Written By: Raed Al-Obaidi
Oilfield Operator:
If you work at am oilfield, you need to understand the main and basic oilfield terms, this will help you better understand the operation sequence, and clarifies the whole matter for you.
In this article, you will find a collection of the important Oilfield terms; so let us begin:
Heavy Crude Oil: when the API of the crude Oil is between 10◦ and 22.3◦.
Light Crude Oil: when the API of the crude Oil is more than 31.1◦.
Sour Oil : the crude oil that contains more than 0.5% of sulfur, it is undesired because it has many bad effects such as: it causes corrosion to the equipment and pipelines, it is hard to refine, and it poisons the catalyst.
Sweet Oil : the crude oil that contains less than 0.5% of sulfur.
Wellhead and X-mas Tree: it is an assembly of valves and fittings that are used to regulate the flow of hydrocarbon liquids and gasses from well, it might be an oil, gas condensate or water injection well.
Choke Valve: this valve is used to regulate the flow and pressure from the well, it is in different types, but the most common one is the one with 64 grade basis; i.e., if the choke is 32/64 opening, it means half an inch opening.
Flowline: you need to transfer the hydrocarbon fluids “liquids and gasses” from the wellhead to the first oilfield facility, it comes with different sizes varies from 1 – 24 inches, there are many factors that determines its size such as the design pressure and the maximum flow, it contains many flanges and valves of different classes “150 – 300 – 600 – 900 – 1500 – 2500” , it is connected to a manifold inside the facility.
Valve: a mechanical device used to regulate the amount and the pressure of the fluids passing through it, it is used for many reasons such as: fully close or fully open, restrict and maintain the required flow, prevent reverse flow and relieve pressure “Safety Valves”.
Check Valve : it is used to prevent reverse – flow , in other words; one – direction flow Valve, this valve protects the equipment affected by reverse flow, for example when the well is stopped because of low well pressure, it might be a reverse flow from the oil facility to the well, this reverse flow will be prevented by Check Valve.
Strainer : it is an equipment used to eliminate the small solid particles and prevent them entering the equipment, in this way you can reduce the maintenance periods, there are 2 main types of strainers: Y-Type strainers and Basket Type Strainers, Strainers are installed before pumps, heat exchangers, control valves, gas turbine combustion chambers and many other equipment.
GOR : or Gas Oil Ratio, it is the ratio of the produced gas to the produced oil under the same conditions “same pressure and temperature “, to better understand this term; let’s assume a well with GOR equals 300, this means that each barrel of oil produced from this well will be associated with the 300 standard cubic feet of gas.
Manifold : is a number of pipes and valves used to determine the amount of hydrocarbons entering each separator or tank, it can be used in many other locations such as tank farms, well manifold and any other pipe distribution or gathering.
Header : any pipe used to gather oil, gas or water from different lines and transfer it to the next process unit, for example; in GOSPs there are many headers, used to gather oil, gas and water from multiple separators.
Storage Tank : it is a cylindrical or spherical vessel used to store oil or water, it is used in different stages of oil production and treatment facilities.
Instrument Air System : used to produce dry compressed air which is used in control valves, it consists of air compressor(s) , dryer(s), and instrument air lines which carries dry compressed air to the control valves in the facility.
Flare System : safely burn the excess hydrocarbon gases that can not be recovered or recycled, it consists of flare stack, and flame arrestor which eliminates hydrocarbon liquid drops to prevent their burn in the flare.
GOSP : an abbreviation for Gas Oil Separator Plant, or Degassing Stations in some other text books, it is the facility in which associated gas and water are separated from oil, and is the first stage of crude oil processing, the separation process happens by separator(s), then each stream is gathered by a header to be processed separately.
Hydrogen Sulfide H2S : a poisonous gas exists in associated gas, very dangerous, and a naturally occurring component of crude oil and natural gas.
Produced Water : the water separated from crude oil using Wet Crude Treatment Facility in addition to the Free Water separated from oil in the GOSPs. it is treated, then either injected to the reservoir or used in irrigation.
Separator : a vessel used to separate associated gas and water from crude oil. it comes in different shapes such as vertical, horizontal or spherical, and may be used as production or test separator.
for more details about separators, read this article Gas Oil Separators
Emergency Shut Down Valve : which is also known as ESDV, from its name we can see that its used in emergency cases such as high pressure or level, it shuts down the whole facility by isolating the inlet streams to the process. it is used in many cases, such as very high level, temperature or pressure, it will shut down the whole process by cutting the feed and sometimes reliefs the gas to the flares to ensure the safety of the facility.
Pressure Safety Valve : which is also known as PSV, is used to relieve excessive pressure from tanks or vessels from any increase beyond the specified design pressure or maximum allowable working pressure.
Vessel Manhole : it is a blind flange of a big size 20″ or greater, used in maintenance cases.
Mist Extractor : it is an internal part of gas separator, used to eliminate small oil droplets escaped with separated gas.
Wave Breaker : mechanical plates installed vertically used in horizontal separators to prevent waves in liquid level, which confuses the liquid level controller and make it give different readings.
Vortex Breaker : it is a mechanical structure in certain shape used to prevent vortex near any liquid outlet.
Foaming in separators : caused by many factors but mostly because of the crude oil nature, to prevent this, you can add defoamer chemicals , or by installing Defoaming Plates which are parallel inclined plates inside the separator, foaming cause reduction of separator volume then decreasing the retention time unless the separator is designed to deal with foaming.
Retention Time : the time which the compound spends in a vessel or a column, it is a very vital parameter when designing any vessel, because of the operation requirement of each component, simply; it is calculated by dividing volume of the vessel on the volumetric flowrate.
Carry-Over : it means liquid droplets escaping with gas phase, it is one of the most common problems in oil industry.
Emulsion Water : consider water in oil emulsion, when water is dispersed in oil, each water droplet is surrounded with a thick film of emulsifiers.
Emulsification : two liquids which are not soluble in each other, but one of them is dispersed, it depends on the chemical nature of the two liquids and the viscosity.
Demulsifier : high molecular weight polymers, used to break emulsions tries to equalize the effect of emulsifiers by reducing the surface tension of the water droplet, and weakening the emulsion film.
Wash Water : it is used to remove salts from crude oil by reducing the concentration of salt solution , it is very important to understand that the wash water ration is very critical, because adding a little amount of it will not be sufficient to dissolve salts, on the other hand; adding too much water will cause the wash water to be emulsified.
Natural Gas : is complex mixture of hydrocarbon compounds especially methane with little amounts of nitrogen and oxygen, it has 2 types: associated gas and free gas.
Associated Gas : the dissolved natural gas with crude oil because of the high reservoir pressure, it is produced with oil, then separated in GOSPs
Free Gas : it is produced from gaseous reservoirs.
Corrosion Inhibitor System :Consists of a tank, 2 pumps and injectors, it is used to inject corrosion inhibitor to gas, oil and water lines, especially in the lines expected to corrode internally.
Burn Pit : it is the pit in which volatile hydrocarbon liquids are burnt, they should be large enough to contain the maximum flame .
Compressor Anti – Surge System : when the compressor suction pressure decreases, a surge happens in the suction, and causes many problems, to prevent this; Anti-Surge System was invented, this system receives many signals: compressor suction flowrate, suction and discharge pressures and suction gas temperature, all these values enter this system which in turn gives a feedback to a recycle valve called Anti – Surge Valve to recycle some of the discharged compressed gas to prevent surge.
for more details, read Surge Control in Centrifugal Compressors
Gas Dew Point : is the temperature (at a given pressure) at which the gas starts to condense out of the gaseous phase.
Tri Ethylene Glycol TEG : is colorless liquid used widely in gas dehydration units, its most important feature is that it absorbs water from gas in large quantities, and can be regenerated to 99.9% concentration again.
Hydrates : crystalline materials composed of water and gas “typically methane” , ice – liked , simply; it is gas trapped in within crystalline structure.
for more details, read What are Hydrates and Hydrate Prevention
Control Valves: the valves used to control pressure, temperature, flow , level or any other operation variable, they are used to decrease human operation mistakes, they are used widely in industry in general, and in oilfield facilities in specific.
Interlock : a control protection system used to protect the equipment from human mistakes, for example: it will not allow the pump to operate when the storage tank level is too low; in this way it will protect the tank from collapse due to vacuum pressure.
Heat Exchanger : it is one of the most important equipment used in oilfield facility, it is used for the heat transfer between two fluids, i.e. ; transfers heat from the hot fluid to the cold fluid, and cools the hot fluid also in the same process, it is a way to conserve energy by decreasing the fuel quantity used for this purpose, and it is an economic way also, and that’s way it is called economizer sometimes, it is to be mentioned that there are many types of heat transfer equipment such as: reboiler, cooling towers, heaters, air cooler and condensers, while the most famous types of heat transfer are: shell and tube, plate and frame.
Storage Tank : cylindrical or spherical vessel used to store crude oil, produced or wash water and fire water.
