Oil industry Jargon de-coded

What comes out of an oil field?
Crude oil. (Texas tea, Black gold)

Gas (Natural gas, Methane).
Condensate and natural gas liquids (only sometimes found in an oil field)

Crude Oil
Crude oil comes in a variety of colours and thicknesses. It may be black, it may be brown, it may be greenish. It may be relatively thin, it may be relatively thick.

The 'thickness', or density, of crude is measured against a scale developed by the American Petroleum Institute. The denser and heavier the oil, the lower on the 'API' scale it is.

Regardless of what it looks like, the raw crude oil as it is pumped out of the ground is not much use. To be able to use crude oil, the different components that make it up need to be seperated out. Crude oil run through various processes in oil refineries will seperate out various proportions of the constituents of that particular crude. But when crude is refined, it yields differing amounts of the various component parts ('fractions'), depending on how the crude was formed, and what kind of organic material it originated from. Crude from one field may have a different 'yeild profile' to crude from a field somewhere else.

Several thousand different chemicals can be identified in the various crude oils.

The huge pressure and high temperature in the deep underground oil reservoir means that some chemical compounds which would be gases at normal temperatures and pressures above the ground remain liquid under the ground, and form a part of the liquid crude. When the crude is pumped up from the depths, the pressure is released and temperature drops. The liquified gases in the crude are then released.
This is normally methane, and is not usually associated with any other volatile compounds which liquify at normal above-ground temperature and pressure. The gas usually associated with oil wells is therefore called 'dry gas'. Historically, the gas that bubbles out as the crude comes to the surface has simply been diverted and burnt ('flared off') from the top of a tall pipe at the well head.

Light crude
Depending on the field, some crude oils are naturally 'runny' and light. They are easy to refine, and are highly sought after. These are lower density oils.

Sweet crude
Crude oil with very little sulfur in it. Excess sulfur has to be removed from crude at the refinery, a process that costs extra money.

Heavy crude
Others are very thick, viscous, and heavy. Heavier oils are often found relatively close to the surface. Any lighter more volatile components that might have been formed have vaporised and found their way to the surface and disappeared. They are made up of large molecules such as hexadecane (16 carbon & 34 hydrogen atoms, or C16H34) and octadecane (18 carbon & 38 hydrogen atoms or C18H38) They have to be refined in specialised refineries especially built to handle them. These large molecules are split or 'cracked' into smaller molecules. Hexadecane - in effect fuel oil - can be cracked down to a mix of octane, hexane, and a little ethylene. Octane and hexane are components of gasoline. This is done by heating.

Sour crude
Some crudes are naturally high in sulphur. If there is more than 2.5% sulfur present, they are called 'sour' crudes.

See below

Natural gas liquids
See below

What comes out of a gas field?
Gas (Natural gas, Methane).

Condensate and natural gas liquids (frequently associated with a gas field)

The pressure and high temperatures in the deep underground gas reservoir means that some low boiling point hydrocarbon compounds (which would be liquids at normal temperatures and pressures above the ground) become gases under the ground.

These 'gasified liquids' form a part of the flow of gas when it is piped up from the reservoir. When the gas is flows up from the depths, the pressure is released and temperature drops. The 'gasified liquids' in the cooling gas stream then condense (just as steam condenses back to water as it cools). These liquid condensates and natural gas liquids are quite usual in gas fields. The gas from gas fields is therefore usually 'wet gas'.

Natural gas liquids 
Natural gas, as sold to the consumer, is methane. Gas wells (and the gas on top of oil wells) contain 5% to 20% of gases and 'gasified liquids' that are not methane.

These 'other' hydrocarbons in the natural gas (methane) stream are either-

(1) gaseous hydrocarbons that can be relatively easily turned into a liquid with application of moderate pressure or freezing,
or :
(2) liquid at normal temperatures and pressures (known as natural gas condensate, or 'natural gasoline'),

The 'normally liquid' portion of the 'natural gas liquids' can be separated from the gas stream either at the oil or gas fields adjacent facilities, or elsewhere at a specialist natural gas processing plant.

The term 'Natural gas liquids' includes both the 'condensed' gaseous liquids captured at specialised natural gas plants, and the 'normally liquid' lease condensate, often removed right at the wellhead.

The gaseous liquids are usually made up of both:
(i) lighter hydrocarbons, predominatly ethane, and propane, and
(ii) heavier hydrocarbons, such as pentane and heavier.

(1) The smaller molecules such as ethane, ethylene, propane, butane, butylene, isobutane, and isobutylene can be retrieved from the natural gas stream and converted into liquids at the specialist natural gas processing plants by methods such as freezing and pressurizing. For example, the second smallest molecule, propane, can be turned into a liquid at -42oC.

These now liquified gases may be mixed together and taken to a specialist plant for fractionation, where the individual products are split out and sold separately. Ethane is an important feedstock in the chemical industry, making, amongst other things, ethylene. Propane is used in home heating and cooking. Butane is used as a gasoline additive as an oxygenate to reduce pollution.

If not sold separately, the fractionates can be mixed together to form 'liquified petroleum gases', or LPG. This blend has to remain pressurized to be liquid. This gas can be held in relatively thin walled bottles, so is sold worldwide for both domestic cooking as 'bottled gas' and as a transport fuel.

Some heavier hydrocarbons with more hydrogen atoms, such as hexane and heptane, can also be recovered from the fractionisation of the gas stream. They can be used to 'make' gasoline, but have to be blended with other liquid hydrocarbons from distillation of crude oil in order to be useful. These heavier gaseous natural gas liquids cannot be counted as 'oil equivalent' by themselves - they depend on crude oil to become useful.

(2) The heavier hydrocarbons that are liquid at normal temperatures are often called 'lease condensate', 'natural gas condensate', 'natural gasoline', or 'casinghead gasoline'.

A typical 'natural gas liquids' breakdown would be about 83% gaseous liquids, and 17% natural gasoline (it varies, and can be as much as 22%).

Condensate refers to a specific portion of the 'Natural Gas Liquids'. It is more usually referred to as 'lease condensate'.

'Lease' condensate
This is a mixture of  those heavier hydrocarbons that condense out to a liquid at normal pressure and temperature which is recovered from the natural gas in the lease operators separation facilities near by the gas field.

It excludes the lighter gaseous molecules in the gas stream, such as propane and butane. As mentioned, these are recovered at specialist natural gas processing plants (see below).

LNG - Liquified Natural Gas
Natural gas (methane) can be transported in its normal gaseous state inside a pipeline. But transcontinental gas pipelines are very expensive. As a result there is increasing demand for natural gas that has been compressed and cooled (to minus 160 degrees celsius) until it is liquid - at which point it is around 1/600th of its original volume - then transported by ship to a facility that can turn the liquid back into a gas in a controlled manner. The gas can then be distributed via pipelines in the usual way.

What comes out of a refinery?

Break-downs of the crude oil that went in.

Crude is heated through a defined temperature range that causes the liquids in the desired fraction to boil off. For 'straight run' gasoline, for example, as the crude is heated at the bottom of a tall 'still' the low boiling point liquids that make up gasoline all vaporise. These 'gasoline vapors' reach the top of the still where temperatures are not more than 200oC, and the vapors of the low boiling point fraction of the crude are drawn off and condensed . It is hotter lower down the column, and higher boiling point liquids are first vaporised, then drawn off and condensed at this lower point.

These tall column stills are known as 'fractionating towers'.

The distilled liquid fractions may then be further refined by removing impurities with various chemicals.

The less desirable higher boiling point liquids that make up 'kerosene' are usually further broken down using catalysts to more desirable liquids suitable for gasoline and for making aviation gas. The gasoline liquids from this process are blended with 'straight run' gasoline. A variety of other chemical techniques, such as isomerisation and dehydrogenation, are used to improve some refinery liquids for use in gasoline.

The light gas oils, or fuel oils, can either be further split for manufacture of more gasoline, or retained and refined for when demand for furnace oil is high (winter), or when extra quantities of deisel fuel are needed. Refineries have some flexibility in changing the product mix between more or less proportions of gasoline versus fuel oils, but it can't be done instantly.

The type of irreducible residues that remain from distillation depends on the makeup of the crude. It may be tars, or 'asphalt'

Some crudes - heavy crudes - have no appreciable gasoline components. They have to be subjected to heating cycles to crack down into useful hydrocarbon liquids to be able to make gasoline. This requires more heating than light crudes. Heavy crudes therefore cost more to process. As a result, heavy crudes are less expensive to buy as the cost of dealing with them is significantly higher and there is less profit in them. In addition, they require specially configured refinery processes requiring more capital to build. Once built, refineries handling heavy crudes make more gross profit (at least) than refineries handling light crude - but only so long as heavu crudes sell cheaper. As more refineries are converted to handle heavy crudes, demand will go up, and the price advatage reduce.

Heavy crude takes more energy to process than light crude. Overall, there is roughly 14%-18% more energy needed to refine a barrel of heavy crude than to refine a barrel of light crude.

The gasoline-burning national car fleet of the USA means that USA refineries try to maximise gasoline production, whereas the increasingly diesel-powered European car fleet means European refineries try to maximise light gas oil and diesel. European refineries typically break a barrel of crude oil down into about 25% gasoline, 50% light gas oil/diesel where USA refineries typically break a barrel of crude down into around 50% gasoline and 25% diesel/heating oil.

Crude oil (UK) or Petroleum (USA) is heated to extract the components with the lowest boiling point. The smaller molecule hydrocarbons that are usually a liquid at ambient temperatures are (smallest molecules to largest) pentane, hexane, heptane,octane, decane, and dodecane. Pentane is a liquid until the temperature hits 36oC, when it volatises into a gas. Dodecane is a liquid until temperatures hit just over 215oC. The other liquids turn into a gas at temperatures between these ranges. When these six liquid hydrocarbons are put into a mixture together, the mixture is called 'gasoline'. Some of the lighter liquids are chemically 'reformed' to make them more suitable as a car fuel.

The heptane component is a straight chain hydrocarbon molecule tending to combust very quickly in high compression engines, causing pre-ignition or 'knocking'. A chemically 're-formed' branch-chained form of octane (C8H18), 'iso octane', is considered the ideal fuel, as it combusts at a slower pace, giving better compression. Iso-octane is given a nominal rating of 100, as the perfectly combusting fuel for modern high compression car engines. Heptane, on the other hand, is given an 'octane rating' of zero.

Blends of gasoline are measured against a standard comprised of a defined proportionate blend of iso-octane and heptane (the 'Research Octane'). The closer to 100 the 'octane rating'* of the gasoline blend is, the better the explosion profile in the engine and the less tendency  to knocking.

Many modern engines have tended to reduce the importance of the octane rating as electronics automatically adjust the timing and fuel:air mix for optimal combustion regardless of the octane rating (to a point).

A barrel of crude ultimately yields about 45% gasoline product.

* Most of the world uses the 'Research Octane Number' (RON) to measure octane. The USA uses an average of RON plus the 'Motor Octane Number'. Thus a 91octane fuel is the equivalent of 87 in USA.

The two heaviest and least volatile components of gasoline, decane and dodecane, when mixed together are known as 'kerosene'. A specially modified blend of kerosine (avgas) is used in jet engines.

A barrel of crude ultimately yields about 4.5% kerosine.

Fuel oils or light gas oil
The liquids with the largest molecules in a crude are hexadecane and octadecane. Heavy crudes have little else. These molecules are heated up and further split apart (with the aid of a catalyst) to make them usable. Hexadecane (C16H34), for example, can be split into various proportions of octane (C8H18), hexane (C6H12) and a small amount of ethylene (C2H4). The octane and hexane liquids are used as components of gasoline.

Light gas oil is also further refined into grades for home heating fuel oil, and highly refined grades for diesel.

A barrel of crude ultimately yields about 36.5% fuel oil.

Lubricating oils
The fraction of the crude that has very many carbon atoms is used as liquid lubricant.

A barrel of crude ultimately yields about 2% lubricating oils.

The fraction of the crude that has even more carbon atoms is used semi-solid grease. High paraffin crudes are best for grease production.

Paraffin wax
The heaviest molecules in the crude are solids at normal temperatures. Paraffin wax is used for candles.

Averaged, a  barrel of crude ultimately yields about 11.5% grease, paraffin wax, tars, ethylene and other miscellaneous products.

The cultural divide

In America, the fuel we put in our cars tank is 'gasoline', always shortened to 'gas'. The tank is called a 'gas tank'.

In the UK and former colonies, the fuel we put in our cars tank is 'petroleum', always shortened to 'petrol'. The tank is called a 'petrol tank'. (But the American term 'gas; has infiltrated the language and is now used interchangably for 'petrol', and almost as frequently).

In USA, the oil that comes out of the ground is called 'crude', or it might be called 'petroleum'. (Petroleum is literally correct, as it comes from the latin 'petra', stone, and 'oleum', oil).

No-one in USA would think of putting 'petroleum' in their car, because it would be tantamount to filling up with crude oil!

In the UK, many cars have been converted to dual fuel - they can run on gasoline or on compressed natural gas. If a driver needs 'gas', they may need gasoline ('petrol') or they may need more natural gas.....

In the UK, the black liquid that comes out of the ground is either called 'crude', or simply 'oil'. Outside the oil industry, crude is never called petroleum in the UK. The idea that you could get petroleum - the stuff you run your car on - straight out of the ground would seem like a bizarre joke.

 © Copyright 2006 Sustainable Living Organisation

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