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each other. For example, a well may be drilled that passes through
a number of formations on its way deeper underground, or
alternately, it may be efficient in a horizontal well to add multiple
completions to drain the formation most effectively. When it is
necessary to separate different completions, hard rubber 'packing'
instruments are used to maintain separation.
 Drainhole completions are a form of horizontal or
slant drilling. This type of completion consists of drilling out
horizontally into the formation from a vertical well, essentially
providing a 'drain' for the hydrocarbons to run down into the well.
These completions are more commonly associated with oil wells
than with natural gas wells.

Wellhead
Wellheads can be Dry or Subsea completion. Dry
Completion means that the well is onshore on the topside structure
on an offshore installation. Subsea wellheads are located under
water on a special sea bed template.
The wellhead consists of the pieces of equipment mounted at the
opening of the well to regulate and monitor the extraction of
hydrocarbons from the underground formation. It also prevents
leaking of oil or natural gas out of the well, and prevents blowouts
due to high pressure formations. Formations that are under high
pressure typically require wellheads that can withstand a great deal
of upward pressure from the escaping gases and liquids. These
wellheads must be able to withstand pressures of up to 140 MPa
(1400 Bar). The wellhead consists of three components: the casing
head, the tubing head, and the 'Christmas tree'

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