Oil & Gas Glossary 1.0

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.

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

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 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.

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.

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

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

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

The state in fluid dynamics of a fluid in motion is determined by the type of fluid (e.g., Newtonian, plastic, pseudoplastic, dilatant); the properties of the fluid such as viscosity and density; the geometry of the system; and the velocity. Thus, under a given set of conditions and fluid properties, the fluid flow can be described as plug flow, laminar (called also Newtonian, streamline, parallel, or viscous) flow, or turbulent flow.

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 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 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.

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.

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.

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.

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.

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.

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.

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

Formation gas that enters the drilling fluid in the annulus.

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

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

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.

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.

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

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.

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

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

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

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

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

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

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

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

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.

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.

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

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.

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

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

A reduction in the pressure of a fluid caused by its motion against an enclosed surface (such as a pipe). As the fluid moves through the pipe, friction between the fluid and the pipe wall and within the fluid itself creates a pressure loss. The faster the fluid moves, the greater are the losses.

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.

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.

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.

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

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

1. a reduction in the amount of force a fluid exerts against a surface, such as the walls of a pipe. It usually occurs because the fluid is moving against the surface and is caused by the friction between the fluid and the surface.

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

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

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.

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.

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.

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.

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

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.

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.

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

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 ratio of effective permeability to absolute permeability. The relative permeability of rock to a single fluid is 1.0 when only that fluid is present, and 0.0 when the presence of another fluid prevents all flow of the given fluid. Compare absolute permeability, effective permeability.

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.

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).

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.

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

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.

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.

Any type of fluid used in the workover operation of a well. See completion fluid.

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.

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.

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.

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.

A substance, usually a solid, that separates from a fluid because of a chemical or physical change in the fluid. v: to separate in this manner

The unit weight of fluid, e.g., pounds per gallon.

Distance between well head and point to which fluid rises in the well.

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.

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.

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 examination of reservoir fluid in a laboratory under various pressures, volumes, and temperatures to determine the characteristics and behavior of the fluid.

The process of raising or lifting fluid from a well by injecting gas down the well through tubing or through the tubing-casing annulus. Injected gas aerates the fluid to make it exert less pressure than the formation does; consequently, the higher formation pressure forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.

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 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 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.

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.

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.

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.

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.

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.

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.

Refers to a fluid piping system in which flow impinges on a lead-filled end (target) or a piping tee when fluid transits a change in direction.

The ability of a rock to transmit fluid through the pore spaces. - A key influence on the rate of flow, movement and drainage of the fluids. There is no necessary relation between porosity and permeability. A rock may be highly porous and yet impermeable if there is no communication between pores. A highly porous sand is usually highly permeable. A measure of the ease with which a fluid flows through the connecting pore spaces of rock or cement. The unit of measurement is the millidarcy. Fluid conductivity of a porous medium. Ability of a fluid to flow within the interconnected pore network of a porous medium.

Flow of a fluid in which no turbulence occurs. The fluid follows a well-defined, continuous path.

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

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 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 withdrawn after a fracture treatment.

A measure of the ability of a single fluid to flow through a rock when another fluid is also present in the pore spaces. Compare absolute permeability, relative permeability.

The amount of fluid placed in a well to serve as a pad, which is a special fluid used for any special purpose.

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

A liquid, usually salt water or oil, but sometimes mud, used in a well when a packer is between the tubing and the casing. Packer fluid must be heavy enough to shut off the pressure of the formation being produced, must not stiffen or settle out of suspension over long periods of time, and must be noncorrosive.

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.

The level to which fluid rises in a well when the well is shut in.

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 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.

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

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

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

The measured 10-min gel strength of a fluid is the maximum reading (deflection) taken from a direct-reading viscometer after the fluid has been quiescent for 10 minutes. The reading is reported in lb/100 sq. ft. See API RP 13B for details of test procedure.

An instrument that measures fluid pressure and usually registers the difference between atmospheric pressure and the pressure of the fluid by indicating the effect of such pressures on a measuring element (e.g., a column of liquid, pressure in a Bourdon tube, a weighted piston, or a diaphragm).

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

A method of stimulating production by opening new flow channels in the rock surrounding a production well. Often call 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 the formation through the cracks. Sand grains, aluminum 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. See explosive fracturing, hydraulic fracturing.

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.

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.

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 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 fluid moving as a unit in which all shear stress occurs at the pipe wall and hole wall. The stream thus assumes the shape of several telescopic layers of fluid with lowest velocities near the pipe and hole walls and the fastest in the middle.

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.

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.

A phenomenon that often occurs in an injection project in which the fluid being injected does not contact the entire reservoir but bypasses sections of the reservoir fluids in a finger-like manner. Fingering is not desirable, because portions of the reservoir are not contacted by the injection fluid.

A measure of the ability of a single fluid (such as water, gas, or oil) to flow through a rock formation when the formation is totally filled (saturated) with a single fluid. The permeability measure of a rock filled with a single fluid is different from the permeability measure of the same rock filled with two or more fluids. See effective permeability.

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 substance that consists of large molecules formed from smaller molecules in repeating structural units (monomers). In oilfield operations, various types of polymers are used to thicken drilling mud, fracturing fluid, acid, water, and other liquids. See micellar-polymer flooding, polymer mud. In petroleum refining, heat and pressure are used to polymerize light hydrocarbons into larger molecules, such as those that make up high-octane gasoline. In petrochemical production, polymer hydrocarbons are used as a feedstock for plastics.

The force that a fluid (liquid or gas) exerts uniformly in all directions within a vessel, pipe, 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.

One of the two valves in a sucker rod pumping system. It moves with the movement of the sucker rod string. On the upstroke, the ball member of the valve is seated, supporting the fluid load. On the downstroke, the ball is unseated, allowing fluid to enter into the production column. Compare standing valve.

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 device installed on a gas lift mandrel, which in turn is put on the tubing string of a gas lift well. Tubing and casing pressures cause the valve to open and close, thus allowing gas to be injected into the fluid in the tubing to cause the fluid to rise to the surface.

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.

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.

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

A mixture in which one liquid, termed the dispersed phase, is uniformly distributed (usually as minute globules) in another liquid, called the continuous phase or dispersion medium. In an oil-water emulsion, the oil is the dispersed phase and the water the dispersion medium; in a water-oil emulsion, the reverse holds. A typical product of oilwells, water-oil emulsion is also used as a drilling fluid.

The apparent loss of weight of an object immersed in a fluid. If the object is floating, the immersed portion displaces a volume of fluid the weight of which is equal to the weight of the object.

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.

A dilatant, or inverted plastic, fluid is usually made up of a high concentration of well-dispersed solids that exhibits a nonlinear consistency curve passing through the origin. The apparent viscosity increases instantaneously with increasing rate of share. The yield point, as determined by conventional calculations from the direct-indicating viscometer readings, is negative; however, the true yield point is zero.

A mechanical fluid-measuring device that measures by filling and emptying chambers of a specific volume. The displacement of a fixed volume of fluid may be accomplished by the action of reciprocating or oscillating pistons, rotating vanes or buckets, rotating disks, or tanks or other vessels that automatically fill and empty. Also called a volume meter or volumeter.

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.

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.

The yield value (commonly called "yield point") is the resistance to initial flow, or represents the stress required to start fluid movement. This resistance is due to electrical charges located on or near the surfaces of the particles. The values of the yield point and thixotropy, respectively, are measurements of the same fluid properties under dynamic and static states. The Bingham yield value, reported in lb/100 square feet, is determined by the direct-indicating viscometer by subtracting the plastic viscosity from the 300-rpm reading.

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 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.

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 pump a quantity of heavy mud into the drill pipe. Before hoisting drill pipe, it is desirable (if possible) to pump into its top section a quantity of heavy mud (a slug) that causes the level of the fluid to remain below the rig floor so that the crew members and the rig floor are not contaminated with the fluid when stands are broken out.

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.

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 pump consisting of a piston that moves back and forth or up and down in a cylinder. The cylinder is equipped with inlet (suction) and outlet (discharge) valves. On the intake stroke, the suction valves are opened, and fluid is drawn into the cylinder. On the discharge stroke, the suction valves close, the discharge valves open, and fluid is forced out of the cylinder.

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.

The conventional method of formation testing. The basic drill stem test tool consists of a packer or packers, valve 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 dean formation fluids at the end of the test. Analysis of the pressure charts is an important part of formation testing.

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 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.

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

1. a fluid that has been passed through a filter.

The process of filtering a fluid.

See fluid loss.

A gelled viscous fluid

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.

Pull on pipe over and beyond its weight in either air or fluid

Nipple; a device through which fluid is circulated.

Drawn in and transported by the flow of a fluid.

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 well using a pumping unit and rods to lift fluid.

2. any pumping procedure in which fluid is pumped into the well against pressure.

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.

Of uniform or similar nature throughout; a substance or fluid with the same property or composition everywhere.

Abbreviation: radioactive densiometer; fluid-measuring device to measure density.

A device to monitor rate of fluid from the annulus.

2. replacement of one fluid by another in the pore space of a reservoir. For example, oil may be displaced by water.

One-hundredth of a poise; a measure of a fluid's viscosity, or resistance to flow.

A special class of saltwater muds in which sea water is used as the fluid phase.

A choke, used to regulate flow of fluid from a well. Different sizes of beans are used for different producing rates.

1. a condition in which fluid is free-falling down the well at a faster rate than the pumps can handle.

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.

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.

Balls made of nylon, hard rubber, or both and used to shut off perforations through which excessive fluid is being lost.

The reciprocal of viscosity. The measure of rate with which a fluid is continuously deformed by a shearing stress; ease of flowing.

A cutoff pup joint below a packer used as a fluid entry device and/or seal assemblies guide

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.

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.

A synthetic high-molecular-weight polymer of acrylonitrile used primarily as a fluid loss control agent

The amount of the pore volume of a reservoir rock that is filled by water, oil, or gas and measured in routine core analysis.

Removing fluid from the tubing in a well, often by means of a swab, to lower the bottomhole pressure in the wellbore at the perforations and induce the well to flow.

A device used to form a seal around a reciprocating or rotating rod (as in a pump) to prevent fluid leakage. Specifically, the movable part of a stuffing box by which the packing is compressed.

Injection of gases or liquids into a reservoir to force oil toward and into producing wells.

A fluid of vapor composed of hydrocarbons; dry gas is nearly free of oil and gasoline vapor.

1. the pressure maintained on equipment or systems through which a fluid flows.

The pressure gradient (psi/ft) at which the formation accepts whole fluid from the wellbore.

2. difference between the annular velocity of the fluid and the rate at which a cutting is removed from the hole.

Tongs that are actuated by air or hydraulic fluid and are used for making up or breaking out sucker rods

See keyway.

An uncontrolled flow of gas, salt water, or other fluid out of the wellbore and into another formation that the wellbore has penetrated.

Preventing the passage of fluid. A formation may be porous yet impermeable if there is an absence of connecting passages between the voids within it. See permeability.

Abbreviation: sacks; used in drilling and mud reports.

Height of drilling mud in the pits

See floating offshore drilling rig.

Abbreviation: barrels per day; often used in drilling reports

The amount of fluid that can be delivered through a permeable filter medium after being subjected to a set differential pressure for a set length of time.

A semisolid, jelly-like state assumed by some colloidal dispersions at rest. When agitated, the gel converts to a fluid state. Also a nickname for bentonite.

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

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

A reservoir formation in which fluid or plastic masses of rock material originated at unknown depths and pierced or lifted the overlying sedimentary strata.

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

International Association of Drilling Contractors

To begin drilling; to start the hole.

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

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.

The random movement exhibited by microscopic particles when suspended in liquids or gases. It is caused by the impact of molecules of fluid surrounding the particle.

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

Abbreviation: mobile offshore drilling unit.

A hole made by drilling or boring; a wellbore.

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

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

Total pressure exerted in the wellbore by a column of fluid and/or back-pressure imposed at the surface.

1. a condition sometimes encountered in a pumping well when dissolved gas, released from solution during the upstroke of the plunger, appears as free gas between the valves. If the gas pressure is sufficient, the standing valve is locked shut, and no fluid enter the tubing.

A hydrocarbon and water compound that is formed under reduced temperature and pressure in gathering, compression, and transmission facilities for gas. Hydrates often accumulate in troublesome amounts and impede fluid flow. They resemble snow or ice.

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

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.

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

The maximum reading (defletion) taken from a direct-reading viscometer after fluid has been quiescent for 10 seconds. It is reported in pounds per 100 square feet. See API-RP13B for details of test procedure.

The topmost portion of a string of sucker rods. It is used for lifting fluid by the rod-pumping method. It has a uniform diameter and is smoothly polished to seal pressure effectively in the stuffing box attached to the top of the well.

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

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

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

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

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

A manifold system of valves, usually situated at the power source, which may be operated manually (or by remote control) to direct pressurized fluid to closing devices at wellhead.

A fluid-pressure test of the casing. Also called a cup test.

The process whereby a volume of fluid equal to the volume of steel in tubular and tools withdrawn from the wellbore is returned to the wellbore.

Prevention of formation fluid flow by maintaining a hydrostatic pressure equal to or greater than formation pressure

2. a large pipe connected to a process tank to provide a statis head that can absorb surges of fluid from the process tank.

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.

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

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

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

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

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

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

An electric or hydraulic pump on an accumulator that pumps hydraulic fluid under high pressure to the blowout preventers so that they may be closed or opened.

A heavy-duty steel, T-shaped pipe fitting that is screwed or flanged to the top of a pumping well. The polished rod works through a stuffing box on top of the tee and in the run of the tee to operate a sucker rod pump in the well. Pumped fluid is discharged through the side opening of the tee.

Pressure of the annular fluid on the casing at the surface when a well is shut in.

See Newtonian fluid.

See plastic fluid

Laboratory analysis of a core sample to determine porosity, permeability, lithology, fluid content, angle of dip, geological age, and probably productivity of the formation.

To displace the wellbore fluid back to the surface; to displace tubing volume back to the pit.

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).

The erratic, nonlinear flow of a fluid, caused by high velocity. Characterized by random eddying flow patterns superimposed on the general flow progressing in a given direction.

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

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.

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

A check valve in the drill string that will allow fluid to be pumped into the well but will prevent flow from entering the string.

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.

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.

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

A laboratory unit used in pilot testing. One gram or pound equivalent, when added to 350 ml of fluid, is equivalent to 1 lb/bbl.

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 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.

A hydraulically operated tool that is run in above the fishing tool and anchored to the casing by slips. It exerts a strong upward pull on the fish by hydraulic power derived from fluid that is pumped down the fishing string.

That velocity at the transitional point between laminar and turbulent types of fluid flow. This point occurs in the transitional range of Reynolds numbers of approximately 2,000 to 3,000.

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.

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.

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.

A pump with an impeller or rotor, an impeller shaft, and a casing, which discharges fluid by centrifugal force.

A device that increases the pressure on a fluid or raises it to a higher level. Various types of pumps include the bottomhole pump, centrifugal pump, hydraulic pump, jet pump, mud pump, reciprocating pump, rotary pump, sucker rod pump, and submersible pump

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.

The heavy steel member, three-, four-, six-, or eight-sided, suspended from the swivel through the rotary table and connected to the topmost joint of drill pipe to turn the drill stem as the rotary table turns. It has a bored passageway that permits fluid

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.

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

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

When explosives are used to fracture a formation. At the moment of detonation, the explosion furnishes a source of high-pressure gas to force fluid into the formation. The rubble prevent fracture healing, making the use of proppants unnecessary. Compare hydraulic fracturing.

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.

1. a valve used to regulate back-pressure on equipment or systems through which a fluid flows.

See low-solids mud

See low-solids mud

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.

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.

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.

The gathering of pressure data and fluid samples from a formation to determine its production potential before choosing a completion method. Testing tools include formation testers and drill stem test tools.

A special drill stem valve that, when in open position, allows fluid to flow through it, thus allowing the valve to be stabbed into the drill stem.

The difference between two fluid pressures; for example, the difference between the pressure in a reservoir and in a wellbore drilled in the reservoir, or between atmospheric pressure at sea level and at 10,000 feet.

The surface tension occurring at the interface between two liquids that do not mix, such as oil and water. Interfacial tension is caused by the difference in fluid pressures of the liquids.

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

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

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.

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.

A drilling mud to which a polymer has been added to increase the viscosity of the 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 well is considered "stabilized" when, in the case of a flowing well, the rate of production through a given size of choke remains constant, or, in the case of pumping well, when the fluid column within the well remains constant in height.

The pressure lost in a pipeline or annulus due to the velocity of the liquid in the pipeline, the properties of the fluid, the condition of the pipe wall, and the alignment of the pipe. In certain mud-mixing systems, the loss of head can be substantial

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

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.

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

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

Pressure of the annular fluid on the casing at the surface when a well is shut in

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.

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. 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 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.

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.

An opening of a measured diameter that is used for measuring the flow of fluid through a pipe, the orifice must be of smaller diameter than the pipe diameter. It is drilled into an orifice plate held by an orifice fitting.

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.