Page 332 - Drilling Technology in Nontechnical Language

Chapter 13 – DRILLING PROBLEMS AND SOLUTIONS 323

cannot be removed. It is not as strong as the overshot, so if it is jarred on,
it will likely pull off the fish.

Fig. 13–7. Die collar

Inside catch tools

Sometimes, a tubular fish has a large outside diameter, which prevents

an overshot from going over it. Casing is a good example. For these fish,

the fishing tool must grip on the inside diameter. There are two types of
tool commonly available: the releasing spear and the taper tap.
The releasing spear works like an overshot in reverse. It has a mandrel

down the middle that has a conical profile outside. Steel slip elements fit
around this mandrel with teeth on the outside. As force is applied, the
mandrel profile pushes outwards on the slip elements, so that the more

tension is applied, the more the slips grip. As with an overshot, it can be
released downhole.
The taper tap works like a die collar in reverse. It has a slightly wedge-
shaped section of bar below, which has threads cut on to the profile. The tap

is lowered into the inside diameter, some weight is set down, and the tap is

rotated. The threads cut into the top ID of the fish to grip it. The taper tap
is not very strong and as with the die collar, it cannot be unlatched once

on the fish.

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