ABSTRACT
Generally, the first stage in the extraction of crude oil is to drill a well into the underground
reservoir. Often many wells (multilateral wells) are drilled into the same reservoir, to ensure
that the extraction rate is economically viable. In addition, some wells (secondary wells) may
be used to pump water, steam, acids or various gas mixtures into the reservoir to raise or
maintain the reservoir pressure, and so maintain an economic extraction rate.
