Page 327 - Drilling Technology in Nontechnical Language

318 Drilling Technology in Nontechnical Language Second Edition

muds, more use of stabilized BHAs, and better awareness of drill crews
has relegated differential sticking to a minority of cases of stuck pipe.
Interestingly, many people immediately assume differential sticking when
a problem occurs and have to be convinced that something else might be
the cause.

Fig. 13–5. Differential sticking

There are four conditions related to differential sticking, all of which
must be present for it to occur. These are as follows:
▪ The presence of a permeable zone covered with wall cake
▪ Static overbalance on the formation
▪ Contact between the wall and drillstring

▪ A stationary string
With wall contact and over a period of time (seconds to minutes), the

stationary tubular pushes into the filter cake. This establishes a contact area
over which differential pressure may act. Larger diameter tubulars form
greater contact areas and therefore are more likely to get stuck. Circulation
will be possible, but there can be no pipe movement until the pipe is freed.
The force required to pull the tubular free is proportional to both
the differential pressure and to the contact area. If this force exceeds the
allowable pull on the pipe, the differential pressure must be reduced or

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