Ideal specific gravity: the ratio of the molecular weight of a gas to the molecular weight of air. Molecular weight of air = 28.9644.
Imbalance penalties: penalties implemented by a pipeline to provide an incentive for shippers to maintain actual receipts and deliveries at nominated and confirmed levels.
Imbalance trading: process by which shippers can acquire gas from, or sell gas to, other customers to minimize or avoid Cash-out.
Improved (enhanced) recovery: the operation whereby natural gas is recovered using any method other than those that rely primarily on the use of natural reservoir pressure, gas lift, or a pump.
Independent Power Producer (IPP): an unregulated power generator that has no franchised retail service erritories.
Indexing: Tying the commodity price of natural gas in a contract to published prices.
Inert gas: a chemically inert gas, resistant to chemical reaction with other substances.
Injected gas: natural gas placed in underground storage or returned to the producing reservoir to maintain pressure.
Interconnector (the European): a 238-km pipeline providing a strategic link between the UK and continental Europe, connecting the two gas transmission systems at Bacton in the UK and Zeebrugge in Belgium.
International load line certificate: a certificate which gives details of the minimum freeboard granted to a particular ship and the position of the appropriate load lines to be marked on her sides. This certificate is issued by a government or duly appointed person or organization such as a classification society.
Interruptible demand: the amount of customer demand that, in accordance with contractual arrangements, can be interrupted by direct control of the system operator, remote tripping, or by action of the customer at the direct request of the system operator.
Interruptible gas: gas sold to customers with a provision that permits curtailment or cessation of service at the discretion of the supplier; the opposite is firm gas.
Interruptible service: gas service which is subject to interruption at the option of the pipeline or local distribution company (LDC).
Interstate market: the market for natural gas in the US that is consumed outside the state in which it is produced or is transported by an interstate pipeline.
Interstate Natural Gas Association of America (INGAA): trade organization that advocates regulatory, and legislative and individual positions of importance to the interstate natural gas pipeline industry in the United States.
Interstate pipeline: a natural gas pipeline company in the US that is engaged in the transportation of natural gas across state boundaries, and is therefore subject to FERC jurisdiction.
Intrastate market: the market for natural gas consumed in the same state as it is produced.
Intrastate pipeline: a natural gas pipeline company that is engaged in the transportation of natural gas within the state in which the gas is produced. subject to regulatory oversight of the applicable state.
IPE: International Petroleum Exchange.
Joule-Thomson Effect: the change in temperature of a fluid which occurs when the fluid is allowed to expand in such a way that no external work is done and no heat transfer takes place. The case of most interest is cooling of a compressed gas upon J-T expansion. Note that the J-T effect is not limited to gases; also J-T expansion can, in some cases, produce an increase in temperature, rather than a decrease, although this is not frequently encountered.
Kilowatt (kW) a measurement of electric power equal to one thousand watts.
Kilowatt year (kW-y): a unit of electrical capacity equivalent to one kilowatt of power used for 8,760 hours.
Kilowatt-hour (kWh): the basic unit for pricing electric energy, equal to one kilowatt of power supplied continuously for one hour (or the amount of electricity needed to light ten 100-watt light bulbs for one hour).
Knot: unit of speed in navigation, which is the rate of one nautical mile (6,080 feet or 1,852 meters) per hour.
Laid-up tonnage: ships not in active service; a ship which is out of commission for fitting out, awaiting better arkets, needing work for classification, etc. See Lay-up
Laytime: time allowed by the shipowner to the voyage charterer or bill of lading holder in which to load and/or discharge the cargo. It is expressed as a number of days or hours.
Layup: to dismantle or unrig a ship for a prolonged period of unemployment.
Line pack: creation of storage within the pipeline by increasing pressure above that which is required for transmission, but still within a safe limit.
Liquefied Natural Gas (LNG): an odorless, colorless, non- corrosive and non-toxic product of natural gas consisting primarily of methane (CH4) that is in liquid form at near atmospheric pressure.
Liquefied Petroleum Gas (LPG): gaseous hydrocarbons at normal temperatures and pressures but that readily turn into liquids under moderate pressure at normal temperatures; e.g., propane and butane.
LNG cargo containment systems: the method of storing LNG during marine transport. One of four methods is normally employed: Self-Supporting Prismatic Type ‘B’ (Conch/lHl), Dual Membrane (Gaz Transport), Single Membrane (Technigaz), and Self-Supporting Spherical Type ‘B’ (Kvaerner Moss).
LNG feedgas requirements to LNG plant: each million tonnes of LNG annually delivered to a customer is equivalent to approximately 130 mmscfd of natural gas. Over a typical twenty-year sale and purchase agreement (SPA), this amounts to 1 tcf (trillion cubic feet) of natural gas. Around 10- 15 per cent of the gas is lost in the process of production, liquefaction and transportation of the LNG, therefore the daily rate of gas production necessary to deliver 1 mtpa (million tonnes per annum) to the customer is about 150 mmscfd. This is equal to 1 .1 tcf over a twenty-year SPA. A world-scale LNG project delivers at least 7 mtpa, which means it requires a feed of over 1 bcf/d (billion cubic feet per day) of natural gas. LNG production has to be sustained at the plateau level for the life of the project so the gas reserves must be able to support production of over 1 bcf/d in the twentieth contract year. The gas reserves for a project of this dimension have to be in excess of 9 tcf when taking into account the gas that must remain in the reservoir to allow production to be maintained over the life of a twenty-year contract.
LNG markets: there are two primary LNG markets: 1) the Atlantic Basin (or western market) includes Belgium, France, Italy, Spain, Portugal, Greece, Turkey, and the US; 2) the East Asian market includes Japan (world’s largest), South Korea and Taiwan, soon to be followed by the large emerging markets of India and China.
LNG project characteristics: primary LNG project components are: 1) upstream development of long-term, natural gas supply for feedgas to an LNG plant; 2) downstream development of liquefaction, storage and loading facilities; 3) marine transportation; and 4) further downstream development of receiving terminals for regasification and pipeline transportation to market. Defining economic characteristics of LNG projects include i. commercial activities organized around project components in which the buyer and seller are closely linked for 20-25 years; ii. significant front-end infrastructure investment for each tonne of LNG delivery capacity — the critical mass of infrastructure for an LNG project must be very large in order to achieve production quantities adequate for realization of economies of scale and to secure project financing; and iii. long-term contracts based on large, proven gas reserves.
LNG refrigerant (for liquefaction) cycles: natural gas liquefaction requires removal of sensible and latent heat over a wide temperature range using a refrigerant. The refrigerant may be part of the natural gas feed (an ‘open-cycle process”) or a separate fluid continuously recirculated through the liquefier (a “closed-cycle process”). Three general types of refrigeration cycle are used: cascade, mixed-refrigerant, and expander cycle.
• cascade refrigerant cycle: feedstock natural gas is cooled, condensed and sub-cooled in heat exchange with propane, ethylene (or ethane) and finally methane in three discrete stages. The three refrigerant circuits generally have multistage refrigerant expansion and compression, each typically operating at three evaporation temperature levels. After compression, propane is condensed with cooling water or air, ethylene is condensed with evaporating propane and methane is condensed with evaporating ethylene.
• expander cycle: in its simplest form, process refrigeration in an expander cycle is provided by compression and expansion of a single-component gas stream. High-pressure cycle gas is cooled in counter-current heat exchange with returning cold cycle gas. The cycle gas is expanded through an expansion turbine, reducing its temperature to a lower temperature than would be given by expansion through a Joule-Thomson valve.
• mixed-refrigerant cycle (MRC): uses a mixed refrigerant(s) instead of the multiple pure refrigerants in the cascade cycle. The mixture composition is specified so the liquid refrigerant evaporates over a temperature range similar to that of the natural gas being liquefied. A mixture of nitrogen and hydrocarbons (usually in the C1 to C5 range) is normally used to provide optimal refrigeration characteristics. M RC provides greater thermodynamic efficiency, lower power requirement and use of smaller machinery.
LNG storage tanks: vessels that are specially constructed to contain LNG. The tanks are generally constructed of nickel steel (steel containing 9% nickel) to withstand cryogenic temperatures, and are insulated to maintain the LNG at —161°C. Some of the stored LNG boils off and the resulting vapor is used as fuel gas for the plant. There are three main designs of LNG storage tanks: single containment, double containment and full containment. The difference in these systems lies in the functionality of the secondary containment, when the primary containment is breached. For single containment, neither liquid nor vapor will be held by the secondary containment; for double containment, liquid will be contained and for full containment, liquid and vapor will be contained.
LNG value chain: in planning, funding and executing an LNG project, each element of the complex chain which links the natural gas in the ground to the ultimate consumer (“from the wellhead to the burner tip”) is considered. The main links are natural gas production, liquefaction, shipping, receiving terminal (including regasification), distribution of the regasified LNG and, lastly consumption of the gas.
Load balancing: process of matching customers’ demand for natural gas with producers’ ability to supply.
Loaded leg: that portion (or subdivision) of a ship’s voyage during which the ship is carrying cargo.
Loading days: the number of days allowed to load a cargo defined in the charter party.
Local distribution company (LDC): a utility that takes natural gas from a local delivery point (generally called the city gate) and distributes it to local customers. A business entity that obtains its primary revenues from the operations of a local retail gas distribution.
Long ton (LIT): 2,240 pounds or 1,016.05 kilograms. See Tonne, metric and Ton, long.
Long-term gas contract: a supply contract in the physical market covering natural gas deliveries.
Looping: laying additional pipeline beside and connected to an existing pipeline in order to increase the capacity of the system.
Lost and unaccounted-for gas: the difference between the quantity of natural gas received into a system and the quantity of natural gas delivered out of a system over a specific period of time.
Major interstate pipeline: in the United States, a pipeline company whose combined sales for resale and gas system
throughput, transported interstate or stored for a fee, exceeded 50 bcf in the previous year.
Manifest: document containing a full statement of the ship’s cargo, extracted from the bill of lading.
Manning scales: the minimum number of officers and crew members that can be engaged on a ship to be considered
as sufficient hands with practical ability to meet every possible eventuality at sea.
Manufactured gas: gas produced by certain processes from oil, coal or coke.
Market center: an interchange where multiple pipelines or electric transmission lines interconnect and form a hub.
Market clearing price: the price at which supply equals demand.
Market-area storage: storage or hub facilities located near natural gas users (markets).
Market-based price: the price for natural gas as determined by the decisions of many buyers and sellers in a market.
Marketing affiliate: a marketer who is owned or controlled by a pipeline company. See FERC Order 497.
Master (Captain): highest officer aboard ship who oversees all ship operations; has general charge of the vessel, overall responsibility. Handles all ship’s records and communications, and receives and implements instructions from home office; takes command of vessel in inclement weather and in crowded or narrow waters. See Crew
Maximum allowable operating pressure (MAOP): the maximum gas pressure at which a pipeline system or process facility is allowed to operate.
Maximum capacity of pipeline: the maximum amount of natural gas a segment of pipeline can contain at a given time.
Maximum daily quantity (MDQ): the maximum daily quantity of natural gas that can be nominated for delivery to a customer’s premises.
Maximum demand: the greatest of all demands of the load that has occurred within a specified period of time.
MMBtu (MMBTU): one million British Thermal Units (BTU5).
MCF, Mcf: a measurement of volume denoting one thousand cubic feet of natural gas. 1 Mcf of gas = 1 .03 million BTUs (also, 1 kWh = 3,412 BTUs). See note under cubic foot for alternative term Terminology
Megajoule (MJ or MMJ): equivalent to one million joules, or 3.6 MJ = 1kWh.
Megawatt (MW): a unit of electric power equal to one million watts, or 1,000 kilowatts.
Meter: a mechanical device for automatically measuring and recording quantities of gas.
Mid-term gas contract: a supply contract in the physical market covering gas deliveries up to 18 months, although most mid-term contracts are for 1 year or less. These contracts can be characterized by 1) variable prices, where the cost of the commodity is indexed over time to the futures price of some published spot price; 2) fixed reservation fee and service fee; and 3) mainly fixed volumes per day or per month with modest variation. These contracts are of long enough term to hedge price risk with financial instruments. These contracts are important for local distribution companies (LDC5) because they can extend over a heating season. See Physical gas contract
Mol%: the molar composition of a sample of natural gas expressed as a percentage of the whole.
Most Favored Nation clause: contract clause that ties the contract price to the rates paid in other contracts, usually specifying the region to be taken into consideration, such as a county, state, field, basin, or other geographic or geologic area.
Mtpa: million tonnes per annum
Multilateral institutions a major source of LNG financing for developing countries; includes Asian Development Bank (ADB), European Bank for Reconstruction and Development (EBRD), International Bank for Reconstruction and Development (IBRD) and the International Finance Corporation (IFC). See Export Credit Agencies (ECAs)
Must-take gas: natural gas supplies committed to a purchaser under terms such as drainage protection or reservoir protection clauses or other provisions that absolutely obligate a purchaser to take natural gas from a supplier.