Questions Asked in Production Engineer Interview:
Surface Facilities Questions & Answers:
Q: What is Crude Oil?
A: Crude oils is a complex mixture Chemicals, especially hydrocarbons.
Q: how crude oil is classified into: sour and sweet oil?
A: if the sulfur content in crude oil is less than 0.5%, it is considered sweet, if it is more than 0.5% then its considered sour oil.
Q: How crude oil is classified into light, medium, heavy and extra-heavy oil?
A: it is classified according to its API gravity as follows :
– Light Oil: if its API is more than 31.1º.
– Medium Oil: if its API is between 31.1º and 22.3º.
– Heavy Oil: if its API is between 22.3º and 10º.
– Extra-heavy oil: if its API is less than 10º.
Q: if the GOR of a certain well is 300, what does that mean?
A: it means that this well produces 300 Standard Cubic Feet “SCF” per each barrel of oil.
Q: what does “Flowline” means?
A: it is the line that connects the oil well to the first production facility, mainly GOSP “Gas Oil Separator Plant”.
its diameter is determined according to wellhead closing pressure, the distance between the wellhead and the GOSP, 1st stage separator pressure, and the oil production maximum flowrate.
Q: what does GOPS mean?
A: it means “Oil Gas Separator Plant”
Q: what does “Manifold” means in GOSP?
A: it is a collection of pipes and valves used to determine the amount of crude oil that enters each separator, sometimes it is used to determine
the crude oil to go to the test separator or production separator.
Q: what does flare system consists of?
A: it consists of : flare stack, flame arrestor, and sometimes Knock out drum which eliminates oil droplets from
gas stream, preventing them from being burned in the flare.
Q: what are the Auxiliary Systems in any oil production facility?
A: auxiliary systems are: Instrument Air System and Fire Fighting system.
Instrument Air system consists of: Air Compressor, Air Dryer system and instrument air pipelines that reach to control valves.
Fire Fighting System consists of: fire water tank, fire fighting pumps, fire water network and foam network connected to oil tanks.
Q: what is “Choke Valve“?
it is a valve used in oil and gas production wells to control the flowrate and the wellhead pressure, it allows fluid flow through a very small opening, this valve opens according to 64 Basis, i.e., 32/64 means half an inch, 64/64 means 1 inch.
Q: What is “Check Valve” ?
A: this valve guarantee one-way flow, in other words; it prevents back flow, in this way you can protect your equipment that might be affected by back pressure.
Q: what does ESDV means?
A: its an abbreviation of “Emergency Shut Down Valve”, when the facility is shut down ,this valve will be closed or opened according to the required situation; i.e., if it is installed at the discharge of a gas compressor station, it should be open when Shut Down happens to dispose all the gas to the blow down, if it is in the suction of any oil facility, it should be close to prevent any further amount of oil entering the facility.
this valve works after getting certain signals like LAHH in a storage tank or separator, or a PAHH which indicates a high value of pressure.
Q: what is gas separator?
A: it is a pressure vessel that deals with well streams then separate them into gas and liquid phases.
Q: how gas separator is classified?
A: Separators are classified in many ways:
1. according to its Shape into: Vertical Separator – Horizontal Separator – Spherical Separator.
2. according to No. of Phases into: 2-phase separator – 3-phase separator.
3. according to operating pressure into:
– high pressure separators “750 – 1500” psi.
– Medium pressure separators “230 – 750” psi.
– Low pressure separators “20 – 230” psi.
4. according to its Function into: Test Separator – Production Separator, test separator is used to test well productivity , while production separator is used as a production facility.
Q: How can you control the separator pressure?
A: separator pressure is maintained by controlling the amount of gas leaving the separator, that is achieved by controlling the gas outlet with a Pressure Control Valve “PCV” ,if not; manual valve is used, when throttling this valve you will raise the separator pressure, and vice versa.
Q: where the separator oil outlet go?
A: the root of separator oil outlet will be as follows:
– if the oil leaving the separator is wet crude, then it will go to the “Wet Crude Treatment Facility”.
– if the oil contains H2S, it will go to the “Oil Sweetening Units” or “H2S Stripping Units”.
– if the oil do not contain water or H2S, then it will be ready to export, or as a refinery feed.
Q: where the separator gas outlet go?
A: it will go to the gas processing facility if it is nearby, if it is far away, then it will go to the gas compressor station, in order to compress it and help it reach this facility.
Q: what is “Gas Dehydration Unit” and what is used for?
A: it is used for removing water vapor from natural gas using one of liquid desiccants such as TEG or DEG, water and H2S reacts to form H2SO4, and that is why Dehydration unit is used.
Q: why mutli-stage separator plat is used?
A: when the GOR is high, there is a need to separate the gas in multiple stages to decrease the pressure gradually and to separate as much as gas possible, the number of stages is determined by a complex calculations, but you have to take into consideration the cost of installing an additional separator which will need also valves and controls.
Q: what is the purpose of the following separator internals?
– Inlet Diverter: making a sudden change in flow speed and direction, helping the initial separation of gas.
– Mist Extractor: to extract the oil droplets from gas leaving the separator.
– Wave Breaker: to prevent wave formation inside the separator, the thing that confuse the level control.
– Vortex Breaker: to prevent vortex formation at the liquid outlet stream, the thing that cause gas pockets.
Q: what is the relation of volumetric flowrate to Retention Time?
A: according to the following equation , it is inverse ratio:
Q: what is Liquid carryover, and how it is happened?
A: it occurs when liquid droplets leaves the separator with oil outlet stream, it has many causes:
1. when the oil entering the separator is much more that its capacity.
2. a problem in the oil outlet valve, this thing will raise the oil level inside the separator, and it may reach the gas outlet.
3. a problem in the gas outlet valve, this thing will cause the separator pressure to be decreased, hence the ΔP between the well and the separator and then the flow to the separator is increased.
Q: what is Gas Blowby, and how its is happened?
A: it occurs when the gas comes out with liquid phase, in this way gas pockets will be formed in the oil pipeline.
it has many causes:
1. when the separator pressure is increased suddenly to high values, this will cause the level to be decreased to a very low level and helps the gas to go with liquid.
2. a problem in the gas outlet valve, or a human mistake when input vessel pressure.
Read Also Liquid Carry Over and Gas – Blowby in Oil – Gas Separators
Q: what is Foaming in oil gas separator?
A: foam is s small bubble of gas surrounded by a thin film of oil, it decrease the separation efficiency and confuse the liquid level transmitter. this phenomenon reduce the retention time because foam takes a volume in the separator. we can handle this in 2 ways:
1. installing “Defoaming Plates” inside the separator.
2. adding chemicals called “Foam Depressants” .
read also Foam in Oil – Gas Separator
hope you will make use of these questions and answers, which are essential for the junior production engineer “oil production and treatment Surface facility”, such as operators technicians and engineers.