Page 322 - Drilling Technology in Nontechnical Language

Chapter 13 – DRILLING PROBLEMS AND SOLUTIONS 313

If pipe does get stuck in such a way that no pipe movement at all
is possible, the immediate actions will usually determine the outcome
(getting free vs. staying stuck). Sticking forces increase with time, so it
is very important to analyze the situation and take immediate action to
get unstuck.

Stuck pipe may be classified into categories according to the main
cause of sticking.

Sticking mechanisms for stuck pipe

Causes of stuck pipe can be classified into three basic categories:
1. Geometry. This relates to dimensional problems in the wellbore.
Circulation is usually possible; the problem will be seen with the
string moving, and only in one direction.
2. Solids. This relates to solid particles in the hole. Circulation may
be restricted or impossible, and hole cleaning may have been
inadequate. This usually occurs when pulling out of the hole.
3. Differential sticking. This relates to mud overbalance over a
permeable formation.
Each of these will be examined in turn.

Geometry-related stuck pipe

There are several different root causes of geometry-related stuck pipe

(fig. 13–3).
If the wellbore is undergauge for any reason, full gauge tools such as
the drill bit or stabilizers can get stuck if moved into the undergauge part of
the hole. Several causes are possible for an undergauge hole. These include
drilling with an undergauge bit, thick filtercake buildup on a permeable

formation, and mobile formations (squeezing salt or shale that moves in to
the wellbore with time).
In deviated wells, it is possible for a keyseat to form. Where the
drillstring (OD of 5”) presses against the inside of the bend in the wellbore,
it can wear a groove into the formation. If this groove becomes deep
enough, when the pipe is pulled out of the hole, the drillpipe will slide

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