Page 50 - Drilling Technology in Nontechnical Language

Chapter 3 – DRILLING A LAND EXPLORATION WELL 41

Directional pro le

A well may be required to be drilled vertically to the target. However,
most wells have some directional requirements. A well may be drilled
directionally for many different reasons:
▪ To reach a target that cannot be reached with a vertical well, such
as below an inaccessible surface feature.
▪ Offshore, many wells can be drilled from a single structure.
These wells must spread out so that they are widely separated
within the reservoir.
▪ Some wells need precise placement within the reservoir to get
the best production from the well, such as intersecting fractures
along a particular direction, or drilling a long horizontal wellbore
just under the top of the reservoir.
▪ If a well is flowing hydrocarbons uncontrollably to the surface, it

might be necessary to drill another well to intersect it, in order to

stop it from flowing. This is called a relief well. A relief well must
be drilled very accurately.

The directional profile is chosen to achieve the well’s objectives at the
lowest cost (fig. 3–4).

Note that once the well starts to deviate, two depths are given for each
position (such as the bottoms of casings). These are measured depth (which
is the depth measured along the casing length) and true vertical depth
(which is the vertical depth below the surface or below sea level).
The largest casing is called the conductor, as shown above. The next
casing is called the surface casing. This terminology is explained later.

Wellhead con guration

The wellhead is the “visible” part of the well. There are different types
for different purposes.
In figure 3–5 are photographs of three wellhead types.

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