Oil & Gas Glossary 1.0

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.

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

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.

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.

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.

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 means of cementing casing in a well so that the casing may, if necessary, be retrieved with minimum difficulty. A special mud, usually an oil mud, is placed in the well ahead of the cement after the casing has been set. Non-solidifying mud is used so that it does not bind or stick to the casing in the hole in the area above the cement. Since the mud does not gel for a long time, the casing can be cut above the cemented section and retrieved. Casing packs are used in wells of doubtful or limited production to permit reuse of valuable lengths of casing.

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

A special tool with a rubber packer or lead seal that is used to repair casing. When casing is damaged downhole, a cut is made below the damaged casing, the damaged casing and the casing above it are pulled from the well, and the damaged casing is removed from the casing string. The tool is made up and lowered into the well on the casing until it engages the top of the casing that remains in the well, and a rubber packer or lead seal in the tool forms a seal with the casing that is in the well. The casing-patch tool is an over-shot-like device and is sometimes called a casing overshot.

The string of casing set in a well after the surface casing but before production casing is set. Keeps hole from caving and seals off troublesome formations. Also called protection casing.

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 location of the bottom of a string of casing that is cemented in a well. Typically, a casing shoe is made up on the end of the casing at this point.

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.

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

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.

Abbreviation: shut-in casing 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.

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 entire length of all the joints of casing run in a well. Most casing joints are manufactured to specifications established by API, although non-API specification casing is available for special situations. Casing manufactured to API specifications is available in three length ranges. A joint of range 1 casing is 16 to 25 feet long; a joint of range 2 casing is 25 to 34 feet long; and a joint of range 3 casing is 34 to 48 feet long. The outside diameter of a joint of API casing ranges from 4 1/2 to 20 inches.

A device secured around the casing at the regular intervals to center it in the hole. Casing that is centralized allows a more uniform cement sheath to form around the pipe.

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 casing sub containing a seal bore and a left-handed thread, run as a crossover between casing sizes, to provide a tubing anchor.

1. a short, heavy, cylindrical section of steel filled with concrete and rounded at the bottom, which is placed at the end of the casing string. It prevents the casing from snagging on irregularities in the borehole as it is lowered. A passage through the center of the shoe allow drilling fluid to pass up into the casing while it is being lowered and allows cement to pass out during cementing operations. Also called casing shoe.

A tool composed of a mandrel on which are mounted several heavy-duty rollers with eccentric roll surfaces. It is used to restore buckled, collapsed, or dented casing in a well to normal diameter and roundness. Made up on tubing or drill pipe and run into the well to the depth of the deformed casing, the tool is rotated slowly, allowing the rollers to contact all sides of the casing and restore it to roughly its original condition.

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 special coupling device inserted one or two joints above the bottom of the casing string that contains a check valve to permit fluid to pass downward but not upward through the casing. The float collar prevents drilling mud from entering the casing while it is being lowered, allowing the casing to float during its descent and thus decreasing the load on the derrick or mat. A float collar also prevents backflow of cement during a cementing operation.

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.

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.

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.

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.

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.

A logging device used to determine accurately the depth of a well; the log measures and records the depth of each casing collar, or coupling, in a well. Since the length of each joint of casing is written down, along with the number of joints of casing that were put into the well, knowing the number and depth of the collars allows an accurate measure of well depth

A tubular section of pipe that is threaded inside and used to connect two joints of casing.

Blade tool used to scrape away junk or debris from inside casing; run on pipe or tubing.

To run and cement casing at a certain depth in the wellbore. Sometimes called set pipe.

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

To pierce the casing wall and cement to provide holes through which formation fluids may enter or to provide holes in the casing so that materials may be introduced into the annulus between the casing and the wall of the borehole. Perforating is accomplished by lowering into the well a perforating gun, or perforator, that fires electrically detonated bullets or shaped charges.

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).

Abbreviation: polished bore receptacle, a section in the casing string to facilitate landing of the production tubing (casing).

A circular device with a frictional gripping arrangement of slips and packing rings used to suspend casing from a casinghead in a well

Pertaining to a wellbore in which casing has been run and cemented. See casing.

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.

To create holes in casing and cement set through a productive formation. A common method of completing a well is to set casing through the oil-bearing formation and cement it. A perforating gun is then lowered into the hole and fired to detonate high-powered jets or shoot steel projectiles (bullets) through the casing and cement and into the pay zone. The formation fluids flow out of the reservoir through the perforations and into the wellbore. See perforating gun.

See casing-patch tool

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.

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.

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.

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

1. to remove with the drill bit the residual cement that normally remains in the lower section of casing and the wellbore after the casing has been cemented.

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.

A perforating gun run in on the casing string.

Casing without perforations

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

1. the operation during the drilling procedure when the cement is drilled out of the casing and the wellbore after the casing has been cemented.

A heavy, flanged steel fitting connected to the first string of casing. It provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off. Also called a spool.

The cementing operation that takes place immediately after the casing has been run into the hole. It provides a protective sheath around the casing, segregates the producing formation, and prevents the undesirable migration of fluids.

Large wrench used for turning when making up or breaking out casing. See tongs.

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.

An accessory attached to the top of the casing to facilitate cementing of the casing. It has passages for cement slurry and retain chambers for cementing wiper plugs.

A length of casing with one thread on the field end and a different thread in the coupling, used to make a changeover from one thread to another in a string of casing.

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 short threaded nipple screwed into the open end of the coupling and over the threaded end of casing to protect the threads from dirt accumulation and damage. It is made of steel or plastic. Also called thread protector.

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.

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.

A casing in which the outside diameter of the joint is the same as the outside diameter of the casing itself.

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).

A short, heavy, cylindrical steel section with a rounded bottom and attached to the bottom of the casing string. It contains a check valve and functions similarly to the float collar but also serves as a guide shoe in the casing.

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.

An acoustic survey or sonic logging method that records the quality or hardness of the cement used in the annulus to bond the casing and the formation. Casing that is well bonded to the formation transmits an acoustic signal quickly; poorly bonded casing transmits a signal slowly. See acoustic survey, acoustic well logging.

A device that is fastened to the outside of casing to remove mud cake from the wall of a hole to condition the hole for cementing. By rotating or moving the casing string up and down as it is being run into the hole, the scratcher, formed of stiff wire, removes the cake so that the cement can bond solidly to the formation.

A rubber-bodied, plastic- or aluminum-cored device used to separate cement and drilling fluid as they are being pumped down the inside of the casing during cementing operations. A wiper plug also removes drilling mud that adheres to the inside of the casing.

Drill pipe, drill collars, casing, or tubing that has inadvertently become immovable in the hole. Sticking may occur when drilling is in progress, when casing is being run in the hole, or when the drill pipe is being hoisted.

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.

The large wrenches used to make up or break out drill pipe, casing, tubing, or other pipe; variously called casing tongs, pipe tongs, and so forth, according to the specific use. Power tongs are pneumatically or hydraulically operated tools that serve to spin the pipe up tight and, in some instances, to apply the final makeup torque.

A special type of nuclear log that measures the depth of each casing collar. Knowing the depth of the collars makes it easy to determine the exact depth of the formation to be perforated by correlating casing-collar depth with formation depth.

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

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 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).

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.

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

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

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

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

An equipment's working pressure times a safety factor.

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

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.

A downhole tool with rough, sharp, extremely hard cutting surfaces for removing metal by grinding or cutting. Mills are run on drill pipe or tubing to grind up debris in the hole, remove stuck portions of drill stem or sections of casing for sidetracking, and ream out tight spots in the casing. They are also called junk mills, reaming mills, and so forth, depending on what use they have.

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

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

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

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

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

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.

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.

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.

An arrangement for producing a well in which one wellbore penetrates two or more petroleum-bearing formations. In one type, multiple tubing strings are suspended side by side in the production casing string, each a different length and each packed to prevent the commingling of different reservoir fluids. Each reservoir is then produced through its own tubing string. Alternatively, a small-diameter production casing string may be provided for each reservoir, as in multiple miniaturized or multiple tubingless completions.

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

The normal pressure divided by true vertical depth.

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.

Generally, the first string of casing in a well. It may be lowered into a hole drilled into the formations near the surface and cemented in place; it may be driven into the ground by a special pile driver (in such cases, it is sometimes called drive pipe); or it may be jetted into place in offshore locations. Its purpose is to prevent the soft formations near the surface from caving in and to conduct drilling mud from the bottom of the hole to the surface when drilling starts. Also called conductor pipe.

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.

Generally, the first string of casing in a well. It may be lowered into a hole drilled into the formations near the surface and cemented in place; or it may be driven into the ground by a special pile drive (in such cases, it is sometimes called drive pipe); or it may be jetted into place in offshore locations. Its purpose is to prevent the soft formations near the surface from caving in and to conduct drilling mud from the bottom of the hole to the surface when drilling starts. Also called conductor pipe.

A single well that produces from two separate formation at the same time. Production from each zone is segregated by running two tubing strings with packers inside the single string of production casing, or by running one tubing string with a packer through one zone while the other is produced through the annulus. In a miniaturized dual completion, two separate 4 1/2-inch or smaller casing strings are run and cemented in the same wellbore.

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.

Casing collar log

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.

1. of a wellbore, having no casing.

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.

To run casing or pipe.

A wellbore in which casing has been run.

To enlarge the wellbore below the casing.

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

Perforations in casing for the inflow of hydrocarbons and gas

Blowing out of formation fluids outside the casing and under the rig

A device to salvage casing on a P&A job.

The area above a packer between casing ID and tubing OD

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.

A tool used to straighten damaged or collapsed casing in a well.

A person who tests pipe and casing for leaks

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.

Commonly called casinghead gas; gas that is produced with oil or from the casing head of an oil well.

The buckling of tubing in a large-diameter pipe or casing.

Oil-well, casing, tubing, or drill pipe.

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.

The depth in the hole at which the tubing, casing, or drill pipe is stuck.

To lower the drill stem, tubing, casing, or sucker rods in to the wellbore.

A method for completing a well in which tubing is set inside 4-1/2-inch or larger casing.

A component of a downhole tool, such as a packer, used to wedge slips into the casing wall.

(v) to place a packer in the wellbore and activate it so that it forms a seal between the tubing and the casing.

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 heaviest-wall casing section of the string, usually located just below the preventers or tree.

1. a circular device with a frictional gripping arrangement used to suspend casing and tubing in a well.

A length of drill or line pipe, tubing, or casing considerably shorter than 30 feet.

A hydraulically powered device used in lieu of a rotary to turn the drill pipe, tubing, or casing in a well.

The pressure at the bottom of a well.

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.

A section of drill pipe, casing, or tubing consisting of four joints screwed together. Compare double, single, thribble.

Equipment operated hydraulically or by compressed air for making up and breaking out drill pipe, casing, tubing, and rods.

A remedial well-servicing activity whereby a cement slurry is pumped into open perfs, split casing, etc., to effect a blockage.

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.

1. in drilling, a plastic mixture of cement and water that is pumped into a well to harden. There it supports the casing and provides a seal in the wellbore to prevent migration of underground fluids.

2. the system of tubulars, packers, and other tools installed beneath the wellhead in the production casing; that is, the tool assembly that provides the hydrocarbon flow path or paths.

A tubular device that, when lowered to a selected depth within a well, fires bullets through the casing to provide holes through which the formation fluids may enter the wellbore.

A powder, consisting of alumina, silica, lime, and other substances that hardens when mixed with water. Extensively used in the oil industry to bond casing to the walls of the wellbore.

A device fitted with shaped charges or bullets that is lowered to the desired depth in a well and fired to create penetrating holes in casing, cement, and formation.

A blowout prevention device consisting of a gland and packing arrangement bolted to the wellhead. It is often used to seal the annular space between tubing and casing.

The set of dense rubber, washer-shaped pieces encircling a packer, which are designed to expand against casing or formation face to seal off the annulus.

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.

Running of a gauge on tubing or slickline to verify casing dimensions.

The depth in the hole at which the drill stem, tubing, or casing is stuck.

A sliding-sleeve ported casing section used in stage cementing.

2. a device, similar to a casing shoe, placed at the end of other tubular goods.

A special-purpose packer placed in the casing to permit a sidetrack operation.

A cylindrical metal ring used to guide, and centralize, packers or tools inside casing.

A tool used to gauge and clean junk and debris from the casing in conjunction with a junk catcher.

To use a whipstock, turbodrill, or other mud motor to drill around broken drill pipe or casing that has become lodged permanently in the hole.

Clamps that grip a stand of casing, tubing, drill pipe, or sucker rods so that the stand can be raised or lowered into the hole.

A rubber plug used in primary cementing operations to displace cement slurry from the casing into the borehole annulus.

1. a hole in the rig floor, 30 to 35 feet (9 to 11 meters) deep, which is lined with casing that projects above the floor and into which the kelly and swivel are placed when hoisting operations are in progress.

A slip employing tungsten-carbide "buttons" in lieu of conventional wicker-type teeth to set tools in very hard casing.

A circular steel device that holds slips supporting a suspended string of drill pipe, casing, or tubing. A spider may be split or solid.

A short string of large-diameter casing used to keep the wellbore open and to provide a means of conveying the upflowing drilling fluid from the wellbore to the mud pit.

A type of acoustic log that records the travel time of sounds through objects, cement, or formation rocks. Often used to determine whether voids exist in the cement behind the casing in a wellbore.

The application of a liquid slurry of cement and water to various points inside or outside the casing. See primary cementing, secondary cementing.

A well completion in which the production casing is less than 4.5 inches in diameter. Compare conventional completion.

A length of pipe whose bottom edge is serrated or dressed with a hard cutting material and that is run into the wellbore around the outside of stuck casing, pipe, or tubing to mill away the obstruction.

A device placed at the end of or beneath an object for various purposes (e.g., casing shoe guide shoe).

A long steel casing that uses an inclined plane to cause the bit to deflect from the original borehole at a slight angle. Whipstocks are sometimes used in controlled directional drilling, in straightening crooked boreholes, and in sidetracking to avoid unretrieved fish.

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.

A downhole tool, composed primarily of slips, a plug mandrel, and a rubber sealing element, that is run and set in casing to isolate a lower zone while an upper section is being tested or cemented.

A long, hollow cylinder, usually steel, through which fluids are conducted. Oilfield tubular goods are casing (including liners), drill pipe, tubing, or line pipe

A hole made in the casing, cement, and formation through which formation fluids enter a wellbore. Usually several perforations are made at a time.

See guide shoe

1. see conductor casing

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.

Spring-loaded buttons on a packer that provide friction with casing to retard movement of one section of a packer while another section rotates for setting.

A tool set temporarily in the casing or well to prevent the passage of cement, thereby forcing it to follow another designated path. It is used in squeeze cementing and other remedial cementing jobs.

A cylindrical metal ring used to guide packers past casing obtrusions.

Steel pipe placed in an oil or gas well as drilling progresses to prevent the wall of the hole from caving in during drilling, to prevent seepage of fluids, and to provide a means of extracting petroleum if the well is productive.

The first casing or conductor string (generally with a diameter of 30 to 36 inches) set when drilling a well from an offshore drilling rig. It prevents sloughing of the ocean-floor formations and is a structural support for the permanent guide base and the blowout preventers.

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

1. to assemble and join parts to form a complete unit (e.g., to make up a string of casing). 2. to screw together two threaded pieces. 3. to mix or prepare (e.g., to make up a tank of mud). 4. to compensate for (e.g., to make up for lost time).

A single length (30 feet or 9 meters) of drill pipe, drill collar, casing, or tubing that has threaded connections at both ends. Several joints screwed together constitute a stand of pipe.

Any packer designed to make a seal between the tubing and the casing during production

See formation pressure

Pressure drop

2. pressure, volume, and temperature.

See extreme-pressure lubricant

A rubber or rubber-like device on a special rod (a swab), which forms a seal between the swab and the wall of the tubing or casing.

A spring-actuated metal band or ring(ferrule) used to expand a liner patch when making casing repairs. See liner patch.

A hydraulically operated tool that is run in above the fishing tool and anchored to the casing by slips. It exerts a strong upward pull on the fish by hydraulic power derived from fluid that is pumped down the fishing string.

A special nipple made up in the tubing, casing, or drill pipe string the configuration of which is such that a tool contacting it can pass through only if the tool is in the proper position or configuration.

To pull the drill stem out of the wellbore to change the bit, to change from a core barrel to the bit, to run electric logs, to prepare for a drill stem test, to run casing, and so on. Also called trip out.

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

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

An elastomer (seal) energized by pressure

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

Flexible coupling used in high-pressure lines.

Abbreviation: choke-line friction pressure.

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

A pump with an impeller or rotor, an impeller shaft, and a casing, which discharges fluid by centrifugal force.

A surface device used in pressure control for slickline.

A pressure-multiplier-type well servicing mobile pump.

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

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

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.

The first string of casing (after the conductor pipe) that is set in a well. it varies in length from a few hundred to several thousand feet. Some states require a minimum length to protect freshwater sands. Compare conductor pipe.

Any kind of pipe. Oilfield tubular goods include tubing, casing, drill pipe, and line pipe. Also called tubulars.

See casing centralizer

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

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

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

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

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

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.

A relatively small container of high explosive that is loaded into a perforating gun. On detonation, the charge releases a small, high-velocity stream of particles (a jet) that penetrates the casing, cement, and formation. See perforating gun.

Two packers separated by a spacer of variable length. A straddle packer may be used to isolate sections of open hole to be treated or tested or to isolate certain areas of perforated casing from the rest of the perforated section.

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.

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

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

An opening at floor level in a side of a derrick or mast. The V-door is opposite the drawworks and is used as an entry to bring in drill pipe, casing, and other tools from the pipe rack. The name comes from the fact that on the old standard derrick, the shape of the opening was an inverted V.

2. to cease producing oil and gas from a well when it becomes unprofitable. A wildcat well may be abandoned after it has proven nonproductive. Several steps are involved in abandoning a well; part of the casing may be removed and salvaged; one or more cement plugs are placed in the borehole to prevent migration of fluids between the different formations penetrated by the borehole; and the well is abandoned. In many states, it is necessary to secure permission from official agencies before a well may be abandoned.

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.

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

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

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

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.

See casing hanger, tubing hanger

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

A part of the brake mechanism consisting of a flexible steel band lined with a material that grips a drum when tightened. On a drilling rig, the brake band acts on the flanges of the drawworks drum to control the lowering of the traveling block and its load of drill pipe, casing, or tubing.

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

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 device installed on a gas lift mandrel, which in turn is put on the tubing string of a gas lift well. Tubing and casing pressures cause the valve to open and close, thus allowing gas to be injected into the fluid in the tubing to cause the fluid to rise to the surface.

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

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.

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

A method of preparing a well for production in which no production casing or liner is set opposite the producing formation. Reservoir fluids flow unrestricted into the open wellbore. An open-hole completion has limited use in rather special situations. Also called a barefoot completion.

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.

Drilling in which the size of the hole is smaller than the conventional hole diameter for a given depth. This decrease in hole size enables the operator to run smaller casing, thereby lessening the cost of completion. See miniaturized completion.

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

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

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

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

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

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

A borehole; the hole drilled by the bit. A wellbore may have casing in it or it may be open (uncased); or part of it may be cased, and part of it may be open. Also called a borehole or hole.

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

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

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

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.

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

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

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

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

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

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

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

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.

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 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.

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

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

An examination of reservoir fluid in a laboratory under various pressures, volumes, and temperatures to determine the characteristics and behavior of the fluid.

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

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

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

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

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.

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 squeeze cementing method in which a packer is set to form a seal between the working string (the pipe down which cement is pumped) and the casing. Another packer or a cement plug is set below the point to be squeeze-cemented. By setting packers, the squeeze point is isolated from the rest of the well. See packer, squeeze cementing.

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.

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.

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.

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.

See hydrostatic pressure

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 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 wireline pressure setting tool for setting permanent downhole tools.

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

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.

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

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 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.

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.

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.

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

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.

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.

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.

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.