Page 183 - Drilling Technology in Nontechnical Language

174 Drilling Technology in Nontechnical Language Second Edition

so the running costs are less, and the rig only needs one location
to be available. Drilling from an offshore platform is done this
way; an offshore platform could have 30 or more wells spreading
out into the reservoir, all coming together on one (or sometimes
two) platforms (see chapter 4).
▪ Salt dome drilling. If a salt dome creates structures around it
that capture hydrocarbons, it may be easier to drill around the salt
dome rather than through it to reach the reservoir (see chapter 2).

▪ Multiple exploration wells from a single wellbore. A well can
be drilled, evaluated, and then cemented back. The well can
then be deviated from the top of cement to a different target.
This might be done to evaluate different compartments in one
reservoir (where internal barriers in the reservoir chop it into
several parts) or to extend the knowledge of the structure from
one well.
▪ Onshore drilling to an offshore reservoir. If an offshore target
can be reached from shore, the economics can be much better
than drilling from offshore. Wytch Farm on the South Coast of
England is the largest onshore oil field in Western Europe—but

a large proportion of it is offshore (fig. 8–1). Development in this

environmentally sensitive area was made possible economically
by drilling under the sea from the land. The wells expanded the
boundaries of extended reach wells at that time. (An extended
reach well is one where the horizontal displacement of the well is
at least twice the vertical depth.)

Fig. 8–1. Wytch Farm development well schematic

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