On this page, you will find the most common technical oil and gas interview questions.
We will skip over basic questions such as “Tell me about yourself?” or “Why should we hire you and not someone else” and instead will focus on more specific questions directly related to the oil and gas industry.
Whether you are a recent graduate or an experienced professional, by familiarizing yourself with these questions and answers, you will be able to make sure your interview goes as smoothly as possible.
In addition to questions that we will discuss today, depending on the position you are applying you may also be asked questions about specific operating systems, software, or hardware used in your role.
Questions may also focus on safety procedures and regulations, production processes, project management skills, and more.
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Oil and Gas Interview Questions and Answers
1. What is the difference between upstream, midstream, and downstream oil and gas sectors?
- Upstream deals with the exploration and production of hydrocarbons
- Midstream deals with the transportation and storage
- Downstream deals with the refining of crude oil
2. What is the difference between sour and sweet crude oil?
Sour crude contains hydrogen sulfide (H2S) while sweet oil doesn’t. Usually, oil with H2S content above 0.5% is considered to be sour.
3. What are some examples of enhanced oil recovery (EOR)?
Thermal recovery – for example, steam injection in SAGD
Chemical flooding – injecting surfactants or polymers to decrease surface tension
Gas injection – using natural gas or carbon dioxide to lower the viscosity of the oil and increase its mobility
Microbial injection – using bacteria to increase production efficiency
4. What are the most popular artificial lift methods?
Sucker rod pump – downhole plunger is used to displace oil to the surface. The surface engine provides energy to the rod attached to the plunger.
Gas lift – this method involves pumping compressed gas to decrease hydrostatic pressure in the well and allow hydrocarbons to flow more easily to the surface.
An electric submersible pump (ESP) – is a downhole centrifugal pump powered by electricity from the surface and usually used on higher-rate wells.
Hydraulic pump – this method works by pumping pressurized fluid from the surface to supply energy to the pump downhole.
Progressive cavity pump (PCP) – downhole stator and rotor create a cavity that draws oil to the surface. The engine is located at the surface and the mechanical force is transferred by a rotating rod.
5. What is the composition of crude oil?
- Paraffins/Alkanes ( ~25%) –
- Naphthenes/Cycloalkanes (~45%)
- Aromatics (20%)
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6. What are some of the properties used to describe reservoir rock?
Porosity – the amount of void space available in the rock between the rock particles in comparison to the total volume of the rock.
Permeability – describes how easily the fluids can flow through the rock.
Rock Compressibility – describes how the rock volume is affected by changes in pressure.
Fluid Saturation – the volume of a particular fluid in comparison to the total pore volume.
Wettability – describes how the fluids behave on the surface of the rock.
7. What is the API gravity of crude oil and how it is calculated?
API stands for American Petroleum Institute and it is used to demonstrate how the density of crude oil compares to the density of water.
API Gravity = (141.5/SG) -131.5
Specific Gravity (SG) = density of oil/density of water
8. What are the casing and cementing?
Casing involves running a steel pipe into the well to prevent hole collapse, allow more well control, and isolate high and low-pressure zones.
Cementing involves filling the space between the casing pipe and the walls of the drilled hole with cement to stabilize the wellbore and prevent the formation fluids from contaminating groundwater.
9. What are the 3 types of reservoir recovery?
- Primary – conventional oil recovery driven by reservoir pressure
- Secondary – injecting water or gas to increase reservoir pressure and push hydrocarbons toward the producing well
- Tertiary (Enhanced Oil Recovery) – injecting chemicals or increasing reservoir temperature to decrease oil viscosity and increase sweeping efficiency
10. What is the difference between enhanced oil recovery and hydraulic fracturing?
Hydraulic fracturing is usually done right after the well is drilled and is used to create fractures in tight formations such as shale to create additional pathways for hydrocarbons to flow toward the wellbore.
Enhanced oil recovery on the other hand is usually performed on older wells by injecting chemicals or increasing temperature to change the oil properties and make it more mobile.
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11. What is gas flaring and why it is performed?
Gas flaring is burning natural gas released during oil extraction or refining processes. It is performed to dispose of small volumes of unwanted natural gas that cannot be economically shipped to the refinery or used on location.
12. What are the main factors affecting oil prices?
- Production costs – how much it costs to get the oil out of the ground
- Transportation costs – the price of oil depends on where the oil is located and how easy it is to get it to the consumer
- Type of oil – sweet lighter oil will be sold at a premium in comparison to heavier sour oil
- Supply and demand – high demand and low supply will drive the price of oil up
- Market speculation – fears and rumors can move the price of oil in both directions
13. What is pipeline pigging?
Pipeline pigging is the process of using a pig to inspect, clean or repair a pipeline. The pigs are usually pushed down the pipeline by the energy of the fluid flowing through the pipeline.
Pigs come in various shapes and sizes depending on the job requirements but in most cases, they have cylindrical shapes. They are made of soft, durable materials such as rubber, plastic, or foam.
14. How is natural gas formed?
Natural gas is formed deep underground from the decomposition of organic matter such as dead plants and animals.
It is a very slow process and it takes millions of years for natural gas to form this way because organic matter needs to be buried and slowly pushed deeper and deeper underground until the right conditions are met.
There under high temperatures and pressure, this organic matter is slowly converted into natural gas.
15. What are some examples of how natural gas is used?
- Cooking food
- Heating water
- Generating electricity
- Transportation
- Chemical synthesis
- Welding metals
- Making fertilizers
- Hydrogen generation
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16. What is coal bed methane?
Coal bed methane or CBM is a natural gas trapped in underground coal deposits. Methane is either trapped as free gas, dissolved in water, or adsorbed into coal.
17. What are some examples of well logging and why it is performed?
Gamma-ray logging – used to detect natural radiation emitted by the formation. This can be used to distinguish between different reservoir rocks and determine reservoir thickness
Sonic logging – used to measure how fast the sound travels through the formation. This can be used to calculate porosity and the type of rocks in the formation.
Spontaneous potential logging – used to determine the porosity of the formation.
Caliper logging – used to measure the size of the hole.
Resistivity logging – performed to determine the resistivity of the formation rock.
Density logging – used in determining the porosity of the formation.
Neutron logging – performed by emitting neutrons from the tool and then determining how they interact with a formation.
18. What is MWD?
Measurement while drilling (MWD) is used to get real-time information about wellbore trajectory as well as other downhole data.
This data is sent via pressure pulses to the surface where it is received by surface transducers.
19. What are methane gas hydrates?
Methane gas hydrates are formed when methane is combined with water at low temperatures and high pressure. The methane molecules don’t chemically react with water to create gas hydrates but instead are bonded to the water with hydrogen bonds.
After gas hydrate is formed it can stay relatively stable even at temperatures above freezing point.
20. What is H2S and why it is so dangerous?
Hydrogen sulfide is a colorless toxic gas that smells like rotten eggs at low concentrations (0.1 ppm). It is highly toxic and can be lethal even in small quantities (>500 ppm), making it extremely dangerous. It acts by paralyzing the respiratory system.
H2S is also a very flammable gas and can damage metals by allowing hydrogen to diffuse into the metal and making it weaker and easier to break.
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21. What are the main ways to transport crude oil?
- Oil Tankers
- Pipelines
- Trucks
- Rail
22. What Is the difference between Brent and WTI crude oil?
WTI is a light sweet crude oil that comes from the oilfields in the US and is stored at Cushing, Oklahoma
Brent is a bit heavier and slightly sourer and comes from various fields in the North Sea
23. What are some examples of how oil is extracted from the oil sands?
Surface mining – is done by using large trucks that load oil sand and transport it to facilities where it undergoes processing to separate the oil from sand by heating it up with water.
Steam Assisted Gravity Drainage (SAGD) – an in-situ oil sand recovery method that involves drilling two wells just a few meters apart from each other. One of the wells is used for steam injection and the other one is for oil production.
Cold Heavy Oil Production With Sand (CHOPS) – this method is similar to conventional horizontal well drilling operations with the only difference being that sand filters are not installed and sand is allowed to flow into the wellbore along with heavy oil.
Cyclic Steam Stimulation (CSS) – steam is injected into the well for a long period of time to heat up the formation. After the steam injection is stopped, the well is put on production.
Vapor Extraction (VAPEX) – similar to SAGD but instead of steam various solvents, and liquid natural gas are injected into the upper well to dissolve bitumen and allow it to flow into the lower well.
24. What are the 3 types of permeability?
Absolute permeability – describes how a single fluid flows through the reservoir rock. This assumes that there is only one type of fluid in the reservoir.
Effective permeability – describes the flow of a particular fluid in the rock when there is another fluid present. For example, describing how oil flows through the rock when there are both oil and water in the reservoir.
Relative permeability – describes the ratio between effective permeability and absolute permeability.
25. What are some examples of chemicals used in hydraulic fracturing?
Friction reducers – used to lower the pumping pressures
Gelling agents – used to increase the viscosity of the fracturing fluid to improve its sand-carrying capacity.
Breakers – used to break down the gel and prevent formation damage
Biocides – used to get rid of the bacteria in the fracturing fluid that can potentially create unwanted by-products like H2S and damage the formation and equipment.
Non-emulsifiers – help to prevent emulsion between frac and formation fluids
Acids – pumped before the frac to prepare the perforations and formation for the frac
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26. What is LNG?
LNG is a natural gas (methane) that is compressed and cooled to transform it into a liquid form. By compressing natural gas its volume can be decreased by up to 600 times.
27. What is Hydraulic Fracturing?
Fracturing basically means creating small pathways in the formation that allow hydrocarbons like oil and gas to flow more easily into the wellbore.
This is achieved by injecting large volumes of fluid and sand under pressure into the formation to break the rock and create high permeability fractures. Fracturing is often performed in tight formations such as shale that have extremely low permeability.
28. What is the purpose of an oil refinery?
Oil refineries are used to process crude oil into useful products like fuel, lubricants, and petrochemicals. The refining process includes various methods such as fractional distillation, hydro-treating, and catalytic cracking.
29. What are OPEC and OPEC+?
OPEC stands for the Organization of the Petroleum Exporting Countries, a cartel of 13 nations that control significant portions of global crude oil production. OPEC+ is a union of OPEC and non-OPEC countries such as Russia and Mexico, that work together to manage global crude oil supply and control prices.
30. What is a blowout preventer?
A blowout preventer (BOP) is a safety device used to prevent an uncontrolled release of hydrocarbons during drilling and intervention operations. Most BOPs usually have metal-type rams that either seal around the pipe in the well or cut it and hold it in place until it can be safely removed after the well is under control.
Four most common types of rams used:
Pipe Rams – seal around the pipe preventing the well fluids from coming to the surface.
Blind Rams – seal the wellbore when there is no pipe in the well.
Shear Rams – cut through the pipe and fully seal the wellbore.
Slip Rams – prevent the pipe from falling into the well or being pushed upward by the well pressure.
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