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Gas Condensate Well: A gas well that produces from a gas reservoir containing considerable quantities of liquid hydrocarbons in the pentane and heavier range generally described as “condensate.” Gas Coning: Gas from a fee gas cap that goes downward toward the top perforations in response to a drawdown. Gas Cut: Liquids with free gas. Usually refers to drilling or completion liquids. May indicate a kick if the gas is present in large enough quantities. Gas Cycling: Process in which produced gas is reinjected into the reservoir after removal of condensate in order to maintain reservoir pressure and prevent condensate from “condensing” in the reservoir (retrograde condensation) and becoming difcult to recover. Gas Day: In the United States, a period of 24 consecutive hours, beginning at 9 am. Central time. Gas Distribution Line: A gas pipeline, normally operating at pressures of 60 pounds per square inch (psi) or less, which transports gas from highpressure transmission lines to end users. Gas Drive: Flooding an oil reservoir from the top of the reservoir or an updip location, to push the oil toward a producing well. Gas Effect (on Logs): A difference in porosities caused by the compressibility of gas in porosities estimated by the formation density log and the neutron density log. Gas Field: (1) A eld or group of reservoirs of hydrocarbons containing natural gas but insignicant quantities of oil. (2) A eld containing natural gas but no oil. Gas Formation Volume Factor: The volume of reservoir gas resulting in one standard cubic foot. Gas Gatherer: The entity that contracts with the producer to take the gas from the wellhead to the plant or market. Gas Gathering System: (1) A system for collecting gas production from different sources for delivery by pipeline to a central point such as a platform or processing facility. The gas sources could be individual wells, smaller gathering systems, eld facilities, and platforms. (2) Central collection point for offshore gas elds. Production is then piped to a central processing system onshore. Gas Gravity: Ratio of the gas density to the density of air. Equal to the ratio of molecular weight of gas to that of air (28.97). Gas Grid: (1) The system of pipelines that run from the wellhead to the city gate. (2) The network of gas transmission and distribution pipelines in a region or country, through which gas is transported to industrial, commercial, and domestic users. Gas Hydrate: Immense deposits of natural gas tied up in clathrate structures with water. Found extensively. See also Hydrate. Gasi–cation: The conversion of soluble and suspended organic materials into gas during anaerobic decomposition. In clariers the resulting gas bubbles can become attached to the settled sludge and cause large clumps of

sludge to rise and ¤oat on the water surface. In anaerobic sludge digesters, this gas is collected for fuel or disposed off using a waste gas burner. (2) The production of gas from liquid or solid fuels. Gas Imbalance: A discrepancy between a transporter’s receipt and deliveries of natural gas for a shipper. Gas Injection: (1) An enhanced recovery technique in which natural gas is injected under pressure into a producing reservoir through an injection well to drive oil to the wellbore and the surface. (2) Associated gas is pumped back into a reservoir to maintain reservoir pressure. In this way, the rate of production of crude oil also can be increased. (3) The process whereby separated associated gas is pumped back into a reservoir for conservation purposes or to maintain the reservoir pressure. (4) The technique of injecting gas into a reservoir. It may be done for pressure maintenance, oil viscosity reduction, light end stripping, or storage. Gas-In-Place: The original amount of gas in the reservoir before production. Gasket: Any of several replaceable seals in equipment or tools. Gas Kick (Drilling): An unexpected and unwanted entry of gas into the wellbore during drilling or well operations. Gas Lift: (1) One of several methods of articial lift. A mechanical process using the continuous or intermittent injection of a gas into the production conduit (tubing or casing) to aerate or displace the produced ¤uids. This creates a reduction of the bottom-hole pressure of the well, increasing or sustaining the ¤ow rate of the well. (2) It is becoming normal practice on FPSOs, particularly for heavy crudes, to facilitate the ¤ow of live crude from the wells by injecting gas either at Xmas tree level or downhole to lower the back pressure on the wells. In fact, the lift gas is the associated gas from the eld, which is treated, compressed, and recirculated into the ¤ow system. (3) Gas from same or nearby eld is mixed with oil in tubing to lessen the weight of liquid column. (4) One of the articial lift methods that uses gas injected down the annulus and interspersed into the ¤owing ¤uids in the tubing to lessen the density and to assist in vertical ¤ow by gas expansion. Gas Lift Dummy: A solid body insert that replaces and blanks off a gas lift mandrel pocket designed for a valve. Gas Lift Mandrel: A section of pipe used in the tubing into which a gas lift valve can be inserted. The mandrel will allow communication with the annulus gas lift supply through the valve. Gas Lift Side Pocket Mandrel: A type of gas lift mandrel that allows fullbore passage. The valve “pocket” is on the side of the pipe. Gas Lift Valve: A pressure-operated valve, placed in gas lift mandrels at designed points in the well. The gas lift supply gas is routed through the valves into the tubing. The top valves close and the lower valves open as the static liquid level drops in the well (the well is unloaded). Gas Lift Valve-Injection Pressure-Operated Valve (Gas Lift): Gas lift valves where injection gas enters the valve and acts on the effective bellows area,

overcoming the precharge in the valve and opening the valve (the retracting bellows lifts the needle off the seat) to allow gas lift gas ¤ow from the gas-lled annulus through the seat and the reverse-¤ow check valve and into the tubing. Gas Lift Valve-Production Pressure-Operated Valve (Gas Lift): Production ¤uid enters the valve and acts on the effective bellows area, compressing the bellows against the precharge pressure, lifting the needle off the seat and opening the valve. The injection gas then ¤ows through the seat, through the reverse-¤ow check valve, and into the tubing. Gas Liquefaction: The process of cooling gas to −162°C, reducing its volume by 600-fold over the gas volume at standard conditions. Gas Lock (Facilities): A gas retention device that permits gaging the tank without loosing gas to the atmosphere. Gas Lock (Pump): A pump lled with gas that it cannot expel and where no further ¤uid will enter the pump. Common in beam lift pumps that pump off or are used in high GOR wells. Gasohol: A blend of nished motor gasoline containing alcohol (generally ethanol but sometimes methanol) at a concentration of 10% or less by volume. Data on gasohol that has at least 2.7% oxygen, by weight, and is intended for sale inside carbon monoxide nonattainment areas are included in data on oxygenated gasoline. See Oxygenates. Gas Oil: (1) A liquid petroleum distillate having a viscosity intermediate between that of kerosene and lubricating oil. It derives its name from having originally been used in the manufacture of illuminating gas. It is now used to produce distillate fuel oils and gasoline. (2) A fraction derived in rening petroleum with a boiling range between kerosene and lubricating oil. It derives its name from having originally been used in the manufacture of illuminating gas. Now supplies distillate-type fuel oils and diesel fuel, also cracked to produce gasoline. Gas/Oil Contact: The changing contact of the gas cap and the oil below in the rock. Gas Oil (Diesel): A distillate, intermediate in character between kerosene and the light lubricating oils. It is used as a heating oil and as a fuel in diesel engines. Gas/Oil Ratio: (1) The number of standard cubic feet of gas produced per barrel of crude oil or other hydrocarbon liquid. In some parts of the world, the units are cubic meters of gas per cubic meter of liquid produced. (2) May refer to a solution gas/oil ratio or total gas/oil ratio. (3) The volume of gas at atmospheric pressure produced per unit of oil produced. Gasoline: (1) The light fuel used to spark-ignition engines in cars, motorcycles, etc. Modern gasolines are blends of petroleum liquids that are produced in several different processes and that generally contain additives. (2) A rened petroleum naphtha that by its composition is suitable for fuel in a reciprocating-type internal combustion engine. ASTM D439 species three grades for various types of motor vehicle operations. Straight-run gasoline

is the product of distillation; cracked gasoline that of a cracking process. (3) A light hydrocarbon mixture having C4-C9 carbon atom hydrocarbons, which are used as fuel for internal combustion engines. (4) Normally C7C10 fuel, with a ¤ash point of −40. Gasoline (Petrol): A light petroleum product with a boiling range between the approximate limits of 30°C and 200°C. Used as a fuel in spark-ignition engines. It is also known as mogas. Gasoline Blending Components: Naphthas that will be used for blending or compounding into nished aviation or motor gasoline (e.g., straight-run gasoline, alkylate, reformate, benzene, toluene, and xylene). Excludes oxygenates (alcohols, ethers), butane, and pentanes plus. Gas Permeation: Invasion of gas into a solid, usually an elastomer, but sometimes referring to a metal. Gas Pipeline: A transmission system for natural gas or other gaseous material. Gas Processing: The separation of oil and gas and the removal of impurities and natural gas liquids (NGL) from natural gas. Gas Processing Plant: A facility that extracts liqueable hydrocarbons or sulfur from natural gas and/or fractionates a liquid stream. Gas Reserves: Those quantities of gas that are anticipated to be commercially recovered from known accumulations from a given date forward. Gas Reservoir: A geological formation containing a single gaseous phase. When produced, the surface equipment may or may not contain condensed liquid, depending on the temperature, pressure, and composition of the single reservoir phase. Gas Revenue: The product of gas volume times gas price; gross cash ¤ow from sales of gas. Gas Saturation: The fraction of the porosity in a zone that is occupied by free gas. Gas Sendout: The total natural gas produced or purchased (including exchange gas receipts), or the net natural gas withdrawn from underground storage within a specied time interval, measured at the point of production, purchase, or withdrawal, adjusted for changes in local storage quantity. Gas Show: Any indication of gas in the drilling ¤uid or cuttings that indicates gas production from a reservoir that has been drilled. Gas Spiking: Adding gas to an injected ¤uid or treatment to reduce the injected water volume and provide energy for ¤owing the well back after the treatment. Gas-to-Liquids: (1) A processing technology that converts natural gas into high-value commodity liquid fuels and blending agents, petrochemical feedstocks, and chemicals by changing its chemical structure. GTL produces products that can be easily traded as commodities on world markets. (2) A process, based on Fischer-Tropsch technology, which polymerizes several gas molecules into a longer-chain hydrocarbon molecule that can exist in liquid phase at ambient conditions. This process is being developed as a competitor to LNG for commercialization of remote gas reserves. (3) The

conversion of natural gas to a liquid form so that it can be transported easily. Typically, the liquid is converted back to natural gas prior to consumption. (4) A conversion of gas to a liqueed state by compression and cooling. Also, a conversion of gas by chemical methods to an easily transportable liquid hydrocarbon of a more stable, longer chain. Gas Treatment: (1) Removal of gas phase impurities, such as sulfur compounds, carbon dioxide, and water vapor from natural gas. (2) Removal of impurities, condensate, hydrogen sulde, and NGLs from natural gas. Gas Turbine: Heat engine with an air compressor, a combustion chamber, and an exhaust gases expansion turbine. It produces mechanical energy (work) from chemical energy provided by burning fuel. After the combustion, gases expand in the turbine blades transmitting the mechanical energy to the shaft. Part of this mechanical energy is used to move combustion air compressor, and another part remains available to move other external machines, such as electrical generators or gas compressors. Gas Turbine Power Plant: A power plant in which the prime mover is a gas turbine. A gas turbine typically consists of an axial-¤ow compressor that feeds compressed air into one or more combustion chambers where liquid or gaseous fuel is burned. The resulting hot gases are expanded through the turbine, causing it to rotate. The rotating turbine shaft drives the compressors as well as the generator, producing electricity. Gas Well: (1) A well drilled and completed that primarily produces natural gas. (2) A well completed for the production of natural gas from one or more gas zones or reservoirs. Such wells contain no completions for the production of crude oil. (3) A well that produces natural gas that is not associated with crude oil. Gate: A movable barrier for the control of liquid ¤ow. There are two types: Sluice gates have a guaranteed maximum leakage rate. Slide gates are not guaranteed to stop the ¤ow of water and are generally used when leakage does not matter or where suspended solids in the liquid would tend to stop the leakage. Gate Valve: A valve with a sliding bar-common in the oileld as tree valves. Gathering: The process of collecting natural gas ¤owing from numerous wells and bringing it together into pooling areas where it is received into transmission pipelines. Gathering Agreement (Contract): An agreement detailing the conditions for entry of the producer’s gas into the gathering system. Gathering Line: (1) Network-like pipeline that transports natural gas from individual wellheads to a compressor station, treating or processing plant, or main trunk transmission line. Gathering lines are generally relatively short in length and smaller in diameter than the gas sales line. (2) Pipeline that moves natural gas or petroleum from wells to processing or transmission facilities. (3) The ¤ow line from the well to the separator or tank battery. Gathering Lines, Systems: The piping networks installed in oil or gas elds to transport petroleum to a processing plant or bulk shipping point.