Uses of Petroleum

Petroleum (or crude oil), is also known as "black gold" (due to its constant want in the world), and it's a thick, dark brown or greenish liquid that can be found in the upper strata of some areas of the Earth's crust. Being a mixture of several hydrocarbons, it's used mostly, by volume, for producing fuel oil and gasoline (petrol), both important sources of what's been called "primary energy", and for producing many chemical products, including solvents, fertilizers, pesticides, and plastics. (The 88% of all petroleum extracted is processed as fuel; the other 12% is converted into other materials such as plastic). Since petroleum is a non-renewable resource, many people are worried about the consequences of its depletion.

How does it form?

Two theories have come up in order to explain its origin: the Biogenic and the Abiogenic.

a) Biogenic theory:

According to this theory, crude oil (which is generally viewed as the product of compression and heating of ancient organic materials over the time) it is formed from the decayed remains of prehistoric small marine animals and algae. (Terrestrial plants tend to form coal.) Over millennia this organic matter, mixed with mud, is buried under thick sedimentary layers of material. The resulting high levels of heat and pressure cause the remains to metamorphose, first into a waxy material known as kerogen, and then into liquid and gaseous hydrocarbons in a process known as catagenesis. The concentration of hydrocarbons in a trap (a sort of drain) forms an oil field, from which the liquid can be extracted by drilling and pumping.

Oil forms at a specific temperature range, called the "oil window". Below the minimum temperature oil does not form, and above the maximum temperature natural gas forms instead.

Three conditions must be present for oil reservoirs to form:

*a rich source rock,

*a migration conduit, and

*a trap that concentrates the hydrocarbons.

The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where kerogen breaks down to oil and natural gas by a large set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions.

Abiogenic theory

The idea of abiogenic petroleum origin was championed in the Western world by astronomer Thomas Gold based on thoughts from Russia (mainly on studies of Nikolai Kudryavtsev) and it proposes that large amounts of carbon exist naturally in the planet, some in the form of hydrocarbons, which migrate upward through deep fracture networks. This theory is a minority opinion.

Extraction

Locating an oil field is the first obstacle to be overcome. Today, petroleum engineers use instruments such as gravimeters and magnetometers in the search for petroleum. In most cases, the first stage in the extraction of crude oil is to drill a well into the underground reservoir (where oil is stored). If the underground pressure in the oil reservoir is sufficient, the oil will be forced to the surface under this pressure. Gaseous fuels or natural gas are usually present, which also supplies needed underground pressure. A complex arrangement of valves is placed on the well head to connect the well to a pipeline network for storage and processing. This is called primary oil recovery. (Usually, only about 20% of the oil in a reservoir can be extracted this way).

Over the lifetime of the well the pressure will fall, and at some point there will be not enough underground pressure to force the oil to the surface. Then, the remaining oil in the well is extracted using secondary oil recovery methods; that use several techniques to aid in recovering oil from depleted or low-pressure reservoirs. Sometimes pumps, such as beam pumps and electrical submersible pumps