Oil and Gas Terms Beginning with “U”

The U-tube effect in well drilling refers to the hydrostatic pressure interaction between two connected fluid columns: the drillstring interior (one leg) and the annulus between the drillstring and the wellbore (the… Read more →

Abbreviation for ultralarge crude carrier. Read more →

The Udden-Wentworth scale is the standard grain size classification system used in sedimentology and petroleum geology to categorize sedimentary particles by their diameter, providing a consistent vocabulary for… Read more →

What Is the Universal Transverse Mercator Grid? The Universal Transverse Mercator (UTM) grid is a standardised planar coordinate system that divides the Earth's surface between 84°N and 80°S latitude into 60… Read more →

A valve installed above the kelly that can be closed manually to protect the rotary hose from high pressure in the drill string. Read more →

(noun) Crude oil with an API gravity of less than 10 degrees and a viscosity typically exceeding 10,000 centipoise at reservoir conditions. Ultra heavy oil does not flow naturally under reservoir pressure and requires… Read more →

The ultra-long spaced electrical log (ULSEL) is a wireline resistivity logging tool designed with electrode spacings of 100 to 1,000 feet (versus the 10-72 inch spacings of conventional resistivity tools) that provides… Read more →

Referring to any particle in the size range 2 to 44 microns. Read more →

A supertanker with 500,000 deadweight tons of capacity or more. The term is commonly abbreviated as ULCC. Read more →

Ultralow interfacial tension (ultralow IFT) in enhanced oil recovery refers to the reduction of the oil-water interfacial tension from its natural value of 15 to 30 millinewtons per meter (mN/m) to values below 0.01… Read more →

What Is an Ultrasonic Caliper? An ultrasonic caliper is a well logging tool that measures borehole diameter and shape using high-frequency (200-500 kHz) acoustic pulse-echo technology, sending ultrasonic pulses radially… Read more →

Ultrasonic measurement in oil and gas operations encompasses the diverse applications of high-frequency sound wave technology (typically 20 kHz to several megahertz) for non-invasive inspection, quantitative… Read more →

Uncertainty in petroleum engineering and exploration is the quantitative expression of the range of possible values that a parameter, outcome, or reserve estimate could take, arising from incomplete knowledge,… Read more →

The uncertainty principle is the fundamental quantum-mechanical principle formulated by German physicist Werner Karl Heisenberg in 1927, stating that certain pairs of physical properties of a particle — canonically… Read more →

An unconformity in geology and petroleum exploration is a buried erosional or non-depositional surface that represents a significant gap in the stratigraphic record — created when sedimentary deposition was interrupted… Read more →

An unconformity trap is a hydrocarbon accumulation whose closure is created by an unconformity, a buried erosional or non-depositional surface that separates older rocks below from younger rocks above and that either… Read more →

An unconventional resource is a hydrocarbon accumulation that requires advanced stimulation or specialized extraction technology to produce at economic flow rates because the reservoir rock has insufficient permeability… Read more →

Underbalance in drilling and well operations refers to a condition in which the hydrostatic pressure exerted by the drilling fluid column (or wellbore fluid column) at the depth of the productive formation is… Read more →

An underground blowout is a well control failure in which formation fluids from a high-pressure zone flow uncontrolled through the wellbore into a lower-pressure formation exposed elsewhere in the open hole section,… Read more →

Gas that is being stored in salt domes, salt layers or depleted oil and gas fields. Read more →

Underpressure describes a subsurface condition in which the pore pressure of a formation is less than the normal hydrostatic pressure expected for its depth, and it is one of the more deceptive pressure regimes a… Read more →

Underreaming is the drilling operation of enlarging a borehole section to a diameter greater than the drill bit that created the original hole — accomplished by deploying an underreamer (a downhole tool with expandable… Read more →

An undersaturated fluid in petroleum engineering refers to a reservoir fluid (oil or gas condensate) whose pressure exceeds the bubble point pressure (for oil) or the dew point pressure (for gas condensate) at reservoir… Read more →

Undershooting is a seismic acquisition technique in which seismic energy sources are detonated on one side of an obstruction (a production platform, a drilling rig, a restricted area) while the receivers are deployed on… Read more →

In sucker-rod pumping, a situation that occurs when the stroke length at the downhole pump is shorter than the surface stroke length. Read more →

The part of the formation that has not been affected by invasion. Read more →

Uniformitarianism is the foundational geological principle that the physical and chemical processes operating on Earth today are the same processes that have operated throughout geological time, and at rates and… Read more →

The combining of multiple wells to produce from a specified reservoir. Read more →

Unitized production is the combined output of oil, gas, and associated liquids drawn from a single reservoir or pool that has been operated as one unit rather than as a patchwork of separately leased tracts, with the… Read more →

A units conversion factor is a numerical constant embedded in an engineering equation that makes the formula valid only for one particular system of measurement units, allowing analysts to apply the same physical… Read more →