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.”
Cricondentherm: The 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 Point: The 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 Gas: A 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 Gas: Gas that is unprocessed or partially processed and has been produced from a strata containing condensable hydrocarbons.
Sour Gas: Gas 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.
Therm: A 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.