Oil

What is Oil?

Oil is a liquid fossil fuel, which scientists believe formed millions of years ago underground by natural processes. Oil has become one of the main sources of energy for transport. Today it is estimated that the world uses more than 80 million barrels of oil each day , while Australia is estimated to use around 875,000 barrels per day.

Oil and gas are formed by a similar process and often occur together.

Most scientists believe that oil was formed from living organisms that died millions of years ago in shallow oceans and seas.

After drifting to the bottom, these organisms were covered by further layers of organic remains, sand and rocks. Scientists believe that as the remains were covered before they could decay, this allowed anaerobic bacteria, assisted by heat and pressure, to begin the process of turning them into oil and gas.

Over thousands of years, oil was trapped deep underground. As the earth shifted and buckled the oil flowed through fault lines into pockets of porous rocks such as sandstone and limestone. Where these porous rocks were under impermeable rock, such as granite or marble, the oil was trapped and could not evaporate to the earth’s surface.

Thousands of years ago people found oil bubbling up to the surface in certain places around the world. This was used as a medicine, for lighting and even as a weapon.

However it wasn’t until the 19th Century that people began systematically looking for oil, initially using it primarily to extract kerosene for lighting and then petrol and diesel for fuel.

Today hundreds of thousands of oil wells around the world extract oil from under the ground.

Over the years, the organisms decayed in the sedimentary layers on the sea or lakebed. In these layers, there was little or no oxygen present. The remains mixed with the sediments and formed a hydrocarbon, rich substance. Over thousands of years new sedimentary layers were deposited. They exerted intense pressure and heat on the source rock, turning the organic material into crude oil and natural gas. The oil flowed from the source rock and accumulated in thicker, more porous limestone or sandstone, called reservoir rock. Movements in the Earth trapped the oil and natural gas in the reservoir rocks between layers of impermeable rock, or cap rock, such as granite or marble.