During drilling, parts of the drill string or other tools may fall into the well or become stuck in the well. These unwanted or accidentally lost objects are referred to as “fish” or “junk”. Since a normal drill bit can’t drill through them, the foreign objects must be removed before drilling can continue. This process of retrieving lost material in the borehole is known as “fishing”.
Fishing for broken bits and dropped tools is expensive, time consuming, and extremely undesirable. The removal of a single “fish” can take days and require a multiple round trips. Fishing is such an expensive proposition that some operators purchase “fishing insurance”, which covers the costs incurred during fishing operations.
Fishing is so common that entire contracting businesses have sprung up that specialize in it.
A variety of tools are used by fishing contractors to release, measure, break up, and retrieve “fish”. These include tolls to go over a fish (overshots), tools to spear a fish (spears), powerful magnets, cutting and explosive tools, tools used to examine the fish, and other innovative equipment. Fishing is an entire field of oilfield operations that lies beyond the scope of this course. For our purposes, it’s enough to know that fishing is an expensive, time consuming process that is best avoided.
Images: “Fishing spinnings in store” by sergeyryzhov via iStock