Page 48 - Drilling Technology in Nontechnical Language

Chapter 3 – DRILLING A LAND EXPLORATION WELL 39

Fig. 3–3. Completion tubing in a well

Positioned within the completion tubing string will be other components

that are necessary to control the flow of fluids (such as valves) or to allow
other tools to be positioned within the tubing. A packer may also be used,
which forms a seal between the outside of the completion tubing and the
inside of the casing in which it is run. A packer would normally be used to

stop hydrocarbons flowing outside of the completion tubing, as shown in
the illustration above.
One device that should be installed in every completion is a subsurface
safety valve (SSSV). Positioned below the surface (or below the seabed),
an SSSV consists of a valve that is held open against a spring by hydraulic
pressure. A small-diameter, high-pressure pipe runs along the outside of
the completion to the surface, and this contains hydraulic fluid, typically at

5,000 psi (34.5 kPa), which holds the valve open. If something disastrous
happens (such as a fire), the well can be quickly closed by removing the

hydraulic pressure. If the wellhead were to be knocked off, the hydraulic

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