The term oilfield is often used as a shorthand to refer to the petroleum industry, typically referring to the oil production (upstream) side of the entire petroleum business. The entire oil industry can be divided into three sectors: upstream (crude production from wells and separation of water from oil), midstream (pipeline and tanker transport of crude) and downstream (refining and marketing of refined products). Oilfield can also sometimes be referring to actual oil fields, depending on the circumstance.
What is an oil field?
An oil field (as opposed to gas field) is a region with mostly oil in the underneath reservoir rocks. An oil field can also have a gas cap, which is one of the reservoir drive mechanisms, but the real prize is the oil. Because the reservoirs typically extend over a large area, possibly several hundred kilometres across, full field exploitation entails multiple oil wells scattered across the area for onshore production. Wells in offshore production are typically fewer numbers and in concentrated clusters with deviation to reach out to the entire reservoir due to much (~10X) higher drilling cost. In addition, an oil field also has flowlines, processing facilities, and pipelines to transport the sale quality crude.
Global oil field distribution
More than 40,000 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 60 billion barrels (9.5×109 m3) estimated in each. Most oil fields are much smaller. According to the US Department of Energy (Energy Information Administration), as of 2003 the US alone had over 30,000 oil fields.
Oil field environment and logistics
Oil fields are typically located in remote regions with hostile environments, especially because the traditional "easy" oil is running out. Although the majority of the oil fields on still onshore in relatively mild climates, the forefront of oil exploration is going to ultra-deepwater (>5,000ft)and Arctic regions (Sakhalin, Alaska, etc.). Because an oil field may be remote from civilization, establishing a field is often an extremely complicated exercise in logistics.
In deepwater, development of an oil field typically requires an offshore platform that takes in production, process the produced fluids, and pump the sale quality crude to refineries via pipelines. In the offshore areas where a pipeline is not an economical option for exporting the crude, a FPSO is often the choice for a large oil field. Personnel and supplies to the platforms or FPSOs are typically transported by helicopters or boats.
In onshore environment, the typical oil field resembles a small self-contained city in the midst of a landscape dotted with drilling rigs, Christmas trees or pump jacks (known as "nodding donkeys" because of their bobbing arm). Several companies, such as BJ Services Company, Bechtel, Esso, Schlumberger, Baker Hughes and Halliburton, have organizations that specialize in the large-scale construction of the infrastructure and providing specialized services required to operate a field profitably. For instance, workers have to work there for months or years and require housing. In turn, housing and equipment require electricity and water. Pipelines in cold areas may need to be heated. Excess natural gas may be burned off if there is no way to make use of it, requiring a furnace and stacks, and pipes to carry it from well to furnace.
The life cycle of an oil field
The life of an oil field is typically classified into early life, mid life, and late life for production planning. The oil field will be shut down after it is no longer economical to produce hydrocarbon. To extend the life of an oil field, enhanced oil recovery methods can be utilized to recover the oil that is left behind after primary recovery and secondary recovery.
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