sand out of the well hole are screening, or filtering systems. Both of these
types of sand barriers can be used in open hole and perforated completions.
· Permanent completions are those in which the completion, and wellhead,
are assembled and installed only once. Installing the casing, cementing,
perforating, and other completion work is done with small diameter tools to
ensure the permanent nature of the completion. Completing a well in this
manner can lead to significant cost savings compared to other types
· Multiple zone completion is the practice of completing a well such that
hydrocarbons from two or more formations may be produced
simultaneously, without mixing with 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.
3.5 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