Discovering new reserves of oil is only the beginning of the story. It's then the job of a new team of economists, scientists and engineers to decide whether - and how - to go into large-scale commercial production.
Once oil or gas have been discovered, it has to be established how much is there, how much can be recovered, what its quality is and how the oil and gas can be transported safely to a refinery or terminal. In other words, is the find economically viable? If so, further wells will have to be drilled and production facilities established.
The recovery factor - the amount of oil that can be economically extractedcompared with the total amount estimated to be in the ground - varies widely. Twenty years ago a recovery factor of about 30 per cent was normal. Today the average is about 45 per cent. Improved technology is likely to increasethis further.
Crude oil is found in underground pockets or traps. Gas and water are generally found in the reservoir too - usually under pressure. This pressure is sometimes sufficient to force the oil to the surface of the well unaided and excess pressure may cause problems.
In the early stages of production an oilfield may have freely flowing wells, but as oil is extracted the pressure decreases and pumpingmay become necessary. Alternatively, it may be possible to increase the pressure by injecting further gas or water into the edges of the reservoir.
In other cases, the pressure is inadequate from the beginning and pumps at the bottom of wells have to be used. The fluid extracted from the well usually contains oil, gas and water. It has to be processed so that the crude oil and gas can be transported by pipeline or tanker.
Crude oil is a natural substance whose composition varies. Even in the same oilfield, where oil is obtained from different depths, it can vary greatly in composition and appearance. It may be an almost colourless liquid or a sluggish, black substance, so heavy that it cannot be pumped at atmospheric temperatures. Generally, however, crude oils look rather like thin, brown treacle.
There is no single solution to the problem of getting oil out. Production and transport methods will depend on where the oil is found, and in particular, whether it has been found under the land or under the sea. Obviously, it is a lot harder and more expensive to drill for oil beneath the sea than on land, which is one reason why the majority of the oil that we use is produced onshore.
There are several different types of platform that can be used, depending on the conditions. Usually, the legs of the platform must extend at least 30 metres above the surface of the sea, keeping all equipment well clear of the largest waves. For smaller offshore discoveries it is not usually economic to install a platform. In some cases, floating or underwater production systems controlled remotely have been developed.
Oil is generally produced in places far away from where it is used: in deserts, frozen wastes, jungles or far offshore. A pipeline hundreds of miles long or super-tanker - or both - may be the only way of getting the oil to the refinery where it will be turned into a useable product.
Тo reach the edges of the reservoir, wells are commonly drilled at an angle. It is now possible drill vertically downwards and then outwards horizontally. This can save a great deal of money, as several wells can be drilled from a single, point and oil extracted from thin seams of rock.
(Material supplied by the Institute of Petroleum)
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