U
uncased hole n: see open hole.
unconsolidated formation n: a loosely arranged,
apparently unstratified section of rock.
unconsolidated sandstone n: a sand formation in
which individual grains do not adhere to one another. If an unconsolidated
sandstone produces oil or gas, it will produce sand as well if not controlled
or corrected.
undergauge bit n: a bit whose outside diameter is
worn to the point at which it is smaller than it was when new. A hole drilled
with an undergauge bit is said to be undergauge.
undergauge hole n: that portion of a borehole
drilled with an undergauge bit.
unit operator n: the oil company in charge of
development and production in an oilfield in which several companies have
joined to produce the field.
unloading a well n: removing fluid from the tubing
in a well, often by means of a swab, to lower the bottomhole pressure in the
wellbore at the perforations and induce the well to flow.
upper kelly cock n: a valve installed above the
kelly that can be closed manually to protect the rotary hose from high
pressure that may exist in the drill stem.
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