In oil well drilling, a fish is a foreign object in the open hole. It could be something simple such as a wrench or sledge hammer that a careless hand dropped, or something more complex, such as several thousand feet of drill pipe which had twisted off. Whatever it is, it has to be removed before drilling can continue. Whenever the well has to change directions or deviate from a true vertical, a directional driller is called in. He specializes in drilling curved wells.
Mud cool the drill bit.
Mud, by means of its weight, prevents high pressure gasses from reaching the surface. Mud engineers are not usually engineers in the academic sense, but are given that title because they have a complex and demanding job. They determine the weight of the mud and ensure all the proper chemicals are added when needed. There are usually 1 or 2 mud engineers on the rig. Logging Companies Loggers are responsible for the actual monitoring and analysis of what is happening down hole.