Oil & Gas Terms in Category E

External cutter

A fishing tool containing metal-cutting knives that is lowered into the hole and over the outside of a length of pipe to cut it.

The severed part of the pipe can then be brought to the surface.

Exploration well

Also called a wildcat.

See wildcat.


A paraffin hydrocarbon, c2h6; under atmospheric conditions, a gas.

One component of natural gas.


The water that touches the edge of the oil in the lower horizon of a formation

Entrained gas

Formation gas that enters the drilling fluid in the annulus.


Clamps that grip a stand of casing, tubing, drill pipe, or sucker rods so that the stand can be raised or lowered into the hole.



A chemical that, when dissolved in water, dissociates into positive and negative ions, thus increasing its electrical conductivity.

See dissociation.


The electrically conductive solution that must be present for a corrosion cell to exist.

Equivalent circulating density (ecd)

The increase in bottomhole pressure expressed as an increase in pressure that occurs only when mud is being circulated.

Because of friction in the annulus as the mud is pumped, bottomhole pressure is slightly, but significantly, higher than when the mud is not being pumped.

Ecd is calculated by dividing the annular pressure loss by 0.052, dividing that by true vertical depth, and adding the result to the mud weight.

Economic limit

When the revenue from the produced fluids falls below the cost of operations set by the company.

each oil well has an “economic limit” to keep from losing money.

The equation’s major parameters are taxes, oil price, operating costs, and royalty fraction.

Thus, raising
taxes on oil increases the economic limit, thereby shortening the life of the well, and decreasing proven oil reserves.


The search for reservoirs of oil and gas, including aerial and geophysical surveys, geological studies, core testing, and drilling of wildcats.

Electric well log

A record of certain electrical characteristics (such as resistivity and conductivity) of formations traversed by the borehole.

It is made to identify the formations, determine the nature and amount of fluids they contain, and estimate their depth.


Drawn in and transported by the flow of a fluid.


The point marking the end of one stage of a process.

In filtrate analysis, the endpoint is the point at which a particular result is achieved through titration.


A tapered connection with 8 threads per inch.

One turn equals 0.125 inches of travel.

Very common oilfield connection.


See emulsifying agent