Glossary

volt.

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

an opening at floor level in a side of a derrick or mast. The V-door is opposite the drawworks and is used as an entry to bring in drill pipe, casing, and other tools from the pipe rack. The name comes from the fact that on the old standard derrick, the shape of the opening was an inverted V.

see direct-indicating viscometer, Fann V-G™ meter.

volt-ampere.

volts, alternating current.

on a dry air cleaner on an engine, a special valve that automatically opens to dump dust accumulated in the chambers of the air cleaner.

1. a space that is theoretically devoid of all matter and that exerts zero pressure. 2. a condition that exists in a system when pressure is reduced below atmospheric pressure.

a device used to prevent a vacuum from occurring in a tank, vessel, piping, and so on.

a device in which entrained gas in the mud returning from the wellbore is removed from the mud by the action of a vacuum inside a tank. The gas-cut mud is pulled into the tank, the gas removed, and the gas-free mud discharged back into the mud pits. Also called a centrifugal degasser.

an instrument used on gas or gasoline engines to indicate the performance characteristics and load.

any pressure below atmospheric pressure.

a device that measures the saturation, or the amount, of each fluid in a core sample by distilling the fluid from the core with heat at pressure below atmospheric. The vacuum retort is used to measure saturation on whole core samples.

see electron tube.

the tendency of elements to form compounds through a shift of electronic structure.

an effect that causes emulsions and colloids to separate; it is particularly prevalent in emulsions and colloids that contain a large number of high-valence ions. See valence.

a single electron or one of two or more electrons in the outer shell of an atom that is responsible for the chemical properties of the atom. Valence electrons of one atom combine with the valence electrons of other atoms to form many compounds. For example, when the valence electrons of sodium and chlorine combine, common table salt, or sodium chloride (NaCl), is formed.

the number of electrons of an element involved in forming a compound.

see thalweg.

1. a device used to control the rate of flow in a line to open or shut off a line completely, or to serve as an automatic or semiautomatic safety device. Those used extensively include the check valve, gate valve, globe valve, needle valve, plug valve, and pressure relief valve. 2. British term for electron tube. See electron tube.

in a two-diaphragm, four-chamber diaphragm displacement meter, the linkage that uses the motion from the crank to slide D-shaped valves over the three ported seats to fill and empty the four measurement chambers alternately.

the phenomenon that occurs during the operating cycle of an engine in which both the intake and exhaust valves are open at the same time. Valve overlap occurs in a four-strokes-per-cycle engine at the end of the engine’s exhaust stroke and the beginning of the intake stroke. Both valves being open allow exhaust gases to finish leaving the cylinder and, at the same time, allow inlet air to begin filling the cylinder. Valve overlap ensures that the cylinder is completely filled with fresh air; also, the cool incoming air helps cool the hot exhaust valve.

an attachment that fits on a valve actuator, and which assures that the valve stem’s movement follows the demands of a controller with great accuracy by acting as a force amplifier between the controller and the actuator. Valve positioners are used where friction occurs between valve stem and packing and when the force of flowing fluid on the valve plug causes unsatisfactory response.

the machined tapered opening on the fluid-end body of a mud pump that holds the valve seat.

a tapered metal ring that seals against the valve pot and holds a valve in a mud pump.

a tray installed in an absorber tower or fractionating column, similar to a bubble-cap tray except that the passageways permitting gas flow upward through the tray possess valves that reduce the size of the passages when the flow rate is reduced. Valve trays are more common than bubble-cap trays, because they are more efficient and less expensive. See bubble-cap trays, tower with trays.

a wind-speed measuring device that consists of flat blades (vanes) mounted in a circle so as to rotate under the action of the wind.

a substance in the gaseous state that can be liquefied by compression or cooling. The terms vapor and gas are technically interchangeable.

losses that occur to hydrocarbon liquids as the lighter components vaporize and leave the liquid.

the existence of a substance in the gaseous state.

see bubble point.

the pressure exerted by the vapor of a substance when the substance and its vapor are in equilibrium. Equilibrium is established when the rate of evaporation of a substance is equal to the rate of condensation of its vapor.

system or method by which vapors are retained and conserved.

1. in petroleum refining, a process unit consisting of a scrubber and a compressor. It is designed to recover petroleum from hydrocarbon vapors and safely to handle toxic gases produced from some wells. 2. in production operations, equipment designed to recover light ends that are released from oil in a stock or other tank.

see condensation trail.

the partition coefficient, usually designated as K, which is equivalent to y/xm, where y is the mole fraction of a given component in the vapor phase that is in equilibrium with x, the mole fraction of the same component in the liquid phase. K is a function of temperature, pressure, and composition of the particular system.

a tank of conventional shape intended primarily for the storage of volatile liquids such as gasoline and so constructed that it can withstand pressures differing only slightly from atmospheric. Such tanks are equipped with special devices that permit gauging without opening the tank to the atmosphere.

1. the act or process of converting a substance into the vapor phase. 2. the state of substances in the vapor phase.

the act of a liquid turning into a vapor.

not susceptible to or affected by vapors. For example, an electrical switch is made vaporproof so that a spark issuing from it will not cause an explosion in the presence of combustible gases (vapors).

volt-ampere reactive.

a Spanish unit of measurement, equal between 31 and 34 inches (78.74 and 86.36 centimetres). In Texas, it is equal to 33.33 inches (84.65 centimetres). Though an ancient unit of measurement, varas often show up on old survey reports in Texas and the southwestern U.S.

volt-ampere reactive in circuits with capacitors.

volt-ampere reactive in circuits with inductors. Also abbreviated VAR L.

see measurand.

see sample rota­meter float.

a ram blowout preventer that contains blocks (rams) that can close and seal on a range of pipe sizes-for example, from 3H- to 5-inch (89- to 127-millimetre) pipe. Variable bore rams contain a large reserve of rubber in the ram block that specially designed antiextrusion plates force into sealing contact with smaller sizes of pipe. The antiextrusion plates also support the excess rubber when wellbore pressure is applied.

a capacitor that is constructed of stationary and movable plates. A shaft attached to the movable plate assembly is turned to rotate the movable plates in and out of the stationary plates. As the area of the movable plates increases or decreases within the stationary plates, the capacity varies. See capacitor.

a clearance pocket that can be adjusted to provide varying amounts of clearance space in a compressor cylinder.

the annual cost of operating and maintaining the system as well as fuel, gas loss, and unaccounted-for gas costs.

on a floating offshore rig or ship, expendable items that increase or decrease the vessel’s weight as they are used and replaced.

in process control, the amount a process variable can change its chemical or physical composition because of changes in pressure, temperature, or volume.

a type of ram blowout preventer that has rams that can close on drill pipe of more than one size. For example, the ram preventer can be fitted with a set of variable rams that can properly close not only on 4-inch drill pipe, but also on 4H- and 5-inch drill pipe. If a drill string is made up of more than one size of pipe, variable rams eliminate the need for having more than one set of conventional pipe ram preventers available for the pipe sizes being run.

of an electric motor when the motor’s speed can be sped up or slowed down by varying the voltage or frequency of the electricity powering the motor.

a wind, generally light, or slow in speed, that frequently changes the direction in which it is blowing.

see rotameter.

the angle by which a compass needle deviates from true north.

volt-ampere reactive in circuits with inductors. Also abbreviated VARH.

variable bore ram.

vertical center of gravity.

volts, direct current.

the representation of a quantity that gives the quantity both magnitude and direction and the components of which transform from one coordinate system to another in the same manner as the components of a displacement. In short, a vector is a quantity-for example force or velocity-made up of components of both direction and magnitude.

the adding together of the components that constitute a vector. See vector.

an elastomer seal energized by pressure. While it is circular in shape, the seal has a V-shaped cross section. See O-ring.

vessel experience factor.

a method of detecting gas leaks in a line by noting the presence or absence of dead grass or other plants near the line. Natural gas kills plant roots over time.

in paint technology, the liquid phase of a paint that carries all the paint’s constituents.

1. speed. 2. the timed rate of linear motion.

see head.

a type of meter that measures the rate of fluid flow through it to determine the quantity of fluid flowing through it.

a mathematical expression that relates the velocity of the fluid flowing in the meter tube upstream from the orifice to the velocity of the fluid flowing through the orifice.

in fluid measurement, a mathematical representation of fluid flow based on predetermined conditions.

the component of the pressure of a moving fluid that is due to the fluid’s velocity and that is commonly equal to the difference between the impact pressure and the static pressure.

the result of a velocity traverse. When fluid flows in a pipe, the fluid’s velocity is not uniform owing to friction as the fluid moves past the pipe’s walls. With some measuring devices, it is important that the device be placed properly within the flow to obtain accurate measurement. Running a velocity traverse to obtain the profile is necessary to properly place the measuring device. See velocity traverse.

see subsurface safety valve.

the speed at which a fluid moves or passes through an object, related to a Pitot tube.

squeezing of the gas flow.

1. an opening in a vessel, line, or pump to permit the escape of air or gas. 2. a device installed on one end of that portion of a pipeline that crosses under a road. The vent marks the boundary of the highway right-of-way and provides an exit for any fluids should the pipeline develop a leak. It also aids in locating line breaks. v: to open a vessel or line so that air or gas can escape.

an opening in a vessel, line, or pump to permit the escape of air or gas.

the drop in pressure resulting from the increased velocity of a fluid as it flows through a constricted section of a pipe.

a nozzle that, because of the venturi effect, increases the velocity of a fluid flowing through it.

in a fluid flow measuring device such as a venturi tube or a Dall tube, the part of the tube that contains the venturi, which is a constricted section that increases the flow’s velocity. From the velocity increase, the quantity of flow can be inferred. See venturi effect.

a short tube with a calibrated constriction that is used in instruments or devices such as jet hoppers. It was developed to take advantage of the principle that a fluid flowing through a constriction has increased velocity and reduced pressure.

a flowmeter used to determine the rate of flow and employing a venturi tube as the primary element for creating differential pressures in flowing gases or liquids. Compare orifice meter.

an electrical measuring instrument that verifies the presence or absence of current or emf in a circuit. A compass needle and a dashboard ammeter are verification indicators.

an imaginary line at right angles to the plane of the horizon. adj: of a wellbore, straight, not deviated.

the vertical location about which the weight (mass) of an object is centered. VCG can be determined by multiplying each component weight by its height and then summing these values and dividing by the total weight of the object. VCG is often critical to the stability of floating vessels because excessive VCG can cause a vessel to capsize.

a heater-treater whose cylinder stands upright, perpendicular to the ground. See heater-treater.

in crane operations, a method of attaching a sling to a load in which only one sling leg suspends the load.

a change in the configuration of a pipeline whereby the pipe is curved from the horizontal to a 90° vertical run, then curved 90° to a horizontal run, curved again to a 90° vertical, and then curved 90° back to horizontal. The effect is to create turbulence in the fluid flow and distribute the S&W evenly in the flowing stream.

the permeability of a pay zone from the bottom to the top of the zone. Compare horizontal permeability.

a clause in an oil or gas lease that excludes, or releases, unproductive formations from the lease at the end of a specified period.

a view of a well plan that shows the projection of the well on the plane and includes the surface location and the center of the target.

a cylindrical separator standing upright, perpendicular to the ground.

a diagram or plot showing portions of wells passing through a vertical section of the earth, located a given distance and direction from a drilling platform.

a preestablished location in the vertical plane along the tank shell corresponding to a given horizontal station. Compare horizontal station.

in geology, the pressure created by the weight of all the liquid and rock above a given depth.

an H-shaped device that supports a pipeline above the ground. Vertical support members are used in parts of the world where frozen earth prevents normal burial of the line. See lowering-up.

vertical component of mooring line tension.

a method of positioning hydrophones in the ocean.

a large oil company that is involved in all aspects of the oil industry, from exploration and production to transportation and refining.

an anchor type embedded into the seafloor using drag embedment techniques. After the flukes are tripped, the anchor achieves its holding capacity through soil reacting with the flukes. VLAs can withstand high vertical loads.

a condition that brings a lost sense of direction and accompanying dizziness that could cause panic in an inexperienced diver.

a supertanker whose capacity is larger than 100,000 deadweight tons (90,720 deadweight tonnes) but less than 500,000 deadweight tons (453,600 deadweight tonnes). Compare ultralarge crude carrier.

containing small cavities that are visible to the naked eye. A vesicular rock is a rock that contains small cavities.

1. a container used as a structural envelope to provide for functions that include storage, settling, separation, and filtration for liquid and/or vapor. Conditions of vessel use include atmospheric and elevated pressures and temperatures. 2. in nautical terms, virtually any watercraft that is larger than a rowboat, especially a ship or offshore drilling unit.

a calcu­lated factor, based on the experience of recent voyages, that reflects the average difference between vessel and shore measurements in terms of percent.

a phenomenon that occurs in drilling from floating offshore rigs (vessels) in which the vessel on the surface is not located directly above the wellhead on the seafloor. While anchoring and dynamic positioning techniques hold offset to a minimum, a certain amount occurs and subsea equipment must be designed to compensate for offset.

visual flight rules.

see shale shaker.

1. a device, positioned in the drill stem between the bit and the drill collars, that absorbs impact loads and vibration from the up-and-down motion of the drill stem. Vibration dampeners are designed to transmit torque while absorbing reciprocative loads that decrease the efficiency of the drill bit. Also called a Shock Sub. 2. a device affixed to an engine crankshaft to minimize stresses that result from torsional vibration of the crankshaft.

the maximum change in operating output, at any measured value within a specific range, when vibration levels of specified amplitude and range or frequencies are applied to the transducer along specified axes.

short length of flexible hose that absorbs some of the vibrating pulsations that originate in a mud pump. Also called shock hose.

used to indicate the period during which a gas sales contract was made or the well spud date.

viscosity breaking, i.e., economically reducing the viscosity of the light end of a heavy fraction.

a device used to determine the viscosity of a substance. Also called a viscosimeter.

see viscometer.

a measure of the resistance of a fluid to flow. Resistance is brought about by the internal friction resulting from the combined effects of cohesion and adhesion. The viscosity of petroleum products is commonly expressed in terms of the time required for a specific volume of the liquid to flow through an orifice of a specific size at a given temperature.

an index used to establish the tendency of an oil to become less viscous at increasing temperatures. Reference oils are a highly paraffinic Pennsylvania oil, rated 100, and a Gulf Coast naphthenic oil, rated 0.

having a high resistance to flow.

see laminar flow.

in aviation, rules established by the United States Federal Aviation Administration (FAA), that point out the weather conditions under which pilots may fly using only their ability to see outside their aircraft. Although the minimum visibility requirements vary in relation to the type of aircraft and the space in which the aircraft flies, in general, when the visibility drops below 3 miles or 5 kilometres-that is, when a pilot cannot see anything beyond a point 3 miles or 5 kilometres from his or her aircraft, the pilot can no longer fly under VFR. Compare instrument flight rules.

a fluoroelastomer used in the seals installed in equipment exposed to H2S. See fluoroelastomer.

a treatment in which electricity is applied to the soil to melt it.

a method of turning a hazardous substance into a more manageable and less harmful material by heating it to a high temperature, which transforms the hazardous substance into a glass-like material.

see sulfuric acid.

vortex-induced vibration.

vertically loaded anchor.

very large crude carrier.

volatile organic compound.

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

readily vaporized.

those hydrocarbons that are readily vaporized.

a readily vaporized compound composed of carbon-containing molecules derived from living organisms.

the tendency of a liquid to assume the gaseous state.

a limited form of remediation; only the lighter fractions of the oil evaporate.

to become gaseous; to pass off as vapor; to make gaseous or to cause to pass off as vapor.

the scientific study of volcanoes and volcanic phenomena. Also called vulcanology.

the unit of electric potential, voltage, or electromotive force in the metric system. See electromotive force.

an expression of apparent, or total, electric power in which power is the product of volts times amperes.

the reactive power in a circuit carrying alternating current when the product of the root-mean-square value of the voltage, expressed in volts, by the root-mean-square value of the current, expressed in amperes, and by the sine of the phase angle between voltage and current, equals 1. See reactive power.

see multimeter.

potential difference or electromotive force, measured in volts.

the voltage developed across an electrical component or conductor as current flows through component or conductor.

in solid-state electronics, the increase in voltage produced by a transistor.

an electronic device, including certain solid-state diodes, that maintains a given voltage across a circuit within required limits despite variations in voltage or load.

in process control, a four-wire process instrument that converts process variables such as temperature, pressure, level, and flow to a proportional signal of 1 to 5 volts DC. A voltage transmitter does not transmit data as accurately as a current transmitter because wire resistance and electrical interference affects its signal.

see metallic-oxide varistor.

see primary cell.

an instrument used to measure, in volts, the difference of potential in an electrical circuit.

electric current that flows through an electrical circuit in an alternating manner-that is, the current reverses direction in the circuit at regular intervals.

electric current that flows through an electrical circuit in one direction only.

the amount of a substance that occupies a particular space.

in process control, a device attached to a valve in which pneumatic pressure in the relay improves (boosts) the valve’s response time.

the condition in which a liquid is heated and free to expand in all directions. Same as liquid expansion.

the amount, or quantity, of a fluid that passes a point for a given time.

see positive-displacement meter.

in offshore drilling from floating rigs, the volume of water the rig displaces as it floats in the water; the underwater volume of the rig. It is usually expressed in cubic metres or cubic feet.

same as mole percent.

a pressure vessel connected to the outlet of a gas supply and used as a gas reservoir.

see positive-displacement meter.

of or relating to measurement by volume.

an equation that can be used to make calculating the maximum amount of casing pressure to expect when a gas kick is circulated out of a shut-in well more accurately reflect reality.

the weight or density of a substance based on its volume (the amount of space it occupies).

1. actual volume of fluid put out by a pump, divided by the volume displaced by a piston or pistons (or other device) in the pump. Volumetric efficiency is usually expressed as a percentage. For example, if the pump pistons displace 300 cubic inches (4,916 cubic centimetres), but the pump puts out only 291 cubic inches (4,769 cubic centimetres) per stroke, then the volumetric efficiency of the pump is 97%. 2. for compressors, the ratio of the volume of gas actually delivered, corrected to suction temperature and pressure, to the piston displacement.

a method of well control in which bottomhole pressure is kept constant when circulation is not possible and gas is migrating up the hole. Bottomhole pressure is maintained slightly higher than formation pressure while the gas is allowed to expand in a controlled manner as it moves to the surface.

pooling of leased tracts willingly undertaken by all the parties involved, both working interest owners and royalty owners.

standards established generally by private sector bodies for use by any person or organization. Includes what are commonly referred to as industry standards and consensus standards, but does not include professional standards of personal conduct, institutional codes of ethics, private standards of individual firms, or standards mandated by law.

unitization that is accomplished with the willing cooperation of the affected parties, both working interest owners and royalty owners.

volt-ohm-milliammeter.

1. a spiral motion of fluid within a limited area, especially a whirling mass of fluid that draws anything near it toward its center. 2. in gas and liquid measurement, a rotational-flow zone that forms on alternate sides of a nonstreamlined body placed in a high-velocity flowing stream.

see swirl pipe.

the short pipe in a cone-shaped separator that extends down into the cone body from the top and that forces the whirling stream of material to start downward toward the small end of the cone body.

in fluid-flow measurement, a device in a meter that uses a piezoelectric crystal to measure the rate of flow. As the fluid flows through the meter, vortices (spiral, or whirling, motions) occur, which the piezoelectric crystal detects. The crystal then produces AC voltage whose frequency is directly proportional to flow rate.

an instrument for detecting vortices induced in a fluid stream by a baffle in the fluid stream to measure instantaneous flow rate.

a shaking motion (a vibration) created in a marine riser system by the tendency of water to swirl (create a vortex) around the riser.

rotational-flow zones that form on alternate sides of a nonstreamlined body placed in a high-velocity flowing stream.

vapor recovery unit.

vertical support member.

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

a rock formation that contains openings (vugs). See vug.

secondary rock porosity formed by the dissolving of the more soluble portions of a rock in waters containing carbonic or other acids.

see vuggy formation.

see volcanology.

a horizontal stiffening and structural member installed near the top of a floating-roof tank to reinforce the tank wall against wind pressure. Also called a wind girder.