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| Sunday, June 29, 2008 |
| Glossary of Exploration & Production Terms |
ACIDIZE: to treat a well with acid, largely hydrochloric, to dissolve some limestone or other
carbonate materials in a producing zone. The object is to enlarge & reopen pores,
vugs, & fractures in the zone to increase the flow of oil or gas into the well bore.
API GRAVITY: the density (weight per unit volume) of crude oil on a scale adopted by
American Petroleum Institute. On the API scale, the higher the gravity the lighter
the oil. Most crude oils range from 27 degrees to 40 degrees API gravity; lower than
those are termed heavy, lighter than that, light oil.
ANNULUS: the space-surrounding pipe suspended in the well bore. The outer wall of the
annulus space may be open hole or it may be a string or larger pipe. In producing
wells, the annular space is that between the tubing & the production string of casing.
ANTICLINE: an elongated fold in rock strata in the form of a buried hill. This is a
common type of oil & gas reservoir, with oil & gas, being lighter, accumulating in
the higher parts of the structure above water.
AQUIFER: water-bearing rock strata of large areal extent. In water drive fields, it is the
water-occupied portion of the producing formation adjacent to or below the oil or
gas-bearing part.
ASSOCIATED GAS: gas occurring in or produced from a gas cap associated with an oil
zone.
BACK PRESSURE: pressure caused by restriction of the natural flow of oil & gas. It may
be imposed at the well head by control valves, chokes or other equipment.
Maintenance of back pressure reduces the pressure differential between the
formation & the well bore so that fluid enters into the well from the reservoir rock
at a reduced rate.
BOTTOM HOLE PRESSURE: the pressure at the bottom of a well; flowing bottom hole
pressure & shut-in bottom hole pressure are measured under flowing & shut-in
condition respectively.
BUBBLE POINT: the pressure at which oil in a reservoir begins to release gas from solution.
BUILD-UP PERIOD: the period during which the pressure of the reservoir system increases, i.e.: buildup after a well is shut in.
CHANNELING: a) by-passing or flow of fluid from an extraneous zone behind casing caused by a faulty cement job; b) by-passing of oil in a water drive field or water flood due to erratic water encroachment.
COMBINATION DRIVE: the energy for production from an oil reservoir derived from a combination of two or more of the primary natural drives, e.g. solution gas drive, water drive, gas cap drive, & gravity segregation.
CONDENSATE: hydrocarbons, which are in the gaseous state under reservoir conditions but which become liquid at the surface and may be recovered by conventional separators. Synonym: distillate (older usage).
CONLOMERATE: a rock stratum composed of rock fragments & pebbles of various shapes & sizes.
CONNATE WATER: the water present at the time of discovery in an oil or gas reservoir in the same zone occupied by an oil & gas. Connate water occurs as a film of water in the pore spaces held there by capillary forces; oil or gas occupies the central area of the pore spaces in the rock. Very little connate water is produced in oil or gas wells.
CYCLING: a method for increasing ultimate condensate recovery from a reservoir: condensate is recovered from produced gas then, after processing, the residue gas is compressed & injected back into the reservoir from which it has been produced. The processing & compression facilities are called a cycling plant.
CENTIPOISE: the unit of measurement of oil & gas viscosity.
DELIVERABILITY: the rate at which a well will deliver gas into a pipeline at a specified pressure.
DELIVERY PRESSURE: the agreed pressure for delivery of gas into a gas pipeline under a gas
purchase contract.
DIFFUSION CONSTANT (hydraulic diffusivity constant): constant used in equations describing flow in a porous medium defined as: Permeability . Porosity x viscosity x compressibility A key parameter used in describing reservoirs for numerical simulation.
DIP: the inclination or slope of sedimentary rock strata, expressed in degrees from the horizontal.
DISSOLVED-GAS DRIVE: a natural productive mechanism in which the energy is from expansion of gas released from solution in reservoir oil as pressure declines. Such expansion drives oil to the well bores.
DOLOMITE: rock resembling limestone but having substantial magnesium carbonate content.
DOME: anticline of more or less circular shape like an inverted bowl.
DOWN-DIP or DOWN-STRUCTURE: lower on a geologic structure, below the apex.
DRAW DOWN PERIOD: the period during which the pressure of the reservoir system is reduced by production. I.e.: “drawn down”.
DRILL STEM TEST: a formation test through drill pipe to determine the presence of oil or gas along with pressure. A drill stem test tool, which contains special valves & pressure recording instruments below a packer, is lowered on drill stem to make the test.
DRY GAS: natural gas that contains no appreciable amount of liquid hydrocarbons, which could be recovered at the surface in a conventional separator.
ECONOMIC LIMIT: the minimum rate of production below which a well or lease is no longer
economic to produce.
ENCROACHMENT: the gradual invasion in a water drive field of water into an oil zone displacing some oils; the invasion may be from either edge water or bottom water.
FAULT: a break or fracture zone in rock strata where the layers of rock on one side have slipped downward or laterally relative to the other.
FAULT TRAP: a structure trap favorable for the accumulation of oil or gas formed when the rock on one side of a fault is moved upward or downward so that one edge of a porous formation comes in contact with a non-permeable formation.
FORMATION: sedimentary rock beds deposited continuously & under same general conditions & of the same geologic age. A formation consists of an individual bed or group of beds distinct in character & persisting over a fairly large area.
4-POINT TEST: gas well flow test intended to measure the deliveribility of a gas well consisting of four sequential flow periods.
FRACTURING: application of hydraulic pressure to the reservoir formation to create or enlarge fractures through which oil or gas may move to the well bore. Such fractures are usually
propped open with a propping agent such as rounded sand grains.
GAS CAP: the portion of an oil reservoir occupied by free gas. This is the gas-occupied space above the gas-oil contact.
GAS CAP DRIVE: a natural oil recovery mechanism in which the expansion of gas from a gas cap displaces oil in the same formation moving oil towards producing wells. The expansion of a gas cap occurs as pressure declines with production.
GAS CONDENSATE RESERVOIR: a reservoir which under initial conditions of temperature & pressure has only a single gas phase, which gas is condensate bearing.
GAS EXPANSION RESERVOIR: term includes gas cap drive fields, solution gas drive fields, & gas reservoirs producing by expansion of the gas alone.
GAS INJECTION: a secondary recovery method in which gas is injected into some wells under
pressure displacing & dragging oil from the injection wells toward producing wells. Gas injection in wet gas reservoir is called cycling.
GAS-OIL CONTACT: the imaginary horizontal line between the oil zone & the free gas zone in an oil & gas reservoir; i.e., the contact between the gas cap & the oil zone.
GAS-OIL RATIO: the ratio of gas to oil produced from a well expressed in cubic feet of gas per barrel of oil.
GAS WELL: a well producing predominantly natural gas. The definition may differ slightly in various states. The term includes:
a) wells which produce natural gas not associated with crude oil;
b) wells producing gas & condensate (also called gas condensate wells);
c) Wells, which produce at a very high gas-oil ratio generally over 100,000 cubic feet per,
barrel.
GEOLOGIC STRUCTURE: a fold, fault or other deformation of the earth’s crust. Common types of geologic structures include: faults, domes, anticlines, monoclines, & synclines.
GEOPHYSICAL SURVEY: field work & study involving geophysical exploration. The purpose is to search for geologic structures favorable to the accumulation of petroleum by means of geophysical methods. The principal geophysical methods are seismic, gravity, magnetic &
geochemical.
GRAVITY DRAINAGE, GRAVITY SEGREGATION: the drainage or flow of oil down structure
by the force of gravity. Conversely, gas, being lighter, will rise above the oil & may be produced from the top of a structure under gravity drainage forces.
HYDRCARBON: a compound whose molecules contain only hydrogen & carbon. Oil & gas are
mixtures of more than one hydrocarbon.
HYDROSTATIC PRESSURE: pressure asserted by a liquid. Normal original reservoir pressure is closely equivalent to the corresponding hydrostatic pressure for a specific depth. Such
pressure may be estimated for salt water as 0.433 psi per foot of depth.
INITIAL POTENTIAL: the production rate reported on the initial completion of a well. This is usually the result of a production test made at the time of completion or shortly thereafter &
reported as the amount of oil & gas produced per day under stated flowing or pumping
conditions as applicable. The reported information may or may not reflect the capacity of the well. In the case of gas wells, the theoretical capacity is reported as the open flow potential.
ISOPACH MAP: a map showing the variation in thickness of a particular rock bed or formation. An isopach is a line every point of which represents the same thickness of a formation.
LENS or LENTICULAR: refers to the shape of a rock zone or formation that lenses or pinches out in some direction.
LITHOLOGY: details or rock characteristics & rock type.
M C F: thousand cubic feet of gas at 60 degrees Fahrenheit & a specified pressure base, usually atmospheric pressure of 14.65 psi. It is the standard unit volume of measure for natural gas.
MILLIDARCY: the unit of measurement of reservoir permeability.
MISCIBLE DISPLACEMENT: an oil recovery process, which involves the injection of a solvent, followed by a displacing fluid. Also called miscible flood.
NATURAL GAS: gas, which occurs naturally, consisting mostly of hydrocarbons, which at
atmospheric conditions of temperature & pressure are in gaseous phase. Most natural gas
contains some non-hydrocarbon gasses such as nitrogen, carbon dioxide, helium & hydrogen sulfide.
NATURAL GAS LIQUID: hydrocarbons found in natural gas, which may be extracted as liquefied petroleum gas & natural gasoline.
NET PAY: that part of a formation at a particular location interpreted as permeable enough & having sufficient oil & gas saturation to be capable of contributing to oil & gas production. Net pay excludes from the gross section the number of feet, which are non-permeable or have insufficient oil or gas saturation to yield production.
NON-ASSOCIATED GAS: gas contained in or produced from a gas reservoir, which has no oil zone.
OIL-WATER CONTACT: the elevation or imaginary horizontal line between the water-bearing zone & the oil productive zone in or at the edge of an oil pool.
OPEN FLOW: the maximum flow rate of a well with no restriction. Open flow capacity as reported for gas wells is the theoretical capacity calculated or extrapolated from tests at various rates of flow.
PAY ZONE or HORIZON: rock strata constituting an oil or gas reservoir & containing recoverable oil or gas.
PERFORATIONS: holes made in casing & the surrounding cement sheath through which formation fluids may flow into the well bore.
PERMEABILITY: the ability of a rock to transmit fluid through interconnected pore spaces. It is expressed in millidarcies (or darcies).
1.) ABSOLUTE PERMEABILITY: the permeability of a rock to a fluid that 100%
saturates the pore space of the rock.
2.) EFFECTIVE PERMEABILITY: the permeability of a rock to a particular fluid when
that fluid has a pore space saturation of less than 100%.
3.) RELATIVE PERMEABILITY: the ratio of effective permeability to the absolute
permeability.
PINCH OUT: a geologic trap in which a porous permeable rock stratum wedges out between non- permeable layers.
POROSITY: the percentage of volume of void (pore) space in a rock.
POTENTIAL: the actual or calculated ability of a well to produce oil or gas as determine by well test.
PRESSURE MAINTENANCE: the maintenance of pressure in an oil or gas reservoir by the
injection of gas or water for the purpose of increasing ultimate recovery and/or maintaining
production rate. In pressure maintenance injection is started fairly early in the life of a
reservoir, whereas in secondary recovery it is started later on after most of the primary
reserves have been recovered.
PRESSURE TRANSIENT: pressure variation with time resulting from a change in flow rate of a well.
PRIMARY PRODUCTION: productions from a reservoir by natural energy, before pressure
maintenance or secondary recovery methods are applied.
PRIMARY RESERVES: oil & gas recoverable by natural reservoir energy, i.e., without pressure maintenance or secondary recovery methods.
PRODUCTION ZONE, HORIZON, RESERVOIR, or SAND: a rock reservoir (stratum) yielding
recoverable oil or gas.
RECOVERY FACTOR: the percentage of oil or gas in place estimated to be ultimately recovered from a reservoir.
a) PRIMARY RECOVERY FACTOR: estimated ultimated recovery by primary or
natural energy drives only.
b) SECONDARY RECOVERY FACTOR: as above but by secondary means in
addition primary.
REEF: a build up of limestone in reef form; a type of stratigraphic reservoir.
REPRESSURE: fluid injection into a partially depleted reservoir to increase pressure & thereby increse production rate & ultimate recovery; a phase of secondary recovery.
RESERVES: the estimated volume of oil and/or gas economically recoverable. Reserves are estimated as of a specified date & may be classified as follows:
1) PROVED RESERVES: reserves which by development, geologic & engineering data are considered with reasonable certainty to be recoverable under existing economic & operating conditions, including that recoverable by secondary methods if actually in operation or proved by a pilot project or project in a closely similar reservoir.
a) Proved Developed Producing Reserves: proved & recoverable from existing wells with existing facilities from presently open completion interval.
b) Proved Behind Pipe Reserves: proved reserves behind the casing in existing wells & which may be produced on recompletion existing wells.
c) Proved Undeveloped reserves: proved but to be realized require new wells on
undrilled acreage, the recompletion by deepening of existing wells, or the initiation of a fluid injection project.
2) PROBABLE RESERVES: reserves which are not proved but which are considered probable of production from geological inference, proximity to proved reserves in the same reservoir, & experience in similar type reservoirs
3) POSSIBLE RESERVES: not proved or probable but speculative.
RESERVOIR ENERGY: the natural forces, which cause oil and/or gas to move toward producing wells. The principal mechanism are: 1) Solution gas drive, 2) Gas cap drive (free gas expansion), 3) Water drive, 4) gravity drainage, 5) expansion of reservoir oil above its bubble point (usually small in degree), 6) A combination of two or more of these.
RESERVOIR, OIL or GAS: a single common accumulation of oil and/or gas in a porous permeable underground rock strata zone completely separate from other zones.
RESERVOIR PRESSURE: the average inter-well pressure in a reservoir. It may be estimated by measuring bottom hole pressure in wells shut-in & extrapolation such measurement to full build-up (pressure equalization between the well bore area & the inter-well area). Synonym: Formation pressure.
RETROGADE CONDENSATION: the condensation in a reservoir of some liquid from a gas under high pressure as pressure is reduced.
SANDSTONE, SAND: a sedimentary rock consisting mostly of sand grains.
SATURATION: the percentage of rock pore space occupied by fluid; thus there is gas, oil & water saturation, being the percentage of pore space occupied respectively by each.
SECONDARY RECOVERY: any method of increasing ultimate recovery of oil or condensate by the application of extrinsic energy. Includes various forms of gas injection, water injection, & injection of miscible fluids (such as LPG). Pressure maintenance is the application of secondary recovery methods in the early life of a reservoir. Thermal methods are usually also included under secondary recovery.
SEDIMENTARY ROCK:SHUT-IN: rock strata formed by deposition of sediments deposited from streams, lakes, seas or other water bodies or deposited from air.
SHUT-IN: to stop a well from producing, i.e., shut-down the pumping unit on a pumping well, or close a valve on the flow line of a flowing oil or gas well.
SHUT-IN PRESSURE: pressure measured after a well has been shut-in for a period; if measured at the wellhead, termed shut-in tubing pressure or shut-in casing pressure; if measured down- hole called shut-in bottom hole pressure.
SKIN EFFECT: the reduction in the permeability of the formation near the well bore as a result of drilling & completion practices.
SKIN FACTOR: a dimensionless constant, which quantitatively relates the pressure drop due to the skin effect to rate of flow. If the permeability in the skin zone is less than the formation skin factor will be positive. If the permeabilities are equal the skin factor will be zero. If a well has been acidified or hydraulically fractured the value will be negative.
SOLUTION GAS: gas dissolved in oil in the reservoir under pressure & which is released
underground & at the surface as pressure is removed.
SOLUTION GAS DRIVE: see Dissolved Gas Drive.
STABILIZED: when the rate of production of a well remains steady on a given size choke or under given pumping conditions.
STANDARD CUBIC FOOT: the volume of gas contained in one cubic foot of space at a standard pressure base (usually 14.65 psi absolute) & standard temperature of 60°F.
STEP OUT WELL: a well drilled in an unproved or semi-proved area in an attempt to extend the productive limits of a field.
STORAGE VOLUME: the volume within the production casing, tubing & well bore between the sand face & the shut-off valve in direct communication with the sand face.
STRATIGRAPHIC: pertaining to rock strata & their characteristics & geometry.
STRATIGRAPHIC TRAP: a reservoir capable of holding oil or gas & limited by non-permeable beds or by a change in the character or continuity of the rock to non-permeable beds.
STRUCTURAL TRAP: a reservoir formed by a fold or fault structure in the earth’s crust & capable of holding oil or gas.
SYNCLINE: a trough-shaped downward fold in the earth’s crust.
THIEF ZONE: a formation or zone causing loss of drilling mud.
TIGHT FORMATION: a zone of quite low permeability & thus low well productivity. Wells in such zones usually require fracturing or other stimulation. Typically, the productive capacity of a new well completed in a tight zone declines rapidly for several months or longer after completion.
TRANSIENT: variation with time.
TRAP: porous rock strata capable of oil or gas by structural folding or faulting and/or stratigraphic limitation.
ULTIMATE RECOVERY: the total recovery of oil and/or gas from a well, lease, or pool including both past production & future recoverable reserves yet to be produced.
UNCONFORMITY: an erosional surface in the geological past on top of which younger strata were deposited, with the younger beds dipping at a different angle than the older beds. It is a type of stratigraphic trap.
UP-DIP: located high or higher on the structure. Synonym: Up-structure.
VISCOSITY: the physical property of a fluid as to its resistance to or ease of flow. The unit of viscosity is the centipoise. The viscosity of water is 1 centipoise; a liquid having a higher viscosity is slower to flow (thicker) than water.
WATER CUSHION: water placed inside drill pipe and above the drill-stem test tool to cushion the sudden inflow of oil or gas form the formation tested when the DST valve is opened.
WATER DRIVE: natural energy derived from water encroachment into an oil or gas reservoir moving oil or gas to producing wells. Encroachment may come from the edge or bottom.
WATER ENCROACHMENT: the invasion of water into an oil or gas zone displacing oil or gas
toward producing wells.
WATER FLOODING: a method of secondary recovery in which water is injected into an oil reservoir through injection wells pushing oil toward producing wells. Water may be injected in one or more lines of wells (line flood), in a five-spot or other pattern (pattern flood), around the
edges of a pool (peripheral flood), or around groups of wells (block flood).
WATER-OIL RATIO: the ratio (barrel/barrel) of the volume of water to volume of oil produced from a well or project.
WATER ZONE: the portion of a reservoir below or adjacent to the oil & gas zone & which would produce only or mostly water.
WEDGE-OUT: see pinch out.
WELL SPACING: the regulation or specification of the acres per well & distance between wells as a conservation or economic measure.
ZONE: an indefinite terms but generally a stratigraphic interval having common rock characteristics. |
posted by Rahman J. @ 6/29/2008 08:22:00 PM   |
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Welcome to POT-15!!!
This's blog gives information all about petroleum & natural gas. All corrections, questions and criticisms to the writer will be highly appreciated for the improvement of this blog.
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