Glossary

oxygen.

a circular seal common in the oilfield. O-rings may be made of elastomer, rubber, plastic, or stainless steel. To seal properly, they all require enough pressure to make them deform against a sealing surface.

oil and gas; used in drilling reports.

oil- and gas-cut mud; used in drilling reports.

oil and salt water; used in drilling reports.

ocean bottom cable.

the depth at which a borehole is drilled to encounter the formation of interest.

a three-dimensional object shaped like a sphere; however, instead of the sphere’s being round, the sphere’s diameter through its equator is greater than its diameter from pole to pole.

slip at an angle between the dip and the strike in a fault plane.

on-board quantity.

the distance actually measured from the tank bottom or datum plate to the established reference point.

1. values observed at temperatures other than the specified reference temperature. 2. hydrometer readings observed at temperatures other than the specified reference temperature.

those volumes of liquid or gas that are indicated by the register on the meter. Compare true volume.

an extrusive igneous rock that cooled so rapidly that no crystals formed at all, i.e., volcanic glass.

oil-cut; used in drilling reports.

formed as a cold front overtakes a warm front or a stationary front and forces the warm air upward.

a congressional act passed “to assure so far as possible every working man and woman in the nation safe and healthful working conditions and to preserve our human resources.” The OSH Act establishes the Occupational Safety and Health Administration as a federal agency and authorizes it to promulgate, modify, or revoke occupational safety and health standards.

a U.S. government agency that conducts research into the causes of occupational diseases and accidents. It is responsible for administration of the certification of respiratory safety equipment. Address: Department of Labor; 200 Constitution Avenue, NW; Washington, DC 20210; 202-576-6339; 800-321-6742.

a type of offshore seismic surveying in which sensors, rather than being towed as streamers, are attached to a cable that is laid on the bottom of the ocean—that is, an ocean bottom cable (OBC). One advantage of OBC seismic acquisition is that undersea obstacles do not limit seismic acquisition as much as they do for streamer surveys. OBC surveys cost significantly more than conventional streamer surveys; however, they can acquire better seismic images than towed streamers and they are not hampered by subsea obstacles.

see Marine Protection, Research, and Sanctuaries Act of 1973.

a tanker ship that is capable of crossing seas or oceans with its cargo of oil. See tanker.

heavy rock that forms when molten rock cools. Oceanic crust is thin—about 5 to 7 miles (8 to 11 kilometres).

oil-cut mud; used in drilling reports.

see full-bore isolation valve.

Outer Continental Shelf.

an MMS program that generates reports and documents to assist state and local officials in planning for potential impacts resulting from offshore oil and gas exploration, development, and production activities.

rules and regulations, set by the Minerals Management Service (MMS) of the U.S. Department of the Interior, that govern oil operations in U.S. waters on the Outer Continental Shelf. Now supplanted by rules published in the Code of Federal Regulations (CFR), Part 250.

OCS Oil and Gas Information Program.

Outer Continental Shelf Lands Act.

a number in a base 8 numbering system that is represented by the digits 0 through 7. Usually, an octal number is written with the subscript 8 to indicate that it is an octal number. For example, 62708 is an octal number.

a paraffinic hydrocarbon, C8H18, that is a liquid at atmospheric conditions and that has a boiling point of 258°F (125.5°C) at 14.7 pounds per square inch (101 kilopascals).

see octane rating.

a classification of gasoline according to its antiknock qualities. The higher the octane number, or rating, the greater the antiknock qualities of the gasoline.

outer or outside diameter.

a chemical, usually a mercaptan, that is added to natural gas so that the presence of the gas can be detected by the smell.

a device used to impart an odor to natural gas, which is naturally odorless. See odorant.

open flow; used in drilling reports.

see cone alignment.

a type of bit wear in which the cutters on the cones wear in an uneven pattern because of the whirling action of the bit as it drills. Whirling is the motion a bit makes when it does not rotate around the center; instead it drills with a spiral motion.

the side of the drawworks opposite the driller. Compare driller’s side.

a by-product of refining used as boiler fuel, but with value as petrochemical feedstock. Composed mainly of ethane, ethylene, propane, propylene, butane, and hydrogen.

gas used on a lease other than the lease from which the gas was produced.

shut in or temporarily unable to produce (said of a well).

an MMS office located in Herndon, Virginia, that functions as a liaison for agency involvement in international activities and provides policy direction for management of mineral resources on the OCS.

part of the Research and Special Programs Administration under DOT that is charged with determining procedures to ensure pipeline safety.

a method of making up and handling pipe on some drilling rigs. Offline stand building allows crewmembers to make up several stands of drill string and casing and rack them back in a portion the derrick that does not interfere with normal drilling operations. They can make up these stands before they are needed during drilling. In short, the crew uses these made up stands later. As drilling progresses and the need for more stands occurs as the hole deepens, crewmembers can make up the stands into the active drill string. Making up the stands ahead of time speeds up the drilling process.

see floating production and system off-loader.

the amount of distance the rig or vessel is displaced from a centrally located point in a mooring.

rule applied by the courts (especially in states that have adopted nonabsolute ownership views of oil and gas) that states that landowners whose property is being drained by wells on neighboring tracts can protect themselves only by drilling wells on their own and producing oil or gas as quickly as they can. Compare rule of capture.

in transmission chain, a combination of roller link and pin link used when a chain has an odd number of pitches.

a type of chain alignment in which the ends of the shafts, and therefore the sprockets, are not in line with each other. Some sprockets can slide on the shaft, so it is possible for them to be misaligned even if the shafts are not. Offset misalignment alternately stresses the link plates on one side of the chain and then those on the other side. Compare angular misalignment.

a roller cone bit each cone of which displays offset from a center point when a line is extended through the middle of each cone. Offset roller cone bits are usually employed to drill soft formations, because the offset causes the teeth on the cone to gouge and scrape the formation. Gouging and scraping action is required to penetrate soft formations.

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

information obtained from wells that are drilled in an area close to where another well is being drilled or worked over. Such information can be very helpful in determining how a particular well will behave or react to certain treatments or techniques.

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

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 qualified and certified person with marine and drilling knowledge who is in charge of all operations on a MODU.

pipeline construction in water depths of 100 feet (30.5 metres) or more.

an immobile offshore structure from which wells are produced.

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

open hole; used in drilling reports.

a unit for measuring electrical resistance. One ohm is equal to the resistance through which a current of 1 ampere will flow when a potential difference of 1 volt exists across a circuit.

a unit for measuring electrical resistance. If a container with sides of 1 metre each is filled with a solution and a resistance of 1 ohm is measured when a current is passed through the container from one face to the opposite face, the resistivity of the unit volume is 1 ohm Ω metre .

a rule that explains the behavior of electrical flow through a conductor. It is stated as R = E/I , where R = resistance in ohms, E = voltage in volts, and I = current in amperes. The law states that resistance, voltage, and current are interrelated and that modifying or changing one value in an electrical circuit modifies or changes the others. It is therefore used to calculate resistance, voltage, and current in electrical circuits.

of or relating to the resistance of an object or a material in terms of ohms. See ohm.

an electrical instrument that measures the resistance of a conductor in ohms. It may be calibrated to read in ohms or megohms.

in electronics, a measure of the resistance of a wire based on the wire’s gauge and length; in general, the heavier (thicker) and longer the wire is, the more resistance it presents. See mil-foot.

an adjustable resistor (a potentiometer) on an ohmmeter that, when turned, varies the resistance in the meter’s circuit. Varying the resistance adjusts the meter’s pointer to indicate the appropriate resistance of the circuit or component being tested.

ohms per mil-foot.

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

an item of production equipment used to separate liquid components of the well fluid from gaseous elements. Separators are either vertical or horizontal and either cylindrical or spherical. Separation is accomplished principally by gravity, the heavier liquids falling to the bottom and the gas rising to the top. A float valve or other liquid-level control regulates the level of oil in the bottom of the separator.

a type of lubrication in high-speed chain-and-sprocket drives in which a portion of the chain passes through an oil bath (sump), which coats all of the chain on each revolution to lubricate it.

oil that was formerly emulsified in a drilling mud that comes out of the mud and rises to the surface in a mud tank.

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

on an engine, a device through which engine lubricating oil is circulated to reduce its temperature to acceptable levels. Some oil coolers depend on the surrounding air to reduce the temperature, but on most large engines, the oil is circulated through tubes that are surrounded by engine coolant.

see depletion allowance.

on an engine, a device used to remove foreign particles from the engine’s lubricating oil. The engine’s oil pump forces the oil through one or more oil filters. Special elements in the filter trap the particles and prevent them from circulating through the engine and possibly damaging it. Many types of filter are available.

crude oil that is estimated to exist in a reservoir but that has not been produced.

this group has the job of preserving the quality and quantity of oil delivered to the pipeline by the shipper.

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

see operator.

see oil sales outlet.

on an engine, a steel trough-like attachment fitted to the bottom of the engine’s crankcase. The engine’s oil pump picks up oil from the pan and circulates it through the engine.

(slang) the oilfield.

a nonoperating interest in oil and gas from one or more leases that provides its owner a fractional share of the oil and gas produced, free of the costs of production, and that terminates when a specified dollar amount or volume of production has been realized. Oil payments may be created and reserved when a lease or royalty interest is assigned, or they may be carved out of a leasehold or royalty interest and assigned to another party.

a congressional act passed to reduce the risk and damages caused by large oil spills on navigable waters. OPA provides for increased federal response authority, increased civil penalties, emphasis on worst-case contingency planning, and a billion-dollar trust fund to help clean up severe spills. The objective of OPA is to prevent discharges of oil into federal waters from vessels and facilities and to ensure that, if such spills occur, owners and operators have the resources to clean them up.

a loose term for an underground reservoir where oil occurs. Oil is actually found in the pores of rocks, not in a pool.

a device through which engine lubricating oil is circulated to reduce its temperature to acceptable levels. Some oil coolers depend on the surrounding air to reduce the temperature, but on most large engines, the oil is circulated through tubes that are surrounded by engine coolant.

a special pump, usually of the gear type, that moves oil through an engine. The pump’s intermeshing gears rotate to build pressure and circulate the oil.

a type of chain grade.

the ring or rings that are located on the lower portion of a piston. They prevent excessive oil from being drawn into the combustion space during the suction stroke.

a drain located about a foot from the bottom of a stock tank. It is used to take oil out of the tank for sale to a pipeline company or other shipper. The space below the outlet allows room for any remaining sediment and water to settle out of the oil. Also called oil outlet, sales outlet.

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

the amount of oil in the pores of a rock.

a gland arrangement that mechanically or hydraulically seals by pressure. It is used to prevent leakage and waste of gas, oil, or water around a wireline (as when swabbing a well).

a person who gathers data on new oil and gas wells and other industry developments.

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

a shale containing hydrocarbons that cannot be recovered by an ordinary oilwell but that can be extracted by mining and processing. The cost of mining and treatment of oil shale is generally too great to compete with the cost of oilwell drilling.

a film of oil floating on water; considered a pollutant.

a quantity of oil that has leaked or fallen onto the ground or onto the surface of a body of water.

a pool of money set up under OPA to provide for increased federal response to oil spills. A $1 billion oil spill cleanup fund (created with an existing $.05/barrel fee on oil) was established under OPA. Half of the fund can be used for a single spill, and spill victims can use the fund when a spiller’s liability limit has been reached, when the spiller is unknown, or when settlement is delayed.

pumping oil, or a mixture of oil and chemicals, to a specific depth in the well to lubricate stuck drill collars.

see oil seep.

a wire-mesh screen, usually located at the point where the oil pump picks up oil from an engine’s oil pan. The screen traps large foreign particles that may not have settled to the bottom of the pan. Compare oil filter.

the final string of casing set in a well after the productive capacity of the formation has been determined to be sufficient. Also called the long string or production casing.

a ship designed to transport oil, liquefied petroleum gas, liquefied natural gas, or synthetic or substitute natural gas. Tankers with a capacity of 100,000 deadweight tons (90,720 deadweight tonnes) or more are supertankers, either large crude carriers, or ultralarge crude carriers. Also called a tank ship.

a device that shows the temperature of the oil in an engine’s lubricating system. Oil whose temperature is too high cannot lubricate properly.

a condition arising from the latter stages of oil whirl. It is a dangerous condition because the rotor uses up the entire bearing clearance and is in direct metal-to-metal contact that will wear away the bearing rapidly and destroy the rotor if not corrected. See oil whirl.

an uneven oil distribution (oil wedge) around the shaft in the journal bearing.

see petroleum window.

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

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 invert-emulsion mud, oil mud.

on an engine, a canister that has a relatively small amount of lubricating oil in the bottom and which filters air entering an engine. The running engine draws air through the cleaner, where the air passes through an element and over the oil bath. Dust and dirt particles in the intake air are removed by the element and by the oil bath.

see oil-bath air cleaner.

in rotary table assemblies, a compartment in the base of the rotary table assembly that contains oil of a specified weight and viscosity and through which parts of the assembly move to be lubricated.

oilwell casing, tubing, drill pipe, and drill collars.

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.

the water contained in an emulsion of oil and water.

a capacitor whose dielectric (insulating material) is paper but which is enclosed by an oil-filled metal container. See capacitor.

see emulsion, reverse emulsion.

any conventional or special water-base mud to which oil has been added. The oil becomes the dispersed phase and may be emulsified into the mud either mechanically or chemically. Also called oil-emulsion mud.

the plane (typically a zone several feet thick) at which the bottom of an oil sand contacts the top of a water sand in a reservoir, i.e., the oil-water interface.

a contact zone. See oil-water contact.

see emulsion, reverse emulsion.

the boundary between the oil on top and the water below when both are contained in the same vessel.

a hydrocarbon reservoir in which the grains of rock are coated not with water but with oil (occurs only rarely).

see wettability.

the instrument used to grant the rights to develop the resources of the land.

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

a combination of oil and water in which droplets of water are dispersed and suspended in the oil or droplets of oil are dispersed and suspended in the water. Most oilfield emulsions are water-in-oil emulsions; that is, the water is dispersed in the oil. To remove the water from the oil, the emulsion must be treated with heat, chemicals, and/or electricity.

a well from which oil is obtained.

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

any pump—surface or subsurface—that is used to lift fluids from the reservoir to the surface. See hydraulic pumping, submersible pump, sucker rod pumping.

a family of chemically active, open-chain hydrocarbons with one carbon-carbon double bond, having the general formula CnH2n. Ethylene and propylene are olefins.

the units in a refinery that produce ethylene and propylene, both for the polymer units (to make polyethylene and polypropylene) and for sale to other chemical and plastics producers.

descriptive of or relating to a tool that is placed, or a technique that is occurring, at or near the bottom of a borehole. For example, a bit is on bottom and drilling.

when a drill ship or barge is on the drill site.

the measurable or estimatable materials—including water, oil, slops, oily residue, oil/water emulsion, sludge, and sediment—remaining on board in vessel cargo tanks and pipelines prior to loading.

see cone alignment.

present on a ship or rig deck and exposed to weather.

gas used in the operation of the lease from which the gas was produced.

see mainline plant.

in process control, a method that uses discrete devices to turn operating devices on or off. These discrete devices include switches that only have two distinct states or conditions.

a tool used to open or close a downhole valve; a tool used to set or release a downhole tool, such as a retrievable bridge plug.

a training level achieved by any employee who has been HAZWOPER trained to assume command of an emergency response situation. On-scene incident commanders must know and be able to implement the employer’s emergency response plan; know how to implement the employer’s incident command system; know and understand the hazards and associated risks for employees working in chemical protective clothing; know how to implement the local emergency response plan; know of the state emergency response plan and of the federal regional response team; and know and understand the importance of decontamination procedures.

1. of a pump or pump station, moving oil by pumping. 2. of a gas processing plant or refinery, in operation or running.

of a tank, open to pump suction.

of a well, being pumped by a beam pumping unit.

said of a person speaking on a two-way radio or a telephone.

of a tank, being emptied into a pipeline.

of a well, being pumped.

said of any pressure-tight vessel or container when the internal pressure is lower than atmospheric pressure.

a storm with a 1/100  probability of occurrence in any year.

a usually toll-free number that a person preparing to excavate near a buried cable or pipeline can call and obtain information about the depth and course of the cable or line so as not to inadvertently cut or puncture the cable or line.

see jet deflection bit.

a pattern of drum spooling in which the wire rope is controlled by grooves to move parallel to drum flanges for 70 to 80 percent of the circumference and then to cross over to start the next wrap.

said of a tool or device that is placed in a well and is not retrievable.

see check valve.

in mathematics, the column of numbers written in the far right-hand column in a group of numbers having more than one digit. For example, in the number 3,583, three is in the ones column. It is a way of denoting that the number 3,583 contains 3 ones. In addition, 3,583 contains 8 tens, 5 hundreds, and 3 thousands. Numbers with only one digit have only a ones column.

oolitic; used in drilling reports.

an ovoid, sandlike particle that is formed when calcite accretes on a smaller particle.

rounded sandlike grains of calcite.

operational amplifier.

Oil Pollution Act of 1990.

the quality or state of being opaque. In paint technology, opacity is a measure of the hiding power of the paint.

Organization of Petroleum Exporting Countries.

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

1. in an electrical circuit, a phenomenon that occurs when a component, such as a wire, breaks or otherwise fails so that the component can no longer carry current. For example, a broken wire in a circuit causes an open circuit. 2. a design that allows a diver to expel all used air directly into the water and avoid rebreathing exhaled carbon dioxide. The open-circuit regulator reduces the air pressure in the tanks to a diver’s ambient pressure, so air can be breathed with no resistance and exhaled air can be expelled into the water.

motor enclosure that allows ample outside air to move through the motor to cool it while affording protection against mild weather conditions. The angle of protection is 15° from the vertical.

the theoretical maximum capacity of a gas well as determined by a test conducted under limiting conditions. The method of determining this potential varies from state to state.

a test made to determine the volume of gas that will flow from a well during a given time span when all surface control valves are wide open.

a petroleum-bearing rock with good porosity and permeability.

1. any wellbore in which casing has not been set. 2. open or cased hole in which no drill pipe or tubing is suspended. 3. the portion of the wellbore that has no casing.

a line drawn on a chart that represents an area of equal barometric pressure (an isobar) that does not assume a circular shape and therefore does not indicate circulation around a center of low pressure. Compare closed isobar.

a control system that does not incorporate automatic feedback; instead, the system uses manual adjustments to maintain the desired function.

a relatively small calibrated tank, open to the atmosphere. Often used to prove meters at loading racks. In use, the meter to be proved is set at zero and the prover tank is filled to a calibrated height while the meter registers the amount of liquid flowing through it. When the tank is filled, the calibrated volume in it is compared to the volume the meter registered. If the meter is inaccurate, it is adjusted or a factor is used to compensate for the inaccuracy.

a diving life-support system in which the diver’s exhalation is vented completely to the water.

see demand regulator.

a road crossing in which the pipeline ditch cuts through the road instead of being bored under it. An open-cut crossing is generally used in sparsely populated areas where the right-of-way crosses little-used dirt or gravel roads. Open-cut crossings are more convenient than bored crossings and also hold down costs.

a method of preparing a well for production in which no production casing or liner is set opposite the producing formation. Reservoir fluids flow unrestricted into the open wellbore. An open-hole completion has limited use in rather special situations. Also called a barefoot completion.

the procedure of recovering lost or stuck equipment in an uncased wellbore.

any log made in uncased, or open, hole.

an electronic device that increases, or amplifies, a signal without feedback from any part of the circuit. See feedback.

the measurement in a tank before a delivery or receipt. Compare closing gauge.

the measurement in a tank before a delivery or receipt.

the ratio between the hydraulic pressure required to open the preventer and the well pressure under the preventer’s packing device or ram.

see bottom plug, wiper plug.

in computer science, any one of the quantities entering into or arising from an operation. See operation.

see joint operating agreement.

see operator.

the condition of a vessel engaged in drilling operations where drilling and/or associated operations are proceeding with the drilling risers connected.

the percentage of time equipment performs the function for which it is designed.

see leasehold interest.

in a blowout preventer stack, the amount of hydraulic pressure supplied by the blowout preventer control unit that is required to open and to close a blowout preventer. See blowout preventer control unit.

tension set in mooring lines at which a rig or vessel will operate after anchors are proof-loaded.

in computer science, a process or procedure that obtains a unique result from any permissible combination of operands. See operand.

an electronic device that increases the magnitude or power level of an electric current (an amplifier) and that has high direct-current stability and high immunity to oscillation, which is achieved by a high amount of negative feedback in the circuit in which the amplifier is installed. See negative feedback.

on a semisubmersible drilling rig, the draft that yields the best motion characteristics when the rig is in the drilling mode with a maximum deck load. See draft.

the person or company, either proprietor or lessee, actually operating an oilwell or lease, generally the oil company that engages the drilling, service, and workover contractors. Compare unit operator.

Office of Pipeline Safety.

an optical plummet or a theodolite equipped with a precision level. See theodolite.

an instrument that determines the temperature of a very hot surface from its incandescent brightness; the image of the surface is focused in the plane of an electrically heated wire, and current through the wire is adjusted until the wire blends into the image of the surface. Also known as disappearing filament pyrometer.

a device in which a moving spot of light controlled mechanically or electronically scans a meter chart. The reflected light generates signals that are used to process information from the chart.

the manner of planning and drilling a well so that the most usable hole will be drilled for the least money.

that rate of flow of fluid from a well that will provide maximum ultimate recovery of fluid from the reservoir.

the amount of water used to give a cement slurry the best properties for a particular application.

an instruction that performs the logical operation “or” on a bit-by-bit basis for its two or more quantities entering into or arising from an operation (its operand), usually storing the result in one of the operand locations. See operand.

a phenomenon that occurs when paint is improperly sprayed onto a surface. It is characterized by a pockmarked appearance that resembles an orange peel; it occurs when the paint fails to achieve a level and uniform surface. See banana peel.

federal regulation adopted in August 1987 to provide mechanisms for resolving take-or-pay liability of gas producers.

the coordinate obtained by measuring parallel to the y-axis. Compare abscissa.

of or relating to the geologic period from approximately 500 million to 430 million years ago, during the early part of the Paleozoic era, or relating to the rocks formed during this period.

a mineral from which a valuable substance such as a metal can be extracted.

chemical compounds that contain carbon atoms, either in straight chains or in rings, and hydrogen atoms. They may also contain oxygen, nitrogen, or other atoms.

rock materials produced by plant or animal life (coal, petroleum, limestone, and so on).

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

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

a clay treated so that it is not hydrophilic for use in oil muds. Also called amine clay, organic clay.

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

turned in a particular direction. See orientation.

a core obtained from a precise angle or direction in a formation to obtain information about formation dip and strike, the direction of deposition, the direction of permeability, the direction of fluid migration, and hole deviation. The location of the core has been pinpointed, or oriented, in the reservoir.

drill pipe run in a well in a definite position, often a requisite in directional drilling.

a perforating technique that uses sensing instruments in a perforating gun to make perforations in a specific direction. It is often used in completions involving multiple production casing strings to perforate one string without damaging another. Also called directional perforating.

1. an opening, mouth, or a vent. 2. an open space allowing passage, such as an aperture, hole, mouth, opening, outlet, or vent. 3. an opening of a measured diameter that is used for measuring the flow of fluid through a pipe or for delivering a given amount of fluid through a fuel nozzle. In 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.

a device specifically designed to hold an orifice plate in a meter installation. Several types are available, including the flange, junior, simplex, and senior.

a factor used in the calculation of gas volume flow through an orifice meter. Mathematical accounting for variations in pressure, temperature, density, and so on, of a gas as it flows through an orifice of a particular size.

an instrument used to measure the flow of fluid through a pipe. The orifice meter is an inferential device that measures and records the pressure differential created by the passage of a fluid through an orifice of critical diameter placed in the line. The rate of flow is calculated from the differential pressure and the static, or line, pressure and other factors such as the temperature and density of the fluid, the size of the pipe, and the size of the orifice.

a circular chart with a printed scale on which are recorded time, static and differential pressure, and sometimes temperature.

see meter installation.

see pressure tap.

a sheet of metal, usually circular, in which a hole of specific size is made for use in an orifice fitting.

the pressure differential that occurs across an orifice plate.

a device (a valve) that controls the flow of fluid in a line, which contains an opening (an orifice) the size of which is varied by a mechanically, hydraulically, pneumatically, or electrically operated piece that contacts the orifice.

a device, including orifice plates, a hose, and a manometer, used to measure the gas flow from a well. Static pressure differences measured on either side of a sharp-edged orifice are converted to flow values. It is used primarily for estimating the amount of gas flowing during a drill stem test, when a high degree of accuracy is not required.

on a flanged fitting, the threaded holes on either side of the orifice plate. Small pipes are screwed into the taps to connect the fitting to a flow recorder. Taps are used so pressure differential on either side of the plate can be measured and recorded. See orifice meter.

oxidation-reduction potential.

oil rig quality.

a light-colored feldspar mineral (KA1Si3O8), common in granite.

the process by which the geometric distortions of an aerial or satellite photographic image of a land area are accounted for and rectified (corrected). Because irregularities occur in the images, especially where mountains and plateaus exist, the images must be corrected to give an accurate picture of the terrain.

an even, rhythmic change in value, position, or state around a mean, or average, value.

an electronic circuit that produces high frequencies without rotational force being required. Oscillator voltages produce output current that periodically reverses, or oscillates.

a test instrument that uses a cathode-ray tube to make visible on a fluorescent screen the instantaneous values and waveforms of electrical quantities that rapidly vary as a function of time or other quantity.

Occupational Safety and Health Act of 1970.

Occupational Safety and Health Administration.

passage of a pure liquid, such as water, into a solution, such as salt water, through a membrane that allows the water to pass through but not the salt. See reverse osmosis.

the force that moves a liquid through a barrier; it is powerful enough to raise sap from the roots to the tops of trees.

before the advent of measurement while drilling (MWD) tools and techniques, a device used by directional drillers to determine which way to turn deflection tools to get the desired drift angle in a hole. This device comprises a protractor and various straight-edged scales that pivot around the protractor to figure the drift angle.

a bit that is no longer of the proper diameter.

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

see ullage.

a graduated plumb bob that is attached to a metal gauge tape and that is of sufficient weight to keep the tape taut.

a measure of the volume of liquid in a storage tank determined by measuring from a reference point at the top of the tank to the surface of the liquid in the tank and subtracting that measurement from the gauge height of the tank. Used when direct measurement of the liquid level is not possible. Also called ullage gauge.

a measure of the space between the top of the liquid in a tank and the reference point on the hatch. The liquid level in the tank is determined by subtracting the outage measurement from the gauging height of the tank.

a method of measuring the liquid level in a tank by measuring the space between the top of the liquid in a tank and the reference point on the hatch. The liquid level in the tank is determined by subtracting the outage measurement from the gauging height of the tank. Compare innage tape-and-bob procedure.

away from the center of the hull or toward the side of an offshore drilling rig.

part of a formation exposed at the earth’s surface. v: to appear on the earth’s surface (as a rock).

horizontal representation of the rock types at the surface or just beneath the layer of soil.

in the telescopic joint of a marine riser assembly, a pipe that attaches to the top joint of the marine riser assembly and to which are attached the riser tensioner lines. The inner barrel of the telescopic joint moves up and down within the outer barrel as the floating offshore rig heaves.

the main bearings of a roller cone bit that reside inside the largest part of the cone. The outer bearings are either roller bearings or journal bearings. Compare inner bearings.

the land seaward from areas subject to state mineral ownership to a depth of roughly 8,000 feet (2,500 metres), beyond which mineral exploration and development are not, at present, feasible. Boundaries of the OCS are set by law. For example, Louisiana owns 3 miles (4.8 kilometres) seaward from the shoreline. In general, the term is used to describe federally controlled areas.

congressional act that authorizes the secretary of the interior to grant mineral leases and to regulate oil and gas activities on OCS lands.

see OCS orders.

distance across the exterior of a circle, especially in the measurement of pipe. Also called outside diameter.

the flow system of a well between the bottom of the hole and the storage tanks.

taken at the level of the bottom of the tank outlet (either fixed or swing pipe) but not higher than 1 metre (0.9144 yard) above the bottom of the tank.

a result that differs considerably from the main body of results in a set.

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

a signal transmitted from a device.

equipment in a PLC system that sends commands in the form of current, voltage, or switch closure to operate other equipment. The output module receives its commands from the PLC processor in the form of digital signals. See programmable logic controller.

the transmission shaft nearest the machinery to be driven. It is driven by the input shaft driven near the power source.

a projecting member run out at an angle from the sides of a portable mast or a land crane to the ground to provide stability and to minimize the possibility of having the mast or the crane overturn.

1. for fluid, to fall down a well faster than it can be pumped. 2. to try to pull out of the well faster than the wireline tools are being blown upwards by unexpected pressure. 3. to attempt to pump out a gas influx before the expansion of gas reduces pressure enough to allow the well to kick.

see external cutter.

the distance across the exterior circle, especially in the measurement of pipe. See diameter.

see water outlet.

an outward force created along a centerline drawn through a cone (the axis) as a roller cone bit rotates.

sediment deposited by meltwater streams beyond an active glacier.

a pump station where one or more tanks are floating on the line. See floating tank.

the extent to which the hydrostatic pressure of the mud column exceeds formation pressure.

the weight (density) of a drilling fluid that develops more hydrostatic pressure than that which is required to equal (balance) formation pressure.

drilling in which the hydrostatic pressure of the mud column exceeds formation pressure.

in a diverter system, a pipe (a line) that is permanently attached to side outlets on the diverter’s housing. Usually, two vent lines are provided so that well fluids can be safely vented away from the rig, regardless of the wind’s direction. See diverter.

that pressure above ambient, at which a breathing gas supply must be supplied to the helmet/mask so that the diver will have a sufficient supply of gas.

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

the pressure exerted by the rock strata on a formation of interest. It is usually considered to be about 1 pound per square inch per foot (22.621 kilopascals per metre).

capacity beyond what is normal, allowed, or desirable.

in regard to land, to convey (intentionally or from ignorance) a larger fraction of interest in property than the owner actually has a right to convey.

the amount by which the actual volume that has passed through the meter exceeds the indicated volume registered by a meter. See absolute error.

the effluent of a cone-shaped centrifuge that passes up the inside of the cone and leaves through the vortex finder.

a pipe installed at the top of a tank to enable the liquid within it to be discharged to another vessel when the tank is filled to capacity.

an excess quantity of fluid used to push acid out of the tubing or casing when an acid mixture is put into a well, thus directing the acid to the desired place in the well.

a hole whose diameter is larger than the diameter of the bit used to drill it. An overgauge hole can occur when a bit is not properly stabilized or does not have enough weight put on it.

ability of a weight on the end of a hoist line to unwind cable from the drum when the brake is released.

the vapor stream leaving the top of a tower, column, or vessel.

in distillation, the product that condenses above the fractionation column.

in distillation, the stream of products that condense above the fractionating column.

in excess of what is necessary or appropriate to kill a well kick.

see abnormal pressure.

said of a well that has produced more than its allowable.

to pull on pipe with enough force to exceed the pipe’s weight.

when applied to metering, indicates that the maximum permitted flow of the meter is being exceeded.

the amount by which the indicated volume registered by a meter exceeds the actual volume that has passed through the meter. Determined by means of a suitable standard device. Compare underregistration.

an interest carved out of the lessee’s working interest. It entitles its owner to a fraction of production free of any production or operating expense, but not free of production or severance tax levied on production. An overriding royalty may be created by grant or by reservation. Commonly, an override is reserved by the assignor in a farmout agreement or other assignment. An override’s duration corresponds to that of the lease from which it was created.

1. a special clutch that permits a rotating member to turn freely under certain conditions but not under others. 2. a clutch that is used in a starter and transmits cranking effort but overruns freely when the engine tries to drive the starter.

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

a special type of engine governor that prevents an engine from running too fast (overspeeding) by shutting down the engine if it overspeeds. See governor.

see overspeed governor.

a special type of engine governor that prevents an engine from running too fast and possibly destroying itself if the regular governor fails.

an engine’s running beyond the maximum speed for which it was designed. Overspeeding an engine can severely damage it.

when spray painting, the paint that misses the surface to be coated.

a low-dip angle (nearly horizontal) reverse fault along which a large displacement has occurred. Some overthrusts, such as many of those in the Rocky Mountain Overthrust Belt, represent slippages of many miles.

adding too much chemical in batch treating, resulting in an emulsion that is very difficult to break.

a rock fold that has become slanted to one side so that the layers on one side appear to occur in reverse order (younger layers beneath older).

see absolute ownership.

a chemical process in which oxygen combines with a compound and causes the compound to lose electrons and gain a more positive charge. For example, when exposed to air (which contains about 21 percent oxygen), iron rusts, which means that part of the iron chemically combines with the oxygen in the air and oxidizes, or becomes rusty. The rust is typically a red iron oxide, which gives iron rust its characteristic color.

the difference in voltage shown when an insert electrode is immersed in a reversible oxidation-reduction system. It is the measurement of the system’s state of oxidation. Also called Eh, redox potential.

a chemical compound in which oxygen is joined with a metal or a nonmetal.

a thin layer of material (a film) that is coated with metallic oxides and is often used as a dielectric in capacitors. See capacitor, dielectric.

1. to combine with oxygen. 2. to remove one or more electrons from an atom, ion, or molecule.

a process where steel is cut using an electric arc, oxygen, and a consumable rod. This method of cutting can be very fast and precise when performed by a skilled diver. Also called underwater burning.

the process of burning a fuel using pure oxygen instead of air as the primary oxidant. Because the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Oxy-combustion is mainly used in welding and cutting metals, especially steel, because oxy-combustion creates higher flame temperatures than can be achieved with an air-fuel flame.

see acetylene welding.

a nonmetallic element constituting 21 percent of the atmosphere by volume that occurs as a diatomic gas, O2, and in many compounds such as water and iron ore. It combines with most elements, is essential for plant and animal respiration, and is required for nearly all combustion.

the eating away of metallic surfaces that occurs when the metal is exposed to oxygen. Oxygen corrosion is accelerated when the metal is exposed to oxygen in the presence of water. In the oilfield, oxygen corrosion is often characterized by red iron oxide (rust) appearing on the surface of the corroded tool.

a harmful reaction experienced by divers breathing extremely high partial pressures of oxygen. Divers may suffer from two forms: one affects the central nervous system; the other affects the pulmonary muscles. Because of these dangers, pure oxygen is not used as a breathing medium below 50 feet (15.2 metres) in commercial operations.

a corrosion cell formed by differing concentrations of oxygen in an electrolyte.

having or containing oxygen.

combining or supplying with oxygen.

ounce.

at ground level, one of the primary ingredients in smog and a poisonous form of pure oxygen. Smog ozone is created by sunlight acting on nitrogen oxides and volatile organic compounds in the air. Ozone high in the atmosphere forms the earth’s main shield against the sun’s ultraviolet radiation.