Glossary Of Industry Terms

This is a collection of terms which are commonly encountered in the oil & gas industry, in general, and particularly when involved with hydrocarbon measurement.

Please click on a category section to view the full list of terms; categories may be opened or closed.

AGA: American Gas Association

API: American Petroleum Institute

ANSI: American National Standards Institute

ASTM: American Society for Testing and Materials

FERC: Federal Energy Regulatory Commission

GPA: Gas Processors Association

GPSA: Gas Processors Suppliers Association

NIST: National Institute of Standards and Technology

Beta Ratio: The measured bore diameter of an orifice plate divided by the measured internal diameter of the meter tube; this ratio should be in the range of 0.20 to 0.60 for minimum uncertainty in measurement.

Btu: A traditional unit of energy known as “British Thermal Unit.” It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit, and is a common unit in the petroleum industry for quantity of energy transferred as heat.

Btu As-Delivered: Heating value term used to indicate that gas is saturated with water at delivery conditions.

Btu Dry: Heating value term used to indicate that the gas does not contain any water vapor.

Btu Wet: Heating value term used to indicate that the gas is saturated with water at base conditions.

Compressed Natural Gas (CNG): Natural gas in high-pressure surface containers that is highly compressed. Used extensively as a transportation fuel for automobiles.

Contract: A legal document which specifies mutually agreed upon terms between buyer and seller for measurement, sampling, auditing, testing, data retention, and settlement of disputes.

Contract Day: A time period of twenty-four (24) consecutive hours beginning at the time specified in the contract except for the days which have been adjusted for Daylight Saving Time.

Contract Hour: The time designated by a gas sales contract for the beginning of a new “Contract Day” or “Gas Day.”

CricondenthermThe highest temperature at which two phases (liquid and vapor for most processes) can coexist. This point has both theoretical and practical importance for transporting natural gas.

Cubic Foot: The volume of a cube with dimensions of one foot (12 inches) in each of its three dimensions.

Dekatherm: Ten (10) therms or one million (1,000,000) British thermal units (Btu).

Flare: Burning of gas for the purpose of safe disposal.

Flash Gas: Gas which evolves (flashes) from a hydrocarbon liquid due to reduction in pressure, increase in temperature, or both.

Formation Production: This is the actual production from an underground reservoir formation. For injection and return operations, such as gas lift systems, formation production is typically determined as the difference between the return volume measured at the wellhead and the injection volume.

Free Liquids: Hydrocarbons, water, or other components which have condensed out of a gaseous stream and are present in a liquid phase in gas meters, equipment, piping, etc.

Full Well Stream: Well stream gas that has not had separable liquids removed, such as water, oil or condensate. When full stream gas is measured through an orifice meter, excessive uncertainty is introduced.

Gallons per Mcf (GPM): The quantity of gallons (at base conditions for that component) of liquefiable hydrocarbons contained in 1,000 standard cubic feet of natural gas.

Heating Value: Quantity of heat produced from the complete combustion of a unit quantity of a hydrocarbon fuel where the products of combustion are gaseous CO2 and liquid water at base conditions. This is measured in Btu per standard cubic foot.

Hydrocarbon Dew PointThe temperature at which liquid hydrocarbons condense out of the gas stream. It is pressure dependent and pipeline specifications are typically based on maximum hydrocarbon dew point.

Lean Gas: Gas containing little or no hydrocarbons which are commercially recoverable as a liquid product.

Liquefied Natural Gas (LNG)Natural gas which has been liquefied by reducing its temperature to minus 260 degrees Fahrenheit at atmospheric pressure. In volume, it occupies 1/600 of that of the vapor at standard conditions.

Mcf: One Thousand (1,000) standard cubic feet of gas. “M” is the Roman numeral equivalent to 1,000 and “cf” is cubic feet.

MMBtu: One Million (1,000,000) British thermal units (Btu). “MM” from the Roman Numeral M (1,000), in this case means one thousand multiplied by one thousand, or one million.

Natural GasA naturally occurring mixture of hydrocarbon and non-hydrocarbon gases found in porous geologic formations beneath the Earth’s surface, often in association with petroleum. Natural gas normally has methane as its principal component.

Pulsation: Pulsation is the presence of pressure waves, in the pipeline at a frequency and of sufficient amplitude so that excessive measurement uncertainty is introduced.

Residue Gas: Natural gas from which processing plant liquid products have been extracted.

Rich GasGas that is unprocessed or partially processed and has been produced from a strata containing condensable hydrocarbons.

Sour GasGas found in its natural state containing such large amounts of sulfur compounds and/or CO2 as to make it impractical to deliver without purifying because of its corrosive effect on piping and equipment (and in the case of sulfur compounds such as hydrogen sulfide, its toxicity).

Standard Cubic Foot (Scf): The most common unit of measurement of gas volume in the U.S. The quantity of gas occupying a cubic foot of space at a specific conditions of temperature and pressure.

Sweet Gas: Gas found in its natural state containing such small amounts of sulfur compounds and/or CO2 that it can be delivered without purifying. Also, gas that has been processed so that it is rendered sweet.

ThermA unit of heat energy normally equal to one hundred thousand (100,000) British thermal units (Btu).

Vacuum: Measurement of the amount that the pressure is less than atmospheric pressure.

Absolute PressurePressure above that of a perfect vacuum; the sum of gauge and atmospheric pressure (designated by psia).

Atmospheric PressureForce per unit area created by the weight of Earth’s atmosphere; atmospheric pressure at sea level is 14.696 pounds per square inch. It will vary from location to location depending primarily upon altitude. It will also vary over time at a given site due to weather conditions. It is primarily for this latter reason that the atmospheric pressure used at a measurement site is typically specified by contract.

Calculation Method: A description of the computation method used to calculate flow rate, including compressibility (or supercompressibility for a differential meter).

CompressibilityThe property of a material which permits it to decrease in volume when subjected to an increase in pressure. In gas-measurement usage, the compressibility factor “Z” is the deviation from the ideal Boyle’s and Charles’ law (ideal gas law) behavior.

Compressor-Generated Pulsation: Pulsation is pressure waves, varying in frequency and amplitude, which can originate from any reciprocating source such as compressor pistons. In most cases, pulsation causes orifice meters to record high and the resulting flow error is often severe.

Correlation Factor: A factor used to compensate for the inherent inaccuracy associated with calculating volumes from averages of the flowing parameters as opposed to the actual instantaneous values used by the original flow-computing device. This factor is only required for recalculation purposes but it is also useful as a validation parameter and is a term unique to the Flow-Cal system.

Differential Pressure: The difference between the pressure upstream and downstream of the primary device, often expressed in inches of water.

Flow Computer: A dedicated computer (secondary device) which performs the volume calculations over small intervals and typically stores 35 days of hourly average flow data in memory.

Flow Time: The amount of time during a given period for which gas was flowing.

Gauge Pressure: Measurement of the amount that the pressure is greater than atmospheric pressure (designated by psig).

Ideal Gas LawA statement of the approximate behavior of a gas for changes in pressure and temperature combining Boyle’s and Charles’ laws. It states that for a given quantity of gas, the absolute pressure times the volume is equal to a constant times the absolute temperature. It is often written {PV=nRT}. The constant is the number of moles of gas times a quantity called the ideal gas constant. Real gasses differ in behavior from the ideal by a factor normally designated “z” and named the compressibility factor {PV=znRT}.

K-Factor: The number of pulses generated by a meter per unit of (nominal) volume.

Meter FreezeMeasurement error resulting from a drop in ambient temperature below the temperature necessary for hydrate formation; this usually occurs when moisture freezes and blocks one or both of the flange tap valves (Tap Freeze) but may also be due to freezing in some other part of the meter station.

Meter Tube MaterialThe material out of which the meter tube is constructed. The meter tube material is crucial to calculating the coefficient of thermal expansion.

Meter Tube Reference Temperature: The temperature at which the reference meter tube internal diameter is calculated.

Mole Percent (Components): The ratio of a particular molecule in a mixture of hydrocarbons and non-hydrocarbons to the entire mixture expressed in moles.

Orifice Plate MaterialThe material out of which the orifice plate is constructed. This is oftentimes stainless steel. The orifice plate material is crucial to calculating the coefficient of thermal expansion to correct the stated orifice diameter to the actual diameter at the temperature of flow.

Orifice Reference TemperatureThe temperature at which the reference orifice plate bore diameter is calculated.

Plate SizeIndicates the measured inside diameter of the orifice plate at a reference temperature (usually 68 degrees Fahrenheit).

Pressure BaseStandard used for determination of gas volumes; volumes are measured at operating pressure and then converted to the appropriate base pressure volumes. Generally, the base pressure value is defined by contract and/or regulation.

Primary Element: Describes the basic type of flow meter used in gas measurement, including orifice, Coriolis, and ultrasonic; for an orifice type of element, the primary device consists of the meter tube, orifice fitting, and orifice plate.

Pulse CountThe total number of pulses registered by a counter over a period of time (usually a contract hour, contract day, or contract month).

Relative Density: The ratio of the density of a substance to a given reference material.

Secondary Element: A device that senses and records data, such as (but not limited to) static pressure, temperature, differential pressure, relative density, and other variables, that are used in volume determinations.

Specific Gravity: A relative density term used in the oil and gas industry. As applied to natural gas, dry air is the reference substance. As applied to petroleum liquids, water is the reference substance.

Static Pressure: Force per unit area inside the pipeline and often expressed in pounds per square inch (psi); also referred to as “line pressure.”

Static Pressure Tap LocationThis identifies which tap is used to measure line pressure. It may be measured either upstream or downstream.

Supercompressibility Factor: A factor used in a volume measurement calculation to correct for deviation from the ideal gas law in differential meters. This is defined as the square root of the ratio between compressibility factor (“Z”) at base conditions and at measurement conditions.

Tap Type: The location of the taps on either side of the orifice plate across which the differential pressure is measured. The most common pressure taps are flange taps. Pipe taps no longer comply with industry standards but are still occasionally encountered. Pressure is measured on each side of the primary device through these taps for differential meters.

Temperature: A degree of hotness or coldness measured on a definite scale.

Temperature Base: Standard used for determination of gas volumes; volumes are measured at operating temperature and then converted to the appropriate base temperature volumes. Normally, the base temperature value is defined by contract and/or regulation. In the United States this temperature is almost always 60 degrees Fahrenheit.

Time Leads Data / Time Trails Data: Flow computers log averages and accumulate flow over a time interval. These terms specify where the period of 1:00 p.m. to 2:00 p.m. is labeled at the 13:00 hour (time leads data) or the 14:00 hour (time trails data) in the computer logs and is a term coined by Flow-Cal.

Tube IDThe inside measured diameter of the meter tube. For orifice measurement, the Tube I.D. used in the calculation is the measurement of the mean inside diameter of the meter run, one inch upstream of the tap, at a reference temperature (usually 68 degrees Fahrenheit).

Turn Down Ratio: A term that refers to the operational range of a device and is defined as the ratio of maximum capacity to minimum capacity at a stated measurement uncertainty. It indicates the range of flow that a meter can measure with acceptable accuracy.

API GravityAn inverse ratio of the density of oil to a relative density (i.e., water). It can be used to compare densities of hydrocarbon liquids and often as a measure of quality.

BarrelCommon unit of volume in petroleum liquid measurement; one barrel is equal to 42 US gallons.

Base Density: The density of a fluid, reported at legal pressure and temperature base.

Basic Sediment and Water (BS&W)The quantity of sediment and water present in crude oil. It is determined by centrifugal or extraction testing and is used for oil classification.

Batch: A discrete shipment of commodity defined by quantity (mass or volume), accounting time interval, or quality.

Combined Correction Factor (CCF)API 12.2.2 specified technique for applying correction factors in order to minimize errors from sequencing and rounding. The sequence says to multiply together all correction factors, then round the CCF to a specified number of decimal places.

Correction for Pressure Factor (CPL): Basic correction factor for compressibility of a liquid.

Correction for Temperature Factor (CTL): Basic correction factor for the effect of temperature on a liquid.

Crude OilA naturally occurring liquid mixture consisting of hydrocarbons and non-hydrocarbons in its unprocessed form. Crude is refined to produce petroleum products such as gasoline.

Delivery TicketA document of record produced to report the quantity of crude oil or other hydrocarbons delivered for custody transfer.

Density Meter Factor: A correction factor applied to a measured density from a density meter, calculated during the meter calibration procedure, usually by use of a Pycnometer.

Extra Heavy Oil (Bitumen)Defined as having API gravity below 10 degrees API.

GallonCommon unit of volume in liquid measurement equal to 4 US quarts or 3.785412 liters.

Gross Observed Volume (GOV): The volume of oil measured at the observed oil temperature and pressure including dissolved or suspended sediment and water but not including free or bottom water.

Gross Standard Volume (GSV)The metered volume corrected to base conditions and also corrected for the performance of the meter (meter factor).

Heavy Crude OilDefined as having API gravity below 22.3 degrees API.

Indicated Volume (IV)The change in the meter register head volume that occurs during a proving run or delivery run. Generally used as the original, raw metered volume.

K-FactorThe number of pulses generated by a meter per unit of quantity (nominal).

Light Crude Oil: Defined as having API gravity higher than 31.1 degrees API.

Medium Crude Oil: Defined as having API gravity between 22.3 degrees API and 31.1 degrees API.

Meter Factor (MF): Dimensionless term established by proving and used to correct the indicated volume of a meter to its actual metered volume. This value should not exceed 4 significant digits.
MF=(Prover Reading)/(Meter Reading)

Meter Proving: Performing a comparison of the registration of a meter to a known traceable standard.

Net Standard Volume (NSV): The gross standard volume corrected for nonmerchantable quantities such as Sediment and Water (S&W).

Observed DensityThe density of a fluid, reported at some observed conditions (any temperature and pressure). For this value to be useful, the temperature and pressure also need to be reported. In the case that observed density is determined with a hydrometer, the observed pressure is assumed to be one atmosphere.

Proving Report: A document showing all the meter and prover data, together with all other parameters necessary to verify the determined meter factor.

Reid Vapor Pressure: The pressure measured when performing a Reid Vapor Pressure test (determine vapor pressure at 100 degrees Fahrenheit). Direct measurement of the actual equilibrium vapor pressure (EVP) of a liquid hydrocarbon mixture is difficult because the liquid changes composition as it vaporizes; therefore, the Reid Vapor Test is used to characterize the relative volatility of different liquid hydrocarbon products.

Sediment and Water (S&W): The portion of delivered volume that represents water as well as nonmerchantable solids suspended in the mixture.

Shakeout Test: A test performed to quantify the amount of S&W in a sample of oil. The sample of oil is placed in a centrifuge which then operates to force entrained impurities to separate from the oil. The results will typically be used to adjust the final volume on which all owners are paid.

Vapor PressureThe Equilibrium Vapor Pressure (EVP) at a given temperature and pressure.

Viscosity: A measure of a fluid’s resistance to deformation due to internal molecular friction. A fluid’s viscosity characterizes its internal resistance to flow in pipeline movements.

WaterdrawA common term used to describe the calibration of a meter prover by displacing water from the prover into field standard test measures (volumetric method) or into a container on a scale (gravimetric method). Its official API definition is “a method of calibrating a meter prover by displacing water from the prover into field standard test measures.”

ASTM Sampling Apparatus (Pig Tail Extension)Tubing, at least 36 inches in length, which extends from the sample cylinder outlet valve to the purge valve and drilled plug assembly on the end of the pig tail.

BellowsA dual-chambered, liquid-filled, accordion-folded device in which the difference in pressure on each side forces the liquid from one chamber to the other. It is a piece of the differential pressure measurement segment on a chart recorder and is contained in the pressure case at the back of most models.

Centering PinsDowels used to align the orifice bore directly in the center of the meter tube.

ChartThe paper upon which a chart recorder’s signals are recorded. It is removable and the digitizing of the recorded signals is typically done at another location so that accurate calculation of the flow can be performed.

Check Meter: A meter station installed on a line in order to act as a second, independent means of measuring hydrocarbon volumes. Check Meters are especially useful when used to independently verify sales volumes.

Clock: The device that turns the chart on a chart recorder proportional to the passage of time so that total cumulative flow can be determined when the flow rate is varying.

Flange Taps: A pair of tap holes in the same radial position where the tap centers are located one inch upstream or downstream of the appropriate plate face.

Flow ConditionerA diffuser plate, tube bundle or other device installed in a meter tube in order to eliminate swirl and/or supply a fully developed flow profile.

Gauge Lines: Tubing used to connect the taps on the meter tube to the transmitter(s).

Heat Exchanger: Equipment built for efficient heat transfer from one fluid to another, often used for producing refined petroleum products.

Line HeaterEquipment designed to heat a flowing fluid for a variety of operational reasons.

LACT Controller: A dedicated configurable device designed to operate or control a LACT unit. These may include data logging and communications capability. This may or may not be a PLC depending upon its programmability.

Lease Automatic Custody Transfer Unit (LACT Unit): A unit that enables automated net volume and quality determination for liquid hydrocarbons as well as delivery into a pipeline or other means of transportation for custody transfer.

ManifoldA combination of one or more block valves and one or more bleed valves, usually ball, plug, or needle valves along with connecting nipples and tees, designed to isolate or block the flow of fluid from the measurement device(s) for a period of maintenance and testing. If the valve bodies and connections are all in the same metal body, this is referred to as a “block” manifold.

Orifice Fitting: A pressure containing pipe element designed to hold the orifice plate concentric and perpendicular to the meter tube, while also providing the ability to remove the plate without disassembling the meter tube.

Orifice Plate: A thin plate in which a circular, concentric, sharp, square-edged bore has been machined to AGA3 specifications.

Pen ArmsThe arms (levers) upon which the recording pens are installed that are connected to the pen linkage.

Pen LinkageThe pivots and levers used to connect the differential, pressure and temperature readings to the pens so that deflection pen is related to the signal being recorded.

PensThe devices that actually record the signals from the sensors by marking on the chart.

Pressure SpringA coiled hollow steel spring the inside of which is connected to the static pressure connection tubing and the uncoiling of which is used to measure that pressure.

Programmable Logic Controller (PLC)A dedicated programmable device designed to operate or control other equipment.

Range Spring: Another piece of the differential pressure measurement segment of a chart recorder attached to the bellows which provides restoring force (resistance) against which the differential pressure acts. It may be changed to alter the range of the differential pressure sensor.

Resistance Temperature Detector (RTD): Temperature sensors prevalent in measurement. The device correlates the resistance of the RTD sensing element with temperature.

Sample CylinderA pressure containing device (pressure bottle and valves) for obtaining gas sample at a sampling location and transporting it to a place where it can be analyzed.

SeparatorA pressure vessel used for separating flowing fluids produced from oil and gas wells into their constituent phases. At the wellhead separator, these are typically oil or wellhead condensate, gas, and water. At downstream locations, a separator may also be referred to as a “Drip” or a “Scrubber,” although scrubber may also refer to a more sophisticated device.

Seal Ring: An O-shaped ring (gasket) designed to fit around an orifice plate and create a seal in order to block any fluid from going around the orifice. It is also part of the centering mechanism so that the orifice plate as installed is in the center of the meter tube and perpendicular to its long axis. They come in various types to fit different manufacturers’ orifice fittings and must be properly sized for the fitting.

Tap Valves: Devices designed to block or allow fluid flow (valve) through a gauge line installed at or near the meter taps.

A closed-end reentrant tube designed for insertion of a temperature-sensing element, and provided with means for pressure-tight attachment to a vessel.

Transmitter/Transducer: A device that converts a signal from a sensor into a form suitable for propagating the measurement information from the site of measurement to the location where the signal is used. Technically, the transducer represents the portion that changes the form of the signal for transmission and the transmitter is the portion that sends the changed signal to where it will be utilized; but because these are typically in the same device, these terms are often used synonymously. The pressure and differential transducer are often combined with a lone digital transmitter and this device is usually referred to in singular form (“differential and pressure transducer” or “differential and pressure transmitter”).

WellheadThe assembly of fittings, valves, and controls located at the surface and connected to the flow lines, tubing, and casing of the well to control the flow from the reservoir.

Binary File – These data files have coded text and numeric values for use by specific programs designed to read them. Generally they cannot be read in a legible format without knowing what program to use.

CFX File – This is a Flow-Cal native binary file format for creating, processing, and storing hydrocarbon liquid and gas measurement information.

FTP (File Transfer Protocol) – This is a high speed communication facility for passing large data files through the internet.

GQ (Gas Quality) Source File Format – This is a Flow-Cal specific text file format for creating, processing, and storing analytical data for hydrocarbon gas and liquid.

PDF (Portable Document Format) – This is a binary file format for storing print formatted documents for transmission via email or other electronic media. It was developed by Adobe and the files can be read by readily available software such as Adobe Acrobat Reader. The documents show in final form, but cannot be easily modified or read by other software.

Source Analysis File Format – The Source Analysis is the basis of gas or liquid quality analysis, as defined by the user. Source data may be from a physical sample or online chromatograph. It is a representative sample either manually entered or directly imported into the FLOWCAL® system and utilized to calculate volumes, mass components, and gas-equivalent values. The file format for import into FLOWCAL, formerly known as GQ Source, is now the Source Analysis File Format.

Text File – This is a data file which consists of ASCII characters that can be opened in notepad or other text reader (word processor) and the characters read as text. It may also be edited using such programs, and may or may not be readily accessible to other software as far as the data contained. (Text files are human readable, binary files are machine readable.)

TSX File – This is a Flow-Cal native binary file format for creating, processing, and storing field test and related information.

VPN (Virtual Private Network) – A VPN extends a private network across a public network such as the Internet.

©2021 Coastal Flow Liquid Measurement, Inc. and Coastal Flow Gas Measurement, Inc., entities of Quorum Business Solutions, Inc.


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