Glossary
Glossary
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
0-9
-
3-D Seismic - A relatively new exploration technique
used in the search for oil and gas underground structures. The
basic premise behind seismic is the same as ultra sound technology
used in the medical field. Sound from a shot hole is recorded from
geophones and interpreted to give a picture of the underlying
structures within the earth. 3-D has now become a common practice
to redefine and identify known as well as unknown structures. Many
times these structures contain traps that hold oil and gas yet to
be discovered.
4-D Seismic - The newest advances in seismic
technology which now takes into consideration a 4th dimension;
which is time. With 4-D seismic geologists are now able to monitor
the movement and the mobility of oil as it is extracted in the
production process.
Abstract
of title - A chronological history of the ownership of a
tract of land.
Acidizing a well - Increasing the flow of oil from a
well by pumping hydrochloric acid into the well under high
pressure. This reopens and enlarges the pores in the oil-bearing
limestone formation.
Acre - The most common of land measure in the United
States. A square 210 feet on a side (44,100 sq. ft) would be a bit
larger than an acre (43,560 sq. ft). There are 640 acres in a
square mile.
Acre-foot - In the U.S., the thickness of a pay zone
is measured in feet, and the area of the reservoir is measured in
acres. An acre-foot is a volume of reservoir rock that is one acre
in area and one foot thick.
AFE (Authorization For Expenditure) - An estimate of
the costs of drilling and completing a proposed well, which the
operator provides to each working interest owner before the well is
commenced.
Annular space - The space between a well's casing and
the wall of the borehole.
Annulus of a well - The space between the surface
casing and the inner, producing well-bore casing.
Anticline - A geological term describing a fold in
the earth's surface with strata sloping downward on both sides from
a common crest. Anticlines frequently have surface manifestations
like hills, knobs, and ridges. At least 80 percent of the world's
oil and gas has been found in anticlines.
API - American Petroleum Institute, a petroleum
industry association that sets standards for oil field equipment
and operations.
API gravity - The gravity (weight per unit of volume)
of crude oil expressed in degrees according to an American
Petroleum Institute recommended system. The higher the API gravity,
the higher the crude. High-gravity crudes are generally considered
more valuable.
Aquifer - An underground water reservoir contained
between layers of rock, sand or gravel.
Associate gas - The gas that occurs with oil either
as free gas or in solution. When occurring alone, it is referred to
as unassociated gas.
Back to top
- B -
Back-in - A type of interest in a well or property
that becomes effective at a specified time in the future, or on the
occurrence of a specified future event.
Barrel Standard - Unit of measurement in the
petroleum industry. One barrel of oil equals 42 U.S. gallons.
Basement rock - Igneous or metamorphic rock lying
below sedimentary formations in the earth's crust. Basement rock
does not contain petroleum deposits.
Basin - A depression in the earth's crust in which
sedimentary materials have accumulated. Such a basin may contain
oil or gas fields.
BCF (billion cubic feet) - The cubic foot is a
standard unit of measure for gas at atmospheric pressure.
Behind pipe - If a well drills through several pay
zones and is completed in the deepest productive reservoir, casing
is set all the way down to the producing zone. Viewed from (a
perspective) inside the borehole, reserves in the shallower pay
zones up the hole are behind the casing.
Bleeding core - A core sample of rock so highly
permeable and saturated that oil drips from it.
Blowout - A sudden escape of oil or gas from a well,
caused by uncontrolled high pressure. It usually occurs during
drilling.
Bonus Money - Paid to a landowner or other holder of
mineral rights by the lessee for the execution of an oil and gas
lease in addition to any rental or royalty obligations specified in
the lease.
BOP (blowout preventer) - An assembly of heavy-duty
valves attached to the top of a well casing to control
pressure.
Bottom-hole pressure - The pressure of the reservoir
or formation at the bottom of the hole. A decline in pressure
indicates some depletion of the reservoir.
Bottom-hole pump - A compact, high-volume pump
located in the bottom of a well, not operated by sucker rods or a
surface power unit.
BS&W (basic sediment and water) - Material pumped
up with oil and gas which must be separated out.
BTU (British thermal unit) - A standard measure of
heat content in a fuel. One Btu equals the amount of energy
required to raise the temperature of one pound of water one degree
Fahrenheit at or near 39.2 degrees Fahrenheit.
Butane - A hydrocarbon associated with
petroleum. It is gaseous at ordinary atmospheric conditions.
Back to top
- C -
Cable drilling - A method of well-drilling that
employs a reciprocating, rather than a rotary, motion to penetrate
rock. In the nineteenth century, until Drake's time, power was
supplied by men. Drake used a steam-powered cable rig. Today, cable
rigs are powered by gasoline or diesel engines.
CAOF (calculated absolute open flow) - A figure
representing a gas well's theoretical producing capability per
day.
Capital asset - An asset acquired as an investment,
for the purpose of creating a product or service intended to be
used in the activities or operations of a business.
Capital costs (Oil & Gas Tax Usage) - For Federal
income tax purposes, the costs of capital expenditures which may be
recovered by deduction against income (through depreciation and
depletion).
Capital expenditure - An expenditure intended to
benefit the future activities of a business, usually by adding to
the assets of a business, or by improving an existing asset.
Capitalize - To treat certain expenditures as capital
expenditures for Federal income tax computations.
Carried Interest - A fractional working interest in
an oil and gas lease that comes about through an arrangement
between co-owners of a working interest.
Casing Pipe - Used in oil wells to reinforce the
borehole. Sometimes several casings are used, one inside the other.
The outer casing, called the "surface pipe,' shuts out water and
serves as a foundation for subsequent drilling.
Casinghead - The portion of the casing that protrudes
above the surface and to which control valves and flow pipes are
attached.
Casinghead gas - Natural gas produced from an oil
well, as opposed to gas produced from a gas well.
Cavings Rock - Fragments that break off from the
walls of a borehole and fall into the borehole during drilling
operations.
Cement - Fluid cement is mixed at the surface, pumped
to the bottom of a cased well, forced to flow around the lower end
of the casing and up into the space between the casing and the
borehole. When the cement solidifies (sets), it holds the casing in
place and provides support.
Cement squeeze - Forcing cement into the
perforations, large cracks, and fissures in the wall of a borehole
to seal them off.
Choke - An orifice installed in a pipeline at the
well surface to control the rate of flow.
Christmas tree - An assembly of valves, gauges, and
chokes mounted on a well casinghead to control production and the
flow of oil to the pipelines.
Clean oil - Crude oil containing less than 1 percent
sediment and water; "pipeline oil", oil clean enough to send
through a pipeline.
CO2 injection - A secondary recovery technique in
which carbon dioxide (CO2) is injected into wells as part of a
miscible recovery program.
Coal gasification - The chemical conversion of coal
to synthetic gaseous fuel.
Coal liquefaction - The chemical conversion of coal to
synthetic liquid fuel.
Cogeneration - The combined production of electrical or
mechanical energy and usable heat energy.
Common carrier - A person or company in the business
of transporting the public or goods for a fee. In the industry, a
person or company engaged in the movement of petroleum products,
like a public utility.
Completed well - A well made ready to produce oil or
natural gas. Completion involves cleaning out the well, running
steel casing and tubing into the hole, adding permanent surface
control equipment, and perforating the casing so oil or gas can
flow into the well and be brought to the surface.
Condensate - Liquid hydrocarbons separated from
natural gas, usually by cooling.
Confirmation well - A well drilled to "prove" the
formation encountered by an exploratory well.
Connate water - The water present in a petroleum
reservoir in the same zone occupied by oil and gas considered by
some to be the residue of the primal sea, connate water occurs as a
film of water around each grain of sand in granular reservoir rock
and is held in place by capillary attraction.
Conveyance - Legal term for transferring the title of
a property from one party to another, typically by deed.
Core - Samples of subsurface rocks taken as a well is
being drilled. The core allows geologists to examine the strata in
proper sequence and thickness.
Cracking - The process of breaking down the larger,
heavier, and more complex hydrocarbon molecules into simpler and
lighter molecules, thus increasing the gasoline yield from crude
oil. Cracking is done by application of heat and pressure, and in
modern time the use of a catalytic agent.
Crude oil - Liquid petroleum as it comes out of the
ground. Crude oils range from very light (high in gasoline) to very
heavy (high in residual oils). Sour crude is high in sulfur
content. Sweet crude is low in sulfur and therefore often more
valuable.
Crude oil equivalent - A measure of energy content
that converts units of different kinds of energy into the energy
equivalent of barrels of oil.
Cuttings - Chips and small rock fragments brought to
the surface by the flow of drilling mud as it is circulated and
examined by geologists for oil content.
- D -
Deductions - Tax items which may be subtracted from
gross income to arrive at taxable income in Federal income tax
computations.
Delay rental - Cash payments to the mineral rights
owner (lessor) by the working interest owner (lessee), for the
privilege of postponing the commencement of drilling operations on
the leased property.
Deliverability - A well's tested ability to
produce.
Depletion, restoration of - In Federal income
taxation, the adding back to income of depletion allowance taken on
minerals not produced.
Development Well - A well drilled in an already
discovered oil or gas field.
Diesel oil - A petroleum fraction composed primarily
of aliphatic (linear of unbranched) hydrocarbons. Diesel oil is
slightly heavier than kerosene.
Differential-pressure sticking - A condition in which
a section of drillpipe becomes stuck in deposits on the wall of the
borehole.
Directional drilling - Drilling at an angle, instead
of on the perpendicular, by using a whipstock to bend the pipe
until it is going in the desired direction. Directional drilling is
used to develop offshore leases, where it is very costly and
sometimes impossible to prepare separate sites for every well; to
reach oil beneath a building or some other location which cannot be
drilled directly; or to control damage or as a last resort when a
well has cratered. It is much more expensive than conventional
drilling procedures.
Distillate - Liquid hydrocarbons, usually colorless
and of high API gravity, recovered from wet gas by a separator that
condenses the liquid out of the gas. The present term is natural
gas.
Distillate fuel oil - A term subject to a variety of
definitions. Sometimes the definition is based on the method of
production, but other definitions are based on boiling range,
viscosity, or use.
Downhole - Refers to equipment or operations that
take place down inside a borehole.
Downstream - All operations taking place after crude
oil is produced, such as transportation, refining, and
marketing.
Drill bit - The part of the drilling tool that cuts
through rock strata.
Drill string - Also called drill pipe or drill stem.
Thirty-foot lengths of steel tubing screwed together to form a pipe
connecting the drill bit to the drilling rig. The string is rotated
to drill the hole and also serves as a conduit for drilling
mud.
Drilling - The act of boring a hole through which oil
or gas may be produced if encountered in commercial
quantities.
Drilling break - A sudden increase in the rate of
drilling.
Drilling fund - The generic term employed to describe
a variety of organizations established to attract venture capital
to oil and gas exploration and development. Typically the fund is
established as a joint venture or limited partnership.
Drilling mud - A mixture of clay, water, chemical
additives, and weighting materials that flushes rock cuttings from
a well, lubricates and cools the drill bit, maintains the required
pressure at the bottom of the well, prevents the wall of the
borehole from crumbing or collapsing, and prevents other fluids
from entering the well bore.
Drilling platform - An offshore structure with legs
anchored to the sea bottom that supports the drilling of up to 35
wells from one location.
Drilling rig - The surface equipment used to drill
for oil or gas, consisting chiefly of a derrick, a winch for
lifting and lowering drill pipe, a rotary table to turn the drill
pipe, and engines to drive the winch and rotary table.
Drillstem test - A test through the drill pipe prior
to completion to determine if oil or gas is present in a
formation.
Dry hole - A well that either produces no oil or gas
or yields too little to make it economic to produce.
Dry natural gas - Natural gas containing few or no
natural gas liquids (liquid petroleum mixed with gas).
Dual completion - Completing a well that draws from
two or more separate producing formations at different depths. This
is done by inserting multiple strings of tubing into the well
casing and inserting packers to seal off all formations except the
one to be produced by a particular string.
Back to top
- E -
Economic interest - An interest in oil and gas in the
ground. It entitles the owner to a deduction from gross income
derived from production of that oil and gas as specified in Federal
income tax regulations.
Electrical well logging - A method of oil exploration
that originated with Conrad Schlumberger, who first tested it in
1927 on a 1,500-meter well in France. As used today, the process is
very simple. Current passes into the ground, through the resistive
medium and into the sonde. The resulting charts show the varying
resistance, the conductance, and the self-potential of the strata
surrounding the well at every level, and geophysicists use them to
assay whether petroleum is present in a formation.
Enhanced oil recovery - Injection of water, steam,
gases or chemicals into underground reservoirs to cause oil to flow
toward producing wells, permitting more recovery than would have
been possible from natural pressure or pumping alone.
Ethanol - The two-carbon-atom alcohol present in the
greatest proportion upon fermentation of grain and other renewable
resources such as potatoes, sugar, or timber. Also called grain
alcohol.
Expenses (Tax Usage) - Expenditures for business
items that have no future life (such as rent, utilities, or wages)
and are incurred in conducting normal business activities.
Exploration - The search for oil and gas. Exploration
operations include: aerial surveys, geophysical surveys, geological
studies, core testing and the drilling of test wells.
Exploratory well - A well drilled to an unexplored
depth or in unproven territory, either in search of a new reservoir
or to extend the known limits of a field that is already partly
developed.
External casing packer - A device used on the outside
of the well casing to seal off formations or protect certain zones.
The packer is run on the casing and expanded against the wall of
the borehole at the proper depth by hydraulic pressure or fluid
pressure from the well.
Extraction plant - A plant for the extraction of the
liquid constituents in casinghead gas or wet gas.
- F -
Farm in - When one company drills wells or performs
other activity on another company's lease in order to earn an
interest in or acquire that lease.
Farm out agreement - An arrangement in which the
responsibility of exploration and development is shifted (by
assignment) from the working interest owner to another party.
Farmer's oil - An expression that refers to the
landowner's share of oil from a well drilled on his property. This
royalty is traditionally one-eighth of the produced oil free of any
expense to the landowner.
Fault - A break in the continuity of stratified rocks
or even basement rocks. Faults are significant to oilmen because
they can form traps for oil when the rock fractures, they can break
oil reservoirs into noncommunicating sections, they help produce
oil accumulations, and they form traps on their own.
Fault trap - A geological formation in which oil or
gas in a porous section of rock is sealed off by a displaced,
nonporous layer.
Fee lands - Privately owned, nonpublic lands.
Feet of pay - The thickness of the pay zone
penetrated in a well.
Field - A geographical area under which one or more
oil or gas reservoirs lie, all of them related to the same
geological structure.
Filter cake - A plastic-like coating that builds up
inside the borehole. Such buildup can cause serious drilling
problems, including sticking of the drillpipe.
Fishing - Recovering the tools or pipe that have been
accidentally lost down the borehole by using specially designed
tools that screw into or grab the missing equipment.
Fishing tools - Special instruments equipped with the
means for recovering objects lost while drilling the well.
Five-spot waterflood program - A secondary-recovery
operation in which four injection wells are drilled in a square
pattern with the production well in the center. Water from the
injection wells moves through the formation, forcing oil toward the
production well.
Flaring - The burning of gas vented through a pipe or
stack at a refinery, or a method of disposing of gas while a well
is being drilled. Flaring is regulated by state agencies. Venting
(letting gas escape unburned) is generally prohibited.
Flooding - One of the methods of enhanced oil
recovery. Water flooding or gas flooding might be considered
secondary recovery methods.
Flow Through concept - In ventures structured as
partnerships (or S corporations), certain items of tax significance
(profit, loss, etc.) are passed on to the partners (or S
corporation shareholders) in the venture. In a venture structured
as a "C" corporation, the responsible tax-paying party would be the
corporation itself (not its shareholders).
Flowing well - A well that produces through natural
reservoir pressure and does not require pumping.
Formation - A geological term that describes a
succession of strata similar enough to form a distinctive
geological unit useful for mapping or description.
Fossil fuels - Fuels that originate from the remains
of living things, such as coal, oil, natural gas, and peat.
Fracturing - A well stimulation technique in which
fluids are pumped into a formation under extremely high pressure to
create or enlarge fractures for oil and gas to flow through.
Proppants such as sand are injected with the liquid to hold the
fractures open.
Front-end costs - Costs that are paid out of initial
investment in a venture, first, before the venture activities
actually begin.
Fuel oil - See Heating oil.
Future prices - Refers to the New York Mercantile
Exchange (NYMEX) which introduced futures contracts for crude oil
in 1985 and natural gas in 1990.
Back to top
- G -
Gamma-ray logging - A technique of exploration for
oil in which a well's borehole is irradiated with gamma rays. The
varying emission of these rays indicates to geologists the relative
density of the rock formation at different levels.
Gas cap - The gas that exists in a free state above
the oil in a reservoir.
Gas condensate - Liquid hydrocarbons present in
casinghead gas that condense when brought to the surface.
Gas lift - A recovery method that brings oil from the
bottom of a well to the surface by using compressed gas. Gas pumped
to the bottom of the reservoir mixes with fluid, expands it, and
lifts it to the surface.
Gas-cut mud - Drilling mud permeated with bubbles of
gas from downhole. The circulation of such mud can be severely
impaired, seriously affecting drilling operations.
Gas-oil ratio - The number of cubic feet of natural
gas produced along with a barrel of oil.
Gasoline - A volatile, inflammable, liquid
hydrocarbon mixture.
General partner - In a limited partnership, the
general partner is responsible for managing the partnership's
activities (and is commonly the party that put the deal together).
His liability to the partnership's creditors is limited.
Geophones - The sound-detecting instruments used to
measure sound waves created by explosions set off during seismic
exploration work.
Geophysicist - A geophysicist applies the principles
of physics to the understanding of geology.
Gravimeter - A geophysical device that has been
particularly useful in finding salt domes. Actually, it is a weight
on a spring. The spring gets longer in high-gravity areas and
shorter in areas of gravity-minus. Magnetism helps the oil
geologist understand its measurements
Groundwater - The water in underground rock strata
that supplies wells and springs.
Gun perforation - A method of creating holes in a
well casing downhole by exploding charges to propel steel
projectiles through the casing wall. Such holes allow oil from the
formation to enter the well.
Gusher - A well drilled into a formation in which the
crude is under such high pressure that at first it spurts out of
the wellhead like a geyser. Gushers are rare today owning to
improved drilling technology, the use of drilling mud to control
downhole pressure, and oilmen's recognition of their
wastefulness.
Back to top
- H -
Heating oil - Oil use for residential heating.
Heavy oil - A type of crude petroleum characterized
by high viscosity and a high carbon-to-hydrogen ration. It is
usually difficult and costly to produce by conventional
techniques.
Held by production - Refers to an oil and gas
property under lease, in which the lease continues to be in force,
because of production from the property.
Horizon - A specific sedimentary layer in a cross
section of land, especially one in which a petroleum reservoir is
found.
Horizontal drilling - The newer and developing
technology that makes it possible to drill a well from the surface,
vertically down to a certain level, and then to turn at a right
angle, and continue drilling horizontally within a specified
reservoir, or an interval of a reservoir.
Horsehead - The curved guide or head piece on the
well end of a pumping jack's walking beam. The guide holds the
short loop of cable, called the bridle, attached to the well's pump
rods.
Hydraulic fracturing - A method of stimulating
production from a low-permeability formation by creating fractures
and fissures by applying very high fluid pressure.
Hydrocarbons - A large class of organic compound of
hydrogen and carbon. Crude oil, natural gas, and natural gas
condensate are all mixtures of various hydrocarbons, among which
methane is the simplest.
Hydrostatic head - The height of a column of liquid.
The difference in height between two points in a body of
liquid.
- I -
In situ - In its original place. Refers to methods of
producing synfuels underground, such as underground gasification of
a coal seam or heating oil shale underground to release its
oil.
Infill drilling - Wells drilled to fill in between
established producing wells to increase production.
Initial potential - Flow rate measured during the
initial completion of a well in a specific reservoir (initial daily
rate of production).
Injection well - A well employed for the introduction
into an underground stratum of water, gas or other fluid under
pressure. Injection wells are employed for the disposal of salt
water produced with oil or other waste. They are also used for a
variety of other purposes: 1) Pressure maintenance, to introduce a
fluid into a producing formation to maintain underground pressures
which would otherwise be reduced by virtue of the production of oil
or gas, 2)Secondary recovery operations, to introduce a fluid to
decrease the viscosity of oil, reduce its surface tension, lighten
its specific gravity, and drive oil into producing wells, resulting
in greater production of oil.
Intangible drilling costs - Expenditures, deductible
for Federal income tax purposes, incurred by an operator for labor,
fuel, repairs, hauling, and supplies used in drilling and
completing a well for production.
Investment Tax Credit (ITC) - A credit against income
taxes, usually computed as a percent of the cost of investment in
certain types of assets.
Isopachous map - A geological map showing the
thickness and shape of underground formations. A tool used to
determine underground oil and gas reservoirs.
Back to top
- J -
Jack or Unit - An oil-pumping unit. The pumping
jack's walking beam provides the up-and-down motion to the well's
pump rods.
Jet fuel - See Kerosene.
Jetting - Injecting gas into a subsurface formation
for the purpose of maintaining reservoir pressure.
Joint - A single section of drill pipe, casing, or
tubing, usually about 30 feet long.
Joint Operating Agreement - A detailed written
agreement between the working interest owners of a property which
specifies the terms according to which that property will be
developed.
Joint venture - A large-scale project in which two or
more parties (usually oil companies) cooperate. One supplies funds
and the other actually carries out the project. Each participant
retains control over his share, including liability and the right
to sell.
- K -
Kelly bushing - Part of the drilling rig, the Kelly
is a long hollow steel bar that connects to the upper end of the
drill string.
Kerogen - The hydrocarbon in oil shale. Scientists
believe that kerogen was the precursor of petroleum and that
petroleum development in shale was somehow prematurely
arrested.
Kerosene - The petroleum fraction containing
hydrocarbons that are slightly heavier than those found in gasoline
and naphtha. Kerosene (also spelled kerosine) was the most
important petroleum product because of its use for home and
commercial lighting; in recent years demand has risen again as a
result of kerosene's use in gas turbines and jet engines.
Kick Occurs - When the pressure encountered in a
formation exceeds the pressure exerted by the column of drilling
mud circulating through the hole. If uncontrolled, a kick leads to
a blowout.
Kill a well - To overcome downhole pressure by adding
weighting elements to the drilling mud
Back to top
- L -
Lag time - The time it takes for cuttings to be
carried (circulated) from the bottom of the borehole up to the
surface by the mud system.
Landman - A self-employed individual or company
employee who secures oil and gas leases, checks legal titles, and
attempts to cure title defects so that drilling can begin.
Landowner royalty - The share of the gross production
of the oil and gas on a property without deducting any of the cost
of producing the oil or gas. The usual landowner's royalty is
one-eighth of gross production.
Law of capture - A legal concept on which oil and gas
law in some states is based: since petroleum is liquid, and hence
mobile, it is not owned until it is produced.
Lease (Oil and Gas) - A contract by which the owner
of the mineral rights to a property conveys to another party, the
exclusive right to explore for and develop minerals on the
property, during a specified period of time.
Lease acquisition costs - Bonus payments.
Lease broker - An individual engaged in obtaining
leases for speculation or resale.
Lease hound - Someone who goes out and aggressively
acquires oil and gas leases from the landowner, and then turns
around and sells or trades them to an oil company planning to drill
a well in the area.
Lease offering (lease sale) - An area of land offered
for lease - usually by the U.S. Department of Interior - for the
exploration for and production of specific natural resources such
as oil and gas. Such a lease conveys no title or occupancy rights
apart from the right to search for and produce petroleum or other
natural resources subject to the conditions stated in the
lease.
Lease or Sublease - Any transaction in which the
owner of operating rights in a property assigns all or a portion of
these rights to any other party.
Lifting costs - The costs of producing oil from a well
or lease; the operating expenses.
Limestone - Sedimentary rock largely consisting of
calcite. On a world-wide scale, limestone reservoirs probably
contain more oil and gas reserves than all other types of reservoir
rock combined.
Limited partner - In a limited partnership, a partner
whose liability is limited to the amount of his investment in the
partnership (plus any assessments and his share of undistributed
partnership earnings).
Limited partnership - A partnership in which the
general partner manages the partnership's activities and is solely
liable for them. The limited partners are liable only to the extent
of their contributions.
LNG (liquefied natural gas) - Natural gas that has
been converted to a liquid through cooling to -260 degrees
Fahrenheit at atmospheric pressure.
Logs - Records made from data-gathering devices
lowered into the wellbore. The devices transmit signals to the
surface which are then recorded on film and used to make the record
describing the formation's porosity, fluid saturation, and
lithology. The filing of a log is required by the Federal
government if the drill site is on Federal land.
Lost circulation - A serious condition that occurs
when drilling mud pumped into the well does not return to the
surface, but goes into the porous formation, crevices, or caverns
instead.
LPG (liquefied petroleum gases) - Hydrocarbon
fractions lighter than gasoline, such as ethane, propane and
butane, kept in a liquid state through compression and/or
refrigeration, commonly referred to as "bottled gas."
- M -
Migration - The movement of oil and gas through
layers of rock deep in the earth.
Milling - Cutting a "window" in a well's casing with
a tool lowered into the hole on the drillstring.
Mineral Rights - The ownership of all rights to gas,
oil, or other minerals as they naturally occur in place, at or
below the surface of a tract of land.
MMCF Million cubic feet. - The cubic foot is a standard
unit of measure for quantities of gas at atmospheric
pressure.
Monocline - A geologic formation in which all the
strata are inclined in the same direction.
Mud - A fluid mixture of clay, chemicals, and
weighting materials suspended in fresh water, salt water, or diesel
oil.
Multiple completion - Completion of a well in more
than one producing formation. The tubing of each production zone
extends up to the Christmas tree to be piped to separate
tankage.
- N -
Natural gas - A mixture of hydrocarbon compounds and
small amounts of various nonhydrocarbons (such as carbon dioxide,
helium, hydrogen sulfide, and nitrogen) existing in the gaseous
phase or in solution with crude oil in natural underground
reservoirs.
Net profits interest - A share of gross production
from a property that is carved out of a working interest, and is
figured as a function of net profits from operation of the
property.
Net Revenue Interest (NRI) - The percentage of
revenues due an interest holder in a property, net of royalties or
other burdens on the property. A landowner leases his mineral
rights to an oilman. The landowner retains a royalty of 1/8
(=12.5%); his net revenue interest is 12.5%. The oilman's net
revenue interest would be 87.5% (=100% - 12.5%).
NGL (natural gas liquids) - Portions of natural gas
that are liquefied at the surface in lease separators, field
facilities, or gas processing plants, leaving dry natural gas. They
include, but are not limited to, ethane, propane, butane, natural
gasoline, and condensate.
- O -
Octane - A hydrocarbon of the paraffin series. It is
liquid at ordinary atmospheric conditions, although small amounts
may be present in the gas associated with petroleum.
Offering memorandum - A legal document provided to
potential investors in a venture describing the terms under which
the investment is being offered.
Offset well - A well drilled near the discovery well.
Also a well drilled to prevent oil and gas from draining from one
tract of land to another where a well is being drilled or is
already producing.
Oil column - The vertical height (thickness) of an
oil accumulation above the oil-water contact.
Oil gravity - The density of liquid hydrocarbons,
generally measured in degrees.
Oil in place - The crude oil estimated to exist in a
field or a reservoir. Oil in the formation not yet produced.
Oil pool - An underground reservoir containing oil.
An oil field may contain one or more pools, each of which has its
own pressure system.
Oil rig - A drilling rig that drills for oil and
gas.
On the pump - A phrase used in reference to a well
that no longer flows from natural reservoir energy by is produced
but means of a pump.
OPEC (Organization of Petroleum Exporting Countries)
- An international oil cartel originally formed in 1960 and
including in 1983: Saudi Arabia, Kuwait, Iran, Iraq, Venezuela,
Quatar, Libya, Indonesia, United Arab Emirates, Algeria, Nigeria,
Ecuador, and Gabon.
Operator - The individual or company responsible for
the drilling, completion and production operations of a well, and
the physical maintenance of the leased property.
Outcrop - A portion of bedrock or other stratum
protruding through the soil level, indicating a fault or some other
oil-bearing formation.
Overriding Royalty (ORRI) - A revenue interest in oil
and gas, created out of a working interest. Like the lessor's
royalty, it entitles the owner to a share of the proceeds from
gross production, free of any operating or production costs.
Overthrust belt - A geological system of faults and
basins in which geologic forces have thrust layers of older rock
above strata of newer rock that might contain oil or natural gas.
The Eastern Overthrust Belt runs from eastern Canada through
Appalachia into Alabama. The Western Overthrust Belt runs from
Alaska through western Canada and the Rocky Mountains into Central
America.
Back to top
- P -
Packer - A flexible rubber sleeve that is part of a
special joint of pipe.
Pay zones - The term to describe the reservoir that
is producing oil and gas within a given wellbore. Pay zones (or oil
reservoirs) can vary in thickness from one foot to several hundred
feet.
Payoff - The time when a well's production begins to
bring in revenues.
Payout - The amount of time it takes to recover the
capital investment made on a well or drilling program.
Perforating gun - An instrument lowered at the end of
a wireline into a cased well. It contains explosive charges that
can be electronically detonated from the surface.
Perforation - A method of making holes through the
casing opposite the producing formation to allow the oil or gas to
flow into the well. See Gun perforation.
Permeability - A measure of the ease with which a
fluid such as water or oil moves through a rock when the pores are
connected. Geologists express permeability in a unit named the
darcy, but oilmen use the millidarcy because most of the rocks they
come in contact with are not very permeable.
Petrochemicals - Chemicals derived from crude oil or
natural gas, including ammonia, carbon black, and other organic
chemicals.
Petroleum - Strictly speaking, crude oil. Also used
to refer to all hydrocarbons, including oil, natural gas, natural
gas liquids, and related products.
Petroleum engineer - A term including three areas of
specialization: 1) Drilling engineers specialize in the drilling,
workover, and completion operations, 2) Production engineers
specialize in studying a well's characteristics and using various
chemical and mechanical procedures to maximize the recovery from
the well, 3) Reservoir engineers design and execute the planned
development of a reservoir. Many U.S. universities offer BS, MS,
and Ph.D. degrees in petroleum engineering.
Petroleum geologist - A geologist who specializes in
the exploration for, and production of, petroleum.
Pinch out - The disappearance of a porous, permeable
formation between two layers of impervious rock over a horizontal
distance.
Pipeline - A tube or system of tubes used for the
transportation of oil or gas. Types of oil pipelines include: lead
lines, form pumping well to a storage tank; flow lines, from
flowing well to a storage tank; lease lines, extending from the
wells to lease tanks; gathering lines, extending from lease tanks
to a central accumulation point; feeder lines, extending from
leases to trunk lines; and trunk lines, extending from a producing
area to refineries or terminals.
Pipeline gas - Gas under enough pressure to enter the
high-pressure gas lines of a purchaser; gas in which enough liquid
hydrocarbons have been removed so that such liquids will not
condense in the transmission lines.
Plug back - To block off the lower section of the
borehole by setting a plug, in order to perform operations in the
upper part of the hole.
Plugged & Abandoned (P&A) - This expression
refers to setting cement plugs in an unsuccessful well (a dry hole)
or a depleted well.
Plugging a well - Filling the borehole of an
abandoned well with mud and cement to prevent the flow of water or
oil from one strata to another or to the surface.
Pool - 1) (noun) An underground reservoir containing
or appearing to contain a common accumulation of oil and natural
gas. A zone of a structure which is completely separated from any
other zone in the same structure is a pool. 2) (verb) To combine
two or more tracts of land into one unit for drilling purposes.
This may be accomplished voluntarily, or through compulsion.
Pooling - A term frequently used interchangeably with
"Unitization" but more properly used to denominate the bringing
together of small tracts sufficient for the granting of a well
permit under applicable spacing rules.
Porosity - A measure of the number and size of the
spaces between each particle in a rock. Porosity affects the amount
of liquid and gases, such as natural gas and crude oil, that a
given reservoir can contain.
Possible reserves - Areas in which production of
crude oil is presumed possible owing to geological inference of a
strongly speculative nature.
Present net value - The present value of the dollars
(income, or stream of income) to be received at some specified time
in the future, discounted back to the present at a specified
interest rate.
Primary recovery - Production in which oil moves from
the reservoir, into the wellbore, under naturally occurring
reservoir pressure.
Primary term - The basic period of time during which
a lease is in effect.
Private Placement Offering - A securities
(investment) offering not intended for the general public. By
meeting certain criteria, such an offering may qualify for
exemptions from registration with the Securities and Exchange
Commission of the Federal government.
Probable reserves - Areas which are unproven but
presumed capable of production because of geological inference, for
instance, proximity to proven reserves in the same reservoir.
Producing horizon - Where the well is actually
produced, since it may be drilled to a greater depth.
Producing platform - An offshore structure with a
platform raised above the water to support a number of producing
wells.
Production - A term commonly used to describe taking
natural resources out of the ground.
Production test - A test made to determine the daily
rate of oil, gas, and water production from a potential pay
zone.
Proppants - Materials used in hydraulic fracturing
for holding open the cracks made in the formation by the fracturing
process. Proppants may consist of sand grains, beads, or other
small pellets suspended in fracturing fluid.
Prospect - A lease or group of leases on which an
operator intends to drill.
Proved behind-pipe reserves - Estimates of the amount
of crude oil or natural gas recoverable by recompleting existing
wells.
Proved developed reserves - Estimates of what is
recoverable from existing wells with existing facilities from open,
producing payzones.
Proved reserves - Estimates of the amount of oil or
natural gas believed to be recoverable from known reservoirs under
existing economic and operating conditions.
Proved undeveloped reserves - Estimates of what is
recoverable through new wells on undrilled acreage, deepening
existing wells, or secondary recovery methods.
Public lands - Any land or land interest owned by the
Federal government within the 50 states, not including offshore
Federal lands or lands held in trust for Native American
groups.
Public Offering - A securities (investment) offering
intended for sale to the general public. It must be registered with
1) the Securities and Exchange Commission of the Federal government
and 2) the securities-regulating agencies of the various states in
which it will be offered.
Pump - A device that is installed inside or on a
production string (tubing) that lifts liquids to the surface.
Pump off - To pump a well so rapidly that the oil
level falls below the pump's standing valve, rendering the well
temporarily dry.
Pumping well - A well that does not flow naturally
and requires a pump to bring product to the surface.
- Q -
Quad - One Quadrillion (1,000,000,000,000,000)
Btus
Quitclaim deed - A document by which one party
(grantor) conveys title to a property, by giving up any claim which
he may have to title (although he does not profess that claim is
necessarily valid).
- R -
R&D - Research and development.
Re-entry - A well was abandoned, but subsequent
drilling and production in the area suggests that a potential pay
zone in the well was missed or passed over.
Reclamation - The restoration of land to its original
condition by regrading contours and replanting after the land has
been mined, drilled, or otherwise has undergone alteration from its
original state.
Recoverable resources - An estimate of resources,
including oil and/or natural gas, both proved and undiscovered,
that would be economically extractable under specified price-cost
relationships and technological conditions.
Reef - A buildup of limestone formed by skeletal
remains of marine organisms. It often makes an excellent reservoir
for petroleum.
Refiner - A person or company that has any part in
the control or management of any operation by which the physical or
chemical characteristics of petroleum or petroleum products are
changed.
Refining - Manufacturing petroleum products by a
series of processes that separate crude oil into its major
components and blend or convert these components into a wide range
of finished products, such as gasoline or jet fuel.
Relief well - A well drilled in a high-pressure
formation to control a blowout.
Reserve - That portion of the identified resource
from which a usable mineral and energy commodity can be
economically and legally extracted at the time of
determination.
Reserve (pool) - A porous and permeable underground
formation of producible oil and/or natural gas, confined by
impermeable rock or water barriers, and characterized by a single
natural pressure system.
Reservoir - A porous, permeable sedimentary rock
formation containing quantities of oil and/or gas enclosed or
surrounded by layers of less permeable or impervious rock. Also
called a "horizon."
Reservoir pressure - The pressure at the face of the
producing formation when the well is shut-in. It equals the shut in
pressure at the wellhead plus the weight of the column of oil in
the hole.
Retained Interest - A fractional interest reserved by
the owner of a whole interest when the balance of the whole
interest is transferred to another party.
Reversionary interest - An interest in a well or
property that becomes effective at a specified time in the future
or on the occurrence of a specified future event.
Risk - The possibility of loss or injury. A level of
uncertainty is associated with the various possible outcomes of the
undertaking. Risk usually refers to a numerical estimate of the
likelihood of the occurrence to these various possible
outcomes.
Rotary drilling - A method of well-drilling that
employs a rotating bit and drilling mud to cut through rock
formations.
Roughnecks - Members of the drilling crew.
Round trip - Pulling the drillpipe from the hole to
change the bit, then running the drillpipe and new bit back in the
hole.
Royalty - A payment to a landowner or mineral rights
owner by a leaseholder on each unit of resources produced.
Royalty Funds - Generally speaking, a royalty fund is
when royalty interests are being bought, sold and held by the
fund's sponsors. In nearly all leasing situations, once a lease has
been developed, it provides a revenue stream. A portion of the
revenue stream is set aside for royalty which generally amounts to
12.5% and overriding royalty &/or carried working interest of
2-5%. In a royalty fund the objective of the fund is to generate
it's revenue from royalties that are held from different producing
fields throughout the country. The main feature to owning a
percentage of a royalty fund is that with an oil royalty the
royalty owner (or interest owner) pays no percentage of operating
or developmental costs associated with the production of the oil or
gas. Royalty programs generally offer a low risk factor along with
a relatively low return. However, their main feature is that these
types of programs last for many, many years.
- S -
Salt dome - A subsurface mound or dome of salt.
Salt-bed storage - Storage of petroleum products in
underground formations of salt whose cavities have been mined or
leached out with superheated water.
Sample - Cuttings of a rock formation broken up by
the drill bit and brought to the surface by the drilling mud. These
are examined by geologists to identify the formation and type of
rock being drilled.
Sample log - A record of rock cuttings made as a well
is being drilled. A record is then kept that shows the
characteristics of the various strata drilled through.
Sandstone - Rock composed mainly of sand-sized
particles or fragments of the mineral quartz.
Saturation - 1. The extent to which the pore space in
a formation contains hydrocarbons or connate water. 2. The extent
to which gas is dissolved in the liquid hydrocarbons in a
formation.
Schlumberger (pronounced "slumber-jay") - The founder
of electrical well logging, now the name for any electrical well
log.
Scout - An individual who observes and reports on
competitor's leasing and drilling activities.
Secondary recovery - The introduction of water or gas
into a well to supplement the natural reservoir drive and force
additional oil to the producing wells.
Section - A square tract of land having an area of
one square mile (=640 acres). There are 36 sections in a
township.
Sedimentary basin - A large land area composed of
unmetamorphized sediments. Oil and gas commonly occur in such
formations.
Sedimentary rock - Rock formed by the deposition of
sediment, usually in a marine environment.
Seismic exploration - A method of prospecting for oil
or gas by sending shock waves into the earth. Different rocks
transmit, reflect, or refract sound waves at different speeds, so
when vibrations at the surface send sound waves into the earth in
all directions, they reflect to the surface at a distance and angle
from the sound source that indicates the depth of the interface.
These reflections are recorded and analyzed to map underground
formations.
Seismograph - A device that records natural or
manmade vibrations from the earth. Geologists read what it has
recorded to evaluate the oil potential of underground
formations.
Selling Expenses - Expenses incurred in marketing
interests in securities and commonly paid out of the investor's
capital investment.
Separator - A pressure vessel used to separate well
fluids into gases and liquids.
Service well - A well drilled in a known oil or
natural gas field to inject liquids that enhance recovery or
dispose of salt water.
Set casing - To cement casing in the well hole,
usually in preparation for producing a commercial well.
Severance - The owner of all rights to a tract of
land can sever the rights to his land (vertically or horizontally).
In horizontal severance, for example, if he chooses to sell all or
part of the mineral rights, two distinct estates are created: the
surface rights to the tract of land and the mineral rights to the
same tract. The two estates may change hands independently of each
other.
Severance tax - Tax paid to the state government by
producers of oil or gas in the state.
Shale - A type of rock composed of common clay or
mud.
Shale oil - The substance produced from the treatment
of kerogen, that hydrocarbon found in some shales, which is
difficult and costly to extract. About 34 gallons of shale oil can
be extracted from one ton of ore.
Shale shaker - A vibrating screen or sieve that
strains cuttings out of the mud before the mud is pumped back down
into the borehole.
Sharing arrangement - An arrangement whereby a party
contributes to the acquisition, or exploration and development, of
an oil and gas property, and receives as compensation, a fractional
interest in that property.
Shoestring sands - Narrow strands of saturated
formation that have retained the shape of the stream bed that
formed them. In the United States, such a formation is located in
Kansas.
Shoot a well - A technique that stimulates production
of a tight formation by setting off charges downhole that crack
open the formation. The early wells were shot with nitroglycerin;
then dynamite was used. The nitro man has been replaced today by
acidizers and frac trucks.
Show - An indication of oil or gas observed and
recorded during the drilling of a well.
Shut-down well/shut-in well - A well is shut down
when initial drilling ceases for one reason or another. A well is
shut in when the wellhead valves are closed, shutting off
production, often while waiting for transportation or for the
market to improve.
Shut-in - To stop a producing oil and gas well from
producing.
Shut-in pressure -The pressure at the wellhead when
valves are closed.
Shut-in Royalty - A special type of royalty
negotiated in the leasing of a property.
Side track - When fishing operations have been unable
to recover an object in the hole that prevents drilling ahead, the
borehole can often be drilled around the obstacle in the original
hole.
Skidding the rig - Moving a derrick from one location
to another on skids and rollers.
Solution gas - Natural gas that is dissolved in the
crude oil in a reservoir.
Sour Crude or Gas - Oil or natural gas containing
sulfur compounds, notably hydrogen sulfide, a poisonous gas.
Source rock - Sedimentary rock, usually shale
containing organic carbon in concentrations as high as 5-10% by
weight.
Spacing unit - The size (amount of surface area) of a
parcel of land on which only one producing well is permitted to be
drilled to a specific reservoir.
Spot market - A short-term contract (typically 30
days) for the sale or purchase of a specified quantity of oil or
gas at a specified price.
Spud - To spud a well means to start the initial
drilling operations.
Squeeze - The procedure of pumping a slurry of cement
into a particular space in the borehole (often the annulus between
the borehole and the casing), so that the cement will solidify to
form a seal.
Step-out well - A well drilled near a proven well,
but located in an unproven area, that determines the boundaries of
the producing formation.
Stipper oil well - An oil well capable of producing
no more than 10 barrels of oil per day.
Stocktank barrel - A barrel of oil at the earth's
surface.
Stratigraphic test - A hole drilled to gather
information about rock strata in an area.
Stratigraphic trap - A porous section of rock
surrounded by nonporous layers, holding oil or gas. They are
usually very difficult to locate, although oilmen believe that most
of the oil yet to be discovered will be found in these traps.
Structural trap - A reservoir created by some
cataclysmic geologic event that creates a barrier and prevents
further migration. The most common structural traps are anticlines,
in which at lease 80 percent of the world's oil and gas have been
discovered.
Structure - Subsurface folds or fractures of strata
that form a reservoir capable of holding oil or gas.
Submersible pump - A bottom-hole pump for use in an
oil well when a large volume of fluid is to be lifted.
Subscription - The manner by which an investor
participates in a limited partnership through investment.
Substructure - A platform upon which a derrick is
erected.
Surface rights - Surface ownership of a tract of land
from which the mineral rights have been severed.
Swab - A hollow rubber cylinder with a flap (check
valve) on the bottom surface. It is lowered below the fluid level
in the well. This opens the check valve allowing fluid into the
cylinder. The check valve flap closes as the swab is pulled back
up, lifting oil to the surface.
Sweet crude - Crude oil with low sulfur content which
is less corrosive, burns cleaner, and requires less processing to
yield valuable products.
Syncline - A downfold in stratified rock that looks
like an upright bowl. Unfavorable to the accumulation of oil and
gas.
Syndication expenses - Expenditures incurred by a
partnership in connection with issuing and marketing its interests
to investors: legal fees of the issuer for securities and tax
advice, accounting fees for audits, and other representations
included in the offering memorandum.
Synfuels - Fuels produced through chemical
conversions of natural hydrocarbon substances such as coal and oil
shale.
Synthetic crude oil (syncrude) - A crude oil derived
from processing carbonaceous material such as shale oil or
unrefined oil in coal conversion processes.
Synthetic gas - Gas produced from solid hydrocarbons
such as coal, oil shale, or tar sands.
Back to top
- T -
Take-or-pay contract - A (long-term) contract between
a gas producer and a gas purchaser, such as a pipeline transmission
company.
Tank bottoms - A mixture of oil, water, and other
foreign matter that collects in the bottoms of stock tanks and
large crude storage tanks and must be cleaned or pumped out on a
regular basis.
Tanker - An ocean going ship which hauls crude
oil.
Tar sand - A sandstone in which the spaces between
grains are filled with a highly viscous tar.
Tar sands - Rocks (other than coal or oil shale) that
contain highly viscous hydrocarbons that are unrecoverable by
primary production methods.
Tax preference items - Certain items of income, or
special deductions from gross income which are given favored
treatment under Federal tax law.
TCF - Trillion cubic feet.
Tectonic map - A geologic map showing the structure
of the earth's crust.
Tertiary recovery - The recovery of oil that involves
complex and very expensive methods such as the injection of steam,
chemicals, gases, or heat, as compared to primary recovery, which
involves depleting a naturally flowing reservoir, or secondary
recovery, which usually involves repressuring or
waterflooding.
Therm - A measure of heat content. One therm equals
100,000 Btus.
Third for a quarter - Sometimes also known as a
"quarter for a third". A widely used arrangement for promoting an
oil deal to another party.
Tight formation - A sedimentary layer of rock
cemented together in a manner that greatly hinders the flow of any
gas through the rock.
Tight hole - A well about which the operator keeps
all information secret.
Tight sand - A formation with low permeability. Gas
produced from a formation so designated by the Federal Energy
Regulatory Commission qualifies for a higher market price.
Time value of money - The concept that a dollar in
hand today is worth more than a dollar that will be received in
some future year.
Title - The combination of factors that, together,
constitute legal ownership of a property.
Tool pusher - The supervisor of drilling rig
operations.
Top lease - A (conditional) type of lease that may be
granted by the mineral-rights owner of a property while a
pre-existing recorded lease of that property is nearing expiration,
but nonetheless is still in effect. The top lease would become
effective only if and when the existing lease expires (or is
terminated).
Total depth (TD) - The maximum depth of a
borehole.
Township - A square tract of land six miles on a
side, it consists of 36 sections of one square mile each.
Transfer rule - When an interest in an oil and gas
property already proven to be capable of commercial production is
transferred, the transferee taxpayer is generally not entitled to
percentage depletion, although he may still be entitled to cost
depletion, in computing his depletion allowance deduction from
gross income.
Trap - A natural configuration of layers of rock
where non-porous or impermeable rocks acts as a barrier, blocking
the natural upward flow of hydrocarbons.
Trip - Making a "trip" is the procedure of pulling
the entire string of drill pipe out of the borehole and then
running the entire length of drill pipe back in the hole.
Tubing - Small diameter pipe, threaded at both ends,
that is lowered into a completed well. Oil and gas are produced
through a string of tubing.
Turnkey - A drilling contract that calls for a
drilling contractor to drill a well, for a fixed price, to a
specified depth. The purpose of drilling a well by turnkey contract
may be related to the timing of Federal income tax deductions. For
income tax purposes, expenses are deductible from gross income as
they are incurred. When a turnkey contract is entered into toward
the end of the current tax year, the drilling costs may be pre-paid
at that time. The idea is to give a working interest owner (or
investor) in the well, the opportunity to deduct the intangible
drilling costs from his gross income in the current tax year.
- U -
Unassociated gas - Natural gas that occurs alone, not
in solution or as free gas with oil or condensate.
Undiscovered recoverable resources - Resources
outside of known fields, estimated from broad geologic knowledge
and theory.
Updip well - A well located high on a structure where
the oil-bearing formation is found at a shallower depth.
Upstream - Activities concerned with finding
petroleum and producing it, compared to downstream which are all
the operations that take place after production.
- V -
Vapor pressure - The pressure exerted by a vapor held
in equilibrium with its solid or liquid state.
Viscosity - A fluid's resistance to flowing.
- W -
Wasting assets - Assets that will eventually lose
their value.
Water drive - The most efficient driving mechanism to
force oil and gas out of the reservoir.
Water-drive reservoir - A reservoir in which the
pressure that forces the oil to the surface is exerted by edge or
bottom water in the field.
Waterflooding - A secondary recovery method in which
water is injected into a reservoir to force additional oil into the
wells.
Well platform - An offshore structure that supports a
well's surface controls and flow piping.
Well program - The procedure for drilling, casing, and
completing a well.
Wellbore - Physically, wellbore refers to a borehole,
in other words a completed well.
Wellhead - A device on the surface used to hold the
tubing in the well. The wellhead is the originating point of the
producing well at the top of the ground.
West Texas Intermediate - Refers to a grade of crude
oil produced in the Permian and Midland basin areas of west Texas.
The price paid for crude oil varies according to quality.
Wet - A reservoir rock is said to be "wet" when it
contains water but no hydrocarbons.
Wet gas - Natural gas containing liquid hydrocarbons
- commonly condensate.
Whipstock - A steel blocking device placed in a
borehole. As drilling is resumed, the whipstock forces the drill
bit to veer off at a slight angle.
Wildcat - An exploration well drilled to a reservoir,
from which no oil or gas has previously been produced in the nearby
surrounding area.
Wildcatter - An operator who drills the first well in
unproven territory.
Working interest - An interest created by the
execution of an oil and gas lease.
Workover - To clean out or work on a well to restore
or increase production.
Workover rig - The rig used when oilmen try to
restore or increase a well's production.
Write-off - In common usage: a reduction in taxable
income that results when allowable deductions are subtracted from
gross income.
- X, Y, Z -
Zone - A specific interval of rock strata containing
one or more reservoirs, used interchangeably with
"formation."
Zone isolation - Sealing off a producing formation
while a hole is being deepened. A special sealant is injected into
the formation, where it hardens long enough for the hole to be
drilled. Afterward, the substance again turns to liquid,
unblocking the formation.
