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How oil is formed and what it is made from

Upon thinking of oil, we might picture a thick, dark coloured, viscous and slightly sticky liquid. Most people are aware that oil is a fossil fuel, and that is comes from under the Earth’s surface, via the oil rigs that are dotted out to sea, around the globe. Desolate places where people work hard, living in basic conditions, to bring us the liquid that helps engines to run and machinery to perform. How did the oil come to be there in the first place, though – and what, exactly, is it made from?

Early oil

The beginnings of the oil we use today can be traced back hundreds of millions of years. The elements carbon and hydrogen provide the basic building blocks for the formation of oil, and this process takes many, many lifetimes to be completed. Of the oil we use today, around 10% comes from the Paleozoic age, which occurred over 250 million years ago. The majority (70%) is said to come from the Mesozoic age, which was next, and the remaining 20% hails from the Cenozoic age, which took place around 65 million years ago.

More oil was formed during the Mesozoic age, and this is thought to be down to the climate at that time. The tropical weather resulted in larger ocean plankton populations, which then fell to the floor and began the process of becoming oil.

Fossil fuels

The term “fossil fuel” is used to describe oil and the other products made from it, and it is so named because of how it came to be. Like a fossil, oil is created from layer upon layer of material from flora and fauna; tiny sea life such as plankton, algae and seaweed that died a long time ago. When ocean life dies, it gradually falls to the sea bed. There, it mixed with clay-like material that originated in the rivers that exist upon the sea bed. The result is a rich, muddy substance.

Conditions must be just right in order for oil to form. The muddy matter is only capable of forming in still waters. Then, this substance must not be exposed to excessive oxygen; if it is, then bacteria will quickly decompose the organic matter within the mud and it will soon be gone. If waters are still and oxygen levels low enough to favour the formation of oil, the muddy matter will become buried beneath sediment. This later becomes sedimentary rock, and, in turn, organic shale.

At the beginning, the ocean itself is like the top layer. Underneath this is the mud layer, and the dead flora and fauna are beneath this. Under those is the ocean floor. Later, the sea remains the top layer, but what is now beneath has changed. A thick layer of rock lies immediately under the sea bed, and the crude oil will be found buried under this.

When the mud-like substance becomes trapped under layers of sand, dirt and more dead and decaying matter, oil formation may begin. Over a long period of time, the plant and animal remains became buried ever deeper under the surface. The consequence of this is a rise in temperature and pressure. This occurs when the organic shale lies between one and two-and-a-half miles below the seabed. Shale is then transformed into kerogen, a waxy substance. Shale containing kerogen is called oil shale.

Heating up

A combination of heat, pressure and the matter itself determine whether the original flora and fauna are destined to become oil or natural gas. If the oil shale’s temperature is over 90°C but under 160°C, then the so-called “oil window” exists and the kerogen becomes oil and natural gas. If temperatures exceed 160°C, the shale will become only graphite and natural gas.

Lower levels of heat make for an oil that is lighter in consistency, and more heat leads to a thicker oil. The most extreme temperatures, meanwhile, tend to lead to the formation of natural gas rather than a liquid substance.

The trapped oil or gas then passes through porous rock, rising until it reaches a point when it can no longer penetrate rock or clay. This rise is due to the fact that oil is lighter than water, so as it moves through it displaces any water present.

Areas known as “reservoir rocks” normally contain large volumes of oil, which have become trapped beneath a thick, dense later of rock. This impermeable rock acts as a seal for the reservoir, preserving it until humans succeed in drilling through to the reservoir.

Down to geology

Sometimes, natural geological changes can result in the oil deposits being drawn closer to the Earth’s surface, and this can make the oil a little easier to reach and retrieve.

This reservoir area is precisely where those working on oil rigs are aiming to reach, so they can draw the oil up to earth and make it into petrol, lubricants, kerosene, waxes and a vast range of other products widely used by modern man.

Offshore drilling workers, to give them their correct title, must drill right through multiple layers of rock and sediment. The equipment they use is known as “production wells’, and these resemble huge drills. They also work in a very similar way. Obtaining oil is a very precise and difficult task, and requires a lot of effort and guidance from industry experts, as well as the offshore drilling workers. The rock that must be drilled through is called “impermeable rock”. If liquids such as water or oil cannot get through such rock, then perhaps it is easy to imagine what a challenging task drilling for oil really is.

Once the oil has been successfully retrieved, it goes through a process of separation and treatment to prepare it for use. This is achieved by combining the oil with water, gas and sand. The water causes emulsification, and after this occurs, the sand, gas and water are separated once more. The oil is then ready to be used for creating all kinds of products, which are sold on to the public and companies all over the world.

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