the walls of the wellbore.

Cement casing to fill the annulus between the casing and the wall of the hole with cement to support the casing and to prevent fluid migration between permeable zones.

Cementing the application of a liquid slurry of cement and water to various points inside or outside the casing.

Cementing company a company whose specialty is preparing, transporting, and pumping cement into a well. Usually, a cementing company’s crew pumps the cement to secure casing in the well.

Cementing head an accessory attached to the top of the casing to facilitate cementing of the casing. It has passages for cement slurry and retainer chambers for cementing wiper plugs. Also called retainer head.

Cementing pump a high-pressure pump used to force cement down the casing and into the annular space between the casing and the wall of the borehole.

Cementing time the total elapsed time needed to complete a cementing operation.

Cement plug 1. a portion of cement placed at some point in the wellbore to seal it. 2. a wiper plug. See cementing, wiper plug.

Centralizer see casing centralizer.

Chain tongs a hand tool consisting of a handle and chain that resembles the chain on a bicycle. In general, chain tongs are used for turning pipe or fittings of a diameter larger than that which a pipe wrench would fit.

Choke a device with an orifice installed in a line to restrict the flow of fluids.

Choke line a pipe attached to the blowout preventer stack out of which kick fluids and mud can be pumped to the choke manifold when a blowout preventer is closed in on a kick.

Choke manifold an arrangement of piping and special valves, called chokes. In drilling, mud is circulated through a choke manifold when the blowout preventers are closed.

Christmas tree the control valves, pressure gauges, and chokes assembled at the top of a well to control the flow of oil and gas after the well has been drilled and completed.

Circulate to pass from one point throughout a system and back to the starting point. For example, drilling fluid is circulated out of the suction pot, down the drill pipe and drill collars, out the bit, up the annulus, and back to the pits while drilling proceeds.

Circulating components the equipment included in the drilling fluid circulating system of a rotary rig. Basically, the components consist of the mud pump, the rotary hose, the swivel, the drill stem, the bit, and the mud return line.

Circulating fluid see drilling fluid, mud.

Circulating pressure the pressure generated by the mud pumps and exerted on the drill stem.

Circulation the movement of drilling fluid out of the mud pits, down the drill stem, up the annulus, and back to the mud pits.

Clay 1. a term used for particles smaller than 1/ 256 millimetre (4 microns), regardless of mineral composition. 2. a group of hydrous aluminum silicate minerals (clay minerals).

Clump weights special segmented weights attached to the guy wires of a guyed compliant platform that keep the guy wires taut as the platform jacket moves with the waves and current of the water.

Coiled tubing a continuous string of flexible steel tubing, often hundreds or thousands of feet long, that is wound onto a reel, often dozens of feet in diameter. The reel is an integral part of the coiled tubing unit, which consists of several devices that ensure the tubing can be safely and efficiently inserted into the well from the surface. Because tubing can be lowered into a well without having to make u joints of tubing, running coiled tubing into the well is faster and less expensive than running conventional tubing. Rapid advances in the use of coiled tubing make it a popular way in which to run tubing into and out of a well. Also called reeled tubing.

Collapse pressure the amount of force needed to crush the sides of pipe until it caves in.

Collar 1. a coupling device used to join tow lengths of pipe, such as casing or tubing. 2. a drill collar. See drill collar.

Collar locator a logging device used to determine accurately the depth of a well; the log measure and records the depth of each casing collar, or coupling, in a well.

Combination trap 1. a subsurface hydrocarbon trap that has the features of both a structural trap and a stratigraphic trap. 2. a combination of two or more structural traps or two or more stratigraphic traps.

Come out of the hole to pull the drill steam out of the wellbore to change the bit, to change from a core barrel to the bit, to run logs, to prepare for a drill stem test, to run casing and so on. Also called trip out.

Commercial quantity an amount of oil and gas production large enough to enable the operator to realize a profit, however small.

Compact a small disk make of tungsten carbide. See insert.

Company hand see company representative.

Company man see company representative.

Company representative an employee of an operating company whose job is to represent the company’s interests at the drilling location.

Complete a well to finish work on a well and bring it to productive status See well completion.

Compliant platform an offshore platform that is designed to flex with wind and waves.

Compound a mechanism used to transmit power from the engines to the pump, the drawworks, and other machinery on a drilling rig. It is composed of clutches, chains and sprockets, belts and pulleys, and number of shafts, both driven and driving. To connect two or more power-producing devices, such as engines, to run driven equipment, such as the drawworks.

Compresion-ignition engine a diesel engine and engine in which the fuel-air mixture inside the engine cylinders is ignited by the heat that occurs when the fuel-air mixture is highly compressed by the engine pistons.

Concrete gravity platform rig a rigid offshore drilling platform built of steel-reinforced concrete and sued to drill development wells.

Conductor casing generally, the first string of casing in a well. Its purpose is to prevent the soft formations near the surface from caving in and to conduct drilling mud from the bottom of the hole to the surface when drilling starts. Also called conductor pipe, drive pipe.

Conductor pipe see conductor casing.

Cone a conical-shaped metal device into which cutting teethe are formed or mounted on a roller cone bit. See roller cone bit.

Confirmation well the second producer in a new field, following the discovery well.

Connection 1. the action of adding a joint of pipe to the drill stem as drilling progresses. 2. a section of pipe or a fitting used to join pipe to pipe or to a vessel.

Contract a written agreement that can be enforced by law and that lists the terms under which the acts required are to performed. A drilling contract covers such factors as the cost of drilling the well (weather by the foot or by the day), the distribution of expenses between operator and contractor, and the type of equipment to be used.

Contract depth the depth of the wellbore at which a drilling contract is fulfilled.

Controlled directional drilling. See directional drilling.

Core a cylindrical sample taken from a formation for a geological analysis. To obtain a solid, cylindrical formation sample for analysis.

Core barrel a tubular device, usually from 10 to 60 feel (3 to 18 metres) long, run at the bottom of the drill pipe in place of a bit and used to cut a core sample.

Crane a machine for raising, lowering and revolving heavy pieces of equipment, especially on offshore rigs and platforms.

Crew the workers on a drilling rig, including the driller, the derrickhand, and the rotary helpers.

Crossover sub a sub that allows different sizes and types of drill pipe to be joined.

Crown the crown block or top of a derrick or mast.

Crown block an assembly of sheaves mounted on beams at the top of the derrick or mast and over which the drilling lie is reeved. See block.

Crude Oil unrefined liquid petroleum. It ranges in density from very light to very heavy and in color from yellow to black, and it may have paraffin, asphalt, or mixed base.

Cutter 1. cutting teeth on the cones of a roller cone bit. 2. the parts of a reamer that actually contact the wall of the hole and open it to full gauge. A three-point reamer has three cutters; a six-point reamer has three cutters. Cutters are available for different formations.

Cuttings the fragments of rock dislodged by the bit and brought to the surface in the drilling fluid.


Daily drilling report a record made each day of the operations on a working drilling rig and, traditionally, phoned or radioed in to the office of the drilling company every morning. Also called morning report.

Daylight tour in areas where three 8-hour tours are worked, the shift on a drilling rig that starts at or about daylight. Compare afternoon tour and morning tour.

Day tour in areas where two 12-hour tours are worked, a period of 12 daylight hours worked by a drilling crew.

Daywork descriptive of work done on daywork rates.

Daywork rates the basis for payment on drilling contracts when the rig owner is paid by the day rather by the foot. Daywork rates are the most common way in which contractors are paid for the rig’s work.

Deadline the drilling line from the crown block sheave to the anchor, so called because it does not move. Compare fastline.

Deadline anchor see deadline tie-down anchor.

Deadline tie-down anchor a device to which the deadline is attached, securely fastened to the mast or derrick substructure. Also called a deadline anchor.

Deflect see deflection.

Deflection a change in the angle of a wellbore. In directional drilling, it is measured in degrees from the vertical.

Degasser the device used to remove gas from drilling fluid.

Density the mass or weight of a substance per unit volume.

Derrick a large load-bearing structure, usually of bolted construction. In drilling, the standard derrick has four legs standing at the corners of the substructure and reaching to the crown block. Compare mast.

Derrick floor also called the rig floor or the drill floor. See rig floor.

Derrickhand the crew member who handles the upper end of the drill string as it is being hoisted out of or lowered into the hole. This person is also responsible for the circulating machinery and the conditioning of the drilling fluid.

Derrickman see Derrickhand.

Desander a centrifugal device for removing sand from drilling fluid to prevent abrasion of the pumps. Compare desilter.

Desilter a centrifugal device for removing very fine particles, or silt, from drilling fluid to keep the amount of solids in the fluid at the lowest possible point. Compare desander.

Development well 1. a well drilled in proven territory in a field to complete a pattern of production. 2. an exploitation well.

Diamond bit a drill bit that has small industrial diamonds embedded in its cutting surface. Cutting is performed by the rotation of the very hard diamonds over the rock surface.

Diapir a dome or anticlinal fold in which a mobile plastic core has ruptured the more brittle overlying rock. Also called piercement dome.

Dies tools used to shape, form, or finish other tools or pieces of metal. For example, a threading die is used to cut threads on a pipe.

Diesel-electric rig see electric rig

Diesel engine a high-compression, internal-combustion engine used extensively for powering drilling rigs. In a diesel engine, air is drawn into the cylinders and compressed to very high pressures; ignition occurs as fuel is injected into the compressed and heated air. Combustion takes place within the cylinder about the piston, and expansion of the combustion products imparts power to the piston.

Directional drilling intentional deviation of a wellbore from the vertical.

Directional hole a wellbore intentionally drilled at an angle from the vertical.

Discovery well the first oil or gas well drilled in a new field that reveals he presence of a hydrocarbon-bearing reservoir.

Displacement fluid in oilwell cementing, the fluid, usually drilling mud or salt water, that is pumped into the well after the cement is pumped into it to force the cement out of the casing and into the annulus.

Doghouse a small enclosure on the rig floor used as an office for the driller and as a storehouse for small objects.

Double a length of drill pipe, casing or tubing consisting of tow joints screwed together. Compare fourble, single, thribble.

Double board the name used for the derrickhand’s working platform (the monkeyboard) when it is located at a height in the derrick or mast equal to tow lengths of pipe joined together. Compare fourble board, thribble board.

Downhole pertaining to the wellbore.

Downhole motor a drilling tool made up n the drill string directly about the bit. It causes the bit to turn while the drill string remains fixed.

Drake well the first well drilled in the United States in search of oil. Some 69 feel (21 metres) deep, it was drilled near Titusville, Pennsylvania, and was completed in 1859. It was named after Edwin L. Drake, who was hired by the well owners to oversee the drilling.

Drawworks the hoisting mechanism on a drilling rig. It is essentially a large winch that spools off or takes in the drilling line and thus raises or lowers the drill steam and the bit.

Drawworks brake the mechanical brake on the drawworks that can prevent the drawworks from moving.

Drawworks drum the spool-shaped cylinder in the drawworks around which drilling line is wound, or spooled.

Drill to bore a hole in the earth, usually to find and remove subsurface formation fluids such as oil and gas.

Drill ahead to continue drilling operations.

Drill bit the cutting or boring element used for drilling. See bit.

Drill collar a heavy, thick-walled tub, usually steel, placed between the drill pipe and the bit in the drill steam.

Drill collar sub a sub made up between the drill string and the drill collars that is used to ensure that the drill pipe and the collar can be joined properly.

Drill column see drill stem.

Drilled show oil or gas in the mud circulated to the surface.

Driller the employee directly in charge of a drilling rig and crew. This person’s main duty is operation of the drilling and hoisting equipment, but the driller is also responsible for downhole condition of the well, operation of downhole stools, and pipe measurements.

Driller’s console a metal cabinet on the rig floor containing the controls that the driller manipulates to operate various components of the drilling rig.

Driller’s control panel see driller’s console.

Driller’s position the area immediately surrounding the driller’s console.

Drill floor also called rig floor or derrick floor. See rig floor.

Drilling contract an agreement made between a drilling company and an operation company to drill and complete a well. It sets for the obligation of each party, compensation, identification, method of drilling, depth to be drilled, and so on.

Drilling contractor and individual or group that owns a drilling rig or rigs and contracts services for drilling wells.

Drilling crew a driller, a derrickhand, and two or more rotary helpers who operate a drilling rig.

Drilling engine an internal-combustion engine used to power a drilling rig.

Drilling engineer an engineer who specializes in the technical aspects of drilling.

Drilling fluid circulating fluid, one function of which is to lift cuttings out of the wellbore and to the surface. Other functions are to cool the bit and counteract downhole formation pressure. Although a mixture of clay and other minerals, water, and chemical additives is the most common drilling fluid, wells can also be drilled by using air, gas, water, or oil-bas mud as the drilling mud. See mud.

Drilling hook the large hook mounted on the bottom of the traveling block and from which the swivel is suspended. When drilling, the entire weight of the drill steam is suspended from the hook.

Drilling line a wire rope used to support the drilling tools. Also called the rotary line.

Drilling mud a specially compounded liquid circulated through the wellbore during rotary drilling operations. See drilling fluid, mud.

Drilling rate the speed with which the bit drills the formation; usually called the rate of penetration (ROP).

Drill pipe seamless steel or aluminum pipe made up in the drill stem between the kelly or top drive on the surface and the drill collars on the bottom. Several joints are made up (screwed together) to from the drill string.

Drill pipe slips see slips

Drill ship a self-propelled floating offshore drilling unit that is a ship constructed to permit a well to be drilled from it. Although not as stable as semisubmersibles, drill ships are capable of drilling exploratory wells in deep, remote waters. See floating offshore drilling rig.

Drill site the location of a drilling rig.

Drill stem all members in the assembly used for rotary drilling from the swivel to the bit, including the Kelly, the drill pipe and tool joins, the drill collars, the stabilizers, and various specialty items. Compare drill string.

Drill stem test (DST) the conventional method of formation testing. The basic drill stem test tool consists of a packer or packers, valves or ports that may be opened and closed from the surface, and two or more pressure-recording devices. The tool is lowered on the drill string to the zone to be tested. The packer or packers are set to isolate the zone from the drilling fluid column. The valves or ports are then opened to allow for formation flow while the recorders chart static pressures. A sampling chamber traps clean formation fluids at the end of the test.

Drill string the column, or string, of drill pipe with attached tool joints that transmits fluid and rotational power from the kelly to the drill collars and the bit. Often, especially in the oil patch, the term is loosely applied to both pipe and drill collars, Compare drill stem.

Drive bushing see kelly bushing.

Drive-in unit a type of portable service or workover rig that is self-propelled, using power from the hoisting engines. The driver’s cab and steering wheel are mounted on the same end as the mast support; thus the unit can be driven straight ahead to reach the wellhead. See carrier rig.

Drive pipe see conductor casing.

Drum a cylinder around which wire rope is wound in the drawworks. The drawworks drum is the part of the hoist on which the drilling line is wound.

Dry a hole is dry when the reservoir is penetrates is not capable of producing hydrocarbons is commercial amounts.

Dry hole any well that does not produce oil or gas in commercial quantities.

Dynamic positioning a method by which a floating offshore drilling rig is maintained in position over on off shore well location without the use of mooring anchors. Generally, several propulsion units, called thrusters, are located on the hulls of the structure and are actuated by a sensing systems. A computer to which the system feeds signals directs the thrusters to maintain the rig location.

Dynamic positioning operator an employee on a drill shop or semisubmersible drilling rig whose primary duty is to monitor, operate, and maintain the equipment that maintains the rig on station while drilling.


Electric drive see electric rig.

Electric-drive rig see electric rig.

Electric generator a machine that changes mechanical energy into electrical energy.

Electric rig a drilling rig on which the energy from the power source-usually several diesel engines-is changed to electricity by generators mounted on the engines. Compare mechanical rig.

Elevator bails see elevator links.

Elevator links cylindrical bars that support the elevators and attach them to the hook. Also called elevator bails.

Elevators clamps that grip a joint of casing, tubing, drill collars, or drill pipe so that the joint can be raised from or lowered into the hole.

Engine a machine for converting the heat content of fuel into rotary motion that can be used to power other machines.

Evening tour see afternoon tour.

Exploitation well a well drilled to permit more effective extraction of oil from a reservoir. Sometimes called a development well.

Exploration the search for reservoirs of oil and gas, including aerial and geophysical surveys, geological studies, core testing, and drilling of wildcats.


Fastline the end of the drilling line that is affixed to the drum or reel of the drawworks, so called because it travels with greater velocity than any other portion of the line. Compare deadline.

Fault a break in the earth’s crust along which rocks on one side have been displaced (upward, downward, or laterally) relative to those on the other side.

Fault trap a subsurface hydrocarbon trap created by faulting, in which an impermeable rock layer has moved apposite the reservoir bed or where impermeable gouge has sealed the fault and stopped fluid migration.

Female connection a pipe, a coupling or a tool threaded on the inside so that only a male connection can be joined to it. Compare male connection.

Field a geographical area in which a number of oil or gas wells product from a continuous reservoir. A field may refer to surface area only or to underground production formations as well.

Fingerboard a rack that supports the tops of the stands of pipe being stacked in the derrick or mast.

Fish an object that is left in the wellbore during drilling or workover operations and that must be recovered before work can proceed. to recover from a well any equipment left there during drilling operations, such as a lost bi or drill collar or part of the drill string.

Fishing the procedure of recovering lost or stuck equipment in the wellbore. See also fish.

Fishing tool a tool designed to recover equipment lost in a well.

Fixed-head bit any bit, such as a diamond bit, whose cutting elements do not move on the face, or head, of the bit. Compare roller cone bit.

Flexible drill pipe specially manufactured drill pipe that has several pressure-tight joints over the length of the pipe. These joints allow the pipe to bend considerable more than regular drill pipe and are sued in directional wells (especially horizontal ones) where the angle of deflection from vertical is relatively abrupt.

Flex point a device that provides a flexible connection between the rise pope and the subsea blowout preventers.

Float collar a special coupling device inserted one or two joins above the bottom of the casing string that contains a check valve to permit fluid to pass downward but not upward through the casing. The float collar prevents drill mud from entering the casing while it is being lowered, allowing the casing to float during its descent and thus decreasing the load on the derrick or mast. A float collar also prevents backflow of cement during a cementing operation.

Floater see floating offshore drilling rig.

Floating offshore drilling rig a type of mobile offshore drilling unit that floats and is not in contact with the seafloor (except with anchors) when it is in the drilling mode. Floating units include drill ships and semisubmersibles. See mobile offshore drilling unit.

Float shoe a short, heavy, cylindrical steel section with a rounded bottom that is attached to the bottom of the casing string. It contains a check valve and functions similarly to the float collar but also serves as a guide shoe for the casing.

Floe floating ice field of any size.

Floor crew those workers on a drilling or workover rig who work primarily on the rig floor.

Floorhand see rotary helper.

Floorman see rotary helper.

Fluid substance that flows and yields to any force tending to change its shape. Liquids and gases are fluids.

Footage rates a fee basis in drilling contracts stipulating that payment to the drilling contractor is made according to the number of feet or metres of hole drilled.

Forge to use hard blows to form and shape metallic ingots into useful items.

Formation a bed or deposit composed throughout of substantially the same kind of rock. Each formation is given a name, frequently as a result of the study of the formation outcrop at the surface and sometimes based on fossils founds in the formation.

Formation boundary the horizontal limits of a formation.

Formation fluid fluid (such as gas, oil, or water) that exists in a subsurface rock formation.

Formation fracturing a method of stimulating production by opening new flow channels in the rock surrounding a production well. Often called a frac job. Under extremely high hydraulic pressure, a fluid (such as distillate, diesel fuel, crude oil, dilute hydrochloric acid, water, or kerosene) is pumped downward through production tubing or drill pipe and forced out below a packer or between two packers. The pressure causes cracks to open in the formation, and the fluid penetrates num pellets, walnut shells, or similar materials (propping agents) are carried in suspension by the fluid into the cracks. When the pressure is released at the surface, the fracturing fluid returns to the well. The cracks partially close on the pellets, leaving channels for oil to flow around them to the well.

Formation pressure the force exerted by fluids in a formation, recorded in the hole at the level of the formation with the well shut in. Also called reservoir pressure or shut-in bottom hole pressure.

Fourble a section of drill pipe, drill collars, or tubing consisting of four points screwed together. Compare double, single, thribble.

Fourble board the name used for the derrickhand’s working platform, or the monkeyboard, when it is located at a height in the derrick equal to approximately four lengths of pipe joined together. Compare double board, thribble board.

Frac job see formation fracturing.

Fracturing a shortened form of formation fracturing. See formation fracturing.

Full-gauge bit a bit that has maintained its original diameter.

Full-gauge hole a wellbore drilled with a full-gauge bit. Also called a true-to-gauge hole.


Gas-cut mud a drilling mud that contains entrained formation gas, giving the mud a characteristically fluffy texture. When entrained gas is not released before the fluid returns to the well, the weight or density of the fluid column is reduced.

Gas drilling see air drilling.

Gauge 1. the diameter of a bit or the hole drilled by the bit. 2. a device (such as a pressure gauge) used to measure some physical property. To measure size, volume, depth, or other measure property.

Gel a semisolid, jellylike state assumed by some colloidal dispersions as rest. When agitated, the gel converts to a fluid state. Also a nickname for bentonite. To take the form of a gel; to set.

Geologist a scientist who gathers and interprets data pertaining to the rocks of the earth’s crust.

Geology the science of the physical history of the earth and its life, especially as recorded in the rocks of the crust.

Geophone an instrument placed on the surface that detects vibrations passing through the earth’s curst. It is used in conjunction with seismography.

Geophysicist one who studies geophysics.

Geronimo see safety slide.

Go in the hole to lower the drill stem, the tubing, or the casing into the wellbore.

Gooseneck the curved connection between the rotary hose and the swivel. See swivel.

Grief stem kelly; kelly joint.

Guidelines lines, usually four, attached to a special guide base to help position equipment (such as blowout preventers) accurately on the seafloor when a well is drilled offshore from a floating vessel.

Guide shoe a short, heavy, cylindrical section of steel filled with concrete and rounded at the bottom, which is placed at the end of the casing string. A passage through the center of the shoe allows drilling fluid to pass up into the casing while it is being lowered and allows cement to pass out during cementing operations. Also called casing show.

Gusher an oilwell that has come in with such great pressure that the oil jets out of the well like a geyser. In reality, a gusher is a blowout and is extremely wasteful of reservoir fluids and drive energy. See blowout.

Guyed-tower platform rig a compliant offshore drilling platform used to drill development wells. The foundation of the platform is a relatively lightweight jacket on which all equipment is placed. A system of guy wires anchored by clump weights helps secure the jacket to the seafloor and allows it to move with wind and wave forces. See platform rig.


Head 1. the height of a column of liquid required to produce a specific pressure. See hydraulic head. 2. for centrifugal pumps, the velocity of flowing fluid converted into pressure expressed in feel or metres of flowing fluid. Also called velocity head. 3. that part machine (such as a pump or an engine) that is on the end of the cylinder opposite the crankshaft. Also called cylinder head.

Hex kelly see kelly.

Hoist 1. an arrangement of pulley and wire rope or chain used for lifting heavy objects; a winch or similar device. 2. the drawworks. To raise or lift.

Hoisting components drawworks, drilling line, and traveling and crown blocks. Auxiliary hoisting components include catheads, catshaft, and air hoist.

Hoisting drum the large flanged spool in the drawworks on which the hoisting cable is wound. See drawworks.

Hole in drilling operations, the wellbore or borehole. See borehole. Wellbore.

Hook a large, hook-shaped device from which the swivel is suspended. It is designed to carry maximum loads ranging from 100 to 650 tons (90 to 590 tonnes) and turns on bearings in its supporting housing.

Hook load the weight of the drill stem that is suspended from the hook.

Hopper a large funnel-or cone-shaped device into which dry components (such as powered clay or cement) can be poured to mix uniformly with water or other liquids.

Horizontal drilling deviation of the borehole at least 80° from vertical so that the borehole penetrates a productive formation in a manner parallel to the formation.

Horsepower a unit of measure of work done by a machine. One horsepower equals 33,000 foot-pounds per minute. (Kilowatts are used to measure power in the international, or SI, system of measurement.)

Hybrid bits combine natural and synthetic diamonds and sometimes tungsten carbide inserts on a fixed-head bit.

Hydraulic 1. of or relating to water or other liquid in motion. 2. operated, moved, or affected by water or liquid.

Hydraulic fracturing an operation in which a specially blended liquid is pumped down a well and into a formation under pressure high enough to cause the formation to crack open, forming passages through which oil can flow into the wellbore.

Hydraulic head 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.

Hydrocarbons organic compounds of hydrogen and carbon whose densities, boiling points, and freezing points increase as their molecular weights increase. Although composed of only two elements, hydrocarbons exist in a variety of compounds, because of the strong affinity of the carbon atom for other atoms and for itself. Petroleum is a mixture of many hydrocarbons.

Hydrogas another term for liquefied petroleum gas (LPG).

Hydrphone a device trailed in a n array behind a boat in offshore seismic exploration that is used to detect sounds reflections, convert them to electric current, and send them through a cable to recording equipment on the boat.

Hydrostatic pressure 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 (9.792 kilopascals per metre) of depth. 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.


IADC International Association of Drilling Contractors.

Idiot stick a shovel

Ignorant end the heavier end of any device (such as a length of pipe or a wrench).

Independent a nonintegrated oil company or an individual whose operations are in the field of petroleum production, excluding transportation, refining, and marketing.

Infilling drilling drilling wells between known producing wells to exploit the resources of a field to best advantage.

Infilling well a well drilled between known producing wells to exploit the reservoir better.

Inland barge rig a floating offshore drilling structure consisting of a barge on which the drilling equipment is constructed. When moved from one location to another, the barge floats. When stationed on the drill site, the barge can be anchored in the floating mode or submerged to rest on the bottom. Typically, inland barge rigs are used to drill wells in marshes, shallow inland bays, and areas where the water is not too deep. Also called swamp barge. See floating offshore drilling rig.

Insert a cylindrical object, rounded, blunt, or chisel-shaped on one end and usually made of tungsten carbide, that is inserted in the cones of a bit, the cutters of a reamer, or the blades of a stabilizer to form the cutting element of the bit or the reamer or the wear surface of the stabilizer. Also called a compact.

Intermediate casing string the string of casing set in a well after the surface casing but before production casing is set to keep the hole from caving and to seal off troublesome formations. In deep wells, one or more intermediate strings may be required. Sometimes called protection casing.

Intermediate string see intermediate casing string.

Internal-combustion engine a head engine in which the pressure necessary to product motion of the mechanism results from the ignition or burning of a fuel-air mixture within the engine cylinder.

International Association of Drilling Contractors (IADC) an organization of drilling contractors that sponsors or conducts research on education, accident prevention, drilling technology, and others matters of interest to drilling contractors and their employees. Its official publication is The Drilling Contractor. Address Box 4287; Houston, TX 77210; (713) 578-7171.

International System of Units (SI) a system of units of measurement based on the metric system, adopted and described by the Eleventh General Conference on Weights and Measures. It provides an international standard of measurements to be followed when certain customary units, both U.S. and metric, are eventually phased out of international trade operations.

Iron Roughneck™ a manufacturer’s name for a floor-mounted combination of a spinning wrench and a torque wrench. The Iron Roughneck™ moves into position hydraulically and eliminates the manual handling involved with suspended individual tools.


Jackup drilling rig a mobile bottom-supported offshore drilling structure with columnar or open-truss legs that support the deck and hull. When positioned over the drilling site, the bottoms of the legs rest on the seafloor. A jackup rig is towed or propelled to a location with its legs up. Once the legs are firmly positioned on the bottom, the deck and the hull height are adjusted and leveled. Also called self-elevation drilling unit.

Jerk line a length of chain used on the automatic cathead of the drilling rig to tighten pipe joints by pulling on the makeup tongs. See makeup tongs.

Jet 1. a hydraulic device operated by a centrifugal pump used to clean the mud pits, or tanks, and to mix mud components. 2. in a perforating gun using shaped charges, a highly penetrating, fast-moving stream of exploded particles that forms a hole in the casing, cement, and formation.

Jet bit a drilling bit having replaceable nozzles through which the drilling fluid is directed in a high-velocity stream to the bottom of the hole to improve the efficiency of the bit. See bit.

Jet-perforate to create holes through the casing with a shaped charge of high explosives.

Joint a single length (from 16 feet to 45 feet, or 5 metres to 14.5 metres, depending on its range length) of drill pipe, drill collar, casing, or tubing that has threaded connections at both ends.

Joint of pipe a length of drill pipe or casing. Both come in various lengths. See range length.

Joule the SI unit of energy work. It is equal to 1 newton-metre (n●m), which is 1 newton of force acting through a distance of 1 metre I the direction of the force.

Junk metal debris lost in a hole.


Kelly the heavy steel tubular device, four-or six-sided, suspended from the swivel through the rotary table and connected to the top joint of drill pipe to turn the drill stem as the rotary table turns. It has a bored passageway that permits fluid to be circulated into the drill stem and up the annulus, or vice versa.

Kelly bushing a special device placed around the kelly that mates with the kelly flats and fits into the master busing of the rotary table. Also called the drive bushing.

Kelly cock a valve installed at one or both ends, of the kelly that is closed when a high-pressure backflow begins inside the drill stem. The valve is closed to keep pressure off the swivel and rotary hose.

Kelly drive bushing a device that fits into the master bushing or the rotary table and through which the kelly runs. When the master bushing rotates the kelly drive bushing, the kelly drive bushing rotate the kelly and the drill stem attached to the kelly.

Kelly flat one of the flat sides of a kelly. Also called a flat.

Kelly hose also called the mud hose or rotary hose. See rotary hose.

Kelly joint see kelly.

Kelly saver sub a sub that fits in the drill stem between the kelly and the drill pipe and prevents wear to the kelly’s threads.

Kelly spinner a pneumatically operated device mounted on top of the kelly that, when actuated, causes the kelly to turn, or spin. It is used when making up or breaking out the kelly from the drill string.

Kelly sub see kelly saver sub.

Kick an entry of water, gas, oil, or other formation fluid into the wellbore during drilling. It occurs because the pressure exerted by the column of drilling fluid is not great enough to overcome the pressure exerted by the fluids in the formation drilled.

Kick fluids oil, gas, water, or any combination that enters the borehole from a permeable formation.

Kick off to deviate a wellbore from the vertical, as in directional drilling.

Kickoff point (KOP) the depth in a vertical hole at which a deviated or slant hole is started used in directional drilling.

Kill to control a kick by taking suitable preventive measures (e.g., to shut in the well with the blowout preventers, circulate the kick out, and increase the weight of the drilling mud).


Land rig any drilling rig that is located on dry land. Compare offshore rig.

Latch on to attach elevators to a section of pipe to pull it out of or run it into the hole.

Lead-tong hand the crew member who operates the lead tongs when drill pipe and drill collars are being handled.

Lead tongs the pipe tongs suspended in the derrick or mast and operated by a chain or a wire rope connected to the makeup cathead or the breakout cathead. Personnel call the makeup tongs the lead tongs if pipe is going into the hole; similarly, they call the breakout tongs the lead tongs if pipe is coming out of the hole.

Lens 1. a porous, permeable, irregularly shaped sedimentary deposit surrounded by impervious rock. 2. a lenticular sedimentary bed that pinches out, or comes to an end, in all directions.

Lens-type trap a hydrocarbon reservoir consisting of a porous, permeable, irregularly shaped sedimentary deposit surrounded by impervious rock. See lens.

Lifting nipple also called hoisting plug or lifting sub. See lifting sub.

Lifting sub a short piece of pipe with a pronounced upset, or shoulder, on the upper end, screwed into drill collars to provide a positive grip for the elevators. Also called a lifting nipple or a hoisting plug.

Liner a string of pipe used to case open hole below existing casing. A liner extends from the setting depth up into another string of casing, usually overlapping about 100 feet (30 metres) into the upper string.

Liner hanger a slip device that attaches the liner to the casing. See liner.

Liquid a state of matter in which the shape of the given mass depends on the containing vessel, but the volume of the mass is independent of the vessel. A liquid is a fluid that is almost incompressible.

Location the place where a well is drilled. Also called well site.

Log a systematic recording of data, such as a driller’s log; a mud log, an electrical well log, or a nuclear log. to record data.

Log a well to run any of the various logs used to ascertain downhole information about a well.

Logging devices any of several electrical, acoustical, mechanical, or nuclear devices that are use to measure and record certain characteristics or events that occur in a well that has been or is being drilled.

Logging while drilling (LWD) logging measurement obtained by measurement-while-drilling techniques as the well is being drilled.

Lost time accident an incident in the workplace that results in an injury serious enough that causes the person injured to be unable to work for a day or more.


Major a large oil company, such as ExxonMobil or Chevron, that not only produces oil, but also transports, refines, and markets it and its products.

Make a connection to attach a joint of drill pipe onto the drill stem suspended in the wellbore to permit deepening the wellbore by the length of the joint (usually about 30 feet, or 9 metres).

Make a trip to hoist the drill stem out of the wellbore to perform one of a number of operations, such as changing bits or taking a core, and then to return the drill stem to the wellbore.

Make hole to deepen the hole made by the bit, i.e., to drill ahead.

Make up 1. to assemble and join parts to form a complete unit (e.g., to make up a string of casing). 2. to screw together two threaded pieces. 3. to mix or prepare (e.g., to make up a tank of mud).

Makeup added to a system (e.g., makeup into another length of pipe).

Make up a joint to screw a length of pipe into another length of pipe.

Makeup cathead a device that is attached to the shaft of the drawworks and used as a power source for screwing together joints of pipe. It is usually located on the driller’s side of the drawworks. Also called spinning cathead. See cathead. Compare breakout cathead.

Makeup tongs tongs used for screwing one length of pipe into another for making up a joint. See lead tongs, tongs.

Male connection a pipe, a coupling, or a tool that has threads on the outside so that it can be joined to a female connection. Compare female connection.

Manifold an accessory system of piping to a main piping system (or another conductor) that serves to divide a flow into several parts, to combine several flows into one, or the reroute a flow to any one of several possible destinations.

Marine riser connector a fitting on top of the subsea blowout preventers to which the riser pipe is connected.

Marine riser pipe see riser pipe.

Marine riser system see riser pipe.

Mast a portable derrick that is capable of being raised as a unit. Compare derrick.

Master bushing a device that fits into the rotary table to accommodate the slips and drive the kelly bushing so that the rotating motion of the rotary table can be transmitted to the kelly. Also called rotary bushing.

Measurement while drilling (MWD) 1. directional and other surveying during routine drilling operations to determine the angle and direction by which the wellbore deviates from the vertical. 2. any system of measuring downhole conditions during routine drilling operations.

Mechanical-drive rig see mechanical rig.

Mechanical rig a drilling in which the source of power is one or more internal-combustion engines and in which the power is distributed to rig components through mechanical devices (such as chains, sprockets, clutches, and shafts). Also called a power rig. Compare electric rig.

Megajoule (MJ) the SI unit of service given by a drilling line when it moves 1,000 newtons of load over a distance of 1,000 metres.

Metre (M) the fundamental unit of length in the international system of measurement (SI). It is equal to about 3.28 fee, 39.97 inches, or 100 centimetres.

Metric system a decimal system of weights and measures based on the metre as the unit of length, the gram as the unit of weight, the cubic metre as the unit of volume, the litre as the unit of capacity, and the square metre as the unit of area. Then international system of measurement (SI) is based on the metric system.

Metric ton a measurement equal to 1,000 kilograms or 2,204.6 avoirdupois. In some oil-producing countries, production is reported in metric tons. Once metric ton is equivalent to about 7.4 barrels (42 U.S. gallons= 1 barrel) of crude oil. In the SI system it is called a tonne.

Mill a downhole tool with rough, sharp, extremely hard cutting surfaces for removing metal by grinding or cutting. They also called junk mills, reaming mills, and so forth, depending on their use. to use a mill to cut or grind metal objects that must be removed from a well.

Mineral rights the rights of ownership, conveyed by deed, of gas, oil, and other minerals beneath the surface of the earth. In the United States, mineral rights are the property of the surface owner unless disposed of separately.

Mix mud to prepare drilling fluids from a mixture of water or other liquids and any other or more of the various dry mud-making materials (such as clay, weighting materials, and chemicals).

MJ megajoule

Mobile offshore drilling unit (MODU) a drilling rig that is used to drill offshore exploration and development wells. It floats on the surface of the water when being moved from one drill site to another, but it may or may not float once drilling begins.

MODU mobile offshore drilling unit.

Monkeyboard the derrickhand’s working platform. As pipe is run into or out of the hole, the derrickhand must handle the top end of the pipe, which may be 90 feet (27 metres) or higher in the derrick or mast. The monkeyboard provides a small platform to raise the derrickhand to the proper elevation for handling the top of the pipe.

Morning tour on rigs in which crews work three 8-hour tours, the tour that typically starts around midnight and last until 700 or 800 A.M.

Motorhand the crew member on a rotary drilling rig, usually the most experienced rotary helper, who is responsible for the care and operation of drilling engines.

Motormand see motorhand.

Mousehole on opening through the rig floor, usually lined with pipe, into which a length of a drill pipe is placed temporarily for later connection to the drill string.

Mousehole connection the procedure of adding a length of drill pipe to the active string. The length to be added is placed in the mousehole, made up to the kelly, then pulled out of the mousehole and subsequently made up into the string. Compare rathole connection.

Mud the liquid circulated through the wellbore during rotary drilling operations. In addition to its function of bringing cuttings to the surface, drilling mud cools and lubricates the bit and the drill stem, protects against blowouts by holding back subsurface pressures, and deposits a mud cake on the wall of the borehole to prevent loss of fluids to the formation. See drilling fluid.

Mud centrifuge a device that used centrifugal force to separate small solid components form liquid drilling fluid.

Mud cleaner a cone-shaped device, a hydrocyclone, designed to remove very fine solid particles from the drilling mud.

Mud engineer an employee of a drilling fluid supply company whose duty it is to test and maintain the drilling mud properties that are specified by the operator.

Mud-gas separator a device that removes gas from the mud coming out of a well when a kick is being circulated out.

Mud hopper see hopper.

Mud hose also called kelly hose or rotary hose. See rotary hose.

Mud line 1. in offshore operations, the seafloor. 2. a mud return line.

Mud logger an employee of a mud logging company who performs mud logging.

Mud logging the recording of information derived from examination and analysis of formation cuttings made by the bit and of mud circulated out of the hole.

Mud pit originally, an open pit dug in the ground to hold drilling fluid or waste materials discarded after the treatment of drilling mud. For some drilling operations, mud pits are used for suction to the mud pumps, settling of mud sediments, and storage of reserve mud. Steel tanks are much more commonly used for these purposes now, but they are still referred to as pits, except offshore, where “mud tanks” is preferred.

Mud pump a large, high-pressure reciprocating pump used to circulate the mud on a drilling rig. Also called a slush pump.

Mud return line a trough or pipe that is placed between the surface connections at the wellbore and the shale shaker and through which drilling mud flows o it return to the surface from the hole. Also called flow line.

Mud tank one of a series of open tanks, usually made of steel plate, through which the drilling mud is cycled to remove sand and fine sediments. Also called mud pits.

Mud weight a measure of the density of a drilling fluid expressed as pounds per gallon, pounds per cubic foot, or kilograms per cubic metre. Mud weight is directly related to the amount of pressure the column of drilling mud exerts at the bottom of the hole.


Natural gas a highly compressible, highly expandable mixture of hydrocarbons with low specific gravity and occurring naturally in gaseous form. Besides hydrocarbon gases, natural gas may contain appreciable quantities of nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor.

Newton (N) an SI unit that expresses force. One Newton equals 1 metre-kilogram per second per second (m●kg/s 2), which is the force required to move 1 kilogram a distance of 1 metre at a velocity of 1 second squared.

Night toolpusher an assistant toolpusher whose duty hours are typically during nighttime hours on a mobile offshore drilling unit.

Nipple up to assemble the blowout preventer stack on the wellhead at the surface.

Nonporous containing no interstices; having no pores.

Normal circulation the smooth, uninterrupted circulation of drilling fluid down the drill stem, out the bi, up the annular space between the pipe and the hole, and back to the surface. Compare reverse circulation.

Nozzle a passageway through jet bits that causes the drilling fluid to be ejected from the bit at high velocity. The jets of mud clear the bottom of the hole.


Offset well a well drilled in the vicinity of other wells to assess the extent and characteristics of the reservoir and, in some cases, to drain hydrocarbons from an adjoining lease or tract.

Offshore that geographic area that lies seaward of the coastline. In general, the term “coastline” means the line of ordinary low water along that portion of the coast that is in direct contact with the open sea or the line marking the seaward limit of inland waters.

Offshore drilling drilling for oil or gas in an ocean, gulf, or sea, usually on the Outer Continental Shelf. A drilling unit for offshore operations may be a mobile floating vessel with a ship or barge hull, a semisubmersible or submersible bas, a self-propelled or towed structure with jacking legs (jackup drilling rig), or a permanent structure used as a productions platform when drilling is completed.

Offshore installation manager (OIM) a qualified and certified person with marine ad drilling knowledge who is in charge of all operations on a MODU.

Offshore production platform an immobile offshore structure from which wells are produced.

Offshore rig any of various types of drilling structures designed for use in drilling wells in oceans, seas, bays, gulfs, and so forth. Offshore rigs include platforms, jackup drilling rigs, semisubmersible drilling rigs, and drill ships. Compare land rig.

Oil a simple o complex liquid mixture of hydrocarbons that can be refined to yield gasoline, kerosene, diesel fuel, and various other products.

Oil-base mud a drilling fluid in which oil is the continuous phase and which contains from less than 2 percent and up to 5 percent water.

Oilfield the surface area overlying an oil reservoir or reservoirs. The term usually includes not only the surface area, but also the reservoir, the wells, and the production equipment.

Oil mud a drilling mud, e.g., oil-base mud and invertemulsion mud, in which oil is the continuous phase.

Oil patch the oilfield.

Oil sand 1. a sandstone that yields oil. 2. (by extension) any reservoir that yields oil, whether or not it is sandstone.

Oil seep a surface location where oil appears, the oil having permeated its subsurface boundaries and accumulated in small pools or rivulets. Also called oil spring.

Oilwell a well from which oil is obtained.

Oilwell cement cement or a mixture of cement and other materials for use in oil, gas, or water wells.

Oil zone a formation or horizon of a well from which oil may be produced. The oil zone is usually immediately under the gas zone and on top of the water zone if all three fluids are present and segregated.

Open 1. of a wellbore, having no casing. 2. of a hole, having no drill pipe or tubing suspended in it.

Open hole 1. any wellbore in which casing has not been set. 2. open or cased hole in which no drill pipe or tubing is suspended. 2. the portion of the wellbore hat has no casing.

Open-hole fishing the procedure of recovering lost or stuck equipment in an uncased wellbore.

Operating company see operator.

Operator the person or company actually operating on oilwell, generally the oil company that hires a drilling contractor.

Organic theory an explanation of the origin of petroleum that holds that they hydrogen and the carbon and animals. The theory further holds that more of this organic material comes from very tiny swamp and sea creatures than comes from larger land creatures.

Organization of Petroleum Exporting Countries (OPEC) an organization of the countries of the Middle East, Southeast Asia, Africa, and South America that produce oil and export it. Members as of 1997 are Algeria, Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, he United Arab Emirates, and Venezuela. The organization’s purpose is to negotiate and regulate oil prices.

Orientation the process of positioning a deflection tool so that it faces in the direction necessary to achieve the desired direction and drift angle for a directional hole.

Outer Continental Shelf (OCS) the land seaward from areas subject to state mineral ownership to a depth of roughly 8,000 feet (2,500 metres), beyond which mineral exploration and development are not, at prescent, feasible. Boundaries of the OCS are set by law. In general, the term is used to describe federally controlled areas.

Out-of-gauge bit a bit that is no longer of the proper diameter.

Out-of-gauge hole a hole that is not in gauge; that is, it is smaller or larger than the diameter of the bit used to drill it.

Outpost well a well located outside the established limits of a reservoir, i.e., a step-out well.

Overshot a fishing tool that is attached to tubing or drill pipe and lowered over the outside wall of pipe lost or stuck in the wellbore. A friction device in the overshot, usually either a basket or a spiral grapple, firmly grips the pipe, allowing the fish to be pulled from the hole.


P&A plug and abandon.

Packer a piece of downhole equipment that consists of a sealing device, a holding or setting device, and an inside passage for fluids. It is used to block the flow of fluids through the annular space between pipe and the wall. A packing element expands to prevent fluid flow except through the packer and tubing.

Pay see pay sand.

Pay formation see pay sand.

Pay sand the producing formation, often one that is not sandstone. Also called pay, pay zone, and producing zone.

Pay zone see pay sand.

PDC polycrystalline diamond compact.

PDC bit a special type of diamond drilling bit that does not use roller cones. Instead, polycrystalline diamond inserts, or compacts, are embedded into a matrix on the bit.

Penetration rate see rate of penetration.

Perforate to pierce the casing wall and cement of a wellbore to provide holes through which formation fluids may enter or to provide holes in the casing so that materials may be introduced into the annulus between the casing and the wall of the borehole.

Perforated completion 1. a well completion method in which the producing zone or zones are casing through, cemented, and perforated to allow fluid flow into the wellbore. 2. a well completed by this method.

Perforated liner a liner that has had holes shot in it by a perforating gun. See liner.

Perforating gun a device fitted with shaped charges or bullets that is lowered to the desired depth in a well and fired to create penetrating holes in casing, cement, and formation.

Perforating truck a special vehicle designed to allow control of a perforating operation within it.

Perforation a hole made in the casing, cement, and formation through which formation fluids enter a wellbore. Usually several perforations are made at at a time.

Permeability 1. a measure of the ease with which a fluid flows through the connecting pore spaces of a rock. The unit of measurement is the millidarcy. 2. fluid conductivity of a porous medium. 3. ability of fluid to flow within the interconnected pore network of a porous medium.

Permeable allowing the passage of fluid. See permeability.

Petroleum a substance occurring naturally in the earth in solid, liquid, or gaseous state and composed mainly of mixtures of chemical compounds of carbon and hydrogen, with or without other nonmetallic elements such as sulfur, or oxygen, and nitrogen. In some cases, especially in the measurement of oil and gas, petroleum refers only to oil-a liquid hydrocarbon-and does not include natural gas or gas liquids such as propane and butane. The API refers that petroleum mean crude oil and not natural gas or gas liquids.

Petroleum geology a study of oil-and gas-bearing rock formations. It deals with the origin, the occurrence, the movement, and the accumulation of hydrocarbon fuels.

Pick up 1. to use the drawworks to lift the bit (or other tool) off bottom by raising the drill stem. 2. to use an air hoist to lift a tool, a joint of drill pipe, or other piece of equipment.

Piercement dome see diapir.

Pin 1. the male section of a tool joint. 2. on a bit, the bit shank, which screws into a bit stub or drill collar.

Pinch-out to end or terminate by a narrowing and tapering off. When a formation pinches out, it narrows and tapers off.

Pipe a long, hollow cylinder, usually steel, through which fluids are conducted.

Pipe rack a horizontal support for tubular goods.

Pipe racker a pneumatic or hydraulic device that, on command from an operator, either picks up pipe from a rack or from the side of the derrick and lifts it into the derrick or takes pipe from out of the derrick and places it on the rack or places it to the side of the derrick.

Pipe ram a sealing component for a blowout preventer that closes the annular space between the pipe and the blowout preventer or wellhead.

Pipe ram preventer a blowout preventer that uses pipe rams as the closing elements. See pipe ram.

Pipe tongs see tongs.

Pipe upset that part of the pipe that has an abrupt increase of dimension.

Pit level height of drilling mud in the mud tanks, or pits.

Platform see platform rig.

Platform jacket a support that is firmly secured to the ocean floor and to which the legs of a platform are anchored.

Platform rig an immobile offshore structure from which development wells are drilled and produced. Platform rigs may be built of steel or concrete and may be rigid or compliant. Rigid platform rigs, which rest on the seafloor, are the concrete gravity platform and the steel-jacket platform. Compliant platform rigs, which are used in deeper waters and yield to water and wind movements, are the guyed-tower platform and the tension-leg platform.

Play 1. the extent of a petroleum-bearing formation. 2. the activities associated with petroleum development in an area.

Plug and abandon (P&A) to place cement plugs into a dry hole and abandon it.

Plug container see cementing head.

Pheumatic operated by air pressure.

Polycrystalline diamond compact (PDC) a dish (a compact) of very small synthetic diamonds, metal powder, and tungsten carbide powder that are used as cutter on PDC bits. Compare thermally stable polycrystalline diamond bits.

Pontoon an attachment, added to a stinger, that is flooded to lower pipeline toward the seafloor at an angle that will not overstress it.

Pore an opening or space within a rock or mass of rocks, usually small and often filled with some fluid (water, oil, gas, or all three). Compare vug.

Porosity 1. the condition of being porous (such as a rock formation). 2. the ratio of the volume of empty space to the volume of solid rock in a formation, indicating how much fluid a rock can hold.

Porous having pores, or tiny openings, as in rock.

Possum belly 1. a receiving tank situated at the end of the mud line. The flow of mud comes into the bottom to the device and travels over baffles to control mud flow over the shale shaker. 2. a metal box under a truck bed that hold repair tool.

Power rig see mechanical rig.

Power swivel a top drive. See top drive.

Pressure the force that a fluid (liquid or gas) exerts uniformly in all directions within a vessel, a pipe, a hole in the ground, and so forth, such as that exerted against the inner wall of a tank or that exerted on the bottom of the wellbore by a fluid. Pressure is expressed in terms of force exerted per unit of area, as pounds per square inch, or in kilopascals.

Preventer shortened form of blowout preventer. See blowout preventer.

Prime mover an internal-combustion engine or a turbine that is the source of power for driving a machine or machines.

Producer 1. a well that produces oil or gas in commercial quantities. 2. an operating company or individual in the business of producing oil; commonly called the operator.

Producing horizon see pay sand.

Producing interval see pay sand.

Producing platform an offshore structure accommodating a number of producing wells.

Producing zone the zone or formation from which oil or gas is produced. See pay sand.

Production 1. the phase of the petroleum industry that deals with bringing the well fluids to the surface and separating them and with storing, gauging, and otherwise preparing the product for the pipeline. 2. the amount of oil or gas produced in a given period.

Production casing the last string of casing set in a well, the inside of which is usually suspended a tubing string.

Production platform see platform rig.

Production well the well through which oil is produced in fields where improved recovery techniques are being applied.

Proppant see propping agent.

Propping agent a granular substance (sand grains, aluminum pellets, or other material) that is carried in suspension by the fracturing fluid and that serves to keep the cracks open when fracturing fluid is with drawn after a fracture treatment.

P-tank see bulk tank.

Pulley a wheel with a grooved rim, used for pulling or hoisting.

Pull out see come out of the hole.

Pull singles to remove the drill stem from the hole by disconnecting each individual joint.

Pump a device that increases the pressure on a fluid or raises it to a higher level.

Pup joint a length of drill or line pipe, tubing, or casing shorter than range 1 (18 feet or 6.26 metres for drill pipe) in length.

Pusher shortened form of toolpusher.


Q is N/A.


Rack framework for supporting or containing a number of loose objects, such as a pipe. 1. to place on a rack. 2. to use on a rack.

Ram the closing and sealing component on a blowout preventer. One of three types-blind, pipe, or shear- may be installed in several preventers mounted in a stack on the top of the wellbore.

Ram blowout preventer a blowout preventer that uses rams to seal off pressure on a hole that is with or without pipe. Also called ram perventer. Compare annular blowout preventer.

Ram preventer see ram blowout preventer.

Range length a grouping of pipe lengths. API designation of range lengths is as follows.

Range 1 Range 2 Range 3

(feet) (mertres) (feet) (metres) (feet) (metres)


16-25 4.88-7.62 25-34 7.62-10.36 34-48 10.36-14.63


18-22 5.49-6.71 27-30 8.23-9.14 38-45 11.58-13.72


20-24 6.10-7.32 28-32 8.53-9.75

Rate of penetration (ROP) a measure of the speed at which the bit drills into formations, usually expressed in feel (metres) per hour or minutes per foot (metre).

Rathole a hole in the rig floor, which is lined with casing that projects about the floor and into which the kelly and swivel are placed when hoisting operations are in progress.

Rathole connection the addition of a length of drill pipe to the active string using the rathole instead of the mousehold, which is the more common connection. Compare mousehole connection.

Rathole rig a small, usually truck-mounted rig, the purpose of which is to drill ratholes for regular drilling rigs that will be moved in later. A rathole rig may also drill the top part of the hole, the conductor hole, before the main rig arrives on location.

Reamer a tool used in drilling to smooth the wall of a well, enlarge the hole to the specified size, help stabilize the bit, straighten the wellbore if kinks or doglegs are encountered, and drill directionally.

Reciprocation a back-and-forth or up-and-down movement (as the movement of a piston in an engine or pump).

Reel a revolving device (such as a flanged cylinder) for winding or unwinding something flexible (such as rope or wire).

Reeve to pass (as a rope) through a hole or opening in a block or similar device.

Reeve the line to string a wire rope drilling line through the sheaves of the traveling and the crown blocks to the hoisting drum.

Remote BOP control panel a device placed on the rig floor that can be operated by the driller to direct air pressure to actuating cylinders that turn the control valves on the main BOP control unit, located a safe distance from the rig.

Remote choke panel a set of controls, usually placed on the rig floor, that is manipulated to control the amount of drilling fluid being circulated through the choke manifold. See chock manifold.

Reserve pit a waster pit, usually an excavated earthen walled pit. It may be lined with plastic or other material to prevent soil contamination.

Reservoir subsurface, porous, permeable rock body in which oil or gas has accumulated.

Reservoir pressure the average pressure within the reservoir at any given time.

Reservoir rock a permeable rock that may contain oil or gas in appreciable quantity and through which petroleum may migrate.

Retainer head see cementing head.

Reverse circulation the course of drilling fluid downward through the annulus and upward through the drill stem. Also referred to as “circulating the short way,” since returns from bottom can be obtained more quickly than in normal circulation. Compare normal circulation.

Rig the derrick or mast, drawworks, and attendant surface equipment of a drilling unit.

Rig crew member see rotary helper.

Rig down to dismantle a drilling rig and auxiliary equipment following the completion of drilling operations. Also called tear down.

Rig floor the area immediately around the rotary table and extending to each corner of the derrick or mast-that is, the area immediately about the substructure on which the drawworks, the rotary table, and so forth rest. Also called derrick floor, drill floor.

Rig manager an employee of a drilling contractor who is in charge of the entire drilling crew and the drilling rig, providing logistics support to the rig crew and liaison with the operation company.

Rig superintendent see toolpusher.

Rig supervisor see toolpusher.

Rig up to prepare the drilling rig for making hole, i.e., to install tools and machinery before drilling is started.

Riser pipe the pipe and special fittings used on floating offshore drilling rigs to establish a seal between the top of the wellbore, which is on the ocean floor, and the drilling equipment, located above the surface of the water. A riser pipe serves as a guide for the drill stem from the drilling vessel to the wellhead and as a conductor of drilling fluid form the well to the vessel. Also called marine riser.

Riser tensioner line a cable that supports the marine riser while compensating for vessel movement.

Rock a hardened aggregate of different minerals. Rocks are divided into three groups on the basis of their mode of origin igneous, metamorphic, and sedimentary.

Rock bit name for the first roller cone bits; now almost obsolete. See roller cone bit.

Rock oil see petroleum.

Roller bit see roller cone bit.

Roller chain a type of chain that is used to transmit power by fitting over sprockets attached to shafts, causing rotation of one shaft by the rotation of another.

Roller cone bit a drilling bit made of two, three, or four cones that are mounted on extremely rugged bearings. The surface of each cone has rows of steel teeth or rows of tungsten carbide inserts. Also called rock bits.

Rotary the machine used to impart rotational power to the drill steam while permitting vertical movement of the pipe for rotary drilling.

Rotary bushing see master bushing.

Rotary drilling a drilling rig that features a system that rotates a bit and, at the same time, has a system that continuously circulates drilling fluid while drilling is going on.

Rotary helper a worker on a drilling or workover rig, subordinate to the driller, whose primary work station is on the rig floor. Sometimes called floorhand, floorman, rig crewman, or roughneck.

Rotary hose a reinforced flexible tube on a rotary drilling rig that conducts the drilling fluid form the standpipe to the swivel and kelly. Also called the mud hose or the kelly hose.

Rotary speed the speed, measured in revolutions per minute, at which the rotary table is operated.

Rotary support table a strong but relatively lightweight device used on some rigs that employ a top drive to rotate the bit. Although a conventional rotary table is not required to rotate the bit on such rigs, crew members mush still have a place to set the slips to suspend the drill string in the hole when tripping or making a connection. A rotary support table provides such a place but does not include all the rotary machinery required in a regular rotary table.

Rotary table the principal component of a rotary, or rotary machine, used to turn the drill stem and support the drilling assembly.

Rotary-table system a series of devices that provide a way to rotate the drill stem and bit. Basic components consist of a turntable, master bushing, kelly drive bushing, kelly and a swivel.

Rotary torque the rotational force applied to turn the drill stem.

Rotate on bottom see rotary helper.

Rotating components those parts of the drilling or workover rig that designed to turn or rotate the drill stem and bit-swivel, kelly, kelly bushing, master bushing, and rotary table.

Roughneck see rotary helper.

Round trip the action of pulling out and subsequently running back into the hole a string of drill pipe or tubing. Making a round trip is also called tripping.

Roustabout a worker on an offshore rig who handles the equipment and supplies that are sent to the rig from the shore base. The head roustabout is very often the crane operator.

Run casing to lower a string of casing into the hole. Also called to run pipe.

Run in to go into the hole with tubing, drill pipe, and so forth.

Run pipe to lower a string of casing into the hole. Also called to run casing.


Safety clamp a clamp placed very tightly around a drill collar that is suspended in the rotary table by drill collar slips. Should the slips fail, the clamp is too large to go through the opening in the rotary table and therefore prevents the drill collar string from falling into the hole.

Safety slide a wireline device normally mounted near the monkeyboard to afford the derrickhand a means of quick exit to the surface in case of emergency. It is usually affixed to a wireline, one end of which is attached to the derrick or mast and the other end to the surface. To exit by the safety slide, the derrickhand grasps a handle on it and rides it down to the ground. Also called a geronimo.

Salt dome a dome that is caused by an intrusion of rock salt into overlying sediments. A piercement salt dome is one that has pushed up so that is penetrates the overlying sediments, leaving them truncated.

Samples 1. the well cutting obtained at designated footage intervals during drilling. From an examination of these cuttings, the geologist determines the type of rock and formations being drilled and estimates oil and gas content. 2. small quantities of well fluids obtained for analysis.

Sand 1. an abrasive material composed of small quartz grains formed from the disintegration of preexisting rocks. Sand consists of particles less than 0.078 inch (2 millimetres) and greater than 0.062 inch 91/16 millimetre) in diameter. 2. sandstone.

Sandstone a sedimentary rock composed of individual mineral grains of rock fragments between 0.002 and 0.079 inches (0.06 and 2 millimetres) in diameter and cemented together by silica, calcite, iron oxide, and so forth. Sandstone is commonly porous and permeable and therefore a likely type of rock in which to find a petroleum reservoir.

Saver sub a device made up in the drill steam to absorb much of the wear between frequently broke joints (such as between the kelly and the drill pipe). See kelly saver sub.

Scratcher a device that is fastened to the outside of casing to remove mud cake from the wall of a hole to condition the hole for cementing. By rotating or moving the casing string up and down as it is being run into the hole, the scratcher, formed of stiff wire, removes the cake so that the cement can bond solidly to the formation.

Seafloor the bottom of the ocean; the seabed.

Seat the point in the wellbore at which the bottom of the casing is set.

Sediment in geology, buried layers of sedimentary rocks.

Sedimentary rock a rock composed of materials that were transported to their present position by wind or water. Sandstone, shale, and limestone are sedimentary rocks.

Seep the surface appearance of oil or gas that results naturally when a reservoir rock becomes exposed to the surface, thus allowing oil or gas to flow out of fissures in the rock.

Seismic of or relating to an earthquake or earth vibration, including those artificially induced.

Seismic data detailed information obtained from earth vibration produced naturally or artificially (as in geophysical prospecting).

Seismic method a method of geophysical prospecting using the generation, reflection, refraction detection, and analysis of sound waves in the earth.

Seismic survey an exploration method in which strong low-frequency sound waves are generated on the surface or in the water to find subsurface rock structures that may contain hydrocarbons. Interpretation of the record can reveal possible hydrocarbon-bearing formations.

Self-elevating substructure a base in which the floor and mast of a drilling rig rests and which, after it is placed in the desired location, is raised into position as a single unit.

Self-propelled unit see carrier rig.

Semisubmerged a state in which a specially designed floating drilling rig (a semisubmersible) floats just below the water’s surface.

Semisubmersible see semisubmersible drilling rig.

Semisubmersible drilling rig a floating offshore drilling unit that has pontoons and columns that, when flooded, cause the unit to submerge to a predetermined depth. Semisubmersibles are more stable than drill ships and are used extensively to drill wildcat wells in rough waters such as the North Sea. See floating offshore drilling rig.

Set back to place stands of drill pipe and drill collars in a vertical position to one side of the rotary table in the derrick or mast of a drilling or workover rig.

Set casing to run and cement casing at a certain depth in the wellbore. Sometimes called set pipe.

Set pipe see set casing.

Shaker shortened form of shale shaker. See shale shaker.

Shale a fine-grained sedimentary rock composed mostly of consolidated clay or mud. Shale is the most frequently occurring sedimentary rock.

Shale shaker a vibrating screen used to remove cuttings from the circulating fluid in rotary drilling operations. The size of the openings in the screen should be carefully selected to the smallest size possible to allow 100 percent flow of the fluid. Also called a shaker.

Shaped charge a relatively small container of high explosive that is loaded into a perforating gun. On detonation, the charge releases a small, high-velocity stream of particles (a jet) that penetrates the casing, cement, and formation. See perforating gun.

Shear ram the component in a blowout preventer that cuts, or shears, through drill pipe and forms a seal against well pressure.

Shear ram preventer a blowout preventer that uses shear rams as closing elements.

Sheave a grooved pulley.

Shoulder the flat portion of a tool joint.

Shut in 1. to close the valves on a well so that is stops producing. 2. to close in a well in which a kick has occurred.

Single a joint of drill pipe. Compare double, fourble, and thribble.

Sinker bar a heavy weight or bar placed on a near a lightweight wireline tool. The bar provides weight so that the tool will lower properly in the well.

Slack off to lower a load or ease up on a line. A driller will slack off on the brake to put additional weight on the bit.

Slingshot substructure see self-elevation substructure.

Slip and cutoff program a procedure to ensure that the drilling line wears evenly throughout its life. After a specified number of ton-miles (megajoules) of use, the line is slipped-i.e., the traveling block is suspended in the derrick or proper on the rig floor so that it cannot move, the deadline anchor bolts are loosened, and the drilling line is spooled onto the drawworks drum. Enough line is slipped to change the major points of war on the line, such as where it passes through the sheaves. To prevent excess line from accumulating on the drawworks drum, the worn line is cut off and discarded.

Slips wedge-shaped pieces of metal with teeth or other gripping elements that are used to prevent pipe from slipping down into the hole or to hold pipe in place.

Sloughing see caving.

Sloughing hole a condition wherein shale that has absorbed water from the drilling fluid expands, sloughs off, and falls downhole. A sloughing hole can jam the drill string and block circulation.

Slurry in drilling, a plastic mixture of cement and water that is pumped into a well harden. There it supports the casing and provides a seal in the wellbore to prevent migration of underground fluids.

Sour crude see sour crude oil.

Sour crude oil oil containing hydrogen sulfide or another acid gas.

Spark ignition (SI) ignition of a fuel-air mixture by means of a spark discharged by a spark plug.

Spark-ignition engine an internal combustion engine that uses electrical spark to ignite the fuel-air mixture inside its cylinders. Usually, the engine employs spark plugs to provide the electrical spark.

Spear a fishing tool used to retrieve pipe lost in a well. The spear is lowered down the hole and into he lost pipe. When weight, torque, or both are applied to the string to which the spear is attached, the slips in the spear expand and tightly grip the inside of the wall of the lost pipe.

Spinning cathead see makeup cathead, spinning chain.

Spinning chain a Y-shaped chain used to spin up (tighten) one join of drill pipe into another.

Spinning wrench air-powered or hydraulically powered wrench used to spin drill pipe when making up or breaking out connections.

Spool the drawworks drum. Also a casinghead or drilling spool. to wind around a drum.

Spud to being drilling a well-i.e., to spud in.

Spud in to begin drilling; to start the hole.

Stab to guide the end of a pipe into a coupling or tool join when making up a connection.

Stabilizer a tool placed on a drill collar near the bit that is used, depending on where it is placed, either to maintain a particular hole angle or to change the angle by controlling the location of the contact point between the hole and the collars.

Stack a rig to store a drilling rig on completion of a job when the rig is to be withdrawn from operation for a time.

Stand the connected joints of pipe racked in the derrick or mast when making a trip. On a rig, the usual stand is about 90 feet (about 2 metres) long (three lengths of drill pipe screwed together), or a thribble.

Standard derrick a derrick that is built piece by piece at the drilling location. Compare mast.

Standpipe a vertical pipe rising along the side of the derrick or mast, which joins the discharge line leading from the mud pump to the rotary hose and through which mud is pumped into the hole.

Steel cone see roller cone bit.

Steel-jacket platform rig a rigid offshore drilling platform used to drill development wells. The foundation of the platform is the jacket, a tall vertical section made of tubular steel members. The jacket, which is usually supported by piles driven ton the seabed, extends upward so that the top rises about the waterline. Additional sections that provide space for crew quarters, the drilling rig, and all equipment needed to drill are placed on top of the jackets. See platform rig.

Steel-tooth bit a roller cone bit in which the surface of each cone is made up of rows of steel teeth. Also called a milled-tooth bit or milled bit.

Stem see sinker bar, swivel stem.

Step-out well a well drilled adjacent to or near a proven well to ascertain the limits of the reservoir; an outpost well.

Stimulation the action of attempting to improve and enhance a well’s performance by the application of horsepower using pumping equipment, placing sad in artificially created fractures in rock, or using chemicals such as acid to dissolve the soluble portion of the rock.

Straight hole a hole that is drilled vertically. The total hole angle is restricted, and the hole does not change direction rapidly-no more than 3° per 100 feet (30.48 metres) of hole.

Stratigraphic trap a petroleum trap that occurs when the top of the reservoir bed is terminated by other beds or by a change of porosity or permeability within the reservoir itself. Compare structural trap.

Stratum singular of strata. A distinct, generally parallel bed of rock.

String up to thread the drilling line through the sheaves of the crown block and the traveling block. One end of the line is secured to the hoisting drum and the other to the derrick substructure.

Structural trap a petroleum trap that is formed because of deformation (such as folding or faulting) of the reservoir formation. Compare stratigraphic trap.

Structure a geological formation of interest to drillers.

Stuck pipe drill pipe, drill collars, casing or tubing that has inadvertently become immovable in the hole.

Sub a short, threaded piece of pipe used to adapt parts of the drilling string that cannot otherwise be screwed together because of difference in thread size or design.

Submerged a state in which a rig that floats on the surface while being moved is in contact with the seafloor when it is in the drilling mode.

Subsea blowout preventer a blowout preventer placed on the seafloor for use by a floating offshore drilling rig.

Subsea engineer see subsea equipment supervisor.

Subsea equipment supervisor an employee on a floating offshore drilling rig whose main responsibility is running, monitoring, and maintaining such subsea equipment as the blowout prevent stack, the marine riser system, and similar subsea equipment.

Subsea riser a vertical section of pipe that connects pipeline on the sea bottom to a production platform on the surface.

Substructure the foundation on which the derrick or mast and usually the drawworks sit.

Subsurface below the surface of the earth (e.g., subsurface rocks).

Subsurface safety valve see tubing safety valve.

Supply reel a spool that holds drilling lien.

Surface casing see surface pipe.

Surface hole that part of the wellbore that is drilled below the conductor hole but above the intermediate hole.

Surface pipe the first string of casing (after the conductor pipe) that is set in a well. It varies in length from a few hundred to several thousand feet (metres). Some states require a minimum length to protect freshwater sands. Compare conductor casing.

Surface safety valve a valve, mounted in the Christmas tree assembly, that stops the flow of fluids from the well if damage occurs to the assembly.

Surface stack a blowout preventer stack mounted on top of the casing string at or near the surface of the ground or the water.

Swamp barge see inland barge rig.

Swamper a helper on a truck, tractor, or other machine.

Sweet crude see sweet crude oil.

Sweet crude oil oil containing little or no sulfur, especially little or no hydrogen sulfide.

Swivel a rotary tool that is hung from the rotary hook and the traveling block to suspend the drill stem and to permit it to rotate freely. It also provides a connection for the rotary hose and a passageway for the flow of drilling fluid into the drill stem.

Swivel stem a length of pipe inside the swivel that is installed to the swivel’s washpipe and to which the kelly (or a kelly accessory, such as the upper kelly cock) is attached. It conducts drilling mud from the washpipe and to the drill stem. See washpipe.


Tally to measure and record the total length of pipe, casing or tubing that is to be run in a well.

Tapered bowl a fitting, usually divided into two halves, that crew members place inside the master busing to hole the slips.

Tear down see rig down.

Telescoping joint a device used in the marine riser system of a mobile offshore drilling rig to compensate for the vertical motion of the rig caused b wind, waves, or weather.

Tensioner system a system of devices installed on a floating offshore drilling rig to maintain a constant tension on the riser pipe, despite any vertical motion made by the rig.

Tension-leg platform rig a compliant offshore drilling platform used to drill development wells. See platform rig.

Thermally stable polycrystalline diamond bit a special type of fired-head bit that has synthetic diamond cutters that do not disintegrate at high temperatures. Compare polycrystalline diamond compact.

Thribble a stand of pipe made up of three joints and handled as a unit. Compare single, double, fourble.

Thribble board the name used for the derrickhand’s working platform, the monkeyboard, when it is located at a height in the derrick equal to three lengths of pipe joined together. Compare double board, fourble board.

Throw the chain to flip the spinning chain up from a tool joint box o that the chain wraps around the tool joint pin after it is stabbed into the box. The stand or joint of drill pipe is turned or spun by a pull on the spinning chain from the cathead on the drawworks.

Thruster see dynamic positioning.

Tight formation a petroleum- or water-bearing formation of relatively low porosity and permeability.

Tight hole 1. a well about which information is restricted for security or competitive reasons. 2. a section of the hole that, for some reason, is undergauge. For example, a bit that is worn undergauge will drill a tight hole.

Tinkerbell line see geronimo.

Ton 1. (nautical) a volume measure equal to 100 square feel applied to mobile offshore drilling rigs. 2. a measure of weight equal to 2,000 pounds. 3. (metric) a measure of weight equal to 1,000 kilograms. Usually spelled “tonne.”

Tong dies very hard and brittle pieces of serrated steel that are installed in the tongs and that grip or bit into the tool joint of drill pipe when the tongs are latched onto the pipe.

Tong hand the member of the drilling crew who handles the tongs.

Tong pull line a length of wire rope one end of which is connected to the end of the tongs and the other end of which is connected to the automatic cathead on the drawworks. When the driller actuates the cathead, it takes in the tong line and exerts force on the tong to either make up or bread out drill pipe.

Tongs the large wrenches used to make up or break out drill pipe, casing, tubing, or other pipe; variously called casing tongs, pipe tongs, and so forth, according to the specific use.

Ton-mile the unit of service given by a hoisting line in moving 1 ton of load over a distance of 1 mile.

Tonne (t) a mass unit in the metric system equal to 1,000 kilograms.

Tool joint a heavy coupling element for drill pipe.

Toolpush Canadian term for toolpusher. See toolpusher.

Toolpusher an employee of a drilling contractor who is in charge of the entire drilling crew and the drilling rig. Also called a drilling forman, rig manager, rig superintendent, or rig supervisor.

Top drive a device similar to a power swivel that is used in place of the rotary table to turn the drill stem. Hung from the hook of the traveling block, a tip drive also suspends the drill stem in the hole and includes power tongs. Modern top drives coming elevators, tongs, swivel, and hook.

Top-drive system see top drive.

Top plug a cement wiper plug that follow cement slurry down the casing. It goes before the drilling fluid used to displace the cement from the casing and separates the fluid from the slurry. See cementing, wiper plug.

Torque the turning force that is applied to a shaft or other rotary mechanism to cause it to rotate or tend to do so. Torque is measured units of length and force (foot-pounds, newton-metres).

Total depth (TD) the maximum depth reached in a well.

Tour a working shift for drilling crew or other oilfield workers. On rigs where a tour is 8 hours, they are called daylight, afternoon (or evening), and morning. Sometimes 12-hour tours are used, especially on offshore rigs, where they are called simply day tour and night tour.

Tower 1. a vertical vessel such as an absorber, fractionator, or still. 2. a cooling tower.

Transmission the gear or chain arrangement by which power is transmitted from the prime mover to the drawworks, the mud pump, or the rotary table of a drilling rig.

Trap a body of permeable oil-bearing rock surrounded or overlain by an impermeable barrier that prevents oil from escaping. The types of traps are structural, stratigraphic, or a combination of these.

Traveling block an arrangement of pulleys, or sheaves, through which drilling line is reeved and which moves up and down in the derrick or mast. See block.

Trip the operation of hoisting the drill stem from and returning it to the wellbore. Shortened form of “make a trip.”

Trip in see go in the hole.

Triple see thribble.

Trip out see come out of the hole.

Tripping the operation of hoisting the drill stem out of and returning it to the wellbore. See make a trip.

Tubing relatively small-diameter pipe that is run into to a well to serve as a conduit for the passage of oil and gas to the surface.

Tubing safety valve a device installed in the tubing string of a producing well to shut in the flow of production if the flow exceeds a preset rate. Also called subsurface safety valve.

Tubular goods any kink of pipe. Oilfield tubular goods include tubing, casing, drill pipe, and line pipe. Also called tubulars.

Tungsten carbide a fine, very hard, gray crystalline powder, a compound of tungsten and carbon. This compound is bonded with cobalt or nickel in cemented carbide compositions and sued for cutting tools, abrasives, and dies.

Tungsten carbide bit a type of roller cone bit with inserts made of tungsten carbide. Also called tungsten carbide insert bit.

Tungsten carbide insert bit see tungsten carbide bit.

Turbodrill a downhole motor that rotates a bit by the action of the drilling mud on turbine blades built into the tool. Most often used in directional drilling.

Turnkey contract a drilling contract that calls for the payment of a stipulated amount to the drilling contractor on completion of the well. In a turnkey contract, the contractor furnishes all material and labor and controls the entire drilling operation, independent of operator supervision. A turnkey contract does not, as a rule, include the completion of a well as a producer.

Turntable see rotary table.

Turn to the right on a rotary rig, to rotate the drill stem clockwise. When drilling ahead, the expression “on bottom and turning to the right” indicated that drilling is proceeding normally.


Uncased hole see open hole.

Undergauge bit a bit whose outside diameter is worn to the point at which it is smaller than it was when new.

Undergauge hole that portion of a borehole drilled with an undergauge bit.

Upper kelly cock a valve installed above the kelly that can me manually closed to protect the rotary hose from high pressure that may exist in the drill stem.

Upset thickness forged to the end of a tubular (such as drill pipe) to give the end extra strength. To forge the ends of tubular products so that the pipe wall acquires extra thickness and strength near the end. Upsetting is usually performed to provide the thickness needed to form threads so that the tubular goods can be connected.


Vacuum degasser a device in which gas-cut mud is degassed by the action of a vacuum inside a tank.

V-belt a belt with a trapezoidal cross section, made to run in sheaves, or pulleys, with grooves of corresponding shape.

V-door an opening at floor level in a side of a derrick or a mast. The V-door is opposite the drawworks and is used as an entry to bring in drill pipe, casing, and other tools from the pipe rack.

Voids cavities in a rock that do not contain solid material but may contain fluids.

Vug 1. a cavity in a rock. 2. a small cavern, larger than a pore but too small to contain a person. Typically found in limestone subject to groundwater leaching.


Waiting on cement (WOC) pertaining to the time when drilling or completion operations are suspended so that the cement in a well can harden sufficiently.

Waterwell a well drilled to obtain a fresh water supply to support drilling.

Weight indicator an instrument near the driller’s position on a drilling rig that shows both the weight of the drill stem that is hanging from the hook (hook load) and the weight that is placed on the bit by the drill collars (weight on bit).

Weight on bit (WOB) the amount of downward force placed on the bit by the weight of the drill collars.

Well the hole made by the drilling bit, which can be open, cased, or both. Also called borehole, hole, or wellbore.

Wellbore a borehole; the hoe drilled by the bit. Also called a borehole or hole.

Well completion 1. the activates and methods of preparing a well for the production of oil and gas or for other purposes, such as injection; the method by which one or more flow paths for hydrocarbons are established between the reservoir and the surface. 2. the system of tubulars, packets, and other tools installed beneath the wellhead in the production casing- that is the tool assembly that provides the hydrocarbon flow path or paths.

Well control the methods used to control a kick and prevent a well from blowing out. Such techniques include, but are not limited to, keeping the borehole completely filled with drilling mud of the proper weight or density during all perations, exercising reasonable care when tripping pipe out of the hole to prevent swabbing, and keeping careful track of the amount of mud put into the hole to replace the volume of pipe removed from the hole during a trip.

Wellhead the equipment installed at the surface of the wellbore.

Well log see log.

Well logging the recording of information about subsurface geologic formations, including records kept by the driller and records of mud and cutting analyses, core analysis, drill stem tests, and electric, acoustic, and nuclear procedures.

Well site the place where a well is drilled.

Wildcat a well drilled in an area where no oil or gas production exists.

Wildcatter one who drills wildcat wells.

Wiper plug a rubber-bodied, plastic- or aluminum- cored device used to separate cement and drilling fluid as they are being pumped down the inside of the casing during cementing operations. A wiper plug also removes drilling mud that adheres to the inside of the casing.

Wireline a small-diameter metal line used in wireline operations. Also called slick line.

Wireline operations the lowering of mechanical tools, such as valves and fishing tools, into the well for various purposes. Electric wireline operations, such as electric well logging and perforating, involve the use of conductor line, which in the oil patch is commonly but erroneously called wireline.

Wire rope a cable composed of steel wires twisted around a central core of fiber or steel wire to create a rope of great strength and considerable flexibility. Often called cable or wireline; however, wireline is a single, slender metal rod, usually very flexible.

WOB weight on bit.

WOC waiting on cement; used in drilling reports.


XYZ is N/A.


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