Page 71 - Drilling Technology in Nontechnical Language

62 Drilling Technology in Nontechnical Language Second Edition

Fig. 3–14. Drillstring

Notice that although the drill collars have straight sides all the way, the
drill pipe has a bulge at each end. The drill pipe itself is fairly thin, and
there is not enough metal to machine a connection onto the pipe itself, so
a thick section with the threaded connection on is welded to each end of a
length of pipe. The pipe part of the drill pipe is called the pipe body, and
the connection part is called the tool joint.

Every component added to the drillstring is measured in feet and
hundredths of a foot, or in meters and millimeters, so it is easy to add
all of the lengths together. The record of pipe lengths is called the tally

(fig. 3–15).
The components from the drill bit to the bottom of the drill pipe are

called the bottomhole assembly (BHA). The BHA can be configured in
many different ways to give a particular weight on the bit and to affect
how it drills.
The well is drilled until it reaches the depth to run the surface casing.

One problem commonly experienced while drilling surface hole is
mud disappearing down hole into the rock, either into fractures or into very
permeable rock. This problem is called lost circulation, or more simply,
losses. Losses might be slight or severe; losing only a small amount of mud
an hour is called seepage losses. Anything over about 30 bbl/hr (4,770 l/hr)
is moderate, and over 60 bbl/hr (9,540 l/hr) is serious. Sometimes the mud

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