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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.
Going
into production
Once oil and/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 extracted compared 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 increase this further.
Crude oil is found in underground pockets or traps. For example:
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| Anticline | A fault which has resulted in oil being trapped |
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 - in fact,
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 pumping may 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 product
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.
Different
methods for different places 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. Some of these are shown in the
diagram. 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. And
a helicopter may be the only way of getting to work offshore!
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.
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.
| To reach the edges of the reservoir, wells are commonly drilled at an angle. It is now possible to 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. |