Page 194 - Drilling Technology in Nontechnical Language

Chapter 8 – DIRECTIONAL AND HORIZONTAL DRILLING 185

Fig. 8–7. A 60-ft drop or pendulum assembly

Once the well is pointing in the desired direction and angle, it can be
locked up to drill straight. This is known as a tangent assembly (fig. 8–8),

or sometimes a packed assembly (because it is packed with stabilizers) or
a stiff assembly (because it is very stiff; that is, it resists bending forces).
In this situation, the directional performance of the assembly is far less
affected by natural formation trends or drilling parameters such as weight
on bit.

In order to get the best drilling performance, it is usually necessary to
get a high weight on the bit. One of the advantages of a tangent assembly is
that high weight on bit can be used to drill fast, without a high risk of the
hole heading off somewhere it should not go. Even a packed assembly will
tend to build very slowly with high weights. Rotary assemblies also have
a tendency to turn to the right. To account for these natural tendencies, the
well can be kicked off and positioned so that it is pointing slightly to the
left of a direct track and slightly low. Then the well will slowly build and
turn right when using the best parameters for drilling fast.

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