The most common problem is that something will break and fall to the bottom of the well. For example, the drillpipe twists off and falls down the well or a cone falls off the tricone bit. This is metal and you cannot drill through it and it is called junk or fish at the bottom of the well. Drilling must be suspended and a special tool called a fishing tool has to be leased from a service company. The fishing tool is then lowered down the well to grapple for the fish in a process called fishing .
Fishing can take days.
While you are fishing, you are not drilling the well but you are still being charged for the drilling rig. This charge can be avoided if fishing insurance is bought before the well is drilled. Another problem, called lost circulation , is caused by drilling into a very permeable formation. The drilling mud is flowing into the lost circulation zone without building up a filter cake along the wellbore. Very little, if any drilling mud is circulating back to the surface.