Petroleum

Petroleum, also called crude oil, is a fossil fuel. Like coal and natural gas, petroleum was formed from the remains of ancient marine organisms, such as plants, algae, and bacteria. Over millions of years of intense heat and pressure, these organic remains (fossils) transformed into carbon-rich substances we rely on as raw materials for fuel and a wide variety of products.

Millions of years ago, algae and plants lived in shallow seas. After dying and sinking to the seafloor, the organic material mixed with other sediments and was buried. Over millions of years under high pressure and high temperature, the remains of these organisms transformed into what we know today as fossil fuels. Coal, natural gas, and petroleum are all fossil fuels that formed under similar conditions.

Today, petroleum is found in vast underground reservoirs where ancient seas were located. Petroleum reservoirs can be found beneath land or the ocean floor. Their crude oil is extracted with giant drilling machines.

Crude oil is usually black or dark brown, but can also be yellowish, reddish, tan, or even greenish. Color variations indicate the distinct chemical compositions of different supplies of crude oil. Petroleum that has few metals or sulfur, for instance, tends to be lighter (sometimes nearly clear).

Petroleum is used to make gasoline, an important product in our everyday lives. It is also processed and part of thousands of different items, including tires, refrigerators, life jackets, and anesthetics.

When petroleum products such as gasoline are burned for energy, they release toxic gases and high amounts of carbon dioxide, a greenhouse gas. Carbon helps regulate Earth’s atmospheric temperature, and adding to the natural balance by burning fossil fuels adversely affects our climate.

There are huge quantities of petroleum found under the Earth’s surface and in tar pits that bubble to the surface. Petroleum even exists far below the deepest wells that are developed to extract it.

However, petroleum, like coal and natural gas, is a non-renewable source of energy. It took millions of years for it to form, and when it is extracted and consumed, there is no way for us to replace it.

Oil supplies will run out. Eventually, the world will reach “peak oil,” or its highest production level. Some experts predict peak oil could come as soon as 2050. Finding alternatives to petroleum is crucial to global energy use, and is the focus of many industries.

Formation of Petroleum

The geological conditions that would eventually create petroleum formed millions of years ago, when plants, algae, and plankton drifted in oceans and shallow seas. These organisms sank to the seafloor at the end of their life cycle. Over time, they were buried and crushed under millions of tons of sediment and even more layers of plant debris.

Eventually, ancient seas dried up and dry basins remained, called sedimentary basins. Deep under the basin floor, the organic material was compressed between Earth’s mantle, with very high temperatures, and millions of tons of rock and sediment above. Oxygen was almost completely absent in these conditions, and the organic matter began to transform into a waxy substance called kerogen.

With more heat, time, and pressure, the kerogen underwent a process called catagenesis and transformed into hydrocarbons. Hydrocarbons are simply chemicals made up of hydrogen and carbon. Different combinations of heat and pressure can create different forms of hydrocarbons. Some other examples are coal, peat, and natural gas.

Sedimentary basins, where ancient seabed’s used to lie, are key sources of petroleum. In Africa, the Niger Delta sedimentary basin covers land in Nigeria, Cameroon, and Equatorial Guinea. More than 500 oil deposits have been discovered in the massive Niger Delta basin, and they comprise one of the most productive oil fields in Africa.