Page 192 - Drilling Technology in Nontechnical Language

Chapter 8 – DIRECTIONAL AND HORIZONTAL DRILLING 183

drillstring) while drilling. Another issue is keeping the hole clean; rotating
the drillstring greatly improves the transport of cuttings out of the hole, and
at high inclinations, sliding the string can lead to cuttings beds building up
and sticking the drillstring. What is needed is a steerable tool that works
with the drillstring rotating, and they do now exist. The drawback is that
they are expensive.

Rotary drilling assemblies

If a drill collar is supported at each end in a position other than vertical,
the weight of the drill collar will cause the middle part to sag. This effect
is used in rotary drilling assemblies to create a side force at the bit in order

to build or drop angle (fig. 8–6).

Fig. 8–6. A 60-ft build rotary assembly

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