Oil & Gas Terms in Category F

Fishtail bit

A drilling bit with cutting edges of hard alloys.

Developed about 1900, and first used with the rotary system of drilling, it is still useful in drilling very soft formations.

Also called a drag bit.

Fire wall

A wall of earth built around an oil tank to hold the oil if the tank breaks or burns.

Float shoe

A short, heavy, cylindrical steel section with a rounded bottom and attached to the bottom of the casing string.

It contains a check valve and functions similarly to the float collar but also serves as a guide shoe in the casing.

Free point

An area or point above the point at which a tubular, such as drill pipe, is stuck in the wellbore.

Fluid loss

The unwanted migration of the liquid part of the drilling mud or cement slurry into a formation, often minimized or prevented by the blending of additives with the mud or cement.



To drive oil from a reservoir into a well by injecting water under pressure into the reservoir formation.

See waterflooding.


To drown out a well with water.


The small pipes and valves that are used to make up a system of piping.

Fishing head

A specialized fixture on a downhole tool that will allow the tool to be fished out after it’s used downhole.

See fish.

Flow tube

An interval device commonly found in subsurface safety valves used to protect the tool’s closure mechanism from the wellbore media.

Fill-up line

The smaller of the side fittings on a bell nipple, used to fill the hole when drill pipe is being removed from the well.

Formation damage

The reduction of permeability in a reservoir rock caused by the invasion of drilling fluid and treating fluids to the section adjacent to the wellbore.

Often call skin damage.

Formation breakdown

An event occurring when borehole pressure is of such magnitude that the exposed formation cannot withstand applied pressure.

Fishing-tool operator

The person (usually a service company employee) in charge of directing fishing operations.

Filter cake


Compacted solid or semisolid material remaining on a filter after pressure filtration of mud with a standard filter press.

Thickness of the cake is reported in thirty-seconds of an inch or in millimeters.


The layer of concentrated solids from the drilling mud or cement slurry that forms on the walls of the borehole opposite permeable formations; also call wall cake or mud cake.

Formation testing

The gathering of pressure data and fluid samples from a formation to determine its production potential before choosing a completion method.

Testing tools include formation testers and drill stem test tools.