- A -

Acidise injecting acid solution down a well to dissolve carbonate rocks in a reservoir and improve the flow of hydrocarbons to the well.

Acoustic log a measurement of the velocities of sound waves imparted to a formation in a well and used mainly for determination of rock porosity.

Acreage the area covered by a company’s exploration permits.

Annulus annular space between drill string and casing or borehole.

Anomaly a divergence from the background levels of physical or chemical properties of an area under survey.

Anticline an upfold in rock strata producing an arch or dome structure. One of the most common hydrocarbon traps.

Anticlinal trap a hydrocarbon trap formed by the upward bowing of strata into a dome or arch.

API American Petroleum Institute. API gravity is a standard method of measuring density of crude oils and is expressed in degrees.

Appraisal well a well or wells drilled to follow up a discovery and evaluate its commercial potential.

- B -

Barrel (bbl) measure of crude oil equal to 42 US gallons, 35 Imperial gallons or 159 litres. Takes its name because the first oil produced in the US was stored and transported in wooden barrels.

Barite a sulphate of barium used to add weight to drilling fluids.

Basin a dip in the earth’s crust usually filled or being filled with sediment. It is a basic concept in petroleum geology.

BCF billion cubic feet (109 cubic feet) = 28. 317 million cubic metres.

Bentonite a type of clay often added to drilling fluid because of its swelling properties when added to water.

Bit the cutting part of the drilling equipment.

Blowout when downhole pressure overcomes the weight of drilling fluid and rises in a well to the surface out of control. An underground blowout is where the overpressuring enters another formation higher in the well, but before it reaches the surface.

Blowout preventer a system of valves and rams set in a well which can be closed successively to counteract the uncontrolled rise of oil or gas from a reservoir below.

bopd barrels of oil per day.

Borehole the wellbore itself, including the open hole or uncased portion of the well. Borehole may refer to the inside diameter of the wellbore wall, the rock face that the bounds the drilled hole.

Bright spot a point on a seismic profile which shows up brighter than surrounding traces because of an increase in amplitude of seismic waves passing from hydrocarbons to water within the pores of a rock.

- C -

Caliper log a measurement of the diameter of a well.

Cap rock an impermeable layer of rock that traps or halts the upward movement of oil and gas, forming the top or cap of a reservoir.

Carbonates sedimentary rocks composed of calcium and/or magnesium carbonate e.g. limestone.

Carboniferous a geological time period approximately 354 to 298 million years ago.

Casing steel pipe screwed together to line the inside of a well bore and cemented into place.

Casing shoe a heavy section steel tube fitted to the lower end of a casing string to protect the end of the string from damage when running into a well.

Cement bond log a measurement of the strength and bonding of cement to the casing in a well.

Choke a valve or valves used to control the flow of hydrocarbons from a well by changing the diameter of the orifice.

Christmas tree the system of valves and controls placed at the wellhead.

City gate the point at which high pressure pipelines deliver gas to low pressure pipelines for distribution to individual users.

Claystone : a sedimentary rock composed predominantly of particles less than silt size usually comprising clay minerals.

Closure a term used to indicate that a trap exists in the subsurface and there are no avenues for hydrocarbons (if present) to escape.

Completion the final preparations to ready a well for production.

Condensate hydrocarbons which are gaseous in a reservoir, but which condense to form a liquid as they rise to the surface where the pressure is much less.

Conductor the first casing string in a well.

Coring an operation whereby a sample of rock being drilled is allowed to pass through the centre of a special bit and be collected in a core barrel mounted directly behind it.

Cretaceous a geological time period approximately 141 to 65 million years ago.

Crown block an assembly of sheaves at the top of the drilling derrick of a rig over which the hoist lines are passed.

Crude Oil the oil that is produced from a reservoir after any associated gas has been removed.

Culmination the highest point on a four-way dip closed structure, also used to indicate that a four-way dip closure exists.

Cuttings rock chips from action of drill bit transported to surface in drilling mud.

- D -

Darcy the unit of measurement of permeability of rock.

Delineation well (see appraisal well).

Depletion reduction in petroleum reserves by production.

Depocentre an area or site of maximum deposition in a sedimentary basin.

Deposition the laying down of potential rock forming material i.e. sediments.

Depression a low place of any size on the Earth’s surface, also may refer to a sedimentary trough or basin.

Development phase the phase in which a proven oil or gas field is brought into production by drilling production wells.

Development well a well drilled specifically into a previously discovered field for the purpose of producing oil or gas.

Diamond bit a drill bit with impregnated diamonds as the cutting edge.

Dip the angle of the plan of a bed relative to the horizontal.

Dipmeter an instrument lowered down the well to measure the dip of the drilled formations relative to the well.

Directional drilling intentional deviation of a well from the vertical.

Downtime the time an operation is postponed, usually due to bad weather or mechanical failure.

Draw-works the hoisting winch for handling drill pipe and casing on a rig.

Drill pipe steel pipe screwed together and used to carry and rotate the drilling tools in a well and to permit the circulation of drilling fluid.

Drilling fluid (see mud).

Drillstem test a valved test tool is lowered down a well on the end of the drill string to a specific reservoir formation and the valve opened to admit formation fluids.

Drill string the column of drill pipe lengths screwed together.

Dry hole a well drilled without finding oil or gas in commercial quantities.

- E -

Electric logs measure of the resistivity of rock formations down a well which leads to determination of the rock types.

Ethane a component of natural gas and the basic feedstock for petrochemical industries.

Exploration well a well drilled without knowledge of the content of the underlying rock structure.

- F -

Facies/lithofacies the rock record of any sedimentary environment, including both physical and organic characters.

Farm-in/out an arrangement between one or more parties and the company or group holding a lease title to an exploration or production area whereby the former pays to earn an interest in the permit. Payment may be in cash or in the form of a work program.

Fault a break or fracture in the earth’s sub-strata where one side of the break moves relative to the other.

Fault trap A hydrocarbon trap which relies on the termination of a reservoir against a seal due to fault displacement.

Field a geographical area under which an oil or gas reservoir lies.

Fishing to retrieve equipment which has fallen into or is caught in the well.

Flaring the practice of burning off waste gas or oil during a test or production cycle.

Fluorescence the luminescence shown when irradiated by ultra-violet light.

Fold/Folding a bend in strata, commonly a product of deformation.

Formation a group of rocks of the same age, extending over a substantial area of a basin.

Four-way dip a structural feature seen on orthogonal seismic lines to dip away in all four possible directions, closure indicating that any hydrocarbons beneath a sealing stratum will be trapped in this feature.

Fraccing a process used to improve the permeability of a tight reservoir. A specially blended fluid, charged with propants like sand or aluminium pellets, is pumped down a well at high pressure to force passageways into the rock. The propants keep them open once the pressure is released.

- G -

Gas in Place (GIP) an estimated measure of the total amount of gas contained in a reservoir and, as such, a higher figure than Recoverable Gas.

Gas/oil ratio (GOR) the ratio of gas to oil by volume, measured during a production test.

Gazetted the advertisement of permits by the government calling for applications for exploration licences.

Generation the process by which organic matter in a source rock is transformed into hydrocarbons in the subsurface.

Geology the science relating to the history and development of the earth’s crust.

Geophones microphones used in seismic surveys to electronically pick up returning shock waves and pass them on to the recording equipment.

Geophysics The physics of the earth, a hybrid discipline involving a combination of physical and geological principles.

Gross pay the total thickness of a reservoir rock, including the impervious layers which do not contain hydrocarbons.

- H -

Horizon a term used in seismic interpretation to identify the signal reflected from a particular layer of rock.

Hydrocarbons general term for oil, gas, condensate and other petroleum products.

Hydrocarbon kitchen the part of a sedimentary basin containing mature petroleum source rocks. General term to denote the place where temperatures and pressures are optimum for the generation of oil or gas.

Hydrocarbon show evidence of hydrocarbons in drill cuttings.

- I -

In-situ (in place) refers to total oil or gas reserves contained in a reservoir in the ground as opposed to those reserves which may be recovered.

Intraformational existing within a geological formation, for example a single shale bed in an alternating sequence of sand and shale.

- J -

Joint Venture a group of companies or individuals who share the cost and rewards of exploring for and producing oil or gas from a permit.

Jurassic : a geological time period approximately 205 to 141 million years ago.

- K -

Kelly hexagonal or square pipe about 15m long attached to the top of the drill string and turned by the rotary table. It is used to transmit the twisting movement from the rotary machinery to the drill string and thus the bit.

Kelly bushing a piece of equipment which fits around the kelly at the point where it passes through the rotary table. It is often used as a datum from which to measure the depth of a well.

Kerogen the organic matter which is the base for the formation of oil or gas.

Kick a sudden influx of high pressure into a well, usually experienced while drilling.

Kill the process of increasing drilling fluid weight to control a potential blowout.

- L -

Lacustrine sediments deposited in a lake environment.

Lead inferred geological feature or structural pattern which on further investigation may be upgraded to a prospect.

Leakoff the magnitude of pressure exerted on a formation that causes fluid to be forced into the formation. The fluid may be flowing into the pore spaces of the rock or into cracks opened and propagated into the formation by the fluid pressure. This term is normally associated with a test to determine the strength of the rock, commonly called a pressure integrity test (PIT) or a leakoff test (LOT). During the test, a real-time plot of injected fluid versus fluid pressure is plotted. The initial stable portion of this plot for most wellbores is a straight line, within the limits of the measurements. The leakoff is the point of permanent deflection from that straight portion. The well designer must then either adjust plans for the well to this leakoff pressure, or if the design is sufficiently conservative, proceed as planned.

Licence an authority to explore for or produce oil or gas in a particular area issued to a company by the governing state.

Limestone a rock composed of calcium carbonate.

Liner steel tube of small diameter extending into a producing reservoir from the bottom of the last string of casing in a well.

Lithology a study of the rock types in a given region, including descriptions of mineral content.

Log(s): see well log.

Log interpretation technical analysis of the results of well logging leading to quantitative estimates of various rock properties including contained liquids and gases.

Logging tools devices lowered down a well to measure various parameters and properties of the formations being drilled.

- M -

Marker crude a commonly traded crude oil in a particular region that is used as a quality standard to price other crudes.

Mature (source) the condition, caused by pressure, temperature and time, in which organic matter in a potential source rock will be converted to hydrocarbons.

Migration the movement of oil/gas from a petroleum source rock into and then within a reservoir rock.

MMSTB millions of standard barrels.

MMCFD millions of cubic feet per day = 28,317 cubic metres per day.

Monkey board the small platform high in the derrick of a rig occupied by the derrickman when guiding stands of drill pipe and casing to and from storage racks during drilling operations.

Mud (drilling fluid) is the suspension of minerals and chemicals in oil or water which forms the well circulatory system.

Mud logging this includes routine geological examination of drill cuttings from a well, plus a record of the variations in drilling rate, mud pumping pressure, depths of formation changes and an analysis of the mud for oil and gas traces.

- N -

Net pay the aggregate thickness of only those parts of the reservoir which contain and produce hydrocarbons.

Nipple a completion component fabricated as a short section of heavy wall tubular with a machined internal surface that provides a seal area and a locking profile.

Nipple down to take apart, disassemble and otherwise prepare to move the rig or blowout preventers.

Nipple up to put together, connect parts and plumbing, or otherwise make ready for use. This term is usually reserved for the installation of a blow-out preventer stack.

Nuclear logs a measurement of gamma rays and thermal neutrons from down hole formations which can be used to determine rock porosity and lithology.

- O -

Oil a mixture of liquid hydrocarbons of different molecular weights.

Oil Field a geographical area under which an oil reservoir lies.

Oil/Gas Seep a natural flow of oil and/or gas to the earth’s surface.

Oil in Place (OIP) an estimated measure of the total amount of oil contained in a reservoir and, as such, a higher figure than Recoverable Oil.

On stream in production.

Open hole refers to a well which has no casing or which is cased only to the top of the reservoir section.

Operator the company which organises the exploration and production programs in a permit on behalf of all the interest holders in the permit.

- P -

Packer a device (often rubber) which seals off a section of the well during testing.

Paper crude crude oil which is sold on the futures market, but which will not be physically produced for several months or longer.

Pay zone a stratum of rock in which oil and/or gas is found, and from which it is produced.

Permeability : a measure of the capacity of rock or stratum to allow water or other fluids such as oil to pass through it.

Permian a geological time period approximately 298 to 251 million years ago.

Permit an area of specified size within a sedimentary basin which is licensed or allocated to a company or companies by the government for the purpose of exploring for and producing oil and gas. In Australia separate licences are issued for exploration and production.

Petroleum a generic name for hydrocarbons, including crude oil, natural gas liquids, natural gas and their products.

Petroleum system the established geological conditions which give rise to petroleum accumulations.

Petrophysical the physical properties of rocks, in this context, as measured by well logs.

Pig a mechanical device sent through a pipeline to scour the inside walls or to run internal checks on the integrity of the line.

Pipeline : a pipe through which oil, its products, or gas is pumped between two points, either offshore or onshore.

Play a specific combination of geological features which is perceived as having potential for petroleum accumulation.

Plug a seal deliberately placed in a well to prevent escape of high pressure material from the substance after it has been abandoned. Usually plugs are of cement.

POOH (pull out of hole) to remove the drill string from the wellbore.

Porosity a measure of the pore space within a rock and expressed as a percentage of volume.

Possible reserves undeveloped oil and/or gas reserves which best judgement indicates may be recoverable from a structure.

Production well (see development well).

Prospect a potential hydrocarbon trap which has been confirmed by geophysical and geological studies to the degree that it can warrant the drilling of an exploration well.

- Q -

Quartz a mineral composed of silicon dioxide.

Quaternary the most recent geological era, commencing approximately 1. 8 million years ago.

- R -

Ream to enlarge a wellbore. Reaming may be necessary for several reasons. Perhaps the most common reason for reaming a section of a hole is that the hole was not drilled as large as it should have been at the outset. This can occur when a bit has been worn down from its original size, but might not be discovered until the bit is tripped out of the hole and some undergauge hole has been drilled. Also, some plastic formations may slowly flow into the wellbore over time, requiring the reaming operation to maintain the original hole size.

Recovery factor the amount of oil or as that can be recovered from a reservoir is considerably less than the total volume of hydrocarbons actually in place. Recovery factor is expressed as a percentage of the total reserves believed to be in place.

Recoverable Gas an estimated measure of the total amount of gas which could be brought to the surface from a given reservoir; this is usually of order 60% – 70% of the estimated Gas in Place.

Recoverable Oil an estimated measure of the total amount of oil which could be brought to the surface from a given reservoir; this is usually less than 50% of the estimated Oil in Place and commonly in the 20% to 40% range.

Refinery an installation that manufactures finished petroleum products from crude oil, unfinished oils, natural gas liquids and other hydrocarbons.

Reservoir a porous rock or formation which holds hydrocarbons within the pore spaces between individual grains.

Risk : an expression of uncertainty (high risk) or uncertainty (no risk) often relating to the presence of principal geological factors controlling oil accumulations.

Rolling cutter bit a bit with hardened steel or tungsten carbide teeth of varying lengths and spacings mounted on three roller cones.

Rotary drilling a system whereby a bit is forced against a rock face and mechanically rotated to penetrate the various formations.

Rotary swivel the part of a rotary drilling rig which connects the travelling block to the drill string.

Rotary table a flat plate in the drill floor which is turned mechanically at varying speeds and imparting the rotary action to the drill string which passes through its centre.

Roughneck a rig worker who handles the drill pipe and other equipment on the drill floor.

Round trip the complete operation of pulling out the drill string from a well (for instance to change a bit) and then running it back into the well.

Roustabout a general labourer on a rig.

Rugosity the irregularity or roughness of a borehole, often caused by unstable formation or by poor drilling practice.

- S -

Sandstone a sedimentary rock composed predominantly of sand sized grains, usually quartz.

Seal an impermeable rock (usually claystone or shale) that prevents the passage of hydrocarbons.

Sediment : solid material, whether mineral or organic, which has been moved from its position of origin and redeposited.

Sedimentary cycle the period encompassing an encroachment of the sea over the land and then a subsequent withdrawal of the sea.

Sedimentary rock a rock formed as a result of the consolidation of sediments.

Seep a point where migrating oil or gas, not already trapped, reaches the earth’s surface.

Seismic survey a method of determining the sub-surface features by sending shock waves into the various buried rock layers in the earth and measuring the time taken to return to the surface.

Sequence a succession of sedimentary rocks laid down sequentially.

Shale a claystone exhibiting a finely laminated structure.

Shale shaker equipment near the rig floor which separates the drill cuttings from the drilling mud.

Shoe (see casing shoe).

Shows the detectable presence of hydrocarbons observed during the drilling of a well.

Sidetracking when a well is deliberately deviated around an obstruction or branched off part way down a completed well to reach another part of the reservoir.

Silt/siltstone rock intermediate in texture and grain size between sandstone and claystone.

Source rock a sedimentary rock which is capable to generating hydrocarbons under optimum maturation conditions of temperature, pressure and time.

Sour crude crude oil that contains appreciable amounts of sulphur compounds.

Spot market the sale of individual shipments of crude oil priced at the international market rate at the time of sale.

Spud in to begin drilling. To start a well.

Spud date the date when drilling of a well begins.

Stack a processed seismic record that contains traces that have been added together from different records to reduce noise and improve overall data quality. The number of traces that have been added together during stacking is called the fold.

Stratigraphy a description of the rock formations in sequence from top to bottom in a sedimentary basin.

Structural Trap a trap formed as a result of folding, faulting or a combination of both.

Structure in oil industry terms it refers to a feature within the earth’s crust with the potential to trap migrating hydrocarbons.

Sweet crude crude oil that is free of sulphur compounds.

- T -

Tectonic descriptive of all movements of the Earth’s crust caused by directed pressures, and the results of those movements.

Tertiary era an era of geological time approximately 65 to 1.8 million years ago.

Test (see wireline test).

Three dimensional seismic survey (3D) a survey with seismic lines set out in close grid pattern to gain better resolution of detail in an area.

Tight a term indicating that a formation has little permeability.

Time map a plan of mapped horizons from the seismic sections where the contours connecting equal values in times of waves reaching the geophones are plotted on the grid map for the survey. To convert this to a geological map, velocity measurements are used to change time to depth values.

Toolpusher the chief driller in charge of operations on the rig floor.

Top drive a drilling system where a motor is attached to the top of the drill string in the rig derrick to impart a rotary action directly, rather than use a Kelly and rotary table.

Top seal an impervious layer of rock which overlies a reservoir rock, thus preventing hydrocarbons from escaping to the surface.

Transmission cost the cost of transporting oil or gas to market, usually refers to pipeline transport and includes a fee for the pipeline owner.

Transmission lines usually refers to high pressure pipelines carrying natural gas from the producing areas to major markets.

Trap a formation in the earth’s sub-surface which prevents the onward migration of hydrocarbons.

Trend a strike direction of a geological feature.

Triassic a geological time period approximately 251 to 205 million years ago.

Tri-cone bit (see rolling cutter bit).

Tubing (see liner).

Turbo drill a drill bit which is rotated via a multi-stage turbine mounted at the bottom of the drill pipe. Power to rotate is supplied by the drilling fluid being pumped down hole from the surface.

- U -

Unconformity lack of parallelism between rock strata in sequential contact, caused by a time break in sedimentation.

Updip : the direction leading most directly to higher elevations on an inclined stratum or structure.

Uplift : elevation of any extensive part of the Earth’s surface relative to some other part.

- V -

Vibroseis a form of survey where the seismic waves are created by mechanically vibrating a steel pad or plate on the earth’s surface.

- W -

Wash a term used to describe loose debris.

Wellbore (see borehole).

Well-log (log) a recording of rock properties obtained by lowering various instruments down a drilled well.

Wellhead price the price at which petroleum producers sell oil or gas from the field.

Wildcat the first well drilled in a new area. It can also mean the first well in a new structure or prospect.

Wireline test a test for hydrocarbons in a formation by lowering a chamber downhole on the end of a wire and allowing reservoir fluids to flow into it.

Workover the re-entry into a completed well for modification or repair and maintenance work.