Petroleum is formed from the remains of prehistoric plants and animals (algae and zooplankton) that have been buried in sand and silt for long periods of time, under high temperature and pressure and in the absence of oxygen. As more and more fossil is buried under sand, the temperature and pressure increase and oxygen level decreases. In such conditions the organic composition cannot rot away like the decomposition of dead plants and animals to form manure. Instead, they are pressurized into oil within rocks known as kerogen.
Primarily, oil is made up of 13% of hydrogen and 85% of carbon; that is why it is called a hydrocarbon. Other elements are considered impurities, and are found in trace amounts (less than 1%) and they include oxygen, sulfur, nitrogen, iron, nickel and copper. Light oils contain up to 97% of hydrocarbon, while heavier oils contain about 50% and other elements. Though the final products result into a homogenous compound, crude oil is heterogeneous, depending on how the atoms are rearranged in their spaces due to temperature and pressure.
Oil is classified based on the location where it is produced, presence of sulfur and density, known as API gravity. Examples of geographical locations of crude oil include West Texas Intermediate (supplies oil to Northern America), Brent (which supplies oil to Europe), Oman (supplies to Asia) and OPEC Reference basket (an oil blend from the Organization of Petroleum Exporting Countries). When crude oil contains relatively little sulfur, it is said to be sweet and when it contains high sulfur, it is said to be sour. It is also referred to as light or heavy if its density is low or high respectively.
Nigeria’s oil is sweet and light and is the largest produced in OPEC.
