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U

U Chart

An attribute control chart that is used to plot the average number of defects per item

A type of shell and tube heat exchanger that has U-shaped tubes connected to a tube sheet at one end of the heat exchanger. The end of the heat exchanger is divided to separate the fluid entering the tubes from the fluid leaving the tubes.

U-tube Manometer

A type of instrument used to measure and indicate pressure; has two legs formed into the shape of a "U"

UPS

An acronym for Uninterruptible Power Supply; a device that provides emergency backup power to network devices during a power outage

UV/VIS Spectroscopy

A form of spectroscopy that uses radiation in the ultraviolet (UV) and visible (VIS) bandwidths of the electromagnetic spectrum

Ultra-long Spaced Electrical Log

A conventional electrical log with very long electrode spacing (ULSEL), with a distance between the current-emitting electrode and the measure electrode of between about 75 ft (23 m) and 1000 ft (305 m). The long spacings are designed to locate objects within tens of feet of the borehole, such as a salt dome or casing in the case of a relief well.

Ultrasonic

An acoustic method with a frequency above the human ear's limit of approximately 20,000 Hertz (the SI unit of frequency, equal to one cycle per second).

Ultrasonic (Sound Waves)

Sound waves of a higher frequency than can be heard.

Ultrasonic Imaging

In borehole logging, ultrasonic imaging is the measurement of acoustic signals that are in the hundreds of kilohertz to the low-megahertz range. Such ultrasonic instruments are mostly of the pulse-echo type, and are used in the borehole televiewer and in various cased hole devices to determine corrosion and cement bond quality.

Ultrasonic Imaging, Ultrasonic

Ultraviolet Light

Ultraviolet light is electromagnetic radiation with wavelengths shorter than visible light.

Unconformity

An unconformity is a surface of contact between two groups of unconformable strata.

Unconsolidated Sediments

Loose materials, ranging from clay to sand to gravel.

Uncontrolled hazardous waste site

An area identified as an uncontrolled hazardous waste site by a governmental body, whether Federal, state, local or other where an accumulation of hazardous substances creates a threat to the health and safety of individuals or the environment or both.

Unconventional Resources

Petroleum accumulations that are pervasive throughout a large area and not significantly affected by hydrodynamic influences. Examples include coal bed methane (CBM)/coal seam gas (CSG), basin-centered gas, shale gas, gas hydrate, natural bitumen, tar sands, and oil shale deposits.

Unconventional reservoirs

Reservoirs with permeability so low (generally less than 0.1 millidarcy) that horizontal hydraulically fractured stimulated wells or other advanced completion techniques must be utilized to extract hydrocarbons at commercial rates. Shale reservoirs such as the Eagle Ford and Barnett, as well as tight reservoirs like the Bakken and Three Forks, both are examples of unconventional reservoirs.

Under Ream, Underream

Under ream is to enlarge a wellbore past its original drilled size. Under reaming is sometimes done for safety or efficiency reasons. Some well planners believe it is safer to drill unknown shallow formations with a small-diameter bit, and if no gas is encountered, to then enlarge the pilot hole.

Under-Ream

Under-ream is to enlarge a wellbore past its original drilled size. Under-reaming is sometimes done for safety or efficiency reasons. Some well planners believe it is safer to drill unknown shallow formations with a small-diameter bit, and if no gas is encountered, to then enlarge the pilot hole.

Underdetermined System

An underdetermined system is the situation when there are less equations than the number of unknowns.

Underground gas storage

Naturally or artificially developed containments in subsurface geological strata used for the storage of natural gas

Undervoltage

Lower than normal voltage.

Undeveloped acreage

Acreage on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil and gas regardless of whether or not the acreage contains proved reserves.

Undisturbed Zone, Uninvaded Zone

The undisturbed or uninvaded zone is the formation near the borehole that has not been affected by mud filtrate invasion.

Undisturbed, or Uninvaded, Zone

The undisturbed, or uninvaded zone, is the formation in the vicinity of the borehole which has not been affected by mud filtrate invasion.

Unequal spread method

A method of offsetting parallel lines in which the travel pieces of the pipes are closer together than the pieces before or after the offset.

Uniaxial

Having, or relating to, a single axis.

Unidirectional Prover

A physical prover in which a fixed volume is determined by the displacer making a one way trip.

Uniform Hazardous Waste Manifest

A document containing information about hazardous waste shipments that allows authorities to keep track of them

Unijunction transistor (UJT)

A specialized transistor with the unique characteristic of being either on or off, depending on the polarity of its emitter with respect to base one.

Unit

In petroleum, the joining of interests in a reservoir or field to provide for development and operations without regard to separate property interests; also the area covered by a unitization agreement. In power generation, a generator and the equipment it requires to make electricity. In process engineering, a group of systems that work together to produce one or more products.

Unit Trip

A condition in which the generator, the turbine, and the boiler in a generating unit are tripped

Unitization

The process of combining multiple oil and gas leases or properties into a single development unit, managed by one operator, to optimize resource recovery and reduce costs. This approach is used when a reservoir spans across different ownership boundaries. The production is then shared among the owners according to an agreed-upon formula, ensuring efficient operation and fair distribution of resources based on each party's contribution.

Unity Power Factor

The ideal condition in a system, when apparent power is the same as working power; expressed as a power factor of 1, or as a 100% power factor.

Unity gain amplifier

An amplifier that has a gain of 1.

Unity gain bandwidth

The range of frequencies within which the open-loop voltage amplification is greater than unity.

Unknown

A quantity whose value is not currently known, but can be found if enough information is given

Unloaders

Devices on the valves which allow the capacity of a compressor to be changed.

Unsaturated molecule

A molecule whose structure allows additional atoms to be added across a double bond.

Unstabilized cat-cracked gasoline

Cat-cracked gasoline that contains light end products.

Unstable (reactive)

A chemical which is the pure state, or as produced or transported, will vigorously polymerize, decompose, condense, or will become self-reactive under conditions of shocks, pressure or temperature.

Unstable (reactive) chemicals

Chemicals that will vigorously polymerize, decompose, or condense, or will become self-reactive under conditions of shock, pressure or temperature

Unstable State

A condition in multivibrator circuits in which an amplifier stage does not remain in a conducting or cutoff state.

Update

To modify a system or process by entering current data.

Upload

Allen-Bradley's term for copying a PLC project from a PLC to a PC

Upper explosive limit (UEL)

The highest concentration of a flammable vapor or gas in the air above which a flame will not be created in the presence of an ignition source; usually expressed as the percent by volume of vapor in an air and vapor mixture.

Upscaling

Reservoir geomodels frequently involve multi-million cell models which are too large to carry out flow simulations. Upscaling is the process to reduce the number of cells.

Upscaling, Upscale

Upscaling, or homogenization, is substituting a heterogeneous property region consisting of fine grid cells with an equivalent homogeneous region made up of a single coarse grid cell with an effective property value.

Upset

Any change in the set point or process variable that increases the error

Upset Failure

An upset failure is when ESD damages a device or component but not enough to cause complete failure.

Upset Trays

An abnormal condition that occurs in a distillation tower when extreme pressure surges physically move trays out of position.

Upstream

A term used for anything located in front of the orifice plate or metering device in a meter tube, before the fluid enters.

Upstroke

The upward movement of the sucker rod string.

Uranium

A chemical element with symbol U and atomic number 92. Uranium deposits occur in many different rock types, from sedimentary to volcanic. Uranium is remobilized from one area and re-precipitated in a host rock where chemical conditions are conducive to concentrating it in higher amounts, or re-deposited due to water actions.

uphole time

The uphole time is the time it takes for a direct wave from the subsurface source to reach the first receiver at the surface.

U