Terminology Series U

Working within Oil and Gas will introduce you to a new industry-specific vocabulary and abbreviations – to help you understand we’ve collated a list of terms beginning with the letter "U".


An abbreviation for ‘ultra large crude carrier.’


A term that refers to any particle with a size range between 2 to 44 microns.

Ultra-Heavy Oil

A term used to describe a hydrocarbon fluid with a gravity of 10° API or lower.

Ultrasonic caliper

A device that uses high-frequency acoustic signals to measure the internal diameter of an open borehole, tubing or casing.  A transducer emits the high-frequency signal which is then reflected back by the item being measured. The diameter is determined by the time it takes for the signal to return (echo) and the fluid acoustic velocity.


The Oil and Gas industry is divided into three sectors, Upstream, Midstream and Downstream. Upstream refers to the early stages of exploration and production, including drilling and extraction.


Stands for ‘United Kingdom Continental Shelf’ which is the offshore waters of the UK Sector.

Undersaturated fluid

A term used to describe a solution where an undissolved solute is present. This is useful in saltwater muds where the undersaturated flued can allow salt to leach into the mud, preventing the hole from closing in on the drilling assembly.

When used to describe moisture in the air, this term refers to humidity less than 100%.


Refers to the quantities of petroleum that are estimated to be contained within accumulations that have not yet been tested by drilling.

Uniaxial compressive strength

This term is a type of measurement used to illustrate a material’s strength. The uniaxial compressive strength is sometimes abbreviated to UCS and describes the maximum axial compressive stress that a right-cylindrical sample of material can endure before failing.

Sometimes referred to as ‘unconfined compressive strength’.

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