The definitions provided in the Midstream Glossary are intended for information purposes only and are not meant to serve as authoritative technical terms or definitions. Users are encouraged to refer to the relevant standards and official documentation for comprehensive and accurate technical definitions.
For questions regarding incorrect/outdated entries or suggestion for adding additional terms, please contact Kristy Morrison.
| Term | Definition | Common Use Example |
|---|---|---|
| absorbent | A fluid used to remove components from a gas stream by direct contact. | The absorbent is used to remove liquefiable hydrocarbons from the gas stream as in a lean oil system. |
| absorber capacity | The maximum volume per day of natural gas that can be processed through an absorber at specified absorption oil rate, temperature, and pressure without exceeding desired recovery, pressure drop or other operating limitations. | The absorber's capacity was designed at 200% of the anticipated initial inlet flow rate. |
| absorber | A tower or column that provides contact between natural gas, being processed and a liquid solvent. | The absorber tower is the first vessel of a lean oil process and operates at line pressure. |
| absorption factor | A factor which is an indication of the tendency for a given gas phase component to be transferred to the liquid solvent. It is generally expressed as A = L/KV where L and V are the molar flows of liquid and vapor, and K is the average value of the vapor-liquid equilibrium constant for the component of concern. | As the absorption factor increases, less stages are required for a component to transfer to the liquid solvent. |
| absorption oil | A hydrocarbon liquid used to absorb and recover components from the natural gas being processed. | The absorption oil is circulated through the tower to absorb the NGLs from the inlet gas stream. |
| absorption plant | A plant that processes natural gas with absorption oil, sometimes referred to as a "lean oil" plant. | The original facility was an absorption plant and was converted to a more efficient process to improve recovery and reduce operational costs. |
| absorption tower | Refer to definition of "absorber." | Trays or packing in the absorption tower increase the surface contact area of the oil to improve the plant efficiency. |
| absorption-refrigeration cycle | A mechanical refrigeration system in which the refrigerant is absorbed by a suitable liquid or solid. The most common system uses ammonia as the refrigerant and water as the absorbing medium. Refer to definition of "compression refrigeration cycle." | The facility has air conditioning for offices provided via absorption-refrigeration cycle using the waste heat from the gas turbine power generating plant. |
| absorption | The operation in which one or more components in the gas phase are transferred to (absorbed into) a liquid solvent. | The tower trays are designed to improve absorption rates and improve the plant’s efficiency. |
| accumulator | A vessel used to facilitate the control of the flow of liquid or the separation of liquid from accompanying gas or vapor as the liquid flows through the plant for further processing. | Off-spec product is stored in an accumulator where it can be retained for further processing. |
| acentric factor | A measure of the non-sphericity of molecules. | Components that have the same acentric factor will have similar behavior at the same conditions of reduced pressure and temperature |
| acid gas | A gas stream that contains hydrogen sulfide and/or carbon dioxide. | The removal of the acid gas from the stream results in a directly proportional reduction in volume. |
| adiabatic expansion | The expansion of a gas, vapor, or liquid stream from a higher pressure to a lower pressure in which the enthalpy of the stream does not change. | An example of adiabatic expansion is the pressure drop through a control valve often resulting in cooling. |
| adsorbent | A solid substance used to remove components from natural gas being processed. | A molecular sieve bed is an example of an adsorbent often used to remove water from an inlet stream. |
| adsorption | Removal of certain components from a gas stream onto a solid substance—including, but not limited to, one or more of the following: acid gases, water vapor, or heavier hydrocarbon vapors. | The acid gases, water vapor, and heavier hydrocarbon vapors are adsorbed on a bed of granular solids due to their molecular attraction to the adsorbent surface. |
| air-cooled exchanger (fin-fan unit or aerial cooler) | A fin tube exchanger which utilizes air for cooling. Ambient air contacts the external fins by fan-forced or natural draft to cool the process fluid inside the tubes. | The compressor skid utilizes an air-cooled exchanger to reduce the discharge temperature of the compressed gas stream. |
| allocation (accounting) | A method for determining the amount of a stream attributable to one of a group of streams. | The US government permits allocation measurement with comingling approvals in many cases. |
| allocation (analytical) | A mathematical technique used to combine two chromatographic analyses through a relationship of the heaviest components. | The allocation calculation used the hexanes plus from the TCD to prorate the hexanes plus components on the FID. See GPA 2186 and GPA 2286 for more details. |
| allowable | The maximum rate, composition or process variable permitted by contract or regulatory body. | The operator had to curtail production as they approached the state allowable for the well. |
| American Gas Association (AGA) | A national trade association of the petroleum industry whose members are U.S. and Canadian distributors of natural, manufactured, and mixed gases. AGA provides information on sales, finances, utilization, and all phases of gas transmission and distribution. | AGA technical standards are referenced in the contract for natural gas custody transfer and related activities. |
| American Petroleum Institute (API) | A national trade association of the petroleum industry which is a standardizing organization for the drilling, producing, refining, transportation, and marketing segments of the industry. | API technical standards are referenced in many contracts as well as state and federal regulations. |
| American Society for Testing and Materials (ASTM International) | An international organization which promotes knowledge of the materials of engineering and the standardization of specifications and methods of testing. | ASTM International test procedures are cited in many product specifications. |
| amine plant | A unit designed to remove the sour components of a stream with a contactor and a regenerator to reuse the amine. | The amine plant was designed to use a primary amine (monoethanolamine or MEA) to remove all of the sour components of the feed gas. |
| amine | Any of several compounds such as, but not limited to, monoethanolamine, HOC2H4NH2, (MEA), employed in treating natural gas. | The amines are generally used in water solutions to remove hydrogen sulfide and carbon dioxide from gas and liquid streams. The amine is circulated through the tower to absorb the acid gases, heated to desorb the acid gases, cooled and recirculated through the tower. |
| API Gravity | An arbitrary scale expressing the relative density of liquid petroleum products. The scale is calibrated in degrees API, calculated by the following formula: (141.5 / relative density) -131.5 | When the API Gravity is greater than 10, the petroleum liquid is lighter than and floats on water; if less than 10, it is heavier than and sinks in water. |
| ash | Non-combustible residue from the gasification or burning of coal or a heavy hydrocarbon. | The liquid hydrocarbons are burned to reduce the sample aliquot to ash for subsequent analytical testing. |
| associated gas | Light hydrocarbons produced as a vapor from an oil reservoir. | The associated gas from the production separator increased as the operating pressure decreased. |
| ASTM distillation | Any distillation made in accordance with an ASTM procedure. Generally, it refers to a distillation test to determine the initial boiling point, the temperature at which percentage fractionations of the sample are distilled, the final boiling point, and the quantity of residue. (For example, see ASTM method D-86.) | The results calculated from the ASTM distillation are used in subsequent calculations. |
| atmospheric pressure | The pressure exerted on the earth by the earth's atmosphere. A pressure of 760 mm of mercury, 29.92 inches of mercury, or 14.696 psia is used for some measurements. | Atmospheric pressure may also refer to the absolute ambient pressure at any given location. The absolute pressure (Psia) is the sum of the gauge pressure (Psig) and the atmospheric pressure. |
| B-P mix | A liquified hydrocarbon product composed chiefly of butanes and propane. | B-P mixes that originate from a refinery, commonly contain olefins. The B-P mix commonly conforms to the specifications as defined in GPA Midstream Publication 2140. |
| back pressure | The pressure held on a piece of equipment or a system through which a fluid (gas and/or liquid) is flowing. | Without sufficient back pressure, the liquid may flash in the metering equipment and cause measurement error. |
| backflush valve | A device used in chromatograph plumbing to reverse flow through a column. | The backflush valve was plumbed to send the hexanes plus components to the detector to be displayed on the chromatogram as a single peak. |
| backflush | A reversal of flow through a piece of equipment. | The chromatograph uses a backflush to group heavier hydrocarbons and reduce analysis time. |
| barrel | A unit of liquid volume measurement which in the US petroleum industry equals 42 U.S. liquid gallons. Other applications may define different volumes for a barrel, such as 55 U.S. liquid gallons in the chemical industry. | This field produces approximately 25,000 barrels of crude oil per day. |
| base conditions | The defined pressure and temperature used in the custody transfer of measurement. | Base conditions can be defined by regulatory parties, contractual obligations, and/or company SOP. |
| bath | A container that is controlled to regulate the temperature of any system placed in or passing through it. | The Reid Vapor Pressure liquid chamber is placed in a bath, maintained at 100°F. |
| billion cubic feet (bcf) | An abbreviation of "billion cubic feet." In the United States, a billion is a thousand million, or 109. | This particular field produces over 200 bcf of natural gas per year. |
| blanket gas | A gas phase in a vessel above a liquid phase that is not the source of the liquid phase used for protecting the liquid from air contamination, for reducing the hazard of detonation, or for pressuring the liquid. | Nitrogen is commonly used as a gas blanket over highly volatile liquids. It is often used in batch processing where tanks are constantly being filled and emptied. |
| bleed | To remove or drain liquid, gas, or other contents at a slow rate from a piece of equipment or pipe. | The drip pot has a bleed valve used to drain the accumulated liquids to the skimmer system. |
| blow case | A small tank in which liquids are accumulated and periodically drained by applying gas or air pressure above the liquid level. | A blow case is usually located below a pipeline or other equipment at a location where a pump is not convenient. |
| blowdown | The act of partially or fully emptying or depressurizing a vessel or pipeline. May also refer to the discarded material. | The discarded material is typically called blowdown. |
| boiler | A closed vessel used to heat a liquid. | The boiler produced 650 psig steam. |
| boiling point | The temperature at a given pressure at which a liquid begins to vaporize. | The boiling point of water is 212°F atmospheric pressure at sea level. |
| bottom hole pressure | The pressure measured in a well at a depth which is at the mid-point of the thickness of the producing zone. | The bottom hole pressure was insufficient to lift the reservoir fluid to the surface. |
| bottom hole temperature | The temperature measured in a well at a depth which is at the mid-point of the thickness of the producing zone. | Due to the high bottom hole temperature the production string required very expensive materials. *Bottom hole temperature doesn’t have major application other than in PVT studies. |
| bottoms | The heavy liquid or residual matter which is withdrawn from the bottom of a distillation tower, or other vessel, during processing or while in storage. | Bottoms are the heaviest product remaining in the liquid phase after distillation. |
| Bourdon tube | A thin-walled flattened tube of elastic metal bent into a circular arc whose application to certain pressure gauges and thermometers depends upon the fact that increase of pressure inside the tube tends to straighten it. | The analog gauge used a Bourdon tube for pressure measurement. |
| Boyle's Law | A thermodynamic law which states that for an ideal gas or mixture of ideal gases at a constant temperature, the product of the absolute pressure times the volume is a constant, i.e., PV = K. | Boyle’s Law could be used at low pressure when gas is nearly ideal. |
| breathing | The movement of vapor in or out of a vessel because of a liquid level change or a change of temperature or atmospheric pressure. | Regarding flashing emissions, breathing losses typically refers to the change in pressure and temperature. Working losses are associated with change in level. It is essential to manage the breathing when working with an internal combustion engine. |
| bridging calculation | A mathematical technique used to combine two chromatographic analyses through a relationship of common components other than the heaviest components. | Pentanes from the TCD and FID were used to calculate the factor used in the bridging calculation. See GPA 2186 and GPA 2286 for more details. |
| bs&w | An acronym for “Basic (or bottom) sediment and water”. | The modern term is S&W, which stands for “Sediment & Water”. Sediment and water are entrained in the oil. At the bottom of the tank lies free water and free sediment. |
| Btu | An acronym for “British thermal unit”. A measure of the quantity of energy transferred as thermal energy. | One Btu is equal to the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. |
| bubble cap | An inverted cup or pan-like device with a notched or slotted periphery set over a chimney-like connection on a tower tray. | Bubble caps are designed to give intimate contact between the down-flowing liquid and the up-flowing vapors. |
| bubble point | The temperature and pressure at which a liquid begins to vaporize. | The bubble point of a pure component liquid is commonly referred to as the boiling point. |
| bulk plant | A wholesale distributing point for products made from natural gas and petroleum. | LPG is often distributed from a bulk plant to rural homes for heating use. |
| butane, commercial | A liquefied hydrocarbon consisting predominately of butane and/or butylenes which is of marketable quality. | Likely conforms to the GPA specification for commercial butane defined in GPA Publication 2140. |
| butane, field grade | A liquefied hydrocarbon consisting predominately of normal butane and isobutane which is produced at a gas processing plant. | Also called "mixed butane." |
| butane, normal | A paraffin hydrocarbon compound having the chemical formula C4H10 and having all its carbon atoms joined in a straight chain. | In commercial transactions, a product meeting the GPA specification for commercial butane and, in addition, containing a minimum of 95 liquid volume percent normal butane. |
| butane | A paraffinic hydrocarbon compound having the chemical formula C4H10. | The butane stream is often sold to a nearby refinery for blending with gasoline. |
| butylene | An olefin hydrocarbon compound having the chemical formula C4H8. | Commonly referred to as butene. |
| bypass valve | A valve which permits flow around a process, system, or piece of equipment. | The bypass valve was opened to pressurize the downstream equipment before opening the main valve. |
| calorific value | The amount of heat produced by the combustion of a quantity of material. | The calorific value is often obtained by burning the sample in a controlled experiment. See Heating Value for clarification. |
| calorimeter | An apparatus which is used to determine experimentally the heating value of a combustible material. | A calorimeter was used to determine the heating value for a flaring operation. |
| carbon black | Extremely fine particles of almost pure amorphous carbon usually produced from gaseous or liquid hydrocarbons. | The plant still produces carbon black for the production of tires. |
| carbon dioxide | A colorless gas having the formula CO2. | When in its solid state, it carbon dioxide is commonly called "dry ice", and can be formed in the top portion of a demethanizer. |
| carbonyl sulfide | A chemical compound having the formula COS, a member of the aldehyde groups containing a carbonyl group and sulfur. | It is a contaminant in liquid hydrocarbons, usually removed to meet sulfur specifications. COS combined with oxygen can produce a slow reaction in the pipeline can form CO2 and elemental sulfur. When combined with water, it can slowly form CO2 and H2S. |
| carryover | An upset condition where liquids or solids are present in a separator overhead stream. | The carryover caused equipment failure at the compressor facility. |
| casinghead gas contract | A contract relating to the purchase and sale of casinghead gas. | The casinghead gas contract limited the amount of gas to be used on the lease per day. |
| casinghead gas | The natural gas that collects in the annular space between the casing and the tubing in oil wells. | Casinghead gas can be used as fuel for heater treaters and other equipment on the lease. |
| catalyst | A substance which promotes or alters chemical reactions without itself undergoing a permanent chemical change. | The catalyst in the Claus unit in the gas plant improves the sulfur production and plant product quality. |
| caustic treater | A vessel holding sodium hydroxide or other alkalis through which a mixture flows for removal of sulfides, mercaptans, or acids. | The propane product was routed through the caustic treater to remove the sulfur contaminants. |
| central facility | A processing installation having two or more sources that provides one or more functions. | Central facilities typically perform functions such as separation, compression, dehydration, treating, gathering and/or delivery of gas & liquids. In the midstream sector, these are often known as central processing facilities. |
| Centrifugal compressor | A device that elevates gas pressure by adding kinetic energy/velocity to the gas as it flows through an impeller. | Centrifugal compressors are used in pipeline booster service where high volume and low compression ratios exist. |
| channeling | The non-uniform flow through a portion of a packed bed or tower. | When mol sieve have unevenly distributed moisture, it can cause channeling inside the dehy that doesn't expose the gas well enough to the mole sieve to dry it out. |
| Charles' Law | Half of the ideal gas law equation stating that at constant pressure the volume of a given mass of an ideal gas changes the volume proportionally with change in an absolute temperature. | Charles's law describes how gases tend to expand when heated. The following equation can be used: V2 = V1(T2/T1) |
| Cheater Pipe (Bar) | An extension of a tool designed to add torque. | Cheater pipes are sometimes prohibited by a company's safety policies. |
| chilled mirror test | A type of humidity measurement technique that uses a refrigerated surface to measure the dew point temperature of a gas. | When the stain tube measurement indicated the gas was not within specification for water content, a chilled mirror test was performed to determine the water content. |
| chiller | An alternative name for a heat exchanger which cools process fluids with a refrigerant. | Natural gas runs through a propane chiller in a gas plant before entering separation. |
| Christmas Tree | A slang term referring to the structure of valves on a wellhead. | The technician took a sample at the Christmas tree. |
| chromatogram | A recording of the electrical signal over time from a gas chromatograph detector. | After reviewing the chromatogram, the analyst realized certain peaks for components of interest were not adequately separated. |
| chromatography | A method of analysis that is used to determine the composition of a hydrocarbon mixture by component. | Chromatography is the process that analysts use to determine gas and NGL composition. |
| Claus Process | A gas treatment to convert hydrogen sulfide into elemental sulfur by use of a furnace and catalyst. | Approximately 90-95% of recovered sulfur is produced by the Claus process. |
| color test | A visual test made against fixed standards to determine specification compliance of the liquid clarity. | The Saybolt color scale is the standard for measuring clarity of a petroleum or other liquid products. -16 is the darkest and +30 is the clearest measure on the scale. |
| combustion | The chemical process of rapid oxidation caused by reaction of oxygen from the air with the material that is being burned. | A heat source was added to the natural gas pilot causing combustion. |
| commercial butane | A liquefied hydrocarbon consisting predominately of butane and/or butylenes which is of marketable quality and complies with GPA Publication 2140 specifications. | Commercial butane is used principally as feedstock for petrochemicals, synthetic rubber, and as blending stocks or feedstocks in the manufacture of motor gasolines. |
| commercial propane | A liquefied hydrocarbon product consisting predominately of propane and/or propylene and ready for end use. | Commercial Propane may or may not be odorized and is commonly used for domestic, commercial and industrial fuels. It is also a suitable fuel for low severity internal combustion engines and typically complies with GPA Publication 2140 specifications. |
| compressibility factor | The ratio of the actual volume of a given mass of gas to its volume calculated from the ideal gas law using given conditions of temperature and pressure. | The compressibility factor is usually expressed as "Z" and is not identical to the compressibility of a gas, which is a common misunderstanding. |
| compression ratio | The absolute discharge pressure from a compressor divided by the absolute intake pressure. | A general rule of thumb is not to exceed a compression ratio of 3-3.5 per stage. Exceeding this can exceed rod load and in turn, cause significant damage. |
| compression | The act of decreasing the volume and increasing the pressure of gas by mechanical means. | Compression was needed to get the lower pressure gas into the higher pressure pipeline. |
| compressor clearance | The ratio of the volume remaining in a compressor cylinder at the end of a compression stroke to the volume displaced by one stroke of the piston. | The capacity of a reciprocating compressor is often controlled by changing the clearance. |
| compressor station | A facility consisting of one or more compressors. | Most transmission lines have a compressor station every 100 miles. |
| compressor | A mechanical device that increases the pressure of a compressible fluid by reducing its volume. | Typical compressor types used in the midstream industry to move gas are reciprocating, screw, and centrifugal. Typically, pump refers to devices used to move liquids and compressors are pumps used to move gas. |
| computational fluid dynamics ("CFD") | The process of mathematically predicting physical fluid flow by use of computer modeling. | When combining flow characteristics and physical properties, CFD can be used to calculate the capacity of pipelines or vessels. |
| condensate well | A gas well producing from a gas condensate reservoir. | Condensate wells often require careful production techniques to ensure the well continues to produce. |
| condensate | A mixture of hydrocarbons that have undergone a change in phase from vapor to liquid due to changes in temperature and pressure. | Condensate is often treated as a separate stream in a facility. It is important to remember that condensate and compressor station gas are not the same thing. |
| condenser | A heat exchanger for cooling vapors to the liquid state. | A condenser is used in a refrigeration loop. |
| connate water | Water in a particular formation which fills a portion of the pore space. | Connate water can be produced if the production rate is too high. |
| control valve | A device to regulate the flow and/or pressure of a fluid. | Most separators have control valves on the outlet streams. |
| cooler | A heat exchanger which reduces the temperature of a fluid by transferring the heat to a non-process medium. | The cooler was used downstream of the compressor to reduce the gas temperature. |
| cooling tower | A structure to cool a stream of circulating water through contact with air, which can be induced by natural draft or by fans. | Cooling tower water flows through shell and tube heat exchangers to cool gas in the processing stream or between compression stages. |
| copper strip test | A procedure used to detect the presence of corrosive contaminants in liquid products. | A copper strip test is typically included in the product specification. |
| corrosion coupon | A piece of metal inserted into a flowing stream to monitor corrosion rate and indicate corrosion-inhibitor effectiveness. | Corrosion coupons allow you to see the rate of corrosion without having to take the pipeline or vessel out of service. |
| corrosion test | A test used to determine the presence or amount of corrosive compounds in a product. | A common method for corrosion testing is the copper strip test. |
| cricondenbar | The maximum pressure for a mixture above which no two phase state can exist, regardless of temperature. | The cricondenbar is the highest pressure point on a phase envelope of a mixture. For pure fluids, the cricondenbar is identical to the critical pressure. |
| cricondentherm | The maximum temperature for a mixture above which no two phase state can exist, regardless of pressure. | The cricondentherm is the highest temperature point on a phase envelope of a mixture. For pure fluids, the cricondentherm is identical to the critical temperature. |
| critical density | The density of a substance at the critical temperature and pressure. | The critical density, i.e., density at the critical point, can be found at the intersection of liquid and vapor density. The density of the vapor and liquid are identical at the critical point. |
| Critical Point | The critical point for a mixture is referred to as the state of pressure and temperature at which all intensive properties of the gas and liquid phases are equal. | At the critical point on a phase envelope, the liquid and vapor phases are indistinguishable. |
| critical pressure | The highest pressure at which a substance can exist in the vapor phase. | Above the critical pressure, the mixture cannot be vaporized regardless of the temperature. |
| critical temperature | The highest temperature at which a substance can exist in the liquid phase. | Above the critical temperature, the mixture cannot be condensed regardless of the pressure. |
| cryogenic plant | A gas processing facility which is capable of producing liquid products at very low operating temperatures. | Most cryogenic plants use turboexpanders or J-T Valves to drop the temperature enough to get liquids (C3+) to condense from the gas stream. |
| damper | A valve, or plate, used to regulate the flow of air or other gases. | A damper is used to control the velocity of the hot exit gasses over a waste heat recovery exchanger. |
| DEA unit | An amine plant using DEA for the reduction of hydrogen sulfide, carbon dioxide, carbonyl sulfide, and other acid gases from sour process streams. | The amine plant was changed from MEA to DEA to minimize corrosion. |
| deaerator | A piece of equipment used for removing air, or other gases, from a process stream, steam condensate, or boiler feed water. | The deaerator was not functioning causing the boiler to surge from the entrained gasses. |
| debutanizer | A distillation tower for separating the butane components and lighter from the pentane and heavier components. | The debutanizer is typically downstream of the depropanizer in the fractionation facility. |
| deethanized product | A liquid from which essentially all ethane and lighter compounds have been removed. | Deethanized product can also be referred to as C3+ |
| deethanizer | A distillation tower for separating ethane and lighter components from the propane and heavier components. | The deethanizer was installed downstream of the demethanizer. |
| degradation product | An undesirable substance which is produced because of some reaction such as cracking, dehydrogenation, or polymerization. | This term often implies the formation of a contaminant or low value product. Amines degrade into salts or solids if the regenerator is too hot. |
| dehydration plant | A facility which contains equipment and apparatus designed to remove water from hydrocarbon streams. | The gas did not meet water quality specifications due to the upset condition at the dehydration plant. |
| dehydration | The act or process of removing water from a system or flowing stream. | Dehydration is a common problem for many who attend the hospitality events at GPA Midstream. |
| dehydrator | The equipment and apparatus designed to remove water from hydrocarbon streams. | Common types of dehydrators are molecular sieves, silica gel, alumina, glycol or methanol. |
| deisobutanizer | A distillation tower for separating the isobutane from the normal butane. | A deisobutanizer is sometimes referred to as a butane splitter. |
| delivery point | The location within a facility or piping system where product changes custody from one party to another. | The inlet meter is designated as the delivery point to the gas processing facility. |
| demethanized mix | A hydrocarbon product from which essentially all methane and lighter materials have been removed. | Demethanized mix may be referred to as demethanized product or y-grade. |
| demethanizer | A distillation tower for separating methane and lighter components from the ethane and heavier components. | The demethanizer is often operated at cryogenic temperatures. |
| depropanizer | A distillation tower for separating propane and lighter components from the butanes and heavier components. | The depropanizer is upstream of the debutanizer in a fractionation facility. |
| desiccant | A solid substance used to remove water. | The desiccant in a gas plant is often silica gel or molecular sieve. |
| detonation | Rapid and explosive combustion that causes a shockwave. | For instance, detonation can be a reference to a phenomenon in the internal combustion engine as found in a gas compressor where ignition timing, inadequate air fuel ratios or high operating temperatures causes the fuel to pre-ignite, causing the unacceptable condition of engine knock. |
| dew point | The temperature at a given pressure at which liquid initially condenses from a gas or vapor. | For example, the temperature at which water vapor starts to condense from a gas mixture (water dew point), or at which hydrocarbons start to condense (hydrocarbon dew point). |
| dewater | The removal of free water at the point of accumulation. | For example, filters, strainers, and low-point drains are common dewater points. |
| Diethanolamine (DEA) | A specific secondary amine with the chemical compound formula of HN(CH2CH2OH)2. | DEA is used to remove H2S from a sour gas and allow some CO2 to pass through treated gas. |
| differential pressure | The difference between any two pressures. | Two examples are: (1) difference in pressure between the upstream and downstream taps of an orifice plate from which the fluid volume passing through the orifice is computed; (2) the pressure drop across the trays of a distillation column. Common symbol: DP. Commonly referred to as Delta P. |
| diluents | Components of a mixture that diminish the value of a property under consideration. | Diluents of natural gas, such as nitrogen and helium are often referred to as "inerts". |
| displacement meter | A device that segments flow to measure the volume of a fluid. | Rotary and Diaphragm meters are examples of displacement meters. Displacement meters are often referred to as "positive displacement meters" or "PD meters". |
| distillate | The product that is condensed from vapor to liquid after a thermal distillation process. | The purity ethane product coming out of a dethanizer and the purity propane product coming out of a depropanizer are examples of distillates. |
| distillation test | Refer to definition of "ASTM distillation." | The ASTM D-86 distillation test is commonly used for product specification. |
| distillation tray | A horizontal device in a tower that holds liquid and provides a vapor-liquid contact. | Types of distillation trays include bubble-cap, perforated, or valve trays. |
| distillation | The process of separating a multiple component feed of differing boiling points using selective vaporization and condensation into two or more products. | In lean oil absorption plants, the term is used to describe the separation of product components from lean absorption oil. |
| distribution system | Any system of pipelines and other equipment by which natural gas or other products are distributed to customers, lease operations, or other points of consumption. | An example of a distribution system is the pipeline system by which natural gas is delivered to commercial and residential customers. |
| disulfides | Chemical compounds containing a sulfur-sulfur linkage. | Disulfides are colorless liquids completely miscible with hydrocarbons and insoluble in water. Mercaptans are converted to disulfides in treating processes employing oxidation reactions. |
| downcomer | A pipe intended for the downward transportation of fluids. | Most commonly a part of a system of distillation or contact trays. It is the passageway for fluids from an upper tray to the tray(s) below. |
| drain system | The valves and piping connected to vessels, process piping and other equipment for the purpose of emptying or removing undesired liquids. | Typically drain systems are designed to be "open" or "closed". A sump or trench drain is an example of an open system. Closed systems are typically pressurized and terminate in a "slop" or "recycle" tank. |
| drip gasoline | Hydrocarbon liquid that separates in a pipeline transporting gas into equipment from which the liquid can be removed. Refer to definition of "condensate." | The drip gasoline is often collected upstream of compression facilities. |
| dry gas | A vapor containing only components that will not condense under expected operating conditions. | One should refer to the presence of hydrocarbon liquids in natural gas as "lean" or rich" in contrast to the presence of water in gas as "wet" or "dry". The terms are interspersed many times and making the distinction during a conversation can allay confusion. |
| dual mixed refrigerant process (DMR process) | A process employed in the liquefication of natural gas where two or more refrigerants are mixed and used in conjunction with multiple stages of compression to produce liquified natural gas (LNG) as efficiently as possible. | Any one refrigerant is not efficient enough to produce temperatures low enough to liquify and maintain liquified natural gas at the required low temperature of typically -162C. Therefore, dual mixed refrigerants are used in large scale facilities because of its ability to achieve the required low temperatures. |
| elute | The act of a component leaving a chromatographic column. | Using a chromatograph, methane typically elutes before ethane. |
| emulsion | The dispersion of fine particles of an immiscible liquid and/or solids with another liquid in which the particles are suspended. | Water and crude oil may be mixed to the point an emulsion is created resembling foam. |
| end point | The maximum temperature observed on the thermometer during an ASTM distillation test. | The end point of the D-86 distillation is often used as a specification for some products. |
| Engler distillation | The process of determining the volatility characteristics of a petroleum product by distilling the product through a range of temperatures. | ASTM D-86 is still referred to as the "Engler Distillation" process. |
| enhanced oil recovery (EOR) | A recovery technique that alters the chemical composition of the oil that makes it easier to extract. | EOR is employed after primary and secondary recovery means. |
| enthalpy | A thermodynamic property equaling the sum of a system's internal energy and the product of its pressure and volume. | The heating value is the negative of the enthalpy of combustion at 60 °F (15 °C) and 14.696 psia (101.325 kPa). |
| entrained gas | Gas in the vapor phase trapped within a liquid because of the pressure and temperature surrounding the fluids. | An example of entrained gas would be in a carbonated beverage bottle where you can see the bubbles forming in the bottle per the change in pressure. |
| entrained liquid | Mist-sized liquid droplets suspended in a vapor. | Entrained liquids can be a real detriment to the accuracy of gas flow meters. |
| entropy | The measure of a system's thermal energy per unit temperature that is not available for useful work. | Flow through a control valve does not change a fluid's entropy, however flow through a turbine meter reduces the fluid's entropy. |
| Environmental Protection Agency (EPA) | A branch of the federal government that oversees and enforces the regulation of how humans & industry interact with nature. | The Environmental Protection Agency (EPA) was established on December 2, 1970 amidst increasing public concern about the impact that human activity could have on the environment. |
| Equation of state (EOS) | A mathematical formula showing the relationship between the values of the pressure, volume, and temperature for the mass quantity of a particular substance. | EOS modeling was used to estimate the volume of flash gas produced in the production separator train. |
| ethane recovery | An operating mode or contractual term used in a gas processing plant where the majority of ethane is directed into the liquid stream. | Ethane recovery is chosen when it is more beneficial from an economic or commercial perspective, and/or necessary from a contractual perspective to sell as a liquid rather than a vapor. |
| ethane rejection | An operating mode or contractual term used in a gas processing plant where the majority of ethane is directed into the gas stream. | Ethane rejection is chosen when it is more beneficial from an economic or commercial perspective, and/or necessary from a contractual perspective to sell as a vapor rather than a liquid. |
| ethane-propane mix (EP-mix) | A product defined by specifications in GPA 2108. | EP mixes are primarily composed of ethane and propane. |
| ethane | A paraffinic compound having the formula C2H6. | Ethane can describe a hydrocarbon stream when it is primarily composed of ethane. |
| ethyl mercaptan | A colorless, flammable, volatile liquid compound of disagreeable odor. | Ethyl mercaptan is used as an odorant in LPG and fuel-gas systems to act as a warning agent. |
| ethylene | An olefinic compound having the formula C2H4. | Ethylene's formal IUPAC name is "ethene." |
| evaporative loss | The decrease in volume due to product volatility. | Evaporative loss must be accounted for in marine cargos. |
| evaporator | A vessel or equipment used to heat or expand a liquid into its vapor phase. | The refrigeration exchanger is sometimes referred to as an evaporator. |
| expansion refrigeration | The cooling obtained from the expansion of a gas. See "Joule-Thompson". | Expansion refrigeration is used to cool a gas when a pressure drop is required by the process. |
| expansion turbine | A centrifugal axial flow device through which a high pressure gas's volume is increased to produce work from the pressure, energy, gas, or steam. | Expansion turbines are commonly referred to as "Turboexpanders". |
| extraction | The process of separating one material from another using effort or force. | The extraction of hydrocarbons from underground resevoirs is considered the upstream sector of the oil & gas industry. |
| feed tank | A vessel from which a stream is batched or continuously fed for further processing. | Feed tanks are commonly found at the front end of fractionation plants to stabilize the feed stream to process. |
| field processing unit | Equipment through which a stream passes before the fluid reaches a plant or sales point. | Field processing units may be separator systems, adsorption units, dehydration units, etc. |
| fifty-percent point | The temperature at which half of a material has distilled during an ASTM D-86 distillation test. | Also referred to as mid-boiling point. |
| fin-tube | A pipe having an extended external surface to increase the contact area with outside fluid. | Fin-tubes aid with the heat exchange process. |
| final boiling point (FBP) | The max temperature at which compounds in a mixture evaporate during distillation. | The final boiling point is one of the six criteria to meet the Texas Railroad Commission well classification requirements. |
| fired heater | A furnace in which natural gas or other fuel is burned to provide energy in the form of heat. | Fired heaters are important to refineries and petrochemical plants because they heat and vaporize hydrocarbon fluids to create necessities like gasoline, diesel, and jet fuel. |
| Flame-Ionization Detector (FID) | A measuring system on a gas chromatograph which ionizes the gas, collecting the ions on plates that produce an electronic signal. | The FID is used on a gas chromatograph because of its high sensitivity. |
| flammable | Capable of being ignited. | Most hydrocarbons are flammable. |
| flare gas | Hydrocarbons in a vapor phase that are burned for the purpose of disposal. | A process upset in the plant caused an increase in flare gas. |
| flash point | The lowest temperature at which vapors from a liquid will ignite. | It is important to be aware of the flash point identified on the MSDS for evaluating safety precautions in an area where flammable materials are used. |
| flash tank | A vessel used for liberating the gas out of a liquid product. | Flash tanks are used to further stabilize the liquid product. |
| flashing | The liberation of gas from liquids due to changes in pressure and/or temperature. | Flashing occurred when the liquid was discharged from the final stage of separation to storage tanks. |
| floating liquified natural gas (FLNG) | Water borne production facilities where natural gas is converted into liquid hydrocarbons to form a more practical means for storage or transport. | Floating LNG (FLNG) production processing and storage ships offer a way to develop offshore natural gas on the open sea. These facilities extract, process, liquefy, and store gas from the seabed. The vessels also offload the materials to a tanker and are taken to the market. |
| flooding (processing) | An overload condition of a process column or vessel which is characterized by excessive buildup of liquids. | Flooding in a tray tower of a distillation column can lead to lower efficiency and the separation performance is decreased dramatically. |
| flooding (reservoir) | A means of improving oil recovery by introduction of a fluid to build reservoir pressure. | Carbon dioxide or water can be used in reservoir flooding to improve the oil recovery. This is a means of secondary recovery. |
| formation gas | Gas initially produced from an underground reservoir. | The reservoir had a low ratio of formation gas to condensate. |
| fouling factor | A factor used in heat transfer calculations that represents the resistance to the flow of heat caused by buildup of a foreign substance in the flowing fluids. | A fouling factor was applied to correct the reading of the thermal mass meter affected by buildup. |
| FPSO | Floating production, storage, and offloading vessel used in offshore operations. | FPSOs are typically used offshore where infrastructure is not present and/or possibly cost prohibitive. |
| frac spread | Difference in value of natural gas liquid products as a liquid and as fuel value in natural gas. These are used to determine optimum recoveries in a gas plant. | Frac spread is driven by current commodity values. |
| fractionation facilities | The plant where the fractionation process is performed. | The fractionation facilities were just recently refurbished to handle the richer natural gas streams being processed. |
| fractionation | The process used to describe separation of hydrocarbon components into two or more products through distillation. | Fractionation is required because produced natural gas normally contains associated natural gas liquids. |
| fractionator | The column that separates hydrocarbon components into two or more products through the distillation process. | A new fractionator was installed as part of the overall plant upgrade. |
| freeze valve | A specially constructed and calibrated valve designed and used solely for determining the water content in the propane product. See ASTM D-2713. | The propane product was within specifications as indicated by the freeze valve test. |
| freezing point | The temperature at which a liquid becomes a solid. | The freezing point of water is at 32 degrees Fahrenheit. |
| full well stream | The total flow stream or effluent from a producing well containing all the constituents of the reservoir fluids | The full well stream of this well has a very high gas-oil ratio. |
| gas blanket | The gas that is added to the head space in order to increase the pressure that exists above the liquid product vapor pressure. | An inert gas blanket was used to reduce the emission of light hydrocarbons. |
| gas cap | The natural gas zone located above the oil zone in a reservoir. | A large gas cap in a reservoir reduces the likelihood of needing secondary recovery for the crude oil present. |
| gas chromatograph | An analytical instrument which separates mixtures of substances into identifiable components. | The inlet gas is analyzed by a gas chromatograph (a "GC") to determine the amount of liquefiable hydrocarbons available for processing. |
| gas condensate reservoir | A hydrocarbon reservoir with natural gas which will yield condensate. | A gas condensate reservoir typically does not have secondary & tertiary recovery methods for extended production, whereas an oil reservoir often would. |
| gas constant | A number which mathematically is the product of the total volume and the total pressure divided by the absolute temperature for one mole of any ideal gas or mixture of ideal gases at any temperature. | The gas constant is correct for ideal gases but is only approximately correct for hydrocarbon natural gas streams. R=10.7316 in US Customary units |
| gas drive | A manner of producing crude oil or other liquids from the reservoir wherein the required energy is provided by existing gas pressure. | Sufficient gas pressure in the reservoir created a gas drive, eliminating the need to artificially lift the crude oil to the surface. |
| gas injection | The addition of gas into a reservoir to maintain or increase the reservoir pressure or reduce the rate of decline of the reservoir pressure. | Gas injection is a technique sometimes used to lengthen the producing life of a reservoir. |
| gas lift | A means of enhancing crude oil or water production by injecting gas into the producing well bore. | A gas lift system injects gas into the well bore to provide the energy to bring crude oil to the surface. |
| gas processing plant | A plant which processes natural gas for recovery of natural gas liquids and sometimes other substances such as sulfur. | Gas processing plants were formerly known as gasoline plants, but the term was changed to distinguish gas processing plants from units in refineries that produce gasoline. |
| gas processing | The separation of a natural gas stream into products that meet market specifications. | Gas processing commonly produces residue gas, helium, carbon dioxide, and natural gas liquids as marketable products. |
| gas reservoir | A geological formation containing a single phase fluid that, when produced, may or may not yield condensed liquid, depending on the temperature, pressure, and composition of the reservoir. | The most abundant component in a gas reservoir is typically methane. |
| gas turbine | An engine in which a gaseous fluid, under pressure or formed by combustion, is directed against a series of blades which converts the energy in the expanding gas into rotary motion. | Gas turbines can be used to drive pumps or to produce electricity. |
| gas well | A drilled and cased bore which facilitates the production of the hydrocarbon contents of a gas reservoir. | A gas well may produce petroleum liquids just as an oil well may produce associated gas. Legal definitions vary among regulatory bodies. |
| gas-cap gas | The gas produced in the natural gas zone above the oil zone in a reservoir. | Over producing the gas-cap gas may shorten the life of the producing reservoir. |
| gas-oil ratio | The ratio of gas to liquid hydrocarbon commonly expressed as cubic feet per barrel, with both volumes corrected to standard conditions. | The gas-oil ratio is also sometimes referred to as GOR or flash factor. This is expressed as standard cubic feet per barrel of stock tank liquid. This value can be determined at various places in the production process, including at the reservoir and at various stages of separation. Some regulatory bodies have statutory definitions relative to gas-oil ratio content. |
| gas-well gas | The hydrocarbon vapor produced or separated at surface conditions from the full well stream produced from a gas reservoir. | The gas-well gas produced from this reservoir has proven to be very lean. |
| gas-well liquids | The hydrocarbon liquid separated at surface conditions from the full well stream produced from a gas reservoir. | The gas-well liquids produced from this reservoir have proven to be very rich in aromatic hydrocarbons. |
| gas | A form of matter having no definite shape or volume unless confined. | When not confined, a gas continues to expand. Technically, a gas will not condense when it is compressed and cooled, because a gas can exist only above the critical temperature for its particular composition. Below the critical temperature, this form of matter is known as a vapor because liquid can exist, and condensation can occur. Sometimes the terms "gas" and "vapor" are used interchangeably; however, the term "vapor" should be used for those streams in which condensation can occur which originate from, or are in equilibrium with, a liquid phase. |
| gasoline | A volatile hydrocarbon product which by its composition is suitable for use as a fuel in spark-ignition internal combustion engines. | The price of motor gasoline has gone down over the last few weeks. |
| gathering system | The network of pipelines which carries hydrocarbon production from wells to processing plants or other facilities. | The gathering system in this field has a relatively low pressure. |
| glycol | An alcohol, containing two hydroxyl radicals, used to dehydrate gaseous or liquid hydrocarbons or to inhibit the formation of hydrates. | In the North Sea, injecting glycol into underwater pipelines, carrying produced natural gas to onshore, can be very effective in the prevention of the formation of hydrates. Commonly used glycols are ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG). |
| GPM gpm | Multiple definitions, see below: (1) gallons per thousand cubic feet ("Gal/MCF"): refers to the liquid volume equivalent of a component vapor volume which could theoretically be recovered. (2) gallons per minute describes a rate of flow in gallons per minute for a liquid. | GPM is frequently used to determine the theoretical allocation of products in gas processing. Calculations for GPM can be found in GPA 2172. The gpm flow rate, when proving the meter, should match the flow rate of the meter in service. |
| gravimetric | A measurement made by weighing. | The calibration blend was produced by gravimetric preparation, weighing the calibration blend as it changed. |
| gravitometer | A device for measuring the relative densities (specific gravities) of solids, liquids or gases at a given temperature and pressure. | Gravitometers & flow meters are used when inferred mass measurement is in use. |
| gravity, API | An inverse measure that is used to determine the density of petroleum products in comparison to water. | API gravity is calculated by the following formula: For reference, as the value increases the density decreases and API gravity of water is 10 degrees API. |
| heat exchanger | Equipment used to transfer thermal energy between two or more fluids during cooling or heating processes. | Types of heat exchangers could be shell & tube, plate & frame, air coolers (fin fan), brazed aluminum (BAHX), waste heat, helical-coil, spiral, direct fired, indirect heaters, and others. |
| heat medium | A fluid used for conveying heat from a heat source to heat dissipating devices. | Steam is the most commonly used heat medium globally. |
| heating value | A term used to describe the thermal energy content of a fuel. | Heating value is commonly expressed in terms of British Thermal Units or BTU. |
| hot carbonate process | The formation of a solid material through the combination of hydrocarbons and water under certain pressure and temperature conditions. | The hot carbonate process or "hot potassium carbonate" process is a method used to remove carbon dioxide from gas mixtures, which is commonly referred to as carbon scrubbing. |
| hydrate off | The shutting down or shutting in of a well or pipeline due to ice-like structures being formed. | A high pressure well may require supplemental heating to reduce the potential to hydrate off. |
| hydrate | An ice-like structure, or "clathrate", consisting of twenty or more water molecules that capture in a caged structure hydrocarbon molecules which are formed at high pressure and low temperature. | Hydrates are often a problem to the hydrocarbon industry because they inhibit flow in wells and pipelines. The most common hydrate we encounter in the hydrocarbon industry is a methane hydrate but there are hydrates that contain other hydrocarbons. |
| Hydrocarbon Component Fraction | A portion of mixture of hydrocarbons usually defined by boiling range such as naptha, gas oil, kerosene, etc. | The hydrocarbon component fraction, as determined by a laboratory distillation assay of a composite sample, was found to have a high gasoline content. The hydrocarbon component fraction can be volume, mole, or mass. |
| hydrogen sulfide (H2S) | An extremely poisonous, flammable gas with a readily noticeable odor in small concentrations. When combined with water it can be highly corrosive. | A common reference is "sour gas". Refer to sour gas definition for additional context. Can smell like rotten eggs. However, it quickly kills the sense of smell in high concentrations. |
| ideal gas (also called "perfect" gas) | A gas where properties are calculated based on the assumption the molecules do not interact with each other. | A gas that obeys the ideal gas law expressed as PV=nRT. |
| immiscible | A liquid or solid that is incapable of mixing or attaining homogeneity with another substance. | Two compounds that are incapable of mixing. I.e. oil and water. |
| incinerator | Flame fired equipment which combusts substances and converts them to ash, gas, and heat. | A thermal oxidizer would be an example of an incinerator. |
| indirect heater | Equipment in which heat from a primary source, usually the combustion of fuel, is transferred to a fluid or solid which then acts as the heating medium. | An indirect heater is often used at the well head to prevent a well from hydrating off. |
| inerts | An element or compound that is not reactive or combustible with the surrounding environment. | Nitrogen and helium are examples of inert constituents of natural gases. Inert gasses dilute the gas, do not burn and add no heating value. Inert gases of natural gas are often referred to as "inerts". |
| inflammable | This means the same thing as "flammable". It means something is "capable of being inflamed", not that something is "not flammable". | This term is not preferred because it is easily confused with "not flammable." |
| injection gas | The vapor phase fluid forced by pressure into a producing formation to increase the rate of production or reduce the rate of decline of the reservoir pressure. | Injection gas is used to prolong the economic productivity of a well. |
| injection well | A well through which the injection gas or other fluid flows into the underground formation. | Injection wells can be production wells where bi-directional flow exists. Not all production wells are injection wells. |
| inlet gas | Gas entering a processing plant, facility, or individual piece of equipment. | The inlet gas to a processing plant passes through various pieces of equipment to provide merchantable products. |
| iron sponge process | A method for removing hydrogen sulfide (H2S) from natural gas by passing the gas over a bed of wood shavings which have been injected with a form of iron oxide. | An iron sponge unit was used on the inlet gas to make the products merchantable. |
| isobutane | A hydrocarbon of the paraffin series with the formula C4H10 having its carbon atoms branched (2-methylpropane). | Isobutane is often referred to as "I-butane" or "I-C4". See also "butane, normal" and refer to GPA 2140 for product specification. Isobutane is commonly used for feedstock when producing polyethylene. Isobutane is also used as part of blended fuels, especially common in fuel canisters, used for camping. |
| isomer | Molecules with an identical chemical formula but different chemical structures. | Isobutane and normal butane are isomers of butane, with each having the chemical formula C4H10. |
| jacket water | Water which fills, or is circulated through, a casing which partially or wholly surrounds a vessel or machine element in order to remove, add, or distribute heat and, thereby, to control the temperature within the vessel or element. | Jacket water is often used to protect in freezing conditions or where the heated product is temperature sensitive. |
| Joule-Thomson effect | The change in gas temperature which occurs when the gas is expanded from a higher pressure to a lower pressure. | Commonly referred to as "JT", the effect for most gases, except hydrogen and helium, is a cooling of the gas. This is a technique utilized when liquifying natural gas. JT can also be used as a backup for cryo-expander plants. |
| jumbo tank cars | Rail tank cars having capacities of 30,000 gallons (114m3) or more. | Another group of rail cars known as "small jumbo" have capacities ranging from 18,000 to 22,000 gallons (68-83m3). "Standard" rail tank cars have a capacity of 10,000 to 11,000 gallons (38-42m3). |
| K value | A number that represents the ratio of gas molar fraction to liquid molar fraction. | Refer to the definition of "vapor-liquid equilibrium ratio." |
| knockout | A vessel used to separate free liquids from flowing streams. | Knockout drums are commonly found on flare lines prior to the flare stack. |
| Kragcoe's correlation | A formula representing a possible mathematical relationship for molar mass and liquid density. | The Kragcoe correlation was used for molar mass estimation because the laboratory did not have instrumentation to determine molar mass. |
| lead acetate test | A method for detecting the presence of hydrogen sulfide in a fluid by discoloration of paper which has been moistened with lead acetate solution. | Lead acetate tests are commonly performed using ASTM D4084. |
| lean amine | Amine solution that has been stripped of absorbed acid gases giving a solution suitable for recirculation to the contactor. | The stripping of the lean amine is controlled by adjusting the reboiler heat input. |
| lean gas | Gas containing little or no recoverable natural gas liquids. | Lean gas is typically found as the residue of gas processing plants but can also be produced directly from some hydrocarbon formations. |
| lean oil | Oil from which the absorbed constituents have been removed. | Lean oil is used to absorb constituents from gas streams in lean oil processing plants. |
| light ends | Low boiling point components of a hydrocarbon fluid. | Methane and ethane are typical light ends of hydrocarbon fluids. |
| light hydrocarbons | Low molecular weight hydrocarbons. | Examples of light hydrocarbons are methane and ethane. |
| liquefaction | The process whereby a substance in its gaseous or solid state is liquefied. | Melting and condensation are both liquefaction processes. |
| liquefiable hydrocarbons | The components of a hydrocarbon gas which are typically recovered as liquid products. | Propane and butanes are typical liquefiable hydrocarbons. |
| liquefied natural gas (LNG) | Natural gas that has been converted from a gaseous state to a liquid state, generally by the use of refrigeration. | LNG is created in a cryogenic plant to allow for easier transportation and storage due to higher density. Typically, LNG is most commonly transported via truck, barge, or ship. LNG is not the same as NGL or LPG. |
| liquefied petroleum gas (LPG) | Commercially available fuel products produced from gas processing, fractionation, and refining. | LPG consists of predominantly propane and butane. Also referred to as LP gas. LPG produced from refining, sometimes referred to as LRG (liquified refinery gas), typically contains olefins. |
| liquid desiccant | A liquid used to remove water from other fluids. | Glycols are commonly used as liquid desiccants. |
| Liquid Volume Percent | A unit of concentration representing the space occupied by a component in a liquid mixture relative to the total space occupied by the mixture, expressed as a percentage. | The term volume percent is commonly understood to represent the liquid volume percent, which is also understood to be 1/2 of proof. |
| loading rack | A structural and piping installation alongside a railroad track or roadway used for the purpose of filling and/or emptying railcars or trucks. | Loading racks are commonly found at gas processing plants, terminals, and refineries to load and unload product. |
| looping | Adding piping with a connection to an existing line at each end. | Looping is commonly performed to provide additional capacity, to provide additional connection points for compression or pumping, or to reduce pressure drop. |
| LTX unit (low temperature extraction unit) | A unit which uses the refrigerating effect of adiabatic expansion for improved liquid recovery from rich gas streams. | LTX units may be referred to as LTS (Low Temperature Separation) units. |
| make-up gas | (1) In contractual terms, the amount of gas delivery specified for which a buyer has paid for but not taken. (2) In gas processing, the amount of gas required to keep the inlet volume or energy whole at the outlet. This is typically defined by contract or regulation. (3) In gas analysis, the additional carrier gas added upstream of the detector to achieve optimal flow | We have provided three of the common definitions for "make-up gas" however more use cases may exist. |
| marketable gas | Gas, which meets the purchaser's or the transporter's specifications. | Marketable gas is also referred to as merchantable gas. |
| Mass Percent | A unit of concentration representing the mass of a component in a mixture relative to the total mass of the mixture, expressed as a percentage. | The mass percent was used to convert the mass of liquid to volume. |
| MER | An acronym related to efficiencies. | "Maximum Efficient Rate" (MER) is the highest rate at which a well or reservoir may be produced without causing physical waste in the reservoir. "Most Efficient Rate" (MER) is the highest rate at which a reservoir can be produced without either reservoir or surface physical waste. For example, a reservoir may be produced at the MER but at such a rate, gas production will be in excess of the capacity of facilities in the field to handle the gas; so a lower rate may be set up for the reservoir to avoid surface waste of valuable hydrocarbons in the form of flared gas. |
| mercaptan | Any of a series of compounds of the general formula RSH, analogous to the alcohols and phenols, but containing sulfur in place of oxygen. "R" in the formula above represents the hydrocarbon radical. I.e., methyl-, ethyl-, propyl-, etc. | Mercaptans are used as an odorant to hydrocarbons lacking a smell, such as propane, so that it's presence can be detected. |
| methane | The lightest member of the aliphatic hydrocarbon series, with a chemical formula of CH4. | Natural gas is composed predominately of methane. |
| methanol (methyl alcohol) | The lightest alcohol, having the chemical formula CH3OH. | Methanol is also referred to as "wood alcohol". It is not recommended to drink this. |
| methyl mercaptan | A colorless, flammable, gas compound of disagreeable odor. | Methyl mercaptan was used to odorize the gas sold by the local distribution company. |
| miscible | A property which indicates whether two fluids can be mixed without separation of the fluids. | Alcohol and water are miscible and can be mixed without separation. |
| mist extractor | Vessel internals which remove free liquid from gas. | A mist extractor can be perforated plates, wire mesh, vanes, etc., |
| MMscf | A unit for measuring or expressing the volume of a million cubic feet of gas at standard conditions. The pressure and temperature conditions for the standard measurement must be defined. | MMCF is often used, and the standard condition is inferred but may not always be the case. |
| modular plant | A facility built primarily in off-site shops on fabricated skids and shipped to the facility site upon completion. | A modular plant is also referred to as a skid mounted plant. |
| mole percent | A unit of concentration representing the number of molecules of a component in a mixture relative to the total number of molecules in the mixture, expressed as a percentage. | The analysis reports the mole percentages for the components of interest. |
| molecular sieves | Synthetic zeolites packaged in bead or pellet form. | Molecular sieves are commonly used in recovering contaminants or impurities from liquid and vapor product streams by selective adsorption and/or a catalyst. |
| Mscf | A unit for measuring or expressing the volume of a thousand cubic feet of gas at standard conditions. The pressure and temperature conditions for the standard measurement must be defined. | MCF is often used and the standard condition is inferred but may not always be the case. |
| naphtha | A mixture of hydrocarbons, mostly pentanes and heavier, with a maximum final boiling point of about 400oF. | Naphtha is commonly used to reduce the viscosity of oil to flow through pipelines. |
| natural gas liquids (NGLs) | Liquid-phase hydrocarbons primarily derived from a natural gas stream. | NGLs include ethane, propane, butanes, and natural gasoline. |
| natural gas | A hydrocarbon mixture that exists in a vapor phase consisting of primarily methane and commonly includes various amounts of other hydrocarbons, carbon dioxide, nitrogen, hydrogen sulfide, and/or helium. | Natural gas is colorless, odorless, and is most commonly used as a heating source as well as to generate electricity. Typically, a sulfur-smell is added for early detection of leaks. |
| natural gasoline | A liquid mixture extracted from natural gas consisting mostly of pentanes and heavier hydrocarbons. | GPA Midstream provides specifications for natural gasolines. Natural gasoline is the same thing as what you put in your car, but it comes straight from the ground (i.e. organic gasoline). It is not suggested that you fill your car from a natural gasoline source. |
| odorant | A foul smelling fluid added to a gas or LP-gas to facilitate detection of leaks. | Commonly used odorants will contain light mercaptan such as methyl, ethyl, and butyl. |
| olefins | Hydrocarbons that feature one or more double bonds between two adjacent carbon atoms and are not classified as aromatic. | Olefins are typically not found in wellstreams and are normally produced in oil refining. |
| open flow potential | A test conducted to determine the allowable production rate of a well. | The open flow potential requirements vary from state to state. |
| operating agreement | The contract between interested parties regarding who operates a plant, a system, or similar installation. | Operating agreements typically exist between producers & gatherers, gatherers & processors, or processors & pipeline operators. |
| optimum rate of flow | A production capacity which will provide the ultimate recovery of fluid from the reservoir. | The optimum rate of flow will typically be less than the open flow potential. |
| orifice meter | A differential pressure device used for the measurement of fluid flow. | Orifice meters can measure gas or liquid flows but are primarily used for gas as well as production measurement. |
| orifice plate | A constricting device inserted into a flowing stream for the purpose of creating a measurable differential pressure. | Orifice plates are the primary device of DP meters. |
| outage | For tanks, tank cars and liquid sample containers, the difference between the full interior volume and the volume of liquid therein. For operations, a time period where equipment or systems are unavailable. | For gasoline and lighter products, regulatory bodies set a minimum limit for outage in storage vessels to provide space for expansion of the liquid. |
| overhead | The vapor stream leaving the top of a column or vessel. | Overhead vapor is the stream leaving the top of a tower. Overhead product is the stream leaving the top of a reflux drum. |
| packed column | A a vessel or conduit filled with small objects that are designed to have a relatively large surface area per unit volume to affect separation. | Packed columns are used in gas chromatography whereas bubble trays or other devices are more common in larger separation units. |
| paraffin | A saturated aliphatic hydrocarbon having the formula CnH2n+2. | Paraffin may also be used to refer to a wax-like substance formed by heavier paraffin hydrocarbons (C18H38 and heavier). Pariffinic hydrocarbons also include lighter components like methane that do not form a wax-like substance. |
| peak day requirements | Maximum quantity commitment to deliver or receive gas in a 24-hour period. | The peak day requirement is specified by contract or tariff and may be considerably greater than the daily average flow. |
| peak shaving | The addition of supplemental power to power grids during periods of high demand. | Peak shaving power plants are used only during periods of high demand to lessen the burden on base load power plants. |
| pentane-plus | A hydrocarbon mixture consisting mostly of C5 and heavier components, extracted from natural gas. | Pentane-plus is also called natural gasoline and can be abbreviated C5+. |
| perforated tray | A vapor-liquid contacting plate containing small orifices through which the fluids flow. | Most cryogenic towers contain perforated trays that aid in the separation of liquids and gases. Perforated tray can also be referred to as a “perforated plate”. |
| petroleum | A material occurring naturally in the earth composed predominately of mixtures of chemical compounds of carbon and hydrogen. | Petroleum is utilized to manufacture a significant amount of consumer products. |
| phase envelope | The combination of a bubble point curve and a dew point curve. | The phase envelope for the mixture indicated that at sampling conditions the mixture was two phase. |
| pigging | The act of forcing an object through a section of piping to clean, inspect, or remove accumulated liquid or debris. | Pigging can be performed periodically to improve pipeline hydraulics. |
| pipe dope | A lubricant designed to protect and seal the threads of a metal conduit. | The pipe fitter elected to use pipe dope instead of thread tape. |
| pipeline quality gas | A hydrocarbon vapor product which meets a transmission company's minimum specifications. | Pipeline quality gas is sent down a transmission line to end users. |
| pipeline | A configuration of pipe and other equipment designed to move fluid from one location to another. | Many pipelines are designed to move a specific product, i.e., natural gas, NGL or crude oil, from production or processing facilities to a market. |
| plant products | Merchantable liquid mixtures extracted from natural gas. | Ethane, propane, and y-grade are examples of plant products. |
| plus fraction | A grouping of non-discrete hydrocarbon components in chemical composition. | Plus fractions, i.e. hexanes plus, heptanes plus, and decanes plus, are commonly expressed in analytical reports along with the plus fraction physical properties. C6H14 and heavier are referred to as C6+ (hexanes plus). |
| point of intersection (PI) | A location where a pipeline's direction changes. | In the field, a PI is typically seen on cross country pipelines and may be marked, but often is not designated except on drawings. |
| pressure swing adsorption (PSA) | An adsorption-desorption cycle that is driven by changes in pressure which effects sorbent capacity. | PSA units are often used for instrument air drying. |
| processing agreement | A contract for taking raw gas fluids and converting them into merchantable products. | Processing agreements are typically entered into between gas owners, plant operators, and/or other associated parties to define the split ratios and associated charges for the merchantable products. |
| propane, commercial | A liquefied hydrocarbon product consisting predominately of propane and/or propylene and is ready for commercial use. | Commercial propane typically complies with GPA Publication 2140 specifications. |
| propane, HD-5 | A specific grade of propane meeting the GPA Publications 2140 HD-5 propane specifications. | HD-5 propane is the most common and highest grade propane available to consumers. |
| propane | A paraffinic compound having the chemical formula C3H8. | Propane is most commonly used for heating. |
| propylene | An olefinic compound having the chemical formula C3H6. | Propylene is a colorless and flammable gas and is often referred to as “propene”. |
| pump | A mechanical device that is used to move a fluid. | Typically, pump refers to devices used to move liquids and compressors are pumps used to move gas. Typical pump types used in the midstream industry to move liquids are reciprocating, screw, and centrifugal. |
| pure component cascade (PCC) | A multiple-stage refrigeration cycle used for LNG production to liquify natural gas utilizing 3 types of refrigerants: propane, ethylene and methane. | A PCC unit is often the main refrigeration unit immediately upstream of a methane tower in an LNG facility. |
| raw gas | Unprocessed natural gas. | Raw gas is often the inlet feed to a gas plant for processing. |
| raw mix liquids | Unfractionated product from a gas processing facility. | Raw mix liquids are fractionated to produce merchantable NGL products. |
| real gas | A vapor phase mixture that deviates from the ideal gas law due to intermolecular forces | Real gas volumes are used to calculate the value of natural gas. |
| reboiler | A device used to heat distillation column bottoms to its boiling point. | The liquid product contained too much ethane due to reboiler temperature being set too low. |
| receiver | A vessel in which a process stream or product, especially a condensed overhead, is temporarily stored. | The reflux to the column is obtained from the overhead receiver. |
| reclaimer | A device which captures undesirable high boiling point contaminants of a stream and separates them from the desired lighter materials. | A reclaimer is often used to purified contaminated glycol. |
| recovery | That percent or fraction of a given component in the plant feed which is recovered as plant product. | The demethanizer is often designed for ninety percent ethane recovery. |
| recycle | The return of a stream or a part of a stream to a previous processing location for additional recovery of the desired components and/or for operational control. | Surge control is a specific type of recycle stream. |
| reflux ratio | The term applied to the distillation process to give a relative measurement to the volume of reflux to the overhead product volume. | The reflux ratio is a key parameter to determining the number of theoretical stages required in the column. |
| reflux | In fractionation or distillation, the portion of condensed overhead product returned to the column to enhance achievable purity of the overhead product. | By increasing the reflux, the purity of the overhead product is increased. |
| refrigeration process | A process that uses compression, liquefication, and evaporation for cooling needs. | The refrigeration process aids in the extraction of NGLs from natural gas. |
| regulator | A valve which controls the flow or pressure of liquid or gas through a line. | Regulators are commonly found at meter stations to control the delivery of fluid. |
| Reid Vapor Pressure (RVP) | A product specification for the heavier liquid products as determined by ASTM test procedure D-323. | The vapor pressure is reported as pounds per sq. in. Reid. The pressure approximates, but is somewhat less than, the absolute vapor pressure of the liquid. |
| relative density | The mass of a specific volume of fluid divided by the mass of a specific volume of reference fluid, per the specified conditions. | Relative density of liquids is most commonly calculated using pure water as the reference fluid. Relative density is sometimes incorrectly referred to as specific gravity. |
| relief system | The equipment used for temporarily releasing fluid to avoid a pressure in excess of the design pressure for a vessel or piping arrangement. | Relief systems can also be referred to as over-pressure protection systems and can be installed as an extra safety measure in case regulation systems fail. The most common relief systems are pressure relief valves (PRV) or pressure safety valves (PSV). |
| reserves | Estimated quantities of gas and liquid hydrocarbon reservoir fluids which geological and engineering data demonstrate with reasonable certainty to be recoverable. | The oil and gas reserves in the area are not currently recoverable due to environmental regulations. |
| residue | The material which remains after a separation process. | Residue gas is that gas remaining after the extraction of liquid products. Residue may also be the heaviest liquid or solid remaining after a distillation or other reclaiming process. |
| retrograde condensation | A phase behavior phenomenon where liquids condense from a gas as pressure is reduced. | The opposite of retrograde consendation is normal condensation, where liquids condense from a gas with an increase of pressure. |
| rich amine | A base solution containing the acid gases it is designed to absorb. | Rich amine is sent to the reboiler to remove the acid gases it absorbed in the contactor, creating lean amine which is returned to the contactor to repeat the cycle. |
| rich gas | A hydrocarbon vapor stream containing a sufficient quantity of liquifiable hydrocarbons deemed economically suitable as feed to a gas processing plant and from which liquid hydrocarbon products can be extracted. | Rich gas has higher theoretical liquid hydrocarbon content than lean gas. |
| rich oil | The oil leaving the bottom of an absorber in lean oil processing plants. | Rich oil is the lean oil plus all the absorbed constituents. |
| rotameter | A gauge that consists of a graduated glass tube containing a free float for measuring the flow of a fluid. | The rotameter was replaced with a digital flow meter in the latest model of the analyzer. |
| S&W | Sediment and water contained in hydrocarbon liquid streams. | The S&W content of the oil is often limited to 0.25% by the contract. |
| sales gas | Gas which meets the specifications of the contract. | Water had to be removed from the wellhead gas to qualify it as sales gas. |
| sampling | The collection of a representative portion of a flowing stream for subsequent analysis to determine product quality. | GPA provides multiple options for properly sampling a natural gas stream. |
| satellite system | A system which is located some distance from the plant for which performs a processing function. | Absorber or compressor systems are the more common examples of satellite systems. |
| saturated compounds | Hydrocarbon compounds having essentially no unsaturated carbon valence bonds. | Most natural gas and natural gas liquids are comprised of saturated compounds. |
| saturated liquid | Liquid which is at its boiling point or is in equilibrium with a vapor phase in its containing vessel. | As the pressure of saturated liquid is reduced, vapors are liberated. |
| saturated vapor | Vapor at its dew point. | As the saturated vapor is cooled, liquids condense out. |
| scrubber | A vessel with or without internals used to separate entrained liquids or solids from gas. | A scrubber may be used to protect downstream rotating equipment or to recover valuable liquids from a gas or vapor stream. |
| separator | A vessel utilizing mechanical and/or thermal means of separating a stream containing two or more phases. | The separator is considered two-phase if gas is separated from liquid and three-phase if the liquid is further separated into an aqueous phase and hydrocarbon phase |
| septum | A membrane used to separate two fluids. | The syringe penetrates the septum, and the sample is injected into the GC inlet, keeping the air from contaminating the sample. |
| short-cycle unit | An adsorption process which has adsorption cycles of relatively short duration. | A short-cycle unit is sometimes referred to as a "fast-cycle unit" or "quick-cycle unit". |
| shrinkage | (1) The reduction in volume and/or heating value of a gas stream due to removal of some of its constituents. (2) The reduction in volume of a liquid stream due to removal of or non-ideal mixing of some of its constituents. (3)The reduction in volume when two or more compounds of varying or different sizes are mixed. | Sometimes shrinkage can be referred to as the unaccounted loss of products from storage tanks. |
| shut-in | Cessation of flow caused by upset conditions or human intervention. | The shut-in of a well, plant, pump, etc., occurs when either inlet or outlet valves are closed. |
| sieve tray | A tray with perforations in a fractionation column. | Sieve trays are the most economical, but least efficient, trays for fractionation. |
| single mixed refrigerant (SMR) | Cycle using various components, such as nitrogen, ethylene, methane, propane, butanes and/or i-pentane in place of the pure hydrocarbon refrigerants utilized in the discrete cooling steps of a cascade refrigerant cycle1. | The SMR cycle is simpler and more efficient than the cascade cycle, and it can operate at lower pressures and temperatures. The SMR cycle is widely used for small-scale LNG plants with capacities between 50,000 gallons per day (gpd) and 500,000 gpd of LNG |
| slop or slop oil | A term rather loosely used to denote mixtures of oil produced at various places in the plant which must be rerun or further processed to be suitable for use. | The slop oil is recycled through the process to make it merchantable. |
| solution gas | Gas which originates from the liquid phase in the oil reservoir. | The solution gas is formed as the oil pressure is reduced or oil temperature increased. |
| sour gas | Gas containing an appreciable quantity of hydrogen sulfide and/or sulfur compounds. | Liquids can also be classified as "sour", such as off-spec propane, however the most common product to be defined as sour is natural gas. |
| specific gravity | See relative density. | Relative density is the preferred term. |
| spectator water | Moisture not formed by the combustion reaction that is present due to humidity in the gas or air feeding the combustion. | Spectator water does not contribute to the gross heating value. |
| splitter | A name applied to fractionators, particularly those separating isomers. | The butane splitter tower pressure was decreased to lower the reboiler temperature to separate butane and isobutane. |
| stabilized condensate | A mixture of hydrocarbons that have undergone a change in phase from vapor to liquid due to changes in temperature and pressure, where the vapor pressure is less than a defined value. | The stabilized condensate is often sold at the truck loading station. |
| stabilizer | A name for a fractionation system that reduces the vapor pressure of a liquid product so that the resulting liquid is less volatile. | The temperature of the stabilizer reboiler was raised to lower the vapor pressure of the product. |
| stack | The vertical chimney-like installation that is the waste disposal system for unwanted vapor streams. | The stack gas is continuously monitored for H2S. |
| stage separation system | A system of vessels wherein the liquid portion of the total wellstream is segregated from the gas portion. | The first stage separator vapors are routed to the high-pressure header. |
| stain tube | Cylindrical glass elements of a portable gas detection system filled with a chemical designed to have a colorimetric change when exposed to specific contaminants. | When the stain tube measurement indicated the gas was not within specification, a sample was obtained of the gas in question for subsequent laboratory analysis. |
| standard cubic foot (scf) | A term used to relate a volume of vapor at specified conditions in U.S. customary units. | The contract defines the standard cubic foot for gas measurement as one cubic foot at a pressure of 14.73 psia and 60 degrees Fahrenheit. |
| standard cubic meter | A term used to relate a volume of vapor at specified conditions in metric units. | The contract defines the standard cubic meter for gas measurement as one cubic meter at a pressure of 101.325 kPa and 20 degrees Celsius. |
| steam plant | One of the names given to a boiler and all of its associated equipment. | The steam plant produces 1000 tons per day of steam. |
| steam, dry | Steam at a temperature above its saturation point containing no liquid water. | The dry steam with 20 degrees of superheat is used to heat the inlet stream. |
| steam, saturated | Steam that exists at its boiling point. | The saturated steam was sent through a steam trap to remove the entrained liquid. |
| still | An apparatus used to separate liquid mixture products through the process of boiling and then condensing the vapor. | The simplest standard distillation apparatus is commonly known as a pot still, consisting of a single heated chamber and a vessel to collect purified alcohol. |
| storage tank | A vessel in which liquid products are stored for sale, use, and/or for retention. | Storage tanks, often referred to as stock tanks, provide a point for product retention while specifications are verified. |
| straddle plant | A facility which processes gas being transported through a transmission pipeline. | The operator of a straddle plant is typically different from the operator of the transmission pipeline and must make up the volume or energy content removed from the pipeline. |
| strapping table | A chart that correlates tank volume to increments of depth. | The operator determined the indicated volume of the liquid in the tank by looking up the depth on the strapping table. |
| strapping | The process of calibrating tank capacity in increments of depth. | The tank strapping was always done by a pair of operators for safety. |
| stripper | A column where absorbed constituents are removed from the absorption oil. | A stripper can be used to remove NGLs from absorption oil. |
| stripping factor | An expression used to quantify the efficiency of desorption in an absorption plant. | Mathematically, the stripping factor is KV/L where K = the equilibrium constant for a component, V = the vapor mole fraction of the component, and L = the liquid mole fraction. The stripping factor increases as the flow rate of gas into the stripping column is increased. |
| sulfur dioxide (SO2) | A heavy, colorless, suffocating gas that is, chemically, an oxide of sulfur. Conversion of the gaseous sulfur oxides to sulfur is necessary for corrosion control, for health and safety reasons, and for complying with governmental standards. | The sulfur dioxide emissions were carefully monitored to prevent the formation of "acid rain." |
| sulfur plant | A plant that makes sulfur from the hydrogen sulfide extracted from natural gas. One-third of the hydrogen sulfide is burned to sulfur dioxide, which is reacted with the remaining hydrogen sulfide in the presence of a catalyst to make sulfur and water. | The Claus unit and associated sulfur handling equipment is often referred to as the sulfur plant. |
| sulfur | A pale yellow, non-metallic chemical element. In its elemental state, called "free sulfur," it has a crystalline or amorphous form. In many gas streams, sulfur may be found as volatile sulfur compounds, i.e., hydrogen sulfide, sulfur oxides, mercaptans, carbonyl sulfide. Reduction of their concentration levels is necessary for corrosion control and, in many cases, necessary for health and safety reasons. | The sulfur produced at the Claus plant was sold by train as molten sulfur. |
| summation factor | Specific values for components in a gas mixture that can be used in a simplified method for calculation of compressibility. | The compressibility from the summation factor method agreed with GERG within equation uncertainty. |
| supercompressibility | The square root of the ratio of the compressibility factor of the gas at a base condition to the compressibility factor of the same gas. In the US, the base conditions are generally 60 degrees Fahrenheit and 14.73 psia. | This is an outdated term and has since been updated to utilize the AGA 8/GERG calculation. |
| surge drum | A vessel used to protect downstream equipment from excessive increase in liquid flow rate. | The surge drum was placed between the production separator and the production pump. |
| surge | A sudden increase in liquid flow rate above the normal flow rate. | The surge volume in the accumulator was 10 bbls. |
| sweet | A fluid where the concentration of sulfur compounds is less than a specified limit. | The production reservoir contained no sulfur contaminants, thereby producing sweet gas and sweet oil. |
| synthetic natural gas (SNG) | A fuel gas that can be produced from fossil fuels such as lignite coal, oil shale, or biofuels. | Synthetic gas is sometimes referred to as "substitute natural gas". |
| synthetic or substitute natural gas (SNG) | Methane and components produced by processes other than at a wellhead. | SNG is commonly recovered from the gases produced in a landfill. |
| tail gas | The sour gas not removed in a sweetening unit. | Tail gas is often treated through additional treatment methods after the sweetening unit. |
| tail gate | The end of a processing plant wherein the residue is last metered. | The tail gate is often located at the plant residue sales meter or allocation meter. |
| take-or-pay clause | A contractual term where a one party agrees to receive a minimum quantity of product for a specified timeline or accept penalty for the unused portion. | A seller of product is guaranteed product delivery or payment if the product is not used. A buyer is guaranteeing a level of service or agreeing to pay a penalty. |
| tank | A container used for holding liquid product. | Tanks come in different shapes and sizes such as upright cylindrical or bullets and have various types of roofs, such as floating or fixed. |
| tanker | A water-borne vessel designed for carrying liquid product. | Tankers are often used to transport LNG, NGLs, or Crude Oil via a waterway. |
| temperature correction factor | A factor for adjusting volumes existing at a non-reference temperature to a specific reference temperature. | In the petroleum industry, temperature correction factors are most commonly adjusting to 60oF. |
| theoretical gallons | The amount of liquid condensable per unit volume of gas at specified conditions. | In the U.S., the term GPM (gallons of liquid hydrocarbon per thousand cubic feet of gas) is used. |
| therm | A unit of total energy equivalent to 100,000 Btu (1.055056 108J). | A dekatherm is equivalent to an MMBTU. |
| Thermal Conductivity Detector (TCD) | A measuring system on a gas chromatograph which uses the difference in heat transfer between the carrier gas and the component exiting the gas chromatograph column to create an electrical signal. | The TCD is used on a gas chromatograph due to its ability to detect components that do not ionize. |
| thermowell | A protective housing into a process vessel or a line which provides a protective barrier while allowing the measurement of the temperature of the product. | The advantage of a thermowell is you can remove temperature detectors without taking the vessel or line out of service. |
| ton | A U.S. customary unit of mass equivalent to two thousand pounds. | For reference, a British Imperial ton also known as a Long Ton, is equivalent to 2,240 lbs. |
| tonne | A Metric unit of mass equivalent to one thousand Kilograms. | For reference, a tonne is equal to 2,204.62 lbs. |
| tower | A vertical structure which can serve a variety of purposes and can leverage elevation. | Towers include absorbers, fractionators, stills, cooling towers, etc. |
| tray spacing | The distance between separation devices in a column. | Tray spacing is used in designing a tower to separate certain components from a gas to liquid phase. |
| tray | Separation devices used in processing plants. | Trays are most often used in distillation towers at the processing plant. |
| trayed column | A vessel using separation devices, usually countercurrently, wherein gas and liquid are contacted. | An example of a trayed column is a demethanizer where heat is applied at the bottom causing cryogenic vapors to be expelled from the top of the column and liquids to be expelled from the bottom of the column. |
| treater | A heated pressure vessel that separates water, gas, and other impurities from crude oil during production. | Treaters are often used for the purpose of removing objectionable compounds like water from oil. Treaters are commonly referred to as "heater treaters" or "production treaters". |
| truck dock | The structure that is built for the convenience of loading and/or unloading product via a vehicle designed for the application. | Loading arms and a meter are often associated with a truck dock. |
| turbid | A liquid which is cloudy, opaque, or thick with suspended matter. | The water in the pond appeared turbid. |
| turnaround | The period of time when a facility is shut down for the repair or replacement of equipment or to perform preventative maintenance. | Turnarounds are typically scheduled for preventative maintenance as needed. However, turnarounds can be scheduled last minute due to unforeseen circumstances requiring immediate maintenance. |
| two-phase flow | A condition where fluids in different thermodynamic states coexist. | Two-phase flow is typically a liquid and a vapor. With changes in pressure and temperature, a single phase source can become two-phase. |
| underground storage | A subsurface geological formation used to hold product and allow the product to be retained, added, or removed as required. | Underground natural gas storage facilities, or "UNGSF" as seen in many regulatory documents, may be constructed by dissolving salt from a salt dome, a mined cavity, or an exhausted oil or gas reservoir. |
| unsaturated compounds | Hydrocarbon compounds having one or more unsaturated carbon valence bonds. | Unsaturated compounds are not found in natural gas or natural gas liquids (NGL) because of their relatively high chemical activity. Unsaturated compounds are produced by a thermal cracking or chemical reaction and can be found in synthetic gas (SG) or light refinery gases (LRG). Examples of unsaturated compounds are ethylene and propylene. |
| vapor pressure | The pressure exerted by a gas in thermodynamic equilibrium with its condensed phase at a given temperature in a closed system. | Vapor pressure is used in product specifications for safe transportation, storage, and handling. The liquid pipeline was maintained well above its vapor pressure to facilitate accurate measurement. |
| vapor recovery | A process designed to recover flash gas from operations at a production facility or plant. | A vapor recovery system is often used to reduce emissions. |
| vapor-liquid equilibrium ratio (K-ratio) | A comparison of molar volumes of vapor and liquid for a component at corresponding state conditions. | Vapor-liquid equilibrium ratio (K) is a function of temperature, pressure and composition of the particular system. |
| vapor | The gaseous phase of a product produced from liquids or solids due to changes in pressure or temperature. | By increasing the temperature or reducing the pressure of a liquid, vapors are formed. For example, when water is heated, steam (or vapor) is created. |
| vaporization loss | A reduction in liquid quantity due to a thermodynamic process converting the liquid to a gaseous state. | Vaporization occurs when liquid enters a warmer vessel or when the operating pressure is below the bubble point of the liquid, resulting in a decrease of liquid quantity. |
| vaporization | The thermodynamic conversion of liquid to a gaseous state. | Vaporization can be caused by the absorption of heat from the atmosphere, heating equipment, or from its own heat content when accompanied by a reduction in pressure. |
| vessel retention time | The amount of time a fluid remains in a vessel. | Vessel retention time can be used when sizing a separator to achieve equilibrium between the gas and liquid phases. |
| volatile | A substance's ability to vaporize or evaporate at normal temperatures and pressures. | Ethane is more volatile than propane. |
| volume-weighted average | The mean value of the space occupied by a substance. | The volume-weighted average was used to calculate prior period adjustments. |
| waste heat boiler | A specialized type of boiler that recovers heat from hot exhaust gases produced by industrial processes, like combustion or furnaces, and uses that heat to generate steam or hot water for further use. | Waste heat boiler increase the efficiency of the plant by reducing the net energy used by the plant. |
| weathering test | An ASTM test (D1837) for liquefied petroleum gas for the determination of non-volatile residue in a sample by evaporation. | The weathering test is a method of boiling a liquid to find what residue is left. |
| weathering | The evaporation of liquid by exposing it to the conditions of atmospheric temperature and pressure. | The liquid was weathered to determine the amount of flash gas and the composition of remaining liquid. |
| weight in air | Weight compared to a standard with no correction for atmospheric conditions of air buoyancy. | The weight in air of the liquid was slightly less than when weighed in a vacuum because of the buoyancy of the liquid in the air. |
| weight in vacuum | Weight compared to a standard in a controlled vacuum cylinder or corrected for air buoyancy. | The weight in vacuum of the liquid was slightly more than when weighed in air because of the buoyancy of the liquid in the air. Also known as weight in vacuo. |
| weighted average | A method of computing an average where the contribution of each data point is based on a corresponding data point. | Typical weighted averages of gas flow include averages weighted by flow quantity or flow time. |
| wellhead | The assembly of fittings, valves, and controls located at the surface and connected to tubing, casing, and flow lines of a well so as to control the flow from a reservoir. | The valve at the wellhead was shut so that the pressure at the meter run wouldn't exceed its maximum allowable operating pressure. |
| wet gas | A vapor containing components that will condense under expected operating conditions. | Gas is commonly considered wet gas if it contains water vapor content of more than 7 pounds per MMcf or a btu content greater than 1,100 btu per standard cubic foot. |
| Wobbe Number | The heating value of a gas divided by the square root of its relative density. | The Wobbe Number is the measure of interchangeability between gases. Wobbe Number is sometimes referred to as the Wobbe Index or the Interchangeability Index. |
