Oil & Gas Terms in Category O

Open hole

Uncased portion of a well.


Said of any pressure-tight vessel or container when the internal pressure is lower than atmospheric pressure

Oil sands

Oil sands, also known as tar sands, or extra heavy oil, are a type of bitumen deposit.

The sands are naturally occurring mixtures of sand or clay, water and an extremely dense and viscous form of petroleum called bitumen.

They are found in large amounts in many countries throughout the world, but are found in extremely large quantities in canada and venezuela.

see here for details.

Oil sand

Any porous stratum bearing oil.

Oil-emulsion mud

A water-base mud in which water is the continuous phase and oil is the dispersed phase.

The oil is spread out, or dispersed, in the water in small droplets, which are tightly emulsified so that they do not settle out.

Because of its lubricating abilities, an oil-emulsion mud increases the drilling rate and ensures better hole conditions than other muds.

Compare oil mud.



A condition in which fluid is free-falling down the well at a faster rate than the pumps can handle.


In wireline, trying to pull out of the well faster than the wireline tools are being blown upwards by unexpected pressure.


Trying to pump out a gas influx before the expansion of gas reduces pressure allowing the well to kick.

Oil country tubular goods

Oil-well, casing, tubing, or drill pipe.


The extent to which the hydrostatic pressure of the mud column exceeds formation pressure.

Overriding royalty interest (contract)

A royalty interest that may be retained by a third party as payment or investment.

This interest normally bears no part of the drilling and completion expenses of the well.





The uncased portion of a well.

All wells, at least when first drilled, have openhole sections that the well planner must contend with.

Prior to running casing, the well planner must consider how the drilled rock will react to drilling fluids, pressures and mechanical actions over time.

The strength of the formation must also be considered.

A weak formation is likely to fracture, causing a loss of drilling mud to the formation and, in extreme cases, a loss of hydrostatic head and potential well control problems.

An extremely high-pressure formation, even if not flowing, may have wellbore stability problems.

Once problems become difficult to manage, casing must be set and cemented in place to isolate the formation from the rest of the wellbore.

While most completions are cased, some are open, especially in horizontal or extendedreach wells where it may not be possible to cement casing efficiently.





To unload or remove something from the container.


To unload or get rid of water from the well.

see also fpso.


Pull on pipe over and beyond its weight in either air or fluid


A fishing tool that is attached to tubing or drill pipe and lowered over the outside wall of pipe or sucker rods lost or stuck in the wellbore.

A friction device in the overshot, usually either a basket or as spiral grapple, firmly grips the pipe, allowing the fish to be pulled from the hole.



Of a wellbore, having no casing.


Of a hole, having no drill pipe or tubing suspended in it.