Page 15 - A Primer of Oilwell Service and Workover Completion

FISHING 

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Petroleum Extension-The University of Texas at Austin

FISHING

ilfield workers have two However, many fishing opera- The most common reason
Onames for pieces of metal tions can be done with wireline for the wall of the hole collapsing
lost or stuck in a well: fish and or coiled tubing run inside the around the pipe is that, under
junk. A fish is a piece of equip- production tubing. certain conditions, salt water
ment, pipe, or any other sizable in pores of the rock can attract
piece of metal in the hole that TYPES OF FISH water in the drilling mud. If
should not be there. Junk is a the formation consists of shale
smaller piece of metal, such as a Fish include drill pipe, drill and the water in the mud is in
broken bit tooth or a hand tool collars, tubing, screen liners, contact with the water in the
that a crewmember dropped packers, and sucker rods that are shale, the water in the mud has
in the well accidentally. Junk either stuck in the well or have a tendency to transfer to the
can interfere with workover or broken off because of mechani- shale. Transferred water causes
well service operations. When cal failure, corrosion, or abra- shale to expand; small sheets of
it does, the operation ceases, sion. shale then flake off into the hole,
and crewmembers have to fish eventually fill it up, and the pipe
(remove) the junk from the well. Drill Pipe sticks.
Similarly, a large piece of equip- Drill pipe or drill collars can Pipe can also get stuck in a
ment, part of the tubing string, get stuck in the hole for several keyseat (fig. .). A keyseat is
or any other large fish impedes reasons: () the hole can collapse caused by a dogleg, which is a
work and must be removed. around the pipe; () the pipe can severely crooked section of
The operation to recover get stuck in a keyseat, a small- hole. (“It’s as crooked as a
a fish or junk is a fishing job. diameter portion of the hole; or dog’s hind leg” is the expression
Fishing often involves rotating () pressure can hold the drill that gives rise to the term.)
a tool in the hole or circula- collars so securely to the wall of The drill pipe tends to lean
tion of a workover fluid, so it the hole that no amount of pull- against the side of the dogleg
may require a larger service rig. ing can free the pipe. and, as the pipe rotates, it digs
out a new, smaller hole in the
side of the main borehole.

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