User:Kikoeta/Petroleum reservoir

= Article Draft = A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.

Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence of high heat and pressure in the Earth's crust. Petroleum reservoirs are broadly classified as conventional and unconventional reservoirs. In conventional reservoirs, the naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability, while in unconventional reservoirs, the rocks have high porosity and low permeability, which keeps the hydrocarbons trapped in place, therefore not requiring a cap rock. Reservoirs are found using hydrocarbon exploration methods.

Oil field


An oil field is an area of accumulation of liquid oil underground in multiple (potentially linked) reservoirs, trapped as it rises by impermeable rock formations. In industrial terms, an oil field implies that there is economic benefit worthy of commercial attention. Oil fields themselves may extend up to several hundred kilometers across the surface, meaning that extraction efforts can be large and spread out across the area. In addition to extraction equipment, there may be exploratory wells probing the edges to find more reservoir area, pipelines to transport the oil elsewhere, and support facilities.

Oil fields can occur anywhere that the geology of the underlying rock allows, meaning that certain fields can be far away from civilization, including at sea. Creating an operation at an oil field can be a logistically complex undertaking, as it involves not only the equipment associated with extraction and transportation, but infrastructure such as roads and housing for workers. This infrastructure has to be designed with the lifespan of the oil field in mind, as production can last many years. Several companies, such as Hill International, Bechtel, Esso, Weatherford International, Schlumberger Limited, Baker Hughes and Halliburton, have organizations that specialize in the large-scale construction of the infrastructure to support oil field exploitation.

The term "oilfield" can be used as a shorthand to refer to the entire petroleum industry. However, it is more accurate to divide the oil industry into three sectors: upstream (crude oil production from wells and separation of water from oil), midstream (pipeline and tanker transport of crude oil) and downstream (refining of crude oil to products, marketing of refined products, and transportation to oil stations).

More than 65,000 oil fields are scattered around the globe, on land and offshore. The largest are the Ghawar Field in Saudi Arabia and the Burgan Field in Kuwait, with more than 66 to 104 billion barrels (9.5×109 m3) estimated in each. In the modern age, the location of oil fields with proven oil reserves is a key underlying factor in many geopolitical conflicts.

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Unconventional reservoirs
Unconventional reservoirs form in completely different ways to conventional reservoirs, the main difference being that they do not have "traps". This type of reservoir can be driven in a unique way as well, as buoyancy might not be the driving force for oil and gas accumulation in such reservoirs. This is analogous to saying that the oil which can be extracted forms within the source rock itself, as opposed to accumulating under a cap rock. Oil sands are an example of unconventional oil reservoir.

It should be noted that unconventional reservoirs and their associated unconventional oil are always changing in their definitions, as they encompass a broad spectrum of petroleum extraction and refinement techniques, as well as many different sources.

Due to how the oil is contained within the source rock, unconventional reservoirs require that the extracting entity function as a mining operation rather than drilling and pumping like a conventional reservoir. This has tradeoffs, with higher post-production costs associated with complete and clean extraction of oil being a factor of consideration for a company interested in pursuing a reservoir. Tailings are also left behind, increasing cleanup costs. Despite these tradeoffs, unconventional oil is being pursued at a higher rate due to scarcity of conventional reservoirs around the world.