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the removal of junk, debris or fish from a wellbore.

Special Operations

For our purposes, special drilling operations include directional drilling,
fishing, and well control. Directional drilling is intentionally drilling the hole off-
vertical for various reasons. Fishing is the operation crew members implement to
retrieve an object in the wellbore that doesn't belong there and impedes drilling. Well
control is the techniques crew members use to regain control of the well should
formation fluids inadvertently enter the well.

Directional and Horizontal Drilling

Often, the drilling crew tries to drill the hole as straight as possible.
Sometimes, however, the operator wants the hole to be drilled at a slant. One area
where operators use slant, or directional drilling, is offshore. From a permanent
platform that the operator installs over the drilling site, the crew must drill several
wells to exploit the reservoir properly. To do so, crew members drill several
directional wells (fig. 184). The crew may drill only the first well vertically; it drills

every other well directionally.
To drill a typical directional well, the crew members drill the first part of the
hole vertically. Then they kick off, or deflect, the hole so that the bottom may end up
hundreds of feet or metres away from its starting point on the surface. By using
directional drilling, the crew can drill forty or more wells into the reservoir from a
single platform.
Another use of directional drilling is horizontal drilling. An operator can better
produce certain reservoirs with horizontal drilling. The drilling crew drills the well
vertically to a point above the reservoir. Then it deflects the well and increases the
angle until it reaches 90 degrees, or horizontal (see fig. 112). This horizontal hole
penetrates the reservoir. When properly applied, one horizontal borehole can produce
a reservoir better than several vertically drilled ones.
In horizontal and directional drilling, the crew can bend the drill stem to a high
degree without breaking it because, first, the crew gradually deflects the hole from
vertical. Usually, crew members deflect the hole over hundreds of feet (or metres) so
that the bend is not sudden. Three to 10 degrees of deflection over 100 feet (or
metres) is not an unusual amount. Second, the drill string is flexible. It is, after all, a
hollow metal tube. The crew can bend it quite a lot without its breaking or
permanently bending. In cases in which the hole needs to curve within a short
distance, they use a special segmented pipe. Segmented pipe is very flexible and can
bend a great deal without breaking.
The crew uses many tools and techniques to drill directionally. One tool is a
downhole motor (fig. 185A), which crew members run with a bent sub (fig. 185B). A
downhole motor is shaped like a piece of pipe. One type has turbine blades inside it.

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