1. n. [Drilling]
Anything left in a wellbore. It does not matter whether the fish consists of junk metal, a hand tool, a length of drillpipe or drill collars, or an expensive MWD and directional drilling package. Once the component is lost, it is properly referred to as simply "the fish." Typically, anything put into the hole is accurately measured and sketched, so that appropriate fishing tools can be selected if the item must be fished out of the hole.
See: back off, drill collar, fishing tool, sidetrack, washover pipe
2. vb. [Drilling]
To attempt to retrieve a fish from a wellbore. Where available, specially skilled individuals, aptly called fishermen, are called onto location to direct and assist with the fishing operations. Depending on the type of fish, the manner in which it was lost, regulatory requirements (for example a fish that includes a nuclear source, such as certain well logging tools), and the value of the fish if recovered, fishing operations may be immediately successful or may be attempted unsuccessfully for several days or even weeks.
3. n. [Formation Evaluation]
The surface electrode used as the reference electrode for the spontaneous potential (SP) measurement. The metal electrode is attached to the end of a long electric cable and typically placed in the mud pit, or, in the case of an offshore rig, in the sea. The SP is a measurement of the natural electrical potential between an electrode in the well and the fixed reference electrode on surface.