The oil exploration industry is a complex one, and it has a language all of its own. In this glossary we have provided simple definitions for some of the more common terms. We would like to acknowledge PetroSearch Training and Consultancy as the source for many of these definitions.
A more comprehensive glossary of almost 5000 technical definitions is available on the Schlumberger website. http://www.glossary.oilfield.slb.com/
A
Anticline
A fold in layered rocks originating below the surface in form of an elongated dome.
Appraisal drilling
Drilling to determine physical extent, reserves and likely production rate of a reservoir, together with properties of oil or gas.
Aquifer
Underground zone of permeable rock saturated with water under pressure.
B
Bit
The cutting or boring element used in drilling oil and gas wells.
Blowout
Uncontrolled flow of gas, oil or other well fluids from a well during drilling due to formation pressure exceeding the pressure exerted by the column of drilling mud.
Blowout Preventer (BOP)
Hydraulically or mechanically actuated high-pressure valve installed at the wellhead to control pressure within the well.
Bottom-hole assembly
Components, together as a group, that make up the lower end of the drill-string (drill bit, drill collars, drill pipe and ancillary equipment.)
C
Cap Rock
Impervious layer which overlies a reservoir rock preventing hydrocarbons escaping.
Capped Well
A well capable of production but lacking wellhead installations and a pipeline connection.
Casing
Steel lining used to exclude unwanted fluids, control well pressures and support side of well bore. Casing Seat - lowest point at which casing is set. Casing head - top of casing set in well; part of casing that protrudes above surface and to which control valves and pipes are attached
Choke
Device to restrict rate of flow during testing of an exploration discovery.
Christmas tree
Valves, pipes, fittings assembled at the top of a completed well used to control the flow of oil and gas.
Close in
To shut in (temporarily) a well that is capable of production.
Condensate
A mixture of pentanes and heavier hydrocarbons that is recovered or recoverable from an underground reservoir. It is gaseous in its virgin state but is liquid under the conditions at which its volume is measured.
Core
A cylindrical sample taken from a formation for the purpose of examination or analysis.
Cuttings
Fragments of rock dislodged by the bit and brought to the surface in the drilling mud.
D
Derrick
Load-bearing tower-like framework over an oil/gas well which holds the hoisting and lowering equipment.
Derrickhand
A crew member whose work station is in the derrick while the pipe is being hoisted or lowered into the hole. He is usually next in line of authority under the driller.
Development Well
Well drilled for oil and gas within a proven field or area for the purpose of completing the desired pattern of production.
Directional Drilling
Controlled drilling at a specified angle from the vertical.
Discovery Well
An exploratory well which discovers a new oil/gas field.
Drawworks
Hoisting mechanism on a drilling rig which spools off or takes in the drilling line and thus raises or lowers the drill string and bit.
Drill bit
Located at end of drill-string cutting head is generally designed with three cone-shaped wheels tipped with hardened teeth. Drill bits used for extra-hard rock are studded with thousands of tiny industrial diamonds.
Drill cuttings
Lifted continually to surface during drilling by a circulating-fluid system driven by a pump. To facilitate removal of cuttings, mud is constantly circulated down through drill pipe, out through nozzles.
Drill pipe
A steel pipe, in approximately 30-foot (9metre) lengths, screwed together to form a continuous pipe extending from the drilling rig to the drilling bit at the bottom of the hole. Rotation of the drill pipe and bit causes the bit to bore through the rock.
Drill Stem Test (DSM)
A conventional method of testing a formation to determine its potential productivity before installing production casing in a well. A testing tool is attached to the bottom of the drill pipe and placed opposite the formation to be tested which has been isolated by placing packers above and below the formation. Fluids in the formation are allowed to flow up through the drill pipe by establishing an open connection between the formation and the surface.
Drill string
String of individual joints of a pipe that extends from the bit to the Kelly and carries the mud down to, and rotates, the bit.
Drilling fluids
While a mixture of clay and water is the most common drilling fluid, wells can also be drilled with air, natural gas, oil, or plain water as the drilling fluid. See also Mud.
Dry Hole
Generally refers to any well that does not produce oil or gas in commercial quantities.
E
Exploration Well
Well drilled in unproven territory.
Farm-in
Transfer of part of an oil or gas interest in consideration for an agreement by transferee(s) to meet certain expenditure that would otherwise have to be undertaken by licensee(s).
F
Fishing
Encompasses both the special equipment and the special procedures to remove undesirable objects from the wellbore.
Formation
Sedimentary bed or deposit composed substantially of the same minerals throughout, and distinctive enough to be a unit.
G
Gas Cap
Free gas, separate from, but overlying an oil zone that occurs within the same producing formation as oil. Since gas is lighter, it occupies the upper part of the reservoir.
Geology
Field of science concerned with the origin of planet earth, its history, its shape, materials forming it and processes that are acting or have acted on it.
Geologist
Scientist whose duties consist of obtaining and interpreting data dealing with the Earths history and its life, especially as recorded in rocks.
H
Horizontal Drilling
Technique for cutting a bore holes in geological strata in a horizontal, rather than normal vertical, direction.
Hydrocarbons
Organic chemical compounds of hydrogen and carbon whose densities, boiling points, and freezing points increase as their molecular weights increase. The molecular structure of the most common petroleum hydrocarbon compounds varies from the simplest - methane, a constituent of natural gas - to the very heavy and complex.
I
Impermeable
When fluids cannot flow through rocks (clays, cemented sandstone or salt) where cracks and pore spaces are very small or are blocked by mineral growth
J
K
Kick
Back pressure in a well from invading oil/gas/water.
L
Liner
Small diameter casing extending into producing layer from just inside bottom of final string of casing cemented in a well.
Liquids
Hydrocarbons in solution in natural gas which are liquefiable at surface temperature and pressure or by treatment and processing.
Log
M
Mature
When source rock starts to generate hydrocarbons.
Migration
Natural movement of oil or gas within or out of a formation.
Monkey Board
Platform on which the derrickhand works during the time the crew is making a trip.
Mousehole
Hole drilled under the derrick floor and temporarily cased in which a single joint of pipe is placed awaiting connection to the drill string.
Mud
Usually colloidal suspensions of clays in water with chemical additives that are circulated through the wellbore during rotary drilling and workover operations. Can use oil as the main medium.
N
O
Oilfield
Loosely defined term referring to an area where oil is found. May also include the oil reservoir, the surface and wells, and production equipment.
Operator
Person, whether proprietor or lessee, who actually operates the well. Generally the oil company by whom the drilling contractor is engaged.
P
Pay Zone (Pay Section)
Producing formation, or that formation which represents the objective of drilling.
Penetration (rate of)
Rate at which the drill bit proceeds in the deepening of the wellbore and usually expressed as feet (meters) per hour.
Perforate
To pierce holes through well casing within and oil or gas-bearing formation by means of a perforating gun lowered down the hole and fired electrically from the surface. The perforations permit production from a formation which has been cased off.
Permeability
Capacity of porous rock formation to allow fluid to flow within the interconnecting pore network.
Play
A group of fields with similar trap structures/ reservoir rock.
Plug and Abandon
Act of placing cement plugs in a hole to prevent unwanted vertical migration in an abandoned well.
Porosity
Volume of pore spaces between mineral grains expressed as a percentage of the total rock volume. Thus porosity measures the capacity of the rock to hold oil, gas or water.
Potential
Actual or maximum volume of oil and/or gas that a well is capable of producing.
Production
The operation of bringing the well fluids to the surface and separating them, and storing, gauging, and otherwise preparing product for the pipeline. Also refers to the amount of oil or gas produced over a given period.
Q
R
Rathole
Shallow bore under the derrick substruchture in which the kelly joint is temporairily set while making connection.
Reserves
Estimated volumes of crude oil, condensate, natural gas and liquid petroleum gas that meet specific criteria.
Proved Reserves: Those quantities of petroleum which can be estimated with reasonable certainty (at least 90% probability) to be commercially recoverable, from a given date, under defined economic conditions, operating methods and regulations. Often referred to as 1P Reserves.
Probable Reserves: Those additional reserves that together with Proved Reserves, are as likely or not (50% probability) to be recovered. Proved plus Probable is often referred to as 2P Reserves.
Possible Reserves: Those additional reserves which are less likely to be recoverable. There should be at least a 10% probability that the Proved plus Probable plus Possible Reserves will be recovered. Proved plus Probable plus Possible is often referred to as 3P Reserves.
Rotary Table/Drilling Table
Turning device on derrick floor in which drill-string is held and rotated.
Roughneck
Industry slang for floorhand.
S
Seal (Cap)
Rocks (salt, clays or cemented sandstone) in right shapes and relative positions to form traps.
Seismic Surveys
Measurements of seismic-wave travel. Seismic exploration is divided into refraction and reflection surveys, depending on whether the predominant portion of the seismic waves' travel is horizontal or vertical. Refraction seismic surveys are used in exploration. Seismic reflection surveys detect boundaries between different kinds of rocks; this detection assists in mapping of geologic structures.
Set casing
Installation of steel pipe or casing in a wellbore, normally cemented in place by surrounding it with a wall of cement.
Shale shaker
Drilling mud passed over to sieve out cuttings.
Sidetracking
Drilling past an obstruction in the hole, usually done using a special tool known as a whipstock.
Source Rocks
Rocks containing sufficient organic substances to generate hydrocarbons.
Spud
Commencment of drilling operations.
Stratigraphic trap
Formed by Earth movements that fold rocks into suitable shapes or juxtapose reservoir and sealing rocks along faults. Traps may also form when rocks are domed over rising salt masses.
Structure
Subsurface geological feature capable of acting as a reservoir for oil and/or gas.
Stuck Pipe
Drill pipe, casing, or tubing that cannot be worked in or out of the hole as desired.
Syncline
Trough-shaped subsurfaces structure of folded stratified rock. Opposite of anticline.
T
Toolpusher
Foreman in charge of the drilling and rig operations and crew members.
Total Depth
Maximum depth reached in a well.
Top Drive
Powerful electric motor that rotates whole drill-string from top down.
Trap
Geological structure in which hydrocarbons build up to from an oil or gas field.
Tripping
Re-insertion of drill-string/ withdrawing drill-string.
Turnkey Contract
Contract under which contractor carries out and completes his assignment for a fixed fee, as opposed to working on per diem basis.
U
V
W
Well Logging
Recording information about subsurface geological formations; methods include records kept by the driller, mud and cutting analysis, drill stem tests and electric and radioactivity procedures.
Wildcat
Well drilled in unproven territory.
Workover
To carry out remedial operations on a producing well with the intention of restoring or increasing production.
