- ABANDON: When production is stopped from a well that is depleted and no longer capable of producing profitably. A wildcat well may also be abandoned after it has been determined that it will not produce.
- ACIDIZING: Treatment of oil-bearing limestone or carbonate formations with a solution of hydrochloric acid and other chemicals to increase production. The acid is forced under pressure into the formation where it enlarges the flow channels by dissolving the limestone.
- AIR DRILLING: Drilling using air as the circulation medium (See DRILLING FLUIDS.)
- A-FRAME: "A"-shaped openwork structure which is the stationary and supporting component of the derrick of a jack-knife rig and to which the derrick is anchored when it is in an upright or drilling position.
- ANGLE OF DEFLECTION: The angle, in degrees, at which a well is deflected from the vertical by means of a whipstock or other deflecting tool.
- ANTICLINE: Arched stratified rock structure with layers dipping downward in opposite directions from the crest.
- BIT: The cutting or boring element used in drilling oil and gas wells.
- BLOWOUT: Uncontrolled flow of gas, oil, or other well fluids from a well during drilling due to formation pressure exceeding the pressure exerted by the column of drilling mud.
- BLOWOUT PREVENTER (BOP): Hydraulically or mechanically actuated high-pressure valve installed at the wellhead to control pressure within the well.
- BREAKOUT: Act of unscrewing one section of pipe from another section, particularly when drill pipe is being withdrawn from the wellbore.
- BREAK TOUR: When drilling crews start working eight-hour or twelve-hour shifts 24 hours a day. Prior to this time crews have been working only during daylight hours while rigging up.
- BRING IN A WELL: Act of completing and brining a well into production.
- BUDDY SYSTEM: Commonly used system among crew members to ensure that each man is accounted for, particularly when pulling a test where gas is encountered.
- CABLE TOOL: Percussion method of drilling whereby the repeated pounding of a heavy bit makes the hole. Largely replaced by the rotary rig.
- CAP ROCK: Impermeable rock overlying an oil or gas reservoir that tends to prevent migration of the reservoir fluids from the reservoir.
- CAPPED WELL: A well capable of production but lacking wellhead installations and a pipeline connection.
- CASING: Steel pipe threaded together and cemented into a well as drilling progresses to prevent the wall of the hole from caving in during drilling and to provide a means of extracting oil/gas if the well is productive.
- CASING HEAD: Heavy steel fitting that connects the first string of casing and provides a housing for the slips and packing assemblies by which subsequent strings of casing are suspended and the annulus sealed off.
- CASING HEAD GAS: Gas dissolved in crude oil which emerges at the casing head when pressure is lowered.
- CASING STRING: Total feet of casing run in a well.
- CATWALK: Steel platform immediately in front of the derrick substructure on which joints of drill pipe are stored prior to being lifted to the derrick floor by the catline.
- CENTRALIZERS: Spring steel guides attached to the casing which help keep it centered in the hole and thus provide for a uniform cement sheath around the casing pipe.
- CHRISTMAS TREE: Valves, pipes, and fittings assembled at the top of a completed well used to control the flow of oil and gas.
- CIRCULATE: Cycling of the drilling fluid through the drill string and wellbore while drilling is temporarily suspended. This is done to condition the drilling fluid and wellbore before drilling proceeds.
- CLOSE IN: To shut in (temporarily) a well that is capable of production.
- COMPLETE A WELL: Finish the work on a well and bring it to a productive state.
- CONDENSATE: Mixture of pentanes and heavier hydrocarbons that may be contaminated with sulfur compounds and is recovered or recoverable form an underground reservoir. It is gaseous in its virgin state but is liquid under the conditions at which its volume is measured.
- CONTRACT DEPTH: Depth that well must be drilled to fulfill the contract.
- CORE: Cylindrical sample taken from a formation for the purpose of examination or analysis.
- CRATERING OR SLOUGHING: When the walls of a hole cave in.
- CROOKED HOLE: Wellbore that has deviated from the vertical inadvertently.
- CUTTINGS: Fragments of rock dislodged by the bit and brought to the surface in the drilling mud.
- DERRICK: Load-bearing towerlike framework over an oil/gas well which holds the hoisting and lowering equipment.
- DERRICKHAND: Crew member whose work station is in the derrick while pipe is being hoisted or lowered into the hole. He is usually next in line of authority under the driller.
- DEVELOPMENT WELL: Well drilled for oil and gas within a proven field or area for the purpose of completing the desired pattern of production.
- DIRECTIONAL DRILLING: Controlled drilling at a specified angle from the vertical.
- DISCOVERY WELL: Exploratory well which discovers a new oil/gas field (see WILDCAT).
- DOGHOUSE: Small house located on the rig floor or nearby that is used as an office for the driller and as a storage place for small tools.
- DOG LEG: A sharp change of direction in the wellbore or an elbow caused by such a change in direction.
- DOWNTIME: When rig operations are temporarily suspended because of repairs or maintenance.
- DRAWWORKS: Hoisting mechanism on a drilling rig which spools off or takes in the drilling line and thus raises or lowers the drill string and bit.
- DRILLERS: Employee directly in charge of a particular crew as opposed to a toolpusher who is in charge of all the crews on a rig. Operation of drilling and hoisting equipment constitutes the driller's main duties.
- DRILLING FOREMAN: Usually the man in charge of a number of rigs; sometimes the operator's representative.
- DRILL PIPE: Steel pipe, in approximately 30-foot (9-meter) lengths, screwed together to form a continuous pipe extending from the drilling rig to the drilling bit at the bottom of the hole. Rotation of the drill pipe and bit causes the bit to bore through the rock.
- DRILL STEM TEST (DST): Conventional method of testing a formation to determine its potential productivity before installing production casing in a well. A testing tool is attached to the bottom of the drill pipe and placed opposite the formation to be tested which has been isolated by placing packers above and below the formation. Fluids in the formation are allowed to flow up through the drill pipe by establishing an open connection between the formation and the surface.
- DRILL STRING: String of individual joints of pipe that extends from the bit to the kelly and carries the mud down to, and rotates, the bit.
- DRILLING FLUIDS: While a mixture of clay and water is the most common drilling fluid, wells can also be drilled with air, natural gas, oil, or plain water as the drilling fluid.
- DRY HOLE: Generally refers to any well that does not produce oil or gas in commercial quantities.
- DUAL COMPLETION: Completion of a well in which two separate formations may be produced at the same time. Production from each zone is segregated by running two tubing strings with packers, or running one tubing string with a packer and producing the other zone through the annulus.
- ELEVATOR: Clamp which grips a stand or column of casing, tubing, drill pipe, or sucker rods so that it can be raised or lowered into the hole.
- EXPLORATION WELL: Well drilled in unproven territory (See WILDCAT).
- FAULT: Geological term denoting a break in the subsurface strata.
- FISH: Any undersirable object accidentally lost in the wellbore which must be removed before drilling can continue.
- FISHING: Encompasses both the special equipment and the special equipment and the special procedures required to remove undersirable objects from the wellbore.
- FLOORHAND: Crew member whose work station is primarily about the rig floor. There are normally tow floorhands on each drilling crews.
- FLOWING PRESSURE: Pressure registered at the wellhead of a flowing well.
- FORMATION: Sedimentary bed or deposit composed substantially of the same minerals throughout and distinctive enough to be a unit.
- FOURBLE: Section of drill pipe, casing, or tubing consisting of four joints screwed together.
- GAS CAP: Free gas, separate from, but overlying an oil zone that occurs within the same producing formation as oil. Since gas is lighter, it occupies the upper part of the reservoir.
- GEOLOGIST: Scientist whose duties consist of obtaining and interpreting data dealing with the earth's history and its life, especially as recorded in rocks.
- GEOLOGRAPH: Patented apparatus which automatically records the rate of penetration and depth during drilling operations.
- GOING IN HOLE: Lowering the drill pipe into the wellbore.
- HOLE: Common term for wellbore.
- HORIZON: Distinct layer or group of layers of rock.
- HYDROCARBONS: Organic chemical compounds of hydrogen and carbon whose densities, boiling points, and freezing points increase as their molecular weights increase. The molecular structure of the most common petroleum hydrocarbon compounds varies from the simplest - methane, a constituent of natural gas - to the very heavy and complex.
- INFILL DRILLING: Drilling of wells according to a planned pattern and spacing to achieve full production from a new field.
- JACK-KNIFE DERRICK: A cantilever mast that can be laid down in one piece for moving, as opposed to a standard derrick which has to be dismantled and re-erected piece by piece.
- JET BIT: Bit having nozzles of various sizes through which the drilling fluid is directed to achieve a desired fluid velocity.
- JOINT: One length of drill pipe or casing.
- JUNK: Debris lost in the hole.
- KELLY: Square or hexagonal steel pipe about 43 feet (13 meters) long which transmits torque from the rotary table to drill string, thus rotating the string and bit.
- KEYSEAT: While drilling a well, a channel or groove is cut in the side of the hole parallel to the axis of the hole. Keyseating takes place as a result of the dragging action of drill pipe through a dog leg.
- KILLING A WELL: The act of bringing a well under control which has blown out or is threatening to blow out; also applies to the procedure of circulating water and mud into a completed well before starting well service operations.
- LATCH ON: Attaching elevators to a section of pipe.
- LAYING DOWN PIPE: The operation of pulling drill pipe or tubing from the hole and laying it down on the pipe rack.
- LEDGE: An irregular wellbore caused by penetration of alternating layers of hard and soft formations where the soft formation has washed out and caused a change of diametrical size.
- LIQUIDS: Hydrocarbons in solution in natural gas which are liquefiable at surface temperature and pressure or by treatment and processing.
- LOCATIONS: Point at which a well is to be drilled. Commonly termed "well site."
- LOG: Systematic recording of data.
- LOST CIRCULATOIN: Loss quantities of whole mud to a formation, usually cavernous, fissured, or coarsely permeable beds. It is indicated by the complete or partial loss of drilling mud returns. Until the zone in which the drilling fluid has been lost is sealed off, drilling cannot be resumed in most cases.
- MAKE A CONNECTION: Act of screwing a single joint of drill pipe into the drilling string suspended in the wellbore. The addition of this joint of pipe permits deepening of the hole the length of the joint added, or about 30 feet (9 meters).
- MAKING HOLE: Refers to progress being made at a given time when the bit is rotating and the wellbore is being deepened. In other words, drilling.
- MAKING A TRIP: Hoisting of the drill string out of, and returning it into, the wellbore. This is done for the purpose of changing bits, preparing to take a core, etc.
- MAKING UP A JOINT: Act of screwing a joint into another section of pipe.
- MAST: Portable derrick capable of being erected as a unit, as opposed to a standard derrick, which cannot be raised to a working position as a unit, since it is of bolted construction and must be assembled part by part.
- MIGRATION: Natural movement of oil or gas within or out of a formation.
- MIXING MUD: Preparation of drilling fluids from a mixture of water and other fluids and one or more of the various dry mud-making materials such as clay, chemical, etc.
- MONKEY BOARD: Platform on which the derrickhand works during the time the crew is making a trip.
- MOTORHAND: Crew member responsible for the care and operation of the rig motors.
- MOUSE HOLE: Hole drilled under the derrick floor and temporarily cased in which a single joint of pipe is placed awaiting connection to the drill string.
- MUD: Usually colloidal suspensions of clays in water with chemical additives that are circulated through the wellbore during rotary drilling and workover operations. Can use oil as the main medium.
- MULTIPLE-ZONE WELL COMPLETION: Completion of a well in such a way that production is obtained from several different formations.
- OFFSET: A lateral deviation created by the tendency of a bit to sidetrack in a soft formation.
- OFFSET WELL: Well location adjoining another well site.
- OILFIELD: Loosely defined term referring to an area where oil is found. May also include the oil reservoir, the surface and wells, and production equipment.
- OPEN HOLE: Uncased part of a well.
- OPERATOR: Person, whether proprietor or lessee, who actually operates the well. Generally, the oil company by whom the drilling contractor is engaged.
- PAY, PAY SAND, OR PAY SECTION: Producing formation, or that formation which represents the objective of drilling.
- PENETRATION, RATE OF: Rate at which the drill bit proceeds in the deepening of the wellbore and usually expressed as feet (meters) per hour.
- PERFORATE: To pierce holes through well casing within an oil or gas-bearing formation by means of a perforating gun lowered down the hole and fired electrically from the surface. The perforations permit production from a formation which has been cased off.
- PERMEABILITY: Capacity of a porous rock formation to allow fluid to flow within the interconnecting pore network.
- PIPE: Oilfield tubular goods such as casing, drill pipe, tubing, or pipeline.
- PIPE RACK: Series of parallel heavy wooden or steel bents secured in place by bracing on which pipe is stored.
- PLUG: Object or device that serves to block a hole or passageway such as a cement plug in a borehole.
- PLUG AND ABANDON: Act of placing cement plugs in a hole to prevent unwanted vertical migration in an abandoned well.
- POROSITY: Volume of pore spaces between mineral grains expressed as a percentage of the total rock volume. Thus porosity measures the capacity of the rock to hold oil, gas, or water.
- POTENTIAL: Actual or maximum volume of oil and/or gas that a well is capable of producing.
- PRODUCTION: The operation of bringing the well fluids to the surface and separating them, and storing, gauging, and otherwise preparing product for the pipeline. Also refers to the amount of oil or gas produced over a given period.
- RATHOLE: Shallow bore under the derrick substructure in which the kelly joint is temporarily set while making a connection.
- RELIEF WELL: Well drilled at an angle from a point close to a "wild" well that will intercept theoriginal well as part of control procedure.
- RESERVOIR: Porous, permeable sedimentary rock structure or trap containing oil and/or gas. A reservoir can contain more than one pool.
- RIG: The derrick, drawworks, and attendant surface equipment of a drilling or workover unit. (Several types of rigs should be included such as deep, shallow, stratigraphic, etc.)
- RIGGING UP: Act of getting a rig assembled and ready to start drilling.
- ROTARY DRILLING: Method of drilling in which the drill pipe is rotated to rotate a bit.
- ROTARY TABLE: Equipment over the wellbore which transfers power from the engines to produce a rotary motion. Via bushings and gears the rotary motion is transferred to the kelly and through to the drill string.
- ROTATING BOTTOM: Making hole.
- ROUGHNECK: Industry slang for floorhand.
- SAFETY WIRE: Steel cable attached to the monkey board and anchored to the ground at some distance from the rig. It is used by the derrickhand to slide clear of danger in an emergency.
- SANDFRAC: Method of fracturing subsurface rock formations by injection of fluid and sand under high pressure to increase permeability. Fractures induced in the rock by the hydraulic pressure are kept open by the grains of sand.
- SCRATCHER: Steel, wire-fingered device fastened to the casing which removes the mud cake from the hole to condition it for cementing.
- SEISMOGRAPH: Apparatus used to measure and record vibrations in the earth. It is used to detect possible oil-bearing structures.
- SET CASING: Installation of steel pipe or casing in a wellbore, normally cemented in place by surrounding it with a wall of cement.
- SIDE TRACKING: Drilling past an obstruction in the hole, usually done using a special tool known as a whipstock.
- SINGLE: One joint of drill pipe.
- SLIM HOLE DRILLING: Drilling in which the hole size is smaller than the conventional hole diameter, enabling the operator to run smaller casing, thereby decreasing the cost of completion.
- SPECIFIC GRAVITY: Ratio of weight of any substance to weight of equal volume of another substance, usually water as the standard for solids and liquid.
- SPUD OR SPUDDING IN: Commencement of actual drilling of well.
- STABILIZER: A centralizer installed in the drill string to center the string in the hole and to stiffen the string to resist bending and deviation.
- STAND OF PIPE: Two, three, and sometimes four joints of pipe fastened together, called a double, thribble, or fourble, respectively.
- STEP-OUT WELL: Well drilled adjacent or near to proven well to ascertain the limits of the reservoir.
- STRATIGRAPHIC TRAP: Subsurface formation created by sedimentation that might trap an accumulation of oil and/or gas.
- STRING: The entire length of casing, tubing, or drill pipe.
- STRUCTURE: Subsurface geological feature capable of acting as a reservoir for oil and/or gas.
- STUCK PIPE: Drill pipe, casing, or tubing that cannot be worked in or out of the hole as desired.
- SUBSTRUCTURE: Foundation on which the derrick and engines sit. Contains space for storage and well control equipment.
- SURFACE CASING: First string of casing set in well.
- SWABBING: Operation using a swab to bring well fluids to the surface when the well does not flow naturally.
- SYNCLINE: Trough-shaped subsurface structure of folded stratified rock. Opposite of anticline.
- TIGHT HOLE: Drilling a well in which the information obtained is restricted and passed only to those authorized to receive it.
- THRIBBLE: Stand of pipe made up of three joints handled as a unit.
- TOOLPUSHER: Foreman in charge of the drilling rig operations and crew members.
- TOTAL DEPTH (TD): Maximum depth reached in a well.
- TOUR: Work shift of a drilling crew, usually pronounced as though it were spelled t-o-w-e-r.
- TRAP: Any geological structure which precludes the migration of oil and gas through subsurface rocks, causing the hydrocarbons to accumulate into pools.
- TRIPPING: Making a trip; operation of hoisting pipe out of, and returning it to, the wellbore.
- TURBODRILL: Downhole assembly of bit and motor in which the bit alone is rotated by means of fluid turbine which is activated by the drilling mud. The mud turbine is usually placed just above the bit.
- TURNING TO THE RIGHT: Slang term referring to actual drilling time as opposed to repair time, trip time, etc.
- TURNKEY CONTRACT: Contract under which contractor carries out and completes his assignment for a fixed fee, as opposed to working on per diem basis.
- TWIST-OFF: To fracture a joint of drill pipe in two, necessitating a recovery or fishing operation.
- VUG: A cavity in a rock.
- WAITING ON CEMENT (W.O.C.): Time period that drilling is suspended while the cement used to hold casing in the wellbore hardens.
- WELLBORE: The hole made by a drilling bit.
- WELL COMPLETION: See COMPLETE A WELL.
- WELL LOGGING: Recording information about subsurface geologic formations; methods include records kept by the driller, mud and cutting analysis, core analysis, drill stem tests, electric and radioactivity procedures.
- WHIPSTOCK: Long steel wedge used to deflect the bit from the original borehole at a slight angle for controlled directional drilling, for straightening crooked holes, and for sidetracking in or to bypass an unretrieved fish.
- WILDCAT: Well drilled in unproven territory.
- WORKOVER: To carry out remedial operations on an producing well with the intention of restoring or increasing production.
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