Oil & Gas Terms in Category R

Reverse out

To displace the wellbore fluid back to the surface; to displace tubing volume back to the pit.

Rockwell hardness test

An arbitrarily defined measure of resistance of a material to indentation under static or dynamic load

Rotary hose

A reinforced flexible tub on a rotary drilling rig that conducts the drilling fluid from the standpipe to the swivel and kelly.

Also called the mud hose or the kelly hose

Relief well

A well drilled near and deflected into a well that is out of control, making it possible to bring the wild well under control.

See wild well.

Ram blowout preventer

A blowout preventer that uses rams to seal off pressure on a hole that is with or without pipe.

Also called a ram preventer.

Reeled tubing

Lighter-duty well maintenance than hydraulic workover, employing small od tubing capable of descending down the production string under well pressure

Reservoir rock

A permeable rock that may contain oil or gas in appreciable quantity and through which petroleum may migrate.


The electrical resistance offered to the passage of current; the opposite of conductivity.

Royalty oil

The mineral owners share of production, taken in oil rather than in cash.

Reverse circulation

The course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus.

Seldom used in open hole, but frequently used in workover operations.

Also referred to as “circulating the short way,” since returns from bottom can be obtained more quickly than in normal circulation.


The closing and sealing component on a blowout preventer.

One of three types–blind, pipe, or shear–may be installed in several preventers mounted in a stack on top of the wellbore.

Blind rams, when closed, form a seal on a hole that has no drill pipe in it; pipe rams, when closed, seal around the pipe; shear rams cut through drill pipe and then form a seal.

Rigid centralizer

A centralizer with ribs that do not bow or flex.

Rack pipe


To place pipe withdrawn from the hole on a pipe rack

To stand pipe on the derrick floor when pulling it out of the hole.

Rotating head

A sealing device used to close off the annular space around the kelly in drilling with pressure at the surface, usually installed above the main blowout preventers.

A rotating head makes it possible to drill ahead even when there is pressure in the annulus that the weight of the drilling fluid is not overcoming; the head prevents the well from blowing out.

It is used mainly in the drilling of formations that have low permeability.

The rate of penetration through such formations is usually rapid.


A porous and permeable underground formation containing an individual and separate natural accumulation of producible hydrocarbons (oil and/or gas) which is confined by impermeable rock or water barriers and is characterized by a single natural pressure system.

A subsurface, porous, permeable rock body in which oil and/or gas is stored, most reservoir rocks are limestones, dolomites, sandstones, or a combination of these.

The three basic types of hydrocarbon reservoirs are oil, gas, and condensate.

An oil reservoir generally contains three fluids – gas, oil, and water – with oil the dominant product.

In the typical oil reservoir, these fluids occur in different phases because of the variance in their gravities.

Gas, the lightest, occupies the upper part of the reservoir rocks; water, the lower part; and oil, the intermediate section.

In addition to its occurrence as a cap or in solution, gas may accumulate independently of the oil; if so, the reservoir is called a gas reservoir.

Associated with the gas, in most instances, are salt water and some oil.

In a condensate reservoir, the hydrocarbons may exist as a gas, but, when brought to the surface, some of the heavier ones condense to a liquid.