gamma ray log n: a type of radioactivity well log that records natural
radioactivity around the wellbore. Shales generally produce higher levels of
gamma radiation and can be detected and studied with the gamma ray tool. See
radioactivity well logging.
gas anchor n: a tubular, perforated device attached
to the bottom of a suckerrod pump that helps to prevent gas lock. The device
works on the principle that gas, being lighter than oil, rises. As well fluids
enter the anchor, gas breaks out of the fluid and exits from the anchor
through perforations near the top. Remaining fluids enter the pump through a
mosquito bill (a tube within the anchor), which has an opening near the
bottom. In this way, all or most of the gas escapes before the fluids enter
gas cap n: a free-gas phase overlying an oil zone
and occurring within the same producing formation as the oil. See reservoir.
gas-cap drive n: drive energy supplied naturally (as
a reservoir is produced) by the expansion of the gas cap. In such a drive, the
gas cap expands to force oil into the well and to the surface. See reservoir
gas-cut mud n: a drilling mud that contains
entrained formation gas, giving the mud a characteristically fluffy texture.
Gas cut mud may cause a lowering of mud weight.
gas drive n: the use of the energy that arises from
the expansion of compressed gas in a reservoir to move crude oil to a wellbore.
Also called depletion drive. See dissolved-gas drive, gas-cap drive, reservoir
gas injection n: the injection of gas into a
reservoir to maintain formation pressure by gas drive and to reduce the rate
of decline of the original reservoir drive. One type of gas injection uses gas
that does not mix (is not miscible) with the oil. Examples of these gases
include natural gas, nitrogen, and flue gas. Another type uses gas that does
mix (is miscible) with the oil. The gas may be naturally miscible or become
miscible under high pressure. Examples of miscible gases include propane,
methane enriched with other light hydrocarbons, methane under high pressure,
and carbon dioxide under pressure. Frequently, water is also injected in
alternating steps with the gas.
gas injection well n: a well into which gas is
injected for the purpose of maintaining or supplementing pressure in an oil
gasket n: any material (such as paper, cork,
asbestos, stainless steel or other types of metal, or rubber) used to seal two
essentially stationary surfaces.
gas lift n: the process of raising or lifting fluid
from a well by injecting gas down the well through tubing or through the
tubing-casing annulus. Injected gas aerates the fluid to make it exert less
pressure than the formation does; the resulting higher formation pressure
forces the fluid out of the wellbore. Gas may be injected continuously or
intermittently, depending on the producing characteristics of the well and the
arrangement of the gas-lift equipment.
gas-lift mandrel n: a device installed in the tubing
string of a gas-lift well onto which or into which a gas-lift valve is fitted.
There are two common types of mandrel. In the conventional gas-lift mandrel,
the gas-lift valve is installed as the tubing is placed in the well. Thus, to
replace or repair the valve, the tubing string must be pulled. In the
sidepocket mandrel, however, the valve is installed and removed by wireline
while the mandrel is still in the well, eliminating the need to pull the
tubing to repair or replace the valve.
gas-lift valve n: a device installed on a gas-lift
mandrel, which in turn is put on the tubing string of a gas-lift well. Tubing
and casing pressures cause the valve to open and close, thus allowing gas to
be injected into the fluid in the tubing to cause the fluid to rise to the
surface. See gas-lift mandrel.
gas-lift well n: a well in which reservoir fluids
are artificially lifted by the injection of gas.
gas lock n: 1. a condition sometimes encountered in
a pumping well when dissolved gas, released from solution during the upstroke
of the plunger, appears as free gas between the valves. If the gas pressure is
sufficient, the standing valve is locked shut, and no fluid enters the tubing.
2. a device fitted to the gauging hatch on a pressure tank that enables manual
dipping and sampling without loss of vapor. 3. a condition that can occur when
gas-cut mud is circulated by the mud pump. The gas breaks out of the mud,
expands, and works against the operation of the piston and valves.
gas well n: a well that primarily produces gas.
Legal definitions vary among the states.
gear reducer n: see speed reducer.
gel n: a semisolid, jellylike state assumed by some
colloidal dispersions at rest.
geologist n: a scientist who gathers and interprets data pertaining to
the formations of the earth’s crust.
Geronimo n: see safety slide.
go in the hole v: to lower the drill stem, the
tubing, the casing, or the sucker rods into the wellbore.
gone to water adj: pertaining to a well in which
production of oil has decreased and production of water has increased (for
example, “the well has gone to water”).
gooseneck n: the curved connection between the
rotary hose and the swivel. See swivel.
gravel n: sand or glass beads of uniform size and
roundness used in gravel packing.
gravel packing n: a method of well completion in
which a slotted or perforated liner, often wire-wrapped, is placed in the well
and surrounded by gravel. If open hole, the well is sometimes enlarged by
underreaming at the point where the gravel is packed. The mass of gravel
excludes sand from the wellbore but allows continued production.
guide shoe n: 1. a short, heavy, cylindrical section
of steel filled with concrete and rounded at the bottom, which is placed at
the end of the casing string. It prevents the casing from snagging on
irregularities in the borehole as it is lowered.
guy line anchor n: a buried weight or anchor to
which a guy line is attached.
guy wire n: a rope or cable used to steady a mast or pole.