Oil & Gas Glossary 1.0

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

A device run on cable-tool drilling line, a service machine, or sand line of a rotary rig to drill up tools, remove downhole debris, and so on.

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

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. Wire rope is used as drilling line (in rotary and cable-tool rigs), coring line, servicing line, winch line, and so on. It is often called cable or wireline; however, wireline is a single, slender metal rod, usually very flexible. Compare wireline.

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

The discharge pipe from a well being drilled by air drilling. The blooey line is used to conduct the air or gas used for circulation away from the rig to reduce the fire hazard as well as to transport the cuttings a suitable distance from the well.

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

A small-diameter metal line used in wireline operations. Also called slick line. Compare conductor line.

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 stem and bit.

1. a scraping tool that is forced through a pipeline or flow line to clean out accumulations of wax, scale, and debris from the walls of the pipe. It travels with the flow of product in the line, cleaning the pipe walls by means of blades or brushes affixed to it. Also called a line scraper or a go-devil.

A wireline attached to a mast, derrick, or offshore platform to stabilize it. See wind guy line.

A small plug that is run through a flow line by pressure to clean the line or test for obstructions (see pig).

A small hydraulic line used to communicate fluid from the surface to a downhole tool, such as a subsurface safety valve.

The valve on the choke and flow line that is nearest to the preventer assembly. Its purpose is to stop the flow through the choke and flow line.

An 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. The drilling line is reeved over the sheaves of the crown block alternately which the sheaves of the traveling block, which is raised and lowered in the derrick by the drilling line. When elevators are attached to a hook on the traveling block and drill pipe latched in the elevators, the pipe can be raised or lowered. See crown block and traveling block.

A buried weight or anchor to which a guy line is attached. See deadman.

An assembly of sheaves, mounted on beams at the tope of the derrick, over which the drilling line is reeved. See 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.

A short length of pipe (a nipple) installed on top of the blowout preventer. The top end of the nipple is flared, or belled, to guide drill tools into the hole and usually has side connections for the fill line and mud return line.

A small-diameter conductive line used in electric wireline operations, such as electric well logging and perforating, in which the transmission of electrical current is required. Compare wireline.

A device used to direct fluid flowing from a well away from the drilling rig. When a kick is encountered at shallow depths, the well often cannot be shut in safely; therefore, a diverter is used to allow the well to flow through a side outlet (a diverter line).

A wireline used on drilling rigs and well servicing rigs to operate a swab or bailer, to retrieve cores or to run logging devices. It is usually 9/16 of an inch (15 millimeters) in diameter and several thousand feet or meters long

A device used to control the rate of flow in a line to open or shut off a line completely, or to serve as an automatic or semiautomatic safety device. Those used extensively include the check valve, gate valve, globe valve, needle valve, plug valve, and pressure relief valve.

4. in hydrostatic testing of a pipeline, a scraper used inside the line to push air out ahead of the test water and to push water out after the test. v: to force a device called a pig through a pipeline or a flow line for the purpose of cleaning the interior walls of the pipe, separating different products, or displacing fluids.

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

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

An employee of a drilling contractor who is in charge of the entire drilling crew and the drilling rig. Also called a toolpusher, drilling foreman, rig supervisor, or rig superintendent.

2. to tie up short with a line.

Abbreviation: through-the-flow-line.

To lower a load or ease up on a line.

A hoisting or pulling line operated from a cathead.

Abbreviation: choke-line friction pressure.

A device that controls the rate of flow of fluid in a line or opens or shuts off the flow of fluid completely. When open, the sealing surface of the valve is moved away from a seat; when closed, the sealing surface contacts the seat to shut off flow. The direction of movement of the valve is usually perpendicular to the seat. Popper valves are used extensively as pneumatic (air) controls on drilling rigs and as intake and exhausts valves in most internal-combustion engines.

A drilling method in which a hole is drilled by a rotating bit to which a downward force is applied. The bit is fastened to and rotated by the drill stem, which also provides a passageway through which the drilling fluid is circulated. Additional joints of drill pipe are added as drilling progresses.

A drilling rig that is used exclusively to drill offshore exploration and development wells and that floats upon the surface of the water when being moved from one drill site to another. It may or may not float once drilling begins. Two basic types of mobile offshore drilling units are used to drill most offshore wildcat wells: bottom-supported drilling rigs and floating drilling rigs.

Connection of treating line during well servicing, from pump trucks to tree/well

A device to monitor rate of fluid from the annulus.

The surface pipe through which oil travels from a well to processing equipment or to storage.

To loosen a tight joint as in line pipe or sucker rods.

2. a hole or opening in a line or vessel into which a gauge or valve may be inserted and screwed tight.

1. a device that is inserted into a pipeline for the purpose of cleaning; a line scraper. Also called a pig.

A device attached to pipeline to permit continuous sampling of the oil, gas, or product flowing in the line.

A threaded nipple with a rounded, closed end used to stop up a hole or close off the end of a line.

A length of drill or line pipe, tubing, or casing considerably shorter than 30 feet.

An individual or group of individuals that own a drilling rig and contract their services for drilling wells.

A drilling mud that contains a minimum amount of solid material (sand, silt, and so on) and that is used in rotary drilling when possible because it can provide fast drilling rates.

A drilling mud that contains a minimum amount of solid material (sand, silt, and so on) and that is used in rotary drilling when possible because it can provide fast drilling rates.

A slot in the edge of the barge hull of a jackup drilling unit over which the drilling rig is mounted and through which drilling tools are lowered and removed from the well being drilled.

A drilling bit with cutting edges of hard alloys. Developed about 1900, and first used with the rotary system of drilling, it is still useful in drilling very soft formations. Also called a drag bit.

A piece of wood or concrete, usually buried, to which a wire guy line is attached for bracing a mast or tower.

The wireline attached to ground anchors to provide lateral support for a mast or derrick.

A surface device used in slickline operations to keep the line lubricated and provide grease for pressure control

A surface device used in slickline operations to keep the line lubricated and provide grease for pressure control

An offshore drilling rig, usually with a large hull. It has a mat or legs that are lowered to the sea-floor and a main deck that is raised above the surface of the water to a distance where it will not be affected by the waves. Also called a jackup drilling rig.

The operation during the drilling procedure at the point of drilling into the pay formation.

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 from the well to the vessel. The riser consists of several sections of pipe and includes special devices to compensate for any movement of the drilling rig caused by waves. It is also called a marine riser.

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 going into the hole.

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

A sheave or pulley that can be opened up for putting a line over the roller or sheave.

A device inserted in a flow line to regulate the rate of flow.

A device placed on a piece of equipment that is lowered into a wellbore so that the equipment may be retrieved by wire line.

A device for maintaining pressure in a line, downstream from the value.

The smaller of the side fittings on a bell nipple, used to fill the hole when drill pipe is being removed from the well.

A loss of pressure that results from friction sustained by a fluid passing through a line, valve, fitting, or other device.

A plug in the flow line at the well head which has a small hole drilled through it through which oil flows, and which keeps a well from flowing at too high a rate.

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 base, a self-propelled or towed structure with jacking legs (jackup drilling rig), or a permanent structure used as a production platform when drilling is completed. In general, wildcat wells are drilled from mobile floating vessels or from jackups, while development wells are drilled from platforms or jackups.

Trade name for a downhole motor driven by drilling fluid that imparts rotary motion to a drilling bit connected to the tool, thus eliminating the need to turn the entire drill stem to make hole. Used in straight and directional drilling.

1. a pipe connection around a valve or other control mechanism that is installed to permit passage of fluid through the line while adjustments or repairs are being made on the control.

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 sometimes referred to as pits.

A chemical used to lighten the water column in gas wells, in oilwells producing gas, and in drilling wells in which air or gas is used as the drilling fluid so that the water can be forced out with the air or gas to prevent its impeding the production or drilling rate.

In a well-control operation, closing the BOP without first opening an alternate flow path up the choke line. When the BOP is closed, pressure in the annulus cannot be read on the casing pressure gauge.

The cutting or boring element used in drilling oil and gas wells. This bit consists of a cutting element and a circulating element. The circulating element permits the passage of drilling fluid and utilized the hydraulic force of the fluid stream to improve drilling rates. In rotary drilling, several drill collars are joined to the bottom end of the drill pipe column, and the bit is attached to the end of the string of drill collars. Most bits used in rotary drilling are roller cone bits, but diamond bits are also used extensively.

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 w

The liquid circulated through the wellbore during rotary drilling and workover operations. In addition to its function of bringing cuttings to the surface, drilling mud cools and lubricates the bit and 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.

A long, hollow cylinder, usually steel, through which fluids are conducted. Oilfield tubular goods are casing (including liners), drill pipe, tubing, or line pipe

An extension from the blowout preventer assembly used to direct control the flow of well fluids from the annulus to the choke.

A device that reduces the pressure or volume of a fluid flowing in a line and maintains the pressure or volume at a specified level.

Any equipment designed to be pumped down a completed well to effect a repair, modify the well's flow, or for other reasons.

A break in subsurface strata. Often strata on one side of the fault line have been displaced (upward, downward, or laterally) relative to their original positions.

A cylindrical or spherical device that is affixed to the end of a wireline just above the hook to keep the line straight and to provide weight. v: to soak metal pieces in a chemical solution to remove dirt and scale from the metal's surface.

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

A type of mobile offshore drilling unit that has a part of its structure in contact with the seafloor when it is on site and drilling a well. The remainder of the rig is supported above the water. The rig can float, however, allowing it to be moved from one drill site to another. Bottom-supported units include submersible rigs and jackup rigs. See mobile offshore drilling unit.

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

A specially compounded liquid circulated through the wellbore during rotary drilling operations. See mud.

A driller, a derrickman, and two or more helpers who operate a drilling or workover rig for one tour each day.

To prepare the drilling rig for making hole; to install tools and machinery before drilling is started.

A device that continually measures and may record the flow rate of mud returning from the annulus and flowing out of the mud return line. If the mud does not flow at a fairly constant rate, a kick or lost circulation may have occurred.

A drilling technique that uses air or gas to which a foaming agent has been added.

A hollow, rubber-faced cylinder mounted on a hollow mandrel with a pin joint on the upper end to connect to the swab line. A check valve that opens upward on the lower end provides a way to remove the fluid from the well when pressure is insufrficien5t to support flow.

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.

A type of mobile offshore drilling unit that floats and is not secured to the seafloor (except for anchors). Floating units include inland barge rigs, drill ships and ship-shaped barges, and semisubmersibles. See mobile offshore drilling unit.

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.

A lease or a number of leases of adjoining tracts of land that constitute a unit of acreage sufficient to justify the expense of drilling a wildcat.

Any kind of pipe. Oilfield tubular goods include tubing, casing, drill pipe, and line pipe. Also called tubulars.

A sealing device used to close off the annular space around the kelly in drilling with pressure at the surface, usually installed above the main blowout preventers. A rotating head makes it possible to drill ahead even when there is pressure in the annulus that the weight of the drilling fluid is not overcoming; the head prevents the well from blowing out. It is used mainly in the drilling of formations that have low permeability. The rate of penetration through such formations is usually rapid.

See electric well log

A flange equipped with plastic pieces to separate its metal parts, thus preventing the flow of electric current. Insulating flanges are often used in cathodic protection systems to prevent electrolytic corrosion and are sometimes installed when a flow line is being attached to a wellhead.

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.

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.

A self-propelled floating offshore drilling unit that is a ship constructed to permit a well to be drilled from it. While not as stable as Semisubmersible, drill ships are capable of drilling exploratory wells in deep, remote waters. They may have a ship hull, a catamaran hull, or a trimaran hull. See floating offshore drilling rig.

A drilling mud, e.g., oil-base mud and invertemulsion mud, in which oil is the continuous phase. It is useful in drilling certain formation that may e difficult or costly to drill with water-base mud. Compare oil emulsion mud.

The supervisor of drilling or workover operations on a rig. Also called a rig manager, rig supervisor, rig superintendent, or tool pusher.

The presence in a drilling fluid of any foreign material that may tend to produce detrimental properties of the drilling fluid.

1. a drilling mud in which the water has an appreciable amount of salt (usually sodium or calcium chloride) dissolved in it. Also called saltwater mud or saline drilling fluid.

1. the operation during the drilling procedure when the cement is drilled out of the casing and the wellbore after the casing has been cemented.

Substances generally regarded as drilling mud contaminants, such as salt and calcium sulfate, are called inhibitors when purposely added to mud so that the filtrate from the drilling fluid will prevent or retard the hydration of formation clays shells.

Steel pipe placed in an oil or gas well as drilling progresses to prevent the wall of the hole from caving in during drilling, to prevent seepage of fluids, and to provide a means of extracting petroleum if the well is productive.

A floating offshore drilling unit that has pontoons and columns that when flooded cause the unit to submerge in the water to a predetermined depth. Living quarters, storage space, and so forth a reassembled on the deck. Semisubmersible rigs are either self-propelled or towed to a drilling site and either anchored or dynamically positioned over the site, or both. In shallow water, some semisubmersibles can be ballasted to rest on the seabed. Semisubmersibles are more stable than drill ships and ship-shaped barges and are used extensively to drill wildcat wells in rough waters such as the North Sea. Two types of semisubmersible rigs are the bottle-type semisubmersible and the column-stabilized semisubmersible. See floating offshore drilling rig.

The first casing or conductor string (generally with a diameter of 30 to 36 inches) set when drilling a well from an offshore drilling rig. It prevents sloughing of the ocean-floor formations and is a structural support for the permanent guide base and the blowout preventers.

Process of separating, or breaking down, an emulsion into oil and water in a vessel or tank on a continuous basis (i.e., no interruption of flow of emulsion into the tank or vessel). Compare batch treating.

1. an automatic valve that opens or closes when an abnormal condition occurs (e.g., a pressure relief valve on a separator that opens if the pressure exceeds the set point, or the shutdown valve at the wellhead that closes if the line pressure becomes too high or too low).

A drilling structure consisting of a barge upon 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 covering the drill site in not too deep. Also called swamp barge. See floating offshore drilling rig.

A device placed in a choke line that regulates the flow through the choke. Flow depends on the size of the opening in the bean; the larger the opening, the greater the flow.

The employee directly in charge of a drilling or workover rig and crew. His main duty is operation of the drilling and hoisting equipment, but he is also responsible for downhole condition of the well, operation of downhole tools, and pipe measurements.

A downhole motor that rotates a bit by the action of the drilling mud on turbine blades b built into the tool. When a turbodrill is used, rotary motion is imparted only at the bit; therefore, it is unnecessary to rotate the drill stem. Although straight holes can be drilled with the tool, it is used most often in directional drilling.

A valve that opens at a preset pressure to relieve excessive pressures within a vessel or line. Also called a relief valve, safety valve, or safety relief valve.

A worker on a drilling or workover rig, subordinate to the driller, whose primary work station is on the rig floor. On rotary drilling rigs, there are at least two and usually three or more rotary helpers on each crew. Sometimes called floor man, roughneck, or rig crewman.

A plan or procedure, with respect to depth, for the type and properties of drilling fluid to be used in drilling a well. Some factors that influence the mud program are the casing program and such formation characteristics as type, competence, solubility, temperature, and pressure.

An agency of the U.S. Department of the Interior that establishes requirements through the code of Federal Regulations (CFR) for drilling while operating on the Outer Continental Shelf of the United States. The agency regulates rig design and construction, drilling procedures, equipment, qualification of personnel, and pollution prevention.

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

The filtration characteristics of a drilling mud. In general, these qualities are inverse to the thickness of the filter cake deposited on the face of a porous medium and the amount of filtrate allowed to escape from the drilling fluid into or through the medium.

Salt of stearic acid that is a saturated, 18-carbon fatty acid. Certain compounds, such as aluminum stearate, calcium stearate, zinc stearate, have been used in drilling fluids for one or more of the following purposes: defoamer, lubrication, air drilling in which a small amount of water is encountered.

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

To obtain cuttings for geological information as formations are penetrated by the bit. The samples are obtained from drilling fluid as it emerges from the wellbore or, in cable-tool drilling, from the bailer. Cuttings are carefully washed until they are free of foreign matter, dried, and labeled to indicate the depth at which they were obtained.

Intentional deviation of a wellbore from the vertical. Although wellbores are normally drilled vertically, it is sometimes necessary or advantageous to drill at an angle from the vertical. Controlled directional drilling makes is possible to reach subsurface areas laterally remote from the point where the bit enters the earth. It often involves the use of turbodrills, Dyna-Drills, whipstocks, or other deflecting rods.

The principal component of a rotary, or rotary machine, used to turn the drill stem and support the drilling assembly. It has a beveled gear arrangement to create the rotational motion and an opening into which bushings are fitted to drive and support the drilling assembly.

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

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.

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. If

A rigid offshore drilling platform that stands on steel caissons and is used to drill development wells. The caissons are firmly affixed to the seafloor, and the drilling and production decks are laid on top of them. The platform is used in certain arctic waters, where the caissons are needed to protect equipment from moving ice. See platform rig.

A reinforced flexible tub on a rotary drilling rig that conducts the drilling fluid from the standpipe to the swivel and kelly. Also called the mud hose or the kelly hose

A freshwater drilling mud using calcium oxide (lime) or calcium sulfate (gypsum) to retard the hydrating qualities of shale and clay formation, thus facilitating drilling. Calcium-treated muds resist scale and any anhydrite contamination but may require further treatment to prevent gelation (solidifcation) under the high temperatures of deep wells.

A procedure whereby the formation immediately below the casing shoe is subjected to a pressure equal to the pressure expected to be exerted later by a higher drilling glut density or by the sum of a higher drilling fluid density and back-pressure created by a kick.

A measure of the ability of a colloidal dispersion to develop and retain a gel form, based on its resistance to shear. The gel, or shear, strength of a drilling mud determines its ability to hold solids in suspension. Sometimes bentonite and other colloidal clays are added to drilling fluid to increase its gel strength.

A jackup drilling unit in which the drilling rig is mounted on two cantilevers that extend outward from the barge hull of the unit. The cantilevers are supported only at the barge end.

Drilling in which the size of the hole is smaller than the conventional hole diameter for a given depth. This decrease in hole size enables the operator to run smaller casing, thereby lessening the cost of completion. See miniaturized completion.

A mobile submersible drilling structure constructed of several steel cylinders, or bottles. When the bottles are flooded, the rig submerges and rests on bottom; when water is removed from the bottles, the rig floats. The latest designs of this type of rig drill in water depths up to 100 feet (30.5 meters). See submersible drilling rig.

See directional drilling.

A formation fluid sampling device, actually run on conductor line rather than wireline, that also logs flow and shut-in pressure in rock near the borehole. A spring mechanism holds a pad firmly against the sidewall while a piston creates a vacuum in a test chamber. Formation fluids enter the tes5t chamber through a valve in the pad. A recorder logs the rate at which the test chamber is filled. Fluids may also be drawn to fill a sampling chamber. Wireline formation tests may be done any number of times during one tip in the hole, so they are very useful in formation testing.

Usually a single well drilled offshore by a mobile offshore drilling unit to produce hydrocarbons from the outer fringes of a reservoir that cannot be produced by primary development wells drilled from a permanent drilling structure (as a platform rig). Sometimes, several satellite wells will be drilled to exploit marginal reservoirs and avoid the enormous expense of erecting a platform.

A classification of commercial drilling-clay preparations having a yield of 35 to 40 barrels per ton and intermediate between bentonite and low-yield clays. Usually prepared by peptizing low-yield calcium montmorillonite clays or, in a few cases, by blending some bentonite with the peptized low yield clay

A device that prevents leakage along a piston, rod, propeller shaft, or other moving part that passes through a hole in a cylinder or vessel. It consists of a box or chamber made by enlarging the hole and a gland containing compressed packing. On a well being artificially lifted by means of a sucker rod pump, the polished rod operates through a stuffing box, preventing escape of oil and diverting it into a side outlet to which is connected the flow line leading to the oil and gas separator or to the field storage tank. For a bottomhole pressure test, the wireline goes through a stuffing box and lubricator, allowing the gauge to be raised and lowered against well pressure. The lubricator provides a pressure-tight grease seal in the stuffing box.

A rigid offshore drilling platform built of steel-reinforced concrete and used to drill development wells. The platform is floated to the drilling site in a vertical position, and at the site tall caissons that serve as the foundation of the platform are flooded so that the platform submerges and comes to rest on bottom. Because of the enormous weight of the platform, the force of gravity alone keeps it in place. See platform rig.

A mobile submersible drilling structure consisting of a barge hull that rests on bottom, steel posts that rise from the top of the barge hull, and a deck that is built on top of the posts, well above the waterline. It is used to drill wells in water no deeper than about 30-35 feet (9-10.7m). Most posted barge submersibles work in inland gulfs and bays. See submersible drilling rig.

A cycle, or down the hole and back, is the time required for the pump to move the drilling fluid in he hole. The cycle in minutes equals the barrels of mud in the hole divided by barrels per minute.

A short, threaded piece of pipe used to adapt parts of the drilling string that cannot otherwise be screwed together because of differences in thread size or design. A sub (i.e., a substitute) may also perform a special function. Lifting subs are used with drill collars to provide a shoulder to fit the drill pipe elevators; a kelly saver sub is placed between the drill pipe and the kelly to prevent excessive thread wear of the kelly and drill pipe threads, a bent sub is used when drilling a directional hole.

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. During drilling, it is usually rotated while drilling fluid is circulated through it. Drill pipe joints are available in three ranges of length: 18 to 22 feet, 27 to 30 feet, and 38 to 45 feet. The most popular length is 27 to 30 feet. It is available with outside diameters ranging from 2 7/8 to 5 1/2 inches. Several joints are made up (screwed together) to form the drill string.

Generally, the first string of casing in a well. It may be lowered into a hole drilled into the formations near the surface and cemented in place; it may be driven into the ground by a special pile driver (in such cases, it is sometimes called drive pipe); or it may be jetted into place in offshore locations. 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.

The insoluble abrasive solids content of a drilling fluid rejected by a 200-mesh screen. usually expressed as the percentage bulk volume of sand in a drilling fluid. This test is an elementary type in that the retained solids are not necessarily silica and may not be altogether abrasive. For additional information concerning the kids of solids retained on the 200-mesh screen, more specific tests would be required. See mesh.

Generally, the first string of casing in a well. It may be lowered into a hole drilled into the formations near the surface and cemented in place; or it may be driven into the ground by a special pile drive (in such cases, it is sometimes called drive pipe); or it may be jetted into place in offshore locations. 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.

A device made up in the drill stem above the mill to collect bits of junk ground away during a milling operation. During milling, drilling mud under high pressure forces bits of junk up the narrow space between the boot sub and the hole wall. When the junk reaches the wider annulus above the boot sub and pressure drops slightly, the junk falls into the boot sub. A boot sub also can be run above the bit during routine drilling to collect small pieces of junk that may damage the bit or interfere with its operation.

See keyway.

See floating offshore drilling rig.

Abbreviation: barrels per day; often used in drilling reports

Height of drilling mud in the pits

Abbreviation: sacks; used in drilling and mud reports.

International Association of Drilling Contractors

To begin drilling; to start the hole.

On or in a ship, offshore drilling rig, or helicopter

The cutting or boring element used for drilling. See bit.

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 of depth (9.792 kilopascals per meter). 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.

Any relatively sticky formation (such as clay) encountered in drilling

The amount of oil in volume-percent in a drilling fluid.

A hole made by drilling or boring; a wellbore.

Formation gas that enters the drilling fluid in the annulus.

A measure of the density of a fluid (such as a drilling mud).

1. toward the stern of a ship or mobile offshore drilling rig

Abbreviation: mobile offshore drilling unit.

The appearance of oil or gas n cuttings, samples, or cores from a drilling well

1. in mud terminology, refers to the density of a drilling fluid.

The strata of rock that overlie the stratum of interest in drilling.

The device used to remove unwanted gas from a liquid, especially from drilling fluid.

A hole dug, usually before drilling of a well, to allow working space for the casinghead equipment.

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

A device used in the testing of filtration properties of drilling mud. See mud.

A portable cable-tool drilling rig, sometimes mounted on a truck or trailer.

Structure at the rig to store and shelter sacked materials used in drilling fluids.

Abbreviation: shut-in drill pipe pressure, used in drilling reports.

Any material added to drilling fluid to change some of its characteristics or properties.

The escape of the liquid part of a drilling mud into permeable formations.

In drilling, to assemble the blowout preventer stack on the wellhead at the surface.

To agitate the drilling fluid in a pit by means of a mud gun, electric mixer, or agitator.

A special valve installed below the kelly. Usually, the valve is open so that drilling fluid can flow out of the kelly and down the drill stem. It can, however, be manually closed with a special wrench when necessary. In one case, the valve is closed and broken out, still attached to the kelly to prevent drilling mud in the kelly from draining onto the rig floor. In another case, when kick pressure inside the drill stem exists, the drill stem safety valve is close to prevent the pressure from escaping up the drill stem.

The coagulation of solids in a drilling fluid, produced by special additives or by contaminants.

The derrick or mast, drawworks, and attendant surface equipment of a drilling or workover unit.

A complex carbohydrate sometimes added to drilling fluids to reduce filtration loss.

2. the liquid portion of drilling mud that is forced into porous and permeable formations next to the borehole.

Sodium hydroxide. Used to maintain an alkaline pH in drilling mud and in petroleum fractions.

A container in which various chemicals are mixed prior to addition to drilling fluid.

1. the workers on a drilling or workover rig, including the driller, derrickman, and rotary helpers

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

A record of information derived from examination of drilling fluid and drill bit cuttings. See mud logging.

The amount by which drilling fluid density is reduced by entrained formation fluids or air.

The fluid used when drilling starts at the surface, often a thick bentonite-lime slurry.

A chemical or combination of chemicals that, when added to a drilling mud, reduces its viscosity.

The dispersion of solids that have stuck together in drilling fluid, usually by means of chemical thinners. See flocculation.

When water-insoluble greasy materials (e.g., emulsifiers, lubricants) separate out of drilling fluids.

To sharpen, repair, or add accessories to items of equipment (such as drilling bits and tool joints).

A drilling fluid containing essentially clay and water; no special or expensive chemicals or conditioners are added.

2. an indicator of wind direction used during drilling or workover operations where hydrogen sulfide (sour) gas may be encountered.

A condition wherein the drilling fluid fails to form measurable gels during a quiescent time interval (usually 10 minutes)

Any drilling fluid, usually oil-base or invert-emulsion muds, the continuous phase of which does not conduct electricity, e.g., oil.

1. 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.

To add solid materials (such as bentonite or other clay) to a drilling fluid composed mainly of clear water to obtain certain desirable properties.

2. to remove the settlings and cavings that are plugged inside a hollow fish (such as drill pipe) during a fishing operation.

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

2. to pull formation fluids into a wellbore by raising the drill stem at a rate that reduces the hydrostatic pressure of the drilling mud below the bit.

A South American tree that is a source of tannin extract, which was extensively used as a thinning agent for drilling mud, but is seldom used today.

A clay mineral often used as an additive to drilling mud. It is a hydrous aluminum silicate capable of reacting with such substances of magnesium and calcium. See bentonite.

A sudden increase in the drill bit's rate of penetration. it sometimes indicates that the bit has penetrated a high-pressure zone and thus warns of the possibility of a kick.

Any of a variety of drilling bits that have no moving parts. As they are rotated on bottom, elements of the bit make hole by being pressed into the formation and being dragged across it. See fishtail bit.

Lead sulfide (PbS). Technical grades (specific gravity about 7) are used for increasing the density of drilling fluids to points impractical or impossible with barite.

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

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

A calibrated funnel used in field tests to determine the viscosity of drilling mud.

Clays that are encountered when drilling various formations; they may or may not be incorporated purposely into the mud system.

A retrievable tool used to suspend drilling temporarily during a storm offshore.

Drilling fluid formulated so that it will not alter the properties of the cuttings the fluid carries up the well.

To increase the weight or density of drilling fluid by adding weighting material.

An instrument for measuring the resistivity of drilling fluids and their cakes.

Movement of drilling fluid from mud pits, down drill stem, up annulus, and back to mud pits.

Pertaining to the time when drilling or completion operations are suspended so that the cement in a well can harden sufficiently.

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 rill directionally. See ream.

The accumulation of oil in the pores of sedimentary rock that yields petroleum on drilling. Not a pool or pond in the ordinary use of the term.

1. to recover from a well any equipment left there during drilling operations, such as a lost bit or drill collar or part of the drill string.

That part of a drilling mud--clay, shale, barite, and other solids--that is dispersed throughout a liquid or gaseous medium, forming the mud.

The person or company, either proprietor or lessee, actually operating an oilwell or lease. Generally, the oil company by whom the drilling contractor is engaged.

Well-control fluid that has been reduced in density or unit weight as a result of entrainment of less-dense formation fluids or air

One of the alkali metal elements with a valence of 1, an atomic number of about 23. Numerous sodium compounds are used as additives to drilling fluids.

A drilling mud to which a polymer has been added to increase the viscosity of the mud.

A drilling fluid with a pH range above 10.5 i.e., a high-alkalinity mud.

A bentonite and diesel oil mixture that is pumped down the drill pipe and into the annulus to mix with drilling mud. The stiff, putty-like material is squeezed into lost circulation zones to seal them.

The sodium or potassium salt of a high-molecular weight fatty acid. Commonly used in drilling fluids to improve lubrication, emulsification, sample size, and defoaming.

A small building, or doghouse, in which members of a drilling rig or roustabout crew change clothes, store personal belongs, and so on.

Weight per unit volume of drilling fluid usually expressed in pounds per gallon or pounds per cubic foot. See hydrostatic pressure.

A substance added to cement slurries or drilling mud to prevent the loss of cement or mud to the formation. See bridging materials.

A non-fermenting cellulose product used in drilling fluids to combat contamination from anhydrite (gypsum) and to lower the water loss of the mud.

1. a short length of surface-hardened pipe that fits inside the swivel and serves as a conduit for drilling fluid through the swivel.

A substance added to cement slurries or drilling mud to prevent the loss of cement or mud to the formation. See bridging materials.

1. the area of the formation that is damaged because of the invasion of foreign substances into the exposed section of the formation adjacent to the wellbore during drilling and completion.

The unwanted migration of the liquid part of the drilling mud or cement slurry into a formation, often minimized or prevented by the blending of additives with the mud or cement.

In drilling-fluid terminology, a chemical is any material that produces changes in the viscosity, yield point, gel strength, fluid loss, and surface tension.

A short string of large-diameter casing used to keep the wellbore open and to provide a means of conveying the upflowing drilling fluid from the wellbore to the mud pit.

An accessory attached o the top of the drill pipe or tubing to form a connection with the mud system to permit circulation of the drilling mud. In some cases, it is also a rotating head.

The electrokinetic portion of the spontaneous potential electric-log curve that can be influenced significantly by the characteristics of the filtrate and mud cake or the drilling fluid that was used to drill the well.

A colloidal clay, composed primarily of montmorillonite, that swells when wet. Because of its gel forming properties, bentonite is a major component of water-based drilling muds. See gel, mud.

1. a passageway through jet bits that causes the drilling fluid to be ejected from the bit at high velocity. The jet of mud clears the bottom of the hole. Nozzles come in different sizes that can be interchanged on the bit to adjust the velocity with which the mud exits the bit.

The fragments of rock dislodged by the bit and brought to the surface in the drilling mud. Washed and dried cuttings samples are analyzed by geologists to obtain information about the formations drilled.

1. the well cuttings 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.

The process of pumping mud downward to the bit and back up tot he surface in a drilling or workover operation. See normal circulation, reverse circulation.

An employee of an operating company whose job is to represent the company's interests at the drilling location.

A reciprocating pump with two pistons or plungers and used extensively as a mud pump on drilling rigs.

Total amount of solids in a drilling fluid as determined by distillation. Includes both the dissolved and the suspended or undissolved solids.

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

The reduction of permeability in a reservoir rock caused by the invasion of drilling fluid and treating fluids to the section adjacent to the wellbore. Often call skin damage.

An instrument used to measure the shear strength, or gel strength, of a drilling fluid. See gel strength

A rotational shear viscometer used for measuring the viscosity and gel strength of drilling fluids. This instrument has been largely superseded by the direct-indicating viscometer.

A long steel casing that uses an inclined plane to cause the bit to deflect from the original borehole at a slight angle. Whipstocks are sometimes used in controlled directional drilling, in straightening crooked boreholes, and in sidetracking to avoid unretrieved fish.

The property exhibited by a fluid that is in a liquid state when flowing and in a semisolid, gelled state when at rest. Most drilling fluids must be thixotropic so that cuttings will remain in suspension when circulation is stopped.

Any of several devices used to agitate, or mix, the liquids and solids that make up drilling fluid. These devices include jet hoppers, paddles, stirrers, mud guns, and chemical barrels.

Determination of the relative percentages of substances, e.g., the suspended solids in a drilling fluid that pass through or are retained on a sequence of screens of decreasing mesh size. Also called sieve analysis.

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

2. the layer of concentrated solids from the drilling mud or cement slurry that forms on the walls of the borehole opposite permeable formations; also call wall cake or mud cake.

Additives that, when added to drilling fluid, lubricate bearing surfaces subjected to extreme pressure.

Descriptive of any tool or device that can be pumped down a wellbore. Pump-down tools are not lowered into the well on wireline; instead, they are pumped down the well with the drilling fluid.

A drilling or workover fluid in which oil is the continuous phase and which contains from less than 2 percent and up to 5 percent water. This water is spread out, or dispersed, in the oil as small droplets. See oil mud.

A beam balance consisting of a cup and a graduated arm carrying a sliding weight and resting on a fulcrum. It is used to determine the density or weight of drilling mud.

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)

Volume flow rate of circulating drilling fluid expressed in gallons or barrels per minute

To enlarge the wellbore by drilling it again with a special bit. Often a rathole is reamed or opened to the same size as the main wellbore. See rathole.

A heavy-mandrel service squeeze tool with on-off tool used in drilling operations during storm interruptions.

Low-solids fluid or drilling mud used when a well is being completed. it is selected not only for its ability to control formation pressure, but also for the properties that minimize formation damage.

When the opposite occurs of what is intended in a drilling fluid. In an invert water-in-oil emulsion, the emulsion is said to be flipped when the continuous and dispersed phases reverse.

One of the alkali metal elements with a valence of 1 and an atomic weight of about 39. Potassium compounds, most commonly potassium hydroxide (KOH), are sometimes added to drilling fluids to impart special properties, usually inhibition.

3. to begin drilling a well; i.e., to spud in.

The half-neutralized sodium salt of carbonic acid, used extensively for treating cement contamination and occasionally other calcium contamination in drilling fluids.

In drilling, the entrance of formation fluids into the wellbore because hydrostatic pressure is less than formation pressure.

2. for mobile offshore drilling rigs, weight added to make the rig more seaworthy, increase its draft, or sink it to the seafloor. Seawater is usually used for ballast, but sometimes concrete or iron is used additionally to lower the rig's center of gravity permanently.

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. Compare lay down pipe.

A walled round hole or well in the hull of a drill ship (usually in the center) through which the drilling assembly and other assemblies pass while a well is being drilled, completed, or abandoned from the drill ship.

A centrifugal device for removing sand from drilling fluid to prevent abrasion of the pumps. It may be operated mechanically or by a fast-moving stream of fluid inside a special cone-shaped vessel. Compare desilter.

Heavy seamless tubing used to rotate the bit and circulate the drilling fluid. Joints of pipe approximately 30 feet (9 meters) long are coupled together by means of tool joints.

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

Semisolid or solid complex, amorphous mixture of organic compounds having no definite melting point or tendency to crystallize. Resins may be a component of compounded materials that can be added to drilling fluids to impart special properties to the system, to wall cake, etc.

All members in the assembly used for rotary drilling from the swivel to the bit, including the kelly, drill pipe and tool joints, drill collars, stabilizers, and various specialty items. Compare drill string.

A silicate mineral characterized by sheet cleavage; i.e., it separates in thin sheets. Biotite is ferromagnesian black mica, and muscovite is potassic white mica. Sometimes mica is used as a lost circulation material in drilling.

Viscosity as measured by the Marsh funnel, based on the number of second it takes for 1,000 cubic centimeters of drilling fluid to flow through the funnel.

1. the weight of a fluid (such as water) displaced by a freely floating or submerged body (such as an offshore drilling rig). if the body floats, the displacement equals the weigh of the body.

The character or state of the drilling mud filter cake. From API RP 13B: notations such as "hard," "soft," "tough," rubbery," and "firm" may be used to convey some idea of cake consistency.

A drilling rig 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.

A fitting placed in the blowout preventer stack to provide space between preventers for facilitating stripping operations, to permit attachment of choke and kill lines, and for localizing possible erosion by fluid flow to the spool instead of to the more expensive pieces of equipment.

The drawworks drum. Also a casinghead or drilling spool.; to wind around a drum

2. a device for the separation of various particles from a drilling fluid, most commonly used as a desander. The fluid is pumped tangentially into a cone, and the fluid rotation provides enough centrifugal force to separate particles by mass weight.

A drilling bit made of two, three, or four cones, or cutters, that are mounted on extremely rugged bearings. the surface of each cone is made of rows of steel teeth or rolls of tungsten carbide inserts. Also called rock bits.

A chemical compound of calcium, sulfur, and oxygen. Although sometimes considered a contaminant of drilling fluids, it may at times be added to them to produce certain properties. Like calcium carbonate it forms scales in water-handling facilities, which may be hard to remove. See gypsum.

A compound in which chromium has a valence of 6. Chromate may be added to drilling fluids either directly or as a constituent of chrome lignites or chrome lignosulfonates. In certain areas, chromate is widely used as a corrosion inhibitor, often in conjunction with lime.

Barium sulfate; a mineral frequently used to increase the weight or density of drilling mud. Its relative density is 4.2 (or 4.2 times denser than water). See barium sulfate, mud.

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

A complex, non-Newtonian fluid in which the shear force is not proportional to the shear rate. Most drilling muds are plastic fluids.

Dissolved calcium ions in sufficient concentration to impart undesirable properties, such as flocculation, reduction in yield of bentonite, and increased fluid loss, in a drilling fluid. See also calcium carbonate, calcium sulfate, gypsum.

A drilling mud in which the continuous phase is water. In water-gas muds, any additives are dispersed in the water. Compare oil-base mud.

The power supplied to a drilling rig by diesel engines driving electric generators; used widely.

1. to collect a mass of sticky consolidated material, usually drill cuttings, on drill pipe, drill collars, bits, and so forth. A bit with such material attached to it is called a balled-up bit. Balling up is frequently the result of inadequate pump pressure or insufficient drilling fluid.

A drilling mud that contains entrained formation gas, giving the mud a characteristically fluffy texture. Then entrained gas in not released before the fluid returns to the well, the weight or density of the fluid column is reduced. Because a large amount of gas in mud lowers its density, gas-cut mud must be treated to reduce the chance of a kick.

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. This procedure is necessary when a kick is being circulated out of a well. See choke manifold.

A well drilled to (1) obtain a water supply to support drilling or plant operations, or (2) obtain a water supply to be used in connection with an improved recovery program.

A formation that absorbs drilling fluid as it is circulated in the well. Lost circulation is caused by a thief formation. Also called a thief sand or a thief zone.

See platform rig.

A jackup drilling rig.

See semisubmersible drilling rig.

An arrangement of piping and special valves, called chokes. In drilling, mud is circulated through a choke manifold when the blowout preventers are closed. In well testing, a choke manifold attached to the wellhead allows flow and pressure control for test components downstream.

A centrifugal device for removing very fine particles, or silt, from drilling fluids to keep the amount of solids in the fluid at the lowest possible point. Usually, the lower the solids content of mud, the faster is the rate of penetration. The desilter work on the same principle as a desander. Compare desander.

Commonly called a "V-G meter." A rotational device powered by means of an electric motor or handcrank. Used to determine the apparent viscosity, plastic viscosity, yield point, and gel strengths of drilling fluids. See direct-reading viscometer

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

The component in a blowout preventer that cuts, or shears, through drill pipe and forms a seal against well pressure. Shear rams are used in floating offshore drilling operations to provide a quick method of moving the rig away from the hole when there is no time to trip the drill stem out of the hole.

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

A compliant offshore drilling platform used to drill development wells. The foundation of the platform is a relatively lightweight jacket upon 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.

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 be the smallest size possible that will allow 100 percent flow of the fluid. Also called a shaker.

The fibrous, flaky, or granular material added to a cement slurry or drilling fluid to aid in sealing formations in which lost circulation has occurred. See lost circulation, lost circulation material.

2. the amount of pressure indicated by a drill pipe pressure gauge when drilling fluid is being circulated by the mud pump. Pressure losses occur as the fluid is circulated.

The thickness of drilling mud filter cake

Departure of the wellbore from the vertical, measured by the horizontal distance from the rotary table to the target. The amount of deviation is a function of the drift angle and hole depth. The term is sometimes used to indicate the angle from which a bit has deviated from the vertical during drilling. See drift angle.

A working shift for drilling crew or other oilfield workers. The most common tour is 8 hours; the three daily tours are called daylight, evening (or afternoon), and graveyard (or morning). Sometimes 12-hour tours are used, especially on offshore rigs; they are called simply day tour and night tour.

Light waves shorter than the visible blue violet waves of the spectrum. Crude oil, colored distillates, residuum, a few drilling fluid additives, and certain minerals and chemicals fluoresce in the presence of ultraviolet light. These substances, when present in mud, may cause the mud to fluoresce.

In drilling-fluid terminology, yield point means yield value (which see). Of the two terms, yield point is more common.

A water-base mud in which water is the continuous phase and oil is the dispersed phase. The oil is spread out, or dispersed, in the water in small droplets, which are tightly emulsified so that they do not settle out. Because of its lubricating abilities, an oil-emulsion mud increases the drilling rate and ensures better hole conditions than other muds. Compare oil mud.

A large, high-pressure reciprocating pump used to circulate the mud on a drilling rig. A typical mud pump is a two-cylinder, double-acting or a three-cylinder, single-acting piston pump whose pistons travel in replaceable liners and are driven by a crankshaft actuated by an engine or a motor. Also called a slush pump.

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.

The mass or weight of a substance per unit volume. For instance, the density of a drilling mud may be 10 pounds per gallon (ppg), 74.8 pounds per cubic foot (lb/ft), or 1,198.2 kilograms per cubic meter (kg/m3). Specific gravity, relative density, and API gravity are other units of density.

A method by which a floating offshore drilling rig is maintained in position over an offshore 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 system. A computer to which the system feeds signals directs the thrusters to maintain the rig on location.

A laboratory unit used for evaluating or testing drilling fluids. One gram of material, when added to 350 milliliters of fluid, is equivalent to 1 pound of material when added to one 42-gal barrel of fluid.

Commonly called a "V-G meter." The instrument is a rotational-type device powered by means of an electric motor or handcrank, and is used to determine the apparent viscosity, plastic viscosity, yield point, and gel strengths (all of which see) of drilling fluids. The usual speeds are 600 and 300 revolutions per minute. See API RP13B for operational procedures. Also see direct-indicating viscometer.

Drill pipe, drill collars, casing, or tubing that has inadvertently become immovable in the hole. Sticking may occur when drilling is in progress, when casing is being run in the hole, or when the drill pipe is being hoisted.

To pump drilling fluid into the wellbore while the pipe is being withdrawn to ensure that the wellbore remains full of fluid even though the pipe is withdrawn. Filling the hole lessens the danger of a kick or of caving of the well or the wellbore.

A drilling mud prepared by adding a surfactant to a water-base mud to change the colloidal state of the clay from that of complete dispersion to one of controlled flocculation. Such muds were originally designed for use in deep, high-temperature wells, but their many advantages (high chemical and thermal stability, minimum swelling effect on clay-bearing zones, lower plastic viscosity, and so on) extend their applicability.

An operation made to determine the angle from which a bit has deviated from the vertical during drilling. There are two basic deviation-survey, or drift-survey, instruments: one reveals the drift angle; the other indicates both the angle and the direction of deviation.

1. 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. It prevents the casing from snagging on irregularities in the borehole as it is lowered. A passage through the center of the shoe allow 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 shoe.

A fluid in which the viscosity remains constant for all rates of shear if constant conditions of temperature and pressure are maintained. Most drilling fluids behave as non-Newtonian fluids, as their viscosity is not constant but varies with the rate of shear.

The machine used to impart rotational power to the drill stem while permitting vertical movement of the pipe for rotary drilling. Modern rotary machines have a special component, the rotary or master bushing, to turn the kelly bushing, which permits vertical movement of the kelly while the stem is turning.

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. The substructure is an assembly of heavy beams used to elevate the derrick and provide space to install blowout preventers, casingheads, and so forth. Because the standard derrick must be assembled piece by piece, it has largely been replaced by the mast, which can be lowered and raised without disassembly.

A soluble compound that concentrates on the surface boundary between two substances such as oil and water and reduces the surface tension between the substances. The use of surfactants permits the thorough surface contact or mixing of substances that ordinarily remain separate. Surfactants are used in the petroleum industry as additives to drilling mud and to water during chemical flooding. See micellar-polymer flooding; surfactant mud

A special coupling device inserted one or two joints 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 drilling 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 mat. A float collar also prevents backflow of cement during a cementing operation.

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 above the piston, and expansion of the combustion products imparts power to the piston.

The course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus. Seldom used in open hole, but frequently used in workover operations. Also referred to as "circulating the short way," since returns from bottom can be obtained more quickly than in normal circulation.

One of a series of devices that continuously monitor the level of the drilling mud in the mud tanks. The indicator usually consists of float devices in the mud tanks that sense the mud level and transmit data to a recording and alarm device (a pit-vo