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Southern African Natural Gas Advisory Service Service
GLOSSARY
Associated Gas: Usually produced as part of crude oil extraction from underground oil reservoirs.
Barrel of oil equivalent [boe]: A unit of comparison between crude oil and other fuels. It is based on the amount of heat released when different fuels such as oil or natural gas are burned. 1 barrel of oil is broadly equivalent to 6 million cubic feet of natural gas in terms of heat released.
Billion cubic feet [bcf]: A common Imperial unit of measurement for large volumes of natural gas. A bcf of natural gas is approximately equivalent to 1 trillion British Thermal Units (Btu).
Billion cubic feet day [bcfd]: An Imperial unit of measurement for daily volumes of natural gas.
Billion cubic meters [bcm]: This metric unit of measurement is used for large volumes of natural gas and is roughly equal to 35.3 billion cubic feet.
British Thermal Unit [Btu]: A British Thermal Unit is the amount of energy needed to heat 1 pound (0.454 kg) of water from 39 degrees Fahrenheit to 40 degrees Fahrenheit under standard pressure. A Btu is equal to 1055 joules and is commonly used in countries using imperial measurements to describe the heat value (energy content) of fuels. The unit is commonly used in the steam generation, power, air conditioning and heating industries. A Therm is used to represent 100,000 Btu's.
Butane: A gaseous hydrocarbon commonly deployed in liquid petroleum gas that is extracted from natural gas or oil refinery processes.
Coal Bed Methane: Natural gas that is mainly methane formed in association with the formation and ageing of underground coal deposits. It is extracted through a series of wells that are sunk into the underground coal beds.
Combined Cycle: A term used to describe a particular type of electricity generation plant. It is a technology that combines conventional gas combustion and heat recovery to greatly increase overall efficiency and reduce wasted heat losses that are characteristic of gas turbine heat losses in single cycle generating plant.
Compressed Natural Gas: Natural gas that is stored and transported in high pressure containers usually at pressures greater than 3000 pounds per square inch (psi) or 200 bar. In the USA and Europe compressed natural gas is widely used for commercial haulage and public transport vehicles.
Condensates: These are light hydrocarbon materials that condense and become liquid above ground from production wells when exposed to surface temperatures and pressure. They are usually present with natural gas production wells.
Cubic feet [cf]: A commonly used Imperial unit of measurement of a volume of gas that fills 1 cubic foot under standard pressure and temperature.
Dry or Lean Gas: Natural gas that is mostly methane remaining after liquid hydrocarbon elements have been removed in gas processing plants making it suitable for transportation through pipelines to end users or for subsequent treatment to produce liquid natural gas.
Ethane: A gaseous hydrocarbon extracted from natural gas or oil refinery processes.
Flaring: Disposing by burning (or flaring) of none saleable or unwanted gas at natural gas well sites and petrochemical processing plants.
Gas Field: A district or area from which natural gas is produced.
Gasification: Process during which liquefied natural gas (LNG) is returned to its vapour or gaseous state through an increase in temperature and a decrease in pressure.
Gigajoule: A metric term used as a measure of a unit of energy. 1 gigajoule is equal to one billion joules.
Joules [J]: A metric unit of energy measurement for gas sales. Since it is a small unit it is commonly used as kilojoules (1 x 1000). 1 kilojoule is equivalent to 0.948 per Btu.
Line pack: The practice of providing gas storage within natural gas pipeline networks facilitated by increasing the line pressure and thereby volumes of gas above normal operating pressures. Line packing is commonly used as a routine gas transmission practice to satisfy short term fluctuations in gas demand.
Liquefied natural gas [LNG]: Natural gas in a liquid state rather than gaseous state. It is achieved by cooling natural gas to minus 161 degrees Centigrade or minus 259 degrees Fahrenheit in cryogenic treatment processes. LNG enables large volumes of natural has to be economically shipped around the world over long distances mainly by sea. On receipt at LNG terminals it is commonly re-gasified and then fed into storage containers or fed into local natural gas distribution networks.
Liquefied Petroleum Gas [LPG]: This is mainly ' bottled gas ' consisting of a mixture of butane and propane that is liquefied at low temperatures and moderate pressures. LP Gas is produced in oil refineries or extracted from natural gas in processing plants.
Manufactured Gas: Gas obtained by destructive distillation of coal, or by thermal decomposition of oil, or by the reaction of steam passing through a bed of heated coal or coke or catalyst beds. Examples include coal gases, coke oven gases, producers gas and blast furnace gas.
MBtu: The abbreviation for a million British Thermal Units (Btu).
Mcf: The abbreviation for a million cubic feet.
Methane: The most abundant, generally odourless and naturally occurring hydrocarbon gas that is the major component of commercial natural gas.
MMcf: The abbreviation for the Imperial unit of gas volume for a million cubic feet.
MMcfd: The abbreviation of the Imperial unit of gas volume production or supply of a million cubic feet a day.
Natural Gas: Mixture of naturally occurring hydrocarbon gases mainly from underground sources that are composed primarily of methane with small elements of ethane, butane, pentane and minimal impurities such as carbon dioxide, helium, hydrogen sulphide and nitrogen.
Natural gas liquids [NGL's]: These are materials that become liquid at surface temperature and pressures at gas production wells that include propane, pentane, butane, ethane and other condensates.
Non Associated Gas: Natural gas produced from dedicated gas production wells where no oil is produced. It is not thereby associated with oil production.
Peak Hour: The one-hour period of the greatest total gas send out or use.
Permeability: A measurement of the ability of a rock to transmit fluid.
Pig: A device used to clean the internal surface of a pipeline. They are usually barrel shaped, made of metal and have brushes and a rubber seal. The forward movement of the pig through the pipeline, together with its rotation, cleans the rust, liquids, and other undesirable substances from the pipeline. They are also used to inspect pipelines and remotely carry out maintenance. They are inserted into the pipeline through a device called a pig-trap.
Pilot: A small flame which is utilised to ignite the gas at the main burner(s).
Pipeline Capacity: Maximum quantity of gas that can be moved through a pipeline system at any given time based on existing service conditions, such as available horsepower, pipeline diameter, maintenance schedules and regional gas demand.
Quad: A unit of energy quantification roughly equivalent to 1 trillion cubic feet (tcf) of natural gas.
Reserves: Hydrocarbons that have a high economic and technical probability of being produced.
Standard temperature and pressure [STP]: Standard benchmark conditions that apply to many natural gas units of measurement and quantification. STP is defined as 20 degree Centigrade and I atmosphere pressure or 14.7 pounds per square inch (psi).
Salt Cavern: An underground natural gas storage cavern developed in a salt dome by the solution mining process.
Sour Gas: Gas having a high sulphur content.
Stranded Gas: Natural gas deposits that have been identified but that are situated either a long way away from necessary transportation infrastructure or for which there is no readily accessible market.
Sweet Gas: Saleable natural gas that contains negligible quantities of carbon dioxide and hydrogen sulphide.
Take or pay [TOP]: This is a feature of mainly bulk natural gas supply and purchase agreements between suppliers and buyers. Such agreements commonly stipulated a minimum quantity of gas contracted to the buyer that must be paid for whether the buyer takes it or not.
Tcf: This is an abbreviation for the Imperial unit of measurement for a trillion cubic feet that is commonly used to describe very large volumes of natural gas. It is frequently used to quantify natural gas fields and discoveries and is roughly equal to 1 quad of energy.
Therm: An energy unit commonly used in Britain for the resale and pricing of natural gas that is equal to 100,000 Btu of energy. 100 cubic feet of gas by volume is approximately equal to 1 therm and is commonly used for resale metering purposes.