Oil & Gas Glossary 1.0

The ratio of the actual volume of gas at a given temperature and pressure to the volume of gas when calculated by the ideal gas law.

2. pressure, volume, and temperature.

Any law relating to the pressure, temperature, or volume of a gas.

The change in volume per unit of volume of a liquid caused by a unit change in pressure at constant temperature

The maximum volume of natural gas that can be processed through an absorber at a specified absorption oil rate, temperature, and pressure without exceeding pressure drop or any other operating limitation.

The amount of the pore volume of a reservoir rock that is filled by water, oil, or gas and measured in routine core analysis.

A device that reduces the pressure or volume of a fluid flowing in a line and maintains the pressure or volume at a specified level.

1. the ratio of the weight of a given volume of a substance at a given temperature to the weight of an equal volume of a standard substance at the same temperature. For example, if 1 cubic inch of water at 39 degrees F weighs 1 unit and 1 cubic inch of another solid or liquid at 39 degrees F weight 0.95 unit, then the relative density of the substance is 0.95. In determining the relative density of gases, the comparison is made with the standard of air or hydrogen.

The average pressure within the reservoir at any given time. Determination of this value is best made by bottomhole pressure measurements with adequate shut-in time. If a shut-in period long enough for the reservoir pressure to stabilize is impractical, then various techniques of analysis by pressure buildup or drawdown tests are available to determine static reservoir pressure.

Determination of the relative percentages of substances, e.g., the suspended solids in a drilling fluid that pass through or are retained on a sequence of screens of decreasing mesh size. Also called sieve analysis.

Laboratory analysis of a core sample to determine porosity, permeability, lithology, fluid content, angle of dip, geological age, and probably productivity of the formation.

2. the measured volume of water that is present in a container and that is not in suspension in the contained liquid at observed temperature.

The recording of information about subsurface geologic formations, including records kept by the driller and records of mud and cutting analyses, core analysis, drill stem tests, and electric, acoustic, and radioactivity procedures. See acoustic log, core analysis, driller's log, drill stem test, electric well log, mud analysis, and radioactivity well logging.

A thick-walled container, usually steel, used to hold devices that determine and record pressure or temperature in a wellbore. See bottomhole pressure.

N: a cylindrical sample taken from a formation for geological analysis. Usually a conventional core barrel is substituted for the bit and procures a sample as it penetrates the formation. v: to obtain a formation sample for analysis.

A measure of the resistance of a fluid to flow. Resistance is brought about by the internal friction resulting from the combined effects of cohesion and adhesion. The viscosity of petroleum products is commonly expressed in terms of the time required for a specific volume of the liquid to flow through a capillary tube of a specific size at a given temperature.

(2) separating gas from that portion of associated and non-associated gas which liquefies at temperature and pressure conditions of the separator.

A sub in a DST string in which pressure and temperature recorders are placed for formation evaluation.

(1) separating casinghead gas from produced crude oil and water at the temperature and pressure conditions of the separator; and

A mechanical fluid-measuring device that measures by filling and emptying chambers of a specific volume. The displacement of a fixed volume of fluid may be accomplished by the action of reciprocating or oscillating pistons, rotating vanes or buckets, rotating disks, or tanks or other vessels that automatically fill and empty. Also called a volume meter or volumeter.

The process whereby a volume of fluid equal to the volume of steel in tubular and tools withdrawn from the wellbore is returned to the wellbore.

A scale of temperature measurement in which zero degrees is absolute zero. On the Rankine absolute temperature scale, in which degrees correspond to degrees Fahrenheit, water freezes at 273 degrees and boils at 373 degrees. See absolute zero.

A given point at a certain temperature and pressure at which no more solid material will dissolve in a liquid.

A hanger used to lock instruments into seating nipple (pressure/temperature bombs, etc.).

A cylindrical ring, usually vise-shaped, employed to back up (or assist) a sealing member against extrusion under temperature and pressure.

The amount of heat required to cause a unit increase in temperature in a unit mass of a substance, expressed as numerically equal to the number of calories needed to raise the temperature of 1 gram of a substance by 1 degree C.

A hydrocarbon and water compound that is formed under reduced temperature and pressure in gathering, compression, and transmission facilities for gas. Hydrates often accumulate in troublesome amounts and impede fluid flow. They resemble snow or ice.

Weight per unit volume of drilling fluid usually expressed in pounds per gallon or pounds per cubic foot. See hydrostatic pressure.

The percentage that the volume of the pore space bears to the total bulk volume. The pore space determines the amount of space available for storage of fluids.

2. the ratio of the mass of a given volume of a substance to the mass of a like volume of a standard substance, such as water or air.

2. small quantities of well fluids obtained for analysis.

The determination of the percentage of particles that pass through several screens of graduated fineness

The conventional method of formation testing. The basic drill stem test tool consists of a packer or packers, valve or ports that may be opened and closed from the surface, and two or more pressure-recording devices. The tool is lowered on the drill string to the zone to be tested. The packer or packers are set to isolate the zone from the drilling fluid column. The valves or ports are then opened to allow for formation flow while the recorders chart static pressures. A sampling chamber traps dean formation fluids at the end of the test. Analysis of the pressure charts is an important part of formation testing.

Density expressed as the ratio of the weight of a volume of substance to the weight of an equal volume of another standard substance. In the case of liquids and solids, the standard is water. In the case of natural gas or other gas materials, the standard is air.

A substance occurring naturally in the earth and composed mainly of mixtures of chemical compounds of carbon and hydrogen, with or without other nonmetallic elements such as sulfur, oxygen, and nitrogen. The compounds that compose it may be in the gaseous, liquid, or solid state, depending on their nature and on the existent conditions of temperature and pressure.

A plan or procedure, with respect to depth, for the type and properties of drilling fluid to be used in drilling a well. Some factors that influence the mud program are the casing program and such formation characteristics as type, competence, solubility, temperature, and pressure.

A compressible fluid that fills any container in which it is confined. Technically, a gas will not condense when it is compressed and cooled, because a gas can exist only above the critical temperature for its particular composition. Below the critical temperature, this form of matter is known as a vapor, because liquid can exist and condensation can occur. Sometimes the terms "gas" and"vapor" are used interchangeably. The latter, however, should be used for those streams in which condensation can occur and that originate form, or are in equilibrium with, a liquid phase.

The point marking the end of one stage of a process. In filtrate analysis, the endpoint is the point at which a particular result is achieved through titration.

A fluid in which the viscosity remains constant for all rates of shear if constant conditions of temperature and pressure are maintained. Most drilling fluids behave as non-Newtonian fluids, as their viscosity is not constant but varies with the rate of shear.

A chemical analysis process where drops of a standard solution are added to another solution or substance to obtain a response: color change, precipitation, or conductivity change, for measurement and evaluation.

A small mud tank with a capacity of 10 to 15 barrels, usually with 1-barrel or H-barrel divisions, used to ascertain the amount of mud necessary to keep the wellbore full with the exact amount of mud that is displaced by drill pipe. When the bit comes out of the hole, a volume of mud equal to that which the drill pipe occupied while in the hole must be pumped into the hole to replace the pipe. When the bit goes back in the hole, the drill pipe displaces a certain amount of mud, and a trip tank can be used again to keep track of this volume.

Abbreviation: static bottomhole temperature

Abbreviation: circulating bottomhole temperature

1. Pit Volume Totalizer.

The recording of information derived from examination and analysis of formation cuttings made by the bit and of mud circulated out of the hole. A portion of the mud is diverted through a gas-detecting device. Cuttings brought up by the mud are examined under ultraviolet light to detect the presence of oil or gas. Mud logging is often carried out in a portable laboratory set up at the well.

The condition of containing more solute in solution than would normally be present at the existing temperature.

An instrument that measures fluid pressure and usually registers the difference between atmospheric pressure and the pressure of the fluid by indicating the effect of such pressures on a measuring element (e.g., a column of liquid, pressure in a Bourdon tube, a weighted piston, or a diaphragm).

Pressure exceeding or falling below the normal pressure to be expected at a given depth. Normal pressure increases approximately 0.465 psi per foot of depth (10.5kPa per meter of depth). Thus, normal pressure at 10,000 feet is 4,650 psi; abnormal pressure at this depth would be higher or lower than 4,650 psi. See pressure gradient.

The amount of oil in volume-percent in a drilling fluid.

The breakdown of a compound or substance by temperature into simple substances or into constituent elements.

A test that measures the reservoir pressure of the well, obtained at a specific depth or at the midpoint of the producing zone. A flowing bottomhole pressure test measures pressure while the well continues to flow; a shut-in bottomhole pressure test measures pressure after the well has been shut in for a specified period of time. See bottomhole pressure, bottomhole pressure gauge.

The maximum volume of oil or gas that a well is capable of producing, calculated from well test data.

A method of determining the amount of pressure that is allowed to appear on the casing pressure gauge as a kick is circulated out of a well. In general, it is determined by slowly pumping mud into the well while it is shut in and observing the pressure at which the formation begins to take mud.

The gauge at the driller's position that records data from the pit-level indicator.

Abbreviation: 1,000 cubic feet of gas, commonly used to express the volume of gas produced, transmitted, or consumed in a given period.

Total pressure measured from an absolute vacuum. It equals the sum of the gauge pressure and the atmospheric pressure corresponding to the barometer (expressed in pounds per square inch).

The amount of pressure that, when applied inside a string of casing, causes the wall of the casing to fail. This pressure is critically important when a gas kick is being circulated out, because gas on the way to the surface expands and exerts more pressure than it exerted at the bottom of the well.

A solution that contains at a given temperature as much of a solute as it can retain. At 68 degrees F it takes 126.5 lb/bbl salt to saturate 1 bbl of fresh water. See supersaturation.

A device used to connect long lines of pipe to allow the pipe joints to expand or contract as the temperature rises or falls.

A substance added to cement to prolong the setting time so that the cement can be pumped into place. Retarders are used for cementing in high-temperature formation

2. the amount of pressure indicated by a drill pipe pressure gauge when drilling fluid is being circulated by the mud pump. Pressure losses occur as the fluid is circulated.

Total pressure exerted in the wellbore by a column of fluid and/or back-pressure imposed at the surface.

Said of any pressure-tight vessel or container when the internal pressure is lower than atmospheric pressure

The person who measures a tank to determine the volume it holds at 1/4" intervals of height.

The amount of pressure exerted inside the drill pipe as a result of circulating pressure, entry of formation pressure into the well, or both.

A measure of the volume of gas produced with oil, expressed in cubic feet per barrel of cubic meters per tonne.

The volume of liquids statistically reported as crude oil, which is produced from oil reservoirs during given period of time.

Instrument used to distill oil, water, and other volatile materials in a mud to determine oil, water, and total solids contents in volume-percent.

The percentage of the total bulk volume of a rock sample that is composed of pore spaces or voids. See porosity.

An operation used to determine temperatures at various depths in the wellbore. It is also used to determine the height of cement behind the casing and to locate the source of water influx into the wellbore.

An organic acid, H2CO2 or HCOOH, used for acidizing oilwells. It is stronger than acetic acid but much less corrosive than hydrofluoric or hydrochloric acid and is usually used for high-temperature wells.

A settled volume of barite particles from a barite slurry placed in the wellbore, usually to seal off a pressured zone.

2. the change (along a horizontal distance) in atmospheric pressure. Isobars drawn on weather maps display the pressure gradient.

A pressure-fight container (bomb) used to record the pressure in a well at a point opposite the producing formation

A sudden, usually short-duration, increase in pressure. When pipe or casing is run into a hole too rapidly, an increase in the hydrostatic pressure results, which may be great enough to create lost circulation

The increase in bottomhole pressure expressed as an increase in pressure that occurs only when mud is being circulated. Because of friction in the annulus as the mud is pumped, bottomhole pressure is slightly, but significantly, higher than when the mud is not being pumped. ECD is calculated by dividing the annular pressure loss by 0.052, dividing that by true vertical depth, and adding the result to the mud weight.

Volume flow rate of circulating drilling fluid expressed in gallons or barrels per minute

Repressuring of an oil-field to maintain original pressure. The use of water flooding or natural gas recycling during primary recovery to provide additional formation pressure and displacement energy that can supplement and conserve natural reservoir drives. Although commonly begun during primary production, pressure maintenance methods are often considered to be a form of enhanced oil recovery.

The percentage of the bulk volume of a rock sample that is composed of interconnected pore spaces that allow the passage of fluids through the sample. See porosity.

An installation designed for one or more specific and limited extraction units, scrubbers, absorbers, drip points, conventional single or multiple stage separation units, LTX low temperature separators, and other types of separation and recovery equipment.

A hypothetical temperature at which there is a total absence of heat. Since heat is a result of energy caused by molecular motion, there is no motion of molecules with respect to each other at absolute zero.

1. a scale of pressure differences in which there is a uniform variation of pressure from point to point. For example, the pressure gradient of a column of water is about 0.433 pounds per square inch per foot (9.794 kilopascals per meter) of vertical elevation. The normal pressure gradient in a formation is equivalent to the pressure exerted at any given depth by a column of 10 percent salt water extending from that depth to the surface 0.465 pounds per square inch per foot or 10.518 kilopascals per meter).

To displace the wellbore fluid back to the surface; to displace tubing volume back to the pit.

The pressure at which a well is circulated during well-killing procedures after killweight mud has filled the drill stem. This pressure is maintained until the well is completely filled with killweight mud.

The difference between two fluid pressures; for example, the difference between the pressure in a reservoir and in a wellbore drilled in the reservoir, or between atmospheric pressure at sea level and at 10,000 feet.

The amount of fluid placed in a well to serve as a pad, which is a special fluid used for any special purpose.

Trade name for a type of pit-level indicator. See pit-level indicator.

1. a measure of volume for petroleum products in the United States. One barrel is the equivalent of 42 U.S. gallons or 0.15899 cubic meters (9,702 cubic inches). One cubic meter equals 6.2897 barrels.

A diagnostic tool used to ascertain whether there is a gas leak in the tubing of a gas lift well. If there is a tubing leak, the pressure on the annulus will equal the pressure on the tubing.

A device to measure bottomhole pressure. See bottomhole pressure bomb.

A pressure-sensing element consisting of a twisted or curved rube of non-circular cross section, which tends to straighten when pressure is applied internally. By the movements of an indicator over a circular scale, a Bourdon tube indicates the pressure applied.

1. an automatic valve that opens or closes when an abnormal condition occurs (e.g., a pressure relief valve on a separator that opens if the pressure exceeds the set point, or the shutdown valve at the wellhead that closes if the line pressure becomes too high or too low).

A procedure whereby the formation immediately below the casing shoe is subjected to a pressure equal to the pressure expected to be exerted later by a higher drilling glut density or by the sum of a higher drilling fluid density and back-pressure created by a kick.

3. the operating pressure level measured downstream from a measuring device.

1.a high-pressure gas injected into a formation to maintain or restore reservoir pressure.

The extent to which the hydrostatic pressure of the mud column exceeds formation pressure.

1. the pressure maintained on equipment or systems through which a fluid flows.

The pressure to which a particular piece of equipment is subjected during normal operations.

An equipment's working pressure times a safety factor.

The pressure resulting from restriction of full natural flow of oil or gas.

The pressure generated by the mud pumps and exerted on the drill stem

The pressure at which a well that has been closed in on a kick is circulated when well-killing procedures are begun

Commonly referred to as snubbing; running of tool and/or pulling of tubing under well pressure.

Of or relating to a condition in which pressure in the wellbore is less than the pressure in the formation.

A device for maintaining pressure in a line, downstream from the value.

In commercial transactions, a product meeting GPA specification for commercial butane and, in addition, containing a minimum of 95 liquid volume percent normal butane. Chemically, normal butane is an aliphatic compound of the paraffin series.

A loss of pressure that results from friction sustained by a fluid passing through a line, valve, fitting, or other device.

A drilling mud prepared by adding a surfactant to a water-base mud to change the colloidal state of the clay from that of complete dispersion to one of controlled flocculation. Such muds were originally designed for use in deep, high-temperature wells, but their many advantages (high chemical and thermal stability, minimum swelling effect on clay-bearing zones, lower plastic viscosity, and so on) extend their applicability.

The mass or weight of a substance per unit volume. For instance, the density of a drilling mud may be 10 pounds per gallon (ppg), 74.8 pounds per cubic foot (lb/ft), or 1,198.2 kilograms per cubic meter (kg/m3). Specific gravity, relative density, and API gravity are other units of density.

2. to lower or raise tools in or out of a well with pressure inside the well. The term comes from the fact that a lubricant (grease) is often used to provide a seal against well pressure while allowing wireline to move in or out of the well.

Pressure at the bottom of a well that is shut in.

Formation fluid pressure equivalent to about 0.465 pounds per square foot of depth from the surface. If the formation pressure is 4,650 pounds per square inch at 10,000 feet, it is considered normal.

A bottomhole pressure test that measures pressure after the well has been shut in for a specified period of time. See bottomhole pressure test.

2. to lower or raise tools in or out of a well with pressure inside the well. The term comes from the fact that a lubricant (grease) is often used to provide a seal against well pressure while allowing wireline to move in or out of the well.

The volume of a cube, all edges of which measure 1 foot. Natural gas in the United States is usually measured in cubic feet, with the most common standard cubic foot being measured at 60 degrees Fahrenheit and 14.65 pounds per square inch absolute, although base conditions vary from state to state.

In a well-control operation, closing the BOP without first opening an alternate flow path up the choke line. When the BOP is closed, pressure in the annulus cannot be read on the casing pressure gauge.

The apparent loss of weight of an object immersed in a fluid. If the object is floating, the immersed portion displaces a volume of fluid the weight of which is equal to the weight of the object.

Additives that, when added to drilling fluid, lubricate bearing surfaces subjected to extreme pressure.

The ratio between the pressure in the hole and the operating-piston pressure needed to close the rams of a blowout preventer.

Prevention of formation fluid flow by maintaining a hydrostatic pressure equal to or greater than formation pressure

The pressure at the bottom of a well when the surface valves on the well are completely closed. It is caused by formation fluids at the bottom of the well.

An event occurring when borehole pressure is of such magnitude that the exposed formation cannot withstand applied pressure.

A method of killing a well that has kicked, in which the choke size is adjusted to maintain a constant casing pressure. This method does not work unless the kick is all or nearly all salt water. if the kick is gas, this method will not maintain a constant bottomhole pressure, because gas expands as it rises in the annulus. In any case, it is not a recommended well-control procedure.

Pressure of the annular fluid on the casing at the surface when a well is shut in.

See back-pressure

The force exerted by a body of fluid at rest. It increases directly with the density and the depth of the fluid and is expressed in pounds per square inch or kilopascals. The hydrostatic pressure of fresh water is 0.433 pounds per square inch per foot of depth (9.792 kilopascals per meter). In drilling, the term refers to the pressure exerted by the drilling fluid in the wellbore. In a water drive field, the term refers to the pressure that may furnish the primary energy for production.

In drilling, the entrance of formation fluids into the wellbore because hydrostatic pressure is less than formation pressure.

The lowest internal pressure at which a failure (of pipe) will take place.

The normal pressure divided by true vertical depth.

The ratio between the pressure required to open the preventer and the well pressure under the rams.

The small amount of additional mud weight carried over that needed to balance formation pressure to overcome the pressure-reduction effects caused by swabbing when a trip out of the hole is made.

A device to provide running the tubing dry with a packer released by elevating tubing pressure, thereby opening the tubing to formation pressure.

The point at which a formation will crack from pressure in the wellbore.

One of a series of devices that continuously monitor the level of the drilling mud in the mud tanks. The indicator usually consists of float devices in the mud tanks that sense the mud level and transmit data to a recording and alarm device (a pit-volume recorder) mounted near the driller's position on the rig floor. If the mud level drops too low or rises too high, the alarm sounds to warn the driller of losing circulation or a kick.

The force exerted by a column of liquid expressed by the height of the liquid above the point at which the pressure is measured. Although "head" refers to distance or height, it is used to express pressure, since the force of the liquid column is directly proportional to its height. Also called head or hydrostatic head. Compare hydrostatic pressure.

An uncontrolled flow of gas, oil, or other well fluids into the atmosphere or into an underground formation. A blowout, or gusher, can occur when formation pressure exceeds the pressure applied to it by the column of drilling fluid.

2. a valve used to regulate automatically a uniform pressure on the inlet side of the valve.

A preventer having a unit of packing material whose closure depends on well pressure coming from below. It is used primarily to strip pipe through the hole or allow pipe to be moved with pressure on the annulus.

A pin shaped like a carpenter's nail and placed in a pressure relief valve. When the pin shears, it opens the valve to relieve pressure inside a vessel.

The pressure in a vessel or container as registered on a gauge attached to the container. This reading does not include the pressure of the atmosphere outside the container.

1. a valve used to regulate back-pressure on equipment or systems through which a fluid flows.

An indicator, mounted in the mud circulating system, that measures and indicates the amount of pressure in the drill stem. See drill stem.

A device that prevents leakage along a piston, rod, propeller shaft, or other moving part that passes through a hole in a cylinder or vessel. It consists of a box or chamber made by enlarging the hole and a gland containing compressed packing. On a well being artificially lifted by means of a sucker rod pump, the polished rod operates through a stuffing box, preventing escape of oil and diverting it into a side outlet to which is connected the flow line leading to the oil and gas separator or to the field storage tank. For a bottomhole pressure test, the wireline goes through a stuffing box and lubricator, allowing the gauge to be raised and lowered against well pressure. The lubricator provides a pressure-tight grease seal in the stuffing box.

A device placed or hung in the casing below the blowout preventer stack to form a pressure tight seal. Pressure is then applied to the blowout preventer stack to test it for leaks

The pressure lost in a pipeline or annulus due to the velocity of the liquid in the pipeline, the properties of the fluid, the condition of the pipe wall, and the alignment of the pipe. In certain mud-mixing systems, the loss of head can be substantial

Generically, a pressure gauge usually used in lines or manifolds. Many companies make pressure gauges. Cameron, now Cooper Oil Tools, makes many types of gauges.

The insoluble abrasive solids content of a drilling fluid rejected by a 200-mesh screen. usually expressed as the percentage bulk volume of sand in a drilling fluid. This test is an elementary type in that the retained solids are not necessarily silica and may not be altogether abrasive. For additional information concerning the kids of solids retained on the 200-mesh screen, more specific tests would be required. See mesh.

Pressure of the annular fluid on the casing at the surface when a well is shut in

Gas pressure built up between the casing and tubing.

The pressure at which a formation will break down, or fracture.

1. to force pipe or tools into a high-pressure well that has not been killed (i.e., to run pipe or tools into the well against pressure when the weight of pipe is not great enough to force the pipe through the BOPs). Snubbing usually requires an array of wireline bocks and wire rope that forces the pipe or tools into the well through a stripper head or blowout preventer until the weight of the string is sufficient to overcome the lifting effect of the well pressure on the pipe in the preventer. In workover operations, snubbing is usually accomplished by using hydraulic power to force the pipe through the stripping head or blowout preventer.

The pressure in a well between the casing and the tubing or the casing and the drill pipe.

An entry of water, gas, oil, or other formation fluid into the wellbore during drilling. It occurs because the pressure exerted by the column of drilling fluid is not great enough to overcome the pressure exerted by the fluids in the formation drilled. If

The force that a fluid (liquid or gas) exerts uniformly in all directions within a vessel, pipe, hole in the ground, and so forth, such as that exerted against the inner wall of a tank or that exerted on the bottom of the wellbore by a fluid. Pressure is expressed in terms of force exerted per unit of area, as pounds per square inch, or in kilopascals.

A device that stores hydraulic fluid under pressure in special containers and provides a method to open and close the blowout preventers quickly and reliably. Usually, compressed air and hydraulic pressure provide the opening and closing force in the unit. See blowout preventer.

A condition in which the drill stem becomes stuck against the wall of the wellbore because part of the drill stem (usually the drill collars) has become embedded in the filter cake. necessary conditions for differential-pressure sticking, or wall sticking, are a permeable formation and a pressure differential across a nearly impermeable filter cake and drill stem. Also called wall sticking. See differential pressure, filter cake.

The pressure at the bottom of a well.

The process of raising or lifting fluid from a well by injecting gas down the well through tubing or through the tubing-casing annulus. Injected gas aerates the fluid to make it exert less pressure than the formation does; consequently, the higher formation pressure forces the fluid out of the wellbore. Gas may be injected continuously or intermittently, depending on the producing characteristics of the well and the arrangement of the gas-lift equipment.

A valve that opens at a preset pressure to relieve excessive pressures within a vessel or line. Also called a relief valve, safety valve, or safety relief valve.

A sealing device used to close off the annular space around the kelly in drilling with pressure at the surface, usually installed above the main blowout preventers. A rotating head makes it possible to drill ahead even when there is pressure in the annulus that the weight of the drilling fluid is not overcoming; the head prevents the well from blowing out. It is used mainly in the drilling of formations that have low permeability. The rate of penetration through such formations is usually rapid.

An operation in which a specially blended liquid is pumped down a well and into a formation under pressure high enough to cause the formation to crack open, forming passages through which oil can flow into the wellbore. Sand grains, aluminum pellets, glass beads, or similar materials are carried in suspension into the fractures. When the pressure is released at the surface, the fractures partially close on the proppants, leaving channels for oil to flow through to the well. Compare explosive fracturing.

A method of stimulating production by opening new flow channels in the rock surrounding a production well. Often call a frac job. Under extremely high hydraulic pressure, a fluid (such as distillate, diesel fuel, crude oil, dilute hydrochloric acid, water, or kerosene) is pumped downward through production tubing or drill pipe and forced out below a packer or between two packers. The pressure causes cracks to open in the formation, and the fluid penetrates the formation through the cracks. Sand grains, aluminum pellets, walnut shells, or similar materials (propping agents) are carried in suspension by the fluid into the cracks. When the pressure is released at the surface, the fracturing fluid returns to the well. The cracks partially close on the pellets, leaving channels for oil to flow around them to the well. See explosive fracturing, hydraulic fracturing.

The process in which reservoir fluids are caused to flow out of the reservoir rock and into a wellbore by natural energy. Gas drives depend on the fact that, as the reservoir is produced, pressure is reduced, allowing the gas to expand and provide the driving energy. Water-drive reservoirs depend on water pressure to force the hydrocarbons out of the reservoir and into the wellbore.

A reduction in the pressure of a fluid caused by its motion against an enclosed surface (such as a pipe). As the fluid moves through the pipe, friction between the fluid and the pipe wall and within the fluid itself creates a pressure loss. The faster the fluid moves, the greater are the losses.

A device made up in the drill stem above the mill to collect bits of junk ground away during a milling operation. During milling, drilling mud under high pressure forces bits of junk up the narrow space between the boot sub and the hole wall. When the junk reaches the wider annulus above the boot sub and pressure drops slightly, the junk falls into the boot sub. A boot sub also can be run above the bit during routine drilling to collect small pieces of junk that may damage the bit or interfere with its operation.

Pressure at the top of a well when it is shut in.

See formation pressure

Pressure drop

See extreme-pressure lubricant

Abbreviation: shut-in casing pressure

2. the process of removing tubing from the well under pressure.

An elastomer (seal) energized by pressure

2. the process of putting tubing into a well under pressure.

Abbreviation: choke-line friction pressure.

Flexible coupling used in high-pressure lines.

2. any pumping procedure in which fluid is pumped into the well against pressure.

A surface device used in pressure control for slickline.

An unloader; provides a means to equalize tubing and annulus pressure.

To overcome pressure in a well by use of mud or water so that surface connections may be removed.

A pressure-multiplier-type well servicing mobile pump.

Abbreviation: shut-in drill pipe pressure, used in drilling reports.

3. trying to pump out a gas influx before the expansion of gas reduces pressure allowing the well to kick.

1. a device that mechanically or hydraulically forces pipe or tools into the well against pressure.

A special valve installed below the kelly. Usually, the valve is open so that drilling fluid can flow out of the kelly and down the drill stem. It can, however, be manually closed with a special wrench when necessary. In one case, the valve is closed and broken out, still attached to the kelly to prevent drilling mud in the kelly from draining onto the rig floor. In another case, when kick pressure inside the drill stem exists, the drill stem safety valve is close to prevent the pressure from escaping up the drill stem.

An injection well used for injecting fluids into an underground stratum to increase reservoir pressure.

A well through which fluids are injected into an underground stratum to increase reservoir pressure and to displace oil.

3. a fractionation system that reduces the vapor pressure so that the resulting liquid is less volatile.

Used to describe packers with one slip system for supporting weight and pressure from above only.

Application of hydraulic pressure to the reservoir formation to create fractures through which oil or gas may move to the well bore.

A device set in tubing, particular collars, to facilities the landing of pressure bombs (recorders).

A closed pressure vessel with a furnace to burn coal, oil, or gas, used to generate steam from water.

A well into which gas in injected for the purpose of maintaining or supplementing pressure in an oil reservoir. More commonly called a gas injection well.

2. the increasing of external pressure on a diver's body caused by improper diving technique.

Rubber seals that energize by pressure only, not mechanical force; plugs and wash tools

An opening or space within a rock or mass of rocks, usually small and often filled with some fluid (water, oil, gas, or all three). Compare vug.

A surface device used in slickline operations to keep the line lubricated and provide grease for pressure control

A surface device used in slickline operations to keep the line lubricated and provide grease for pressure control

Abbreviation: a generic term for pressure setting assembly; a tool that is used to set permanent tools on electric wireline, through explosive force.

2. a device fitted to the gauging hatch on a pressure tank that enables manual dipping and sampling without loss of vapor.

Removing fluid from the tubing in a well, often by means of a swab, to lower the bottomhole pressure in the wellbore at the perforations and induce the well to flow.

A drillable tool configuration allowing the opening of formation pressure, during drillout, prior to cutting through the tools slips.

2. to pull formation fluids into a wellbore by raising the drill stem at a rate that reduces the hydrostatic pressure of the drilling mud below the bit.

1. a cementing operation in which cement is pumped behind the casing under high pressure to recement channeled areas or to block off an uncementred zone.

A sudden increase in the drill bit's rate of penetration. it sometimes indicates that the bit has penetrated a high-pressure zone and thus warns of the possibility of a kick.

A rapid increase in n pressure downhole that occurs when the drill stem is lowered too fast or when the mud pump is brought up to speed after starting.

2. the use of a high-pressure water stream to dislodge clingage and sediment from the bulkheads, bottoms, and internal structures of a vessel's cargo tanks.

1. to drive oil from a reservoir into a well by injecting water under pressure into the reservoir formation. See waterflooding.

A pipe through which pressure is bled, as from a pressurized tank, vessel, or other pipe.

To bleed pressure from casing of a dead well, then from tubing, then from casing, and so on so that the well will start to flow.

A bradenhead pack; no packer, very limited pack pressure capability.

The upward encroachment of water into a well caused by pressure drawdown from production.

The pressure gradient (psi/ft) at which the formation accepts whole fluid from the wellbore.

A sub with a ball seat run on top of a hydraulically set packer to set the packer.

Abbreviation: pounds per square inch absolute. See absolute pressure.

The ability of the formations to withstand applied pressure. Also called formation integrity.

A small plug that is run through a flow line by pressure to clean the line or test for obstructions (see pig).

Fracture induced by means of hydraulic or mechanical pressure exerted on the formation.

2. in wireline, trying to pull out of the well faster than the wireline tools are being blown upwards by unexpected pressure.

An accessory or integral part of a packer used to limit the packer's upward movement under pressure.

2. in reference to engines, a term used to describe the resistance to the flow of exhaust gas through the exhaust pipe.

Tubing pressure acting on the net piston area and causing a force to be exerted on a mandrel.

A valve that will open automatically when pressure gets too high.

Reduce pressure by letting oil or gas escape at a low rate.

A paraffinic hydrocarbon that is a gas at ordinary atmospheric conditions but is easily liquefied under pressure. It is a constituent of liquefied petroleum gas.

The control valves, pressure gauges, and chokes assembled at the top of a well to control the flow of oil and gas after the well has been drilled and completed.

The amount of fluid that can be delivered through a permeable filter medium after being subjected to a set differential pressure for a set length of time.

To cause a gas or liquid to mingle slowly with another gas or liquid usually by pressure.

1. the high-pressure spraying of the crude oil cargo to dislodge or dissolve clingage and sediment from the walls, cross members, and lines in the compartments of a vessel during the unloading operation.

Lighter-duty well maintenance than hydraulic workover, employing small OD tubing capable of descending down the production string under well pressure

A device made up in the drill stem and lowered into the well to allow the casing and blowout preventers to b pressure-tested. The sealing device is cup-shaped and is therefore called a cup.

A phenomenon in which a pressure concession occurs by suddenly stopping the flow of liquids in a closed container. Also called water hammer.

A method of severing steel pipe in a well by applying high-pressure jets of a very corrosive substance against the wall of the pipe. The resulting cut is very smooth.

A valve installed above the kelly that can be closed manually to protect the rotary hose from high pressure that may exist in the drill stem

1. to move the drill stem up and down in the hole over a short distance without rotation. Careless execution of this operation creates pressure surges that can cause a formation to break down, resulting in lost circulation.

A system of operating a certain oil and condensate reservoir in order to conduct some form of pressure maintenance, repressuring, waterflood, or other cooperative form to increase ultimate recovery.

A tool employing tripping devices that limit tool movement from pressure either above or below the tool

1. a condition sometimes encountered in a pumping well when dissolved gas, released from solution during the upstroke of the plunger, appears as free gas between the valves. If the gas pressure is sufficient, the standing valve is locked shut, and no fluid enter the tubing.

2. the pressure-sealing element of a stripper blowout preventer See stripper head.

Terminology used to describe a screen that, when packed off by gels, will give a pressure rise at the surface, thereby "telling" the tool operator that the gel has reached a certain location. Also called tattle-tale.

The topmost portion of a string of sucker rods. It is used for lifting fluid by the rod-pumping method. It has a uniform diameter and is smoothly polished to seal pressure effectively in the stuffing box attached to the top of the well.

A fluid-pressure test of the casing. Also called a cup test.

A series of hydraulic rams to restrain and pull tubing under well pressure, temporarily attached to the wellhead for workover.

Water put into an empty string of pipe in a wellbore to prevent the pipe from being crushed by pressure in the annulus.

1. the process of lowering the drill stem into the wellbore when the well is shut in on a kick and when the weight of the drill stem is sufficient to overcome the force of well pressure.

An electric or hydraulic pump on an accumulator that pumps hydraulic fluid under high pressure to the blowout preventers so that they may be closed or opened.

Low-solids fluid or drilling mud used when a well is being completed. it is selected not only for its ability to control formation pressure, but also for the properties that minimize formation damage.

See hydrostatic pressure

A special type of flanged connection in which a metal ring (resting in a groove in he flange) serves as a pressure seal between the two flanges.

A method of squeeze cementing in which cement is pumped in and the pumps are stopped for a few minutes. Pumping is started and stopped until the desired pressure is obtained.

A mechanically operated (tubing rotation) valve u used to shut off formation pressure above a packer, thus testing all connections form the packer to the tree.

A test used to determine the amount of pressure required to cause a formation to fracture.

A wireline pressure setting tool for setting permanent downhole tools.

A method of producing a well in which only production casing is set through the pay zone, with no tubing or inner production string used to bring formation fluids to the surface. This type of completion has its best application in low-pressure, dry-gas reservoirs.

1.a low-pressure area, around which wind flow is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The term is sometimes used to describe storms occurring in the atmosphere; in the Indian Ocean it is used to designate a tropical cyclone.

A flanged fitting that supports the tubing string, seals off pressure between the casing and the outside of the tubing, and provides a connection that supports the Christmas tree.

A tubular device employed as an isolation tool inside the Christmas tree, to increase the tree's pressure rating during stimulation.

To drain off liquid or gas, generally slowly, through a valve called a bleeder. To bleed down, or bleed off, means to release pressure slowly from a well or from pressurized equipment.

A method for killing well pressure in which circulation is commenced immediately and mud weight is brought up in steps, or increments, usually a point at a time. Also called circulate-and-weight method.

1. compacted solid or semisolid material remaining on a filter after pressure filtration of mud with a standard filter press. Thickness of the cake is reported in thirty-seconds of an inch or in millimeters.

A hollow, rubber-faced cylinder mounted on a hollow mandrel with a pin joint on the upper end to connect to the swab line. A check valve that opens upward on the lower end provides a way to remove the fluid from the well when pressure is insufrficien5t to support flow.

A liquid, usually salt water or oil, but sometimes mud, used in a well when a packer is between the tubing and the casing. Packer fluid must be heavy enough to shut off the pressure of the formation being produced, must not stiffen or settle out of suspension over long periods of time, and must be noncorrosive.

A paraffin hydrocarbon, a gas in atmospheric conditions but is easily liquefied under pressure. It is a constituent of liquefied petroleum gas. See commercial butane, field-grade butane, normal butane.

The formation and collapse of vapor- or gas-filled cavities that result from a sudden decrease and increase of pressure. Cavitation can cause mechanical damage to adjacent surfaces in meters, valves, pumps, and pipes at locations where flowing liquid encounters a restriction or change in direction.

Gas that enters the wellbore when the mud pump is shut down and pipe is being pulled from the wellbore. The gas may enter because of the reduction in bottomhole pressure when the pump is shut down, because of swabbing, or because of both.

A blowout preventer that uses rams to seal off pressure on a hole that is with or without pipe. Also called a ram preventer.

A mixture of hydrocarbons that existed in the liquid phase in natural phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities.

The equipment installed at the surface of the wellbore. A wellhead includes such equipment as the casinghead and tubing head. adj: pertaining to the wellhead (e.g., wellhead pressure).

The relatively small amount of gas that enters a well when the mud pump is stopped for a connection to be made. Since bottomhole pressure decreases when the pump is stopped, gas may enter the well.

2. the cylindrical part of a sucker rod pump in which the piston-like plunger moves up and down. Operating as a piston inside a cylinder, the plunger and barrel create pressure energy to lift well fluids to the surface.

1. a reduction in the amount of force a fluid exerts against a surface, such as the walls of a pipe. It usually occurs because the fluid is moving against the surface and is caused by the friction between the fluid and the surface.

The forcing of cement slurry by pressure to specified points in a well to cause seals at the points of squeeze. It is a secondary cementing method that is used to isolate a producing formation, seal off water, repair casing leaks, and so forth.

2. to dose the blowout preventers on a well to control a kick. The blowout preventers close off the annulus so that pressure from below cannot flow to the surface.

Oil as it exists at atmospheric conditions in a stock tank. Stock tank oil lacks much of the dissolved gas present at reservoir pressure and temperatures.

A device that increases the pressure on a fluid or raises it to a higher level. Various types of pumps include the bottomhole pump, centrifugal pump, hydraulic pump, jet pump, mud pump, reciprocating pump, rotary pump, sucker rod pump, and submersible pump

1. to collect a mass of sticky consolidated material, usually drill cuttings, on drill pipe, drill collars, bits, and so forth. A bit with such material attached to it is called a balled-up bit. Balling up is frequently the result of inadequate pump pressure or insufficient drilling fluid.

(n) a device with an elastomer packing element that depends on pressure below the packing to effect a seal in the annulus. Used primarily to run or pull pipe under low or moderate pressures. This device is not dependable for service under high differential pressures. Also called a stripper.

A procedure by which acid is forced into a formation under pressure high enough to cause the formation to crack. The acid acts on certain kinds of rocks, usually carbonates, to increase the permeability of the formation. Compare matrix acidizing.

When explosives are used to fracture a formation. At the moment of detonation, the explosion furnishes a source of high-pressure gas to force fluid into the formation. The rubble prevent fracture healing, making the use of proppants unnecessary. Compare hydraulic fracturing.

2. the pressure drop from the outer limits of drainage to the wellbore caused by the relatively thin veneer (or skin) of the affected formation. Skin is expressed in dimensionless units: a positive value denotes formation damage; a negative value indicate improvement. Also called skin effect.

The gathering of pressure data and fluid samples from a formation to determine its production potential before choosing a completion method. Testing tools include formation testers and drill stem test tools.

An arrangement of piping and special valves, called chokes. In drilling, mud is circulated through a choke manifold when the blowout preventers are closed. In well testing, a choke manifold attached to the wellhead allows flow and pressure control for test components downstream.

An oilwell that has come in with such great pressure that the oil jets out of the well like a geyser. In reality, a gusher is a blowout and is extremely wasteful of reservoir fluids and drive energy. In the early days of the oil industry, gushers were common and many times were the only indication that a large reservoir of oil and gas had been struck. See blowout.

The component in a blowout preventer that cuts, or shears, through drill pipe and forms a seal against well pressure. Shear rams are used in floating offshore drilling operations to provide a quick method of moving the rig away from the hole when there is no time to trip the drill stem out of the hole.

To start the mud pump for restoring circulation of the mud column. Because the stagnant drilling fluid has thickened or gelled during the period of no circulation, high pump pressure is usually required to break circulation.

A measure of the density of a drilling fluid expressed as pounds per gallon, pounds per cubic foot, or kilograms per cubic meter. Mud weight is directly related to the amount of pressure the column of drilling mud exerts at the bottom of the hole.

A method of killing a well in which the mud level in the pits is held constant while the choke size is reduced and the pump speed slowed. It is not effective, and therefore, is not recommended, because casing pressure increases to the point at which the formation fractures or casing ruptures, and control of the well is lost.

A large, high-pressure reciprocating pump used to circulate the mud on a drilling rig. A typical mud pump is a two-cylinder, double-acting or a three-cylinder, single-acting piston pump whose pistons travel in replaceable liners and are driven by a crankshaft actuated by an engine or a motor. Also called a slush pump.

A device used to control the rate of flow in a line to open or shut off a line completely, or to serve as an automatic or semiautomatic safety device. Those used extensively include the check valve, gate valve, globe valve, needle valve, plug valve, and pressure relief valve.

Circulating fluid, one function of which is to force cuttings out of the wellbore and to the surface. Other functions are to cool the bit and to counteract downhole formation pressure. While a mixture of barite, clay, water, and chemical additives is the most common drilling fluid, wells can also be drilled by using air, gas, water, or oil-base mud as the drilling fluid. See mud.

A globe valve that contains a sharp, pointed, needle-like plug that is driven into and out of a cone-shaped seat to control accurately a relatively small rate of fluid flow. In a fuel injector, the fuel pressure forces the needle valve off its seat to allow injection.

N:a unit of measure of permeability. A porous medium has a permeability of 1 darcy when differential pressure of 1 atmosphere across a sample 1 centimeter long and 1 square centimeter in cross section will force a liquid of 1 centipoise of viscosity through the sample at the rate of 1 cubic centimeter per second. The permeability of reservoir rocks is usually so low that it is measured in millidarcys.

A cast-iron or magnesium drillable tool consisting of a packing assembly and a back-pressure valve. It is used to close off the annular space between tubing or drill pipe and casing to allow the placement of cement or fluid through the tubing or drill pipe at any predetermined point behind the casing or liner, around the shoe, or into the open hole around the shoe.

A vessel used to bury pipeline beneath the seafloor. The barge moves itself forward by means of anchors. A jet sled is lowered over the pipeline, and as the barge pulls it over the pipe, high-pressure jets of water remove soil from beneath the pipe, allowing the pipe to fall into the jetted-out trench.

A dart-shaped drill pipe inside blowout preventer installed on top of the drill stem when the well is kicking through the drill stem. It is stabbed in open then closed against pressure.

A substance that consists of large molecules formed from smaller molecules in repeating structural units (monomers). In oilfield operations, various types of polymers are used to thicken drilling mud, fracturing fluid, acid, water, and other liquids. See micellar-polymer flooding, polymer mud. In petroleum refining, heat and pressure are used to polymerize light hydrocarbons into larger molecules, such as those that make up high-octane gasoline. In petrochemical production, polymer hydrocarbons are used as a feedstock for plastics.

One of several valves installed at the wellhead to prevent the escape of pressure either in the annular space between the casing and drill pipe or in open hole (i.e., hole with no drill pipe) during drilling completion operations. Blowout preventers on land rigs are located beneath the rig at the land's surface; on jackup or platform rigs, at the water's surface; and on floating offshore rigs, on the seafloor.

A workover performed with a continuous steel tube, normally 3/4 inch to 1 inch outside diameter, which is run into the well in one piece inside the normal tubing. Lengths of the tubing up to 16,000 feet are stored on the surface on a reel in a manner similar to that used for wireline. The unit is rigged up over the wellhead. The tubing is injected through a control head that seals off the tubing and makes a pressure-tight connection. A unique feature of the unit is that it allows continuous circulation while it is being lowered into the hole.

A formation fluid sampling device, actually run on conductor line rather than wireline, that also logs flow and shut-in pressure in rock near the borehole. A spring mechanism holds a pad firmly against the sidewall while a piston creates a vacuum in a test chamber. Formation fluids enter the tes5t chamber through a valve in the pad. A recorder logs the rate at which the test chamber is filled. Fluids may also be drawn to fill a sampling chamber. Wireline formation tests may be done any number of times during one tip in the hole, so they are very useful in formation testing.

A variation of squeeze cementing for wells with two producing zones in which (1) the upper fluid sand is perforated; (2) tubing is run with a packer, and the packer is set between the two perforated intervals; (3) water is circulated between the two zones to remove as much mud as possible from the channel; (4) cement is pumped through the channel and circulated; (5) the packer is released and picked up above the upper perforation, a low squeeze pressure is applied, and the excess cement is circulated out. The process is applicable where there is communication behind the pipe between the two producing zones because of channeling of the primary cement or where there is essentially no cement in the annulus.

A process used to repair a hole in the casing by pumping cement down tubing or drill pipe. First, the casinghead, or bradenhead, is closed to prevent fluids from moving up the casing. Then the rig's pumps are started. Pump pressure moves the cement out of the tubing or pipe and, since the top of the casing is closed, the cement goes into the hole in the casing. The tubing or pipe is pulled from the well and the cement allowed to harden. The hardened cement seals the hole in the casing. Although the term "bradenhead squeezing" is still used, the term "bradenhead" is obsolete. See annular space, casinghead, squeeze.

A porous and permeable underground formation containing an individual and separate natural accumulation of producible hydrocarbons (oil and/or gas) which is confined by impermeable rock or water barriers and is characterized by a single natural pressure system. A subsurface, porous, permeable rock body in which oil and/or gas is stored, Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. The three basic types of hydrocarbon reservoirs are oil, gas, and condensate. An oil reservoir generally contains three fluids - gas, oil, and water - with oil the dominant product. In the typical oil reservoir, these fluids occur in different phases because of the variance in their gravities. Gas, the lightest, occupies the upper part of the reservoir rocks; water, the lower part; and oil, the intermediate section. In addition to its occurrence as a cap or in solution, gas may accumulate independently of the oil; if so, the reservoir is called a gas reservoir. Associated with the gas, in most instances, are salt water and some oil. In a condensate reservoir, the hydrocarbons may exist as a gas, but, when brought to the surface, some of the heavier ones condense to a liquid.