Abstract

Fishing is the process of removal of equipment that has become stuck or lost in the wellbore. Its name derives from a period in which a hook attached to a line was lowered into the borehole. The fish, or lost object, is classified as tubular (drill pipe, drill collars, tubing, casing) or miscellaneous (bit cones, small tools, wire line, chain, junk). Industry wide, twenty-five per cent of drilling costs may be attributed to fishing.

Operator error, equipment decline, and failure to clean the hole are the cause of many fishing jobs. Running more mud weight than necessary can cause differential (wall) sticking. When hole conditions permit, differentially stuck pipe may be freed by spotting nitrogen. Worn or improperly shopped tool joints may part while tripping or drilling ahead. Interior corrosion in the body of drill pipe may cause torsion failure.

Fishing equipment for tubular goods includes overshots, baskets, spears taper taps, die collars, mills, washpipe, jar-bumper sub assemblies, surface bumpers, safety joints, bent joints, wall hooks, circulating subs, and cutters. Additional tools for fishing junk are the magnet and the junk shot.

The cardinal rule of fishing is "Know when to quit." Close cooperation between geology, engineering, and accounting is necessary to a successful fishing job. Sidetracking or abandonment may be cheaper than prolonged fishing operations. A fish on the bank is a liability when its recovery costs more money than leaving it in the borehole.