Acid

Pertaining to an aqueous solution, such as a water-base drilling fluid, which has more hydrogen ions (H+) than hydroxyl ions (OH-) and pH less than 7..

Acidizing

The pumping of acid into the wellbore to remove near-well formation damage and other damaging substances. This procedure commonly enhances production by increasing the effective well radius. When performed at pressures above thepressure required to fracture the formation, the procedure is often referred to as acid fracturing.

Accelerator

A downhole tool used in conjunction with a jar to store energy that is suddenly released when the jar is activated. The energy provides an impact force that operates associated downhole tools or, in a contingency role, helps release a tool string that has become stuck. Depending on the operating mode, the energy in tension or compression can be stored by means of a mechanical spring or a compressible fluid such as nitrogen gas. Accelerators should be selected on the basis of their compatibility with the jar to be used.

Accumulator     

A device used in a hydraulic system to store energy or, in some applications, dampen pressure fluctuations. Energy is stored by compressing a precharged gas bladder with hydraulic fluid from the operating or charging system. Depending on the fluid volume and precharge pressure of the accumulator, a limited amount of hydraulic energy is then available independent of any other power source. Well pressure-control systems typically incorporate sufficient accumulator capacity to enable the blowout preventer to be operated with all other power shut down.

Back up

To hold one end of a threaded connection while the other is turned to make up the joint. To ensure a secure connection, many types of threaded joints are made up to specific torque requirements in oil- and gas-well applications. This process requires the controlled application of force to the rotating component and a means of stabilizing and securing the corresponding stationary component to which it is being connected.

Bridging Material

Solids added to a drilling fluid to bridge across the pore throat or fractures of an exposed rock thereby building a filter cake to prevent loss of whole mud or excessive filtrate. Bridging materials are commonly used in drilling fluids and in lost circulationtreatments. For reservoir applications, the bridging agent should be removable-common products include calcium carbonate(acid-soluble), suspended salt (water-soluble) or oil-soluble resins. For lost-circulation treatments, any suitably sized products can be used, including mica, nutshells and fibers. These products are more commonly referred to as lost-circulation material (LCM).

BalancePoint

The point at which the forces acting on a tubing string suspended in a live wellbore are equal. Under these conditions, the weight of the tubing string is balanced by the wellbore pressure acting to expel the string from the wellbore. The friction caused by the tubing string passing through the stripper or wellhead sealing device acts to extend the interval over which the balance point is apparent.

Batch Mixer

A vessel and mixing system used to prepare treatment fluids. A batch mixer is generally equipped with a means of adding dry and liquid chemicals, an agitation or circulation system and a manifold system to deliver the prepared fluid to storage tanks or treating pumps.

Blind Shear Ram              

A blowout preventer (BOP) closing element fitted with hardened tool steel blades designed to cut the drillpipe or tubing when the BOP is closed, and then fully close to provide isolation or sealing of the wellbore. A shear ram is normally used as a last resort to regain pressure control of a well that is flowing. Once the pipe is cut (or sheared) by the shear rams, it is usually left hanging in the BOP stack, and kill operations become more difficult. The joint of drillpipe or tubing is destroyed in the process, but the rest of the string is unharmed by the operation of shear rams.

Broach

A downhole tool used to repair the internal diameter of the production tubing where a slight collapse or a dent has occurred. Cutting profiles on a broach removes the tubing-wall material to allow subsequent passage of tools and equipment of a prescribed diameter.

encountered under static or slow-moving conditions.

Braided Line

A type of multistrand wireline used for slickline applications in which higher tension or weight-carrying ability is required. The most common size of braided line is 3/16-in. diameter, although special heavy applications use 1/4-in. and 5/16-in. sizes. When larger sizes are used, it may be necessary to kill the well due to the effect of wellhead pressure on the relatively large cross-sectional area of the line entering the wellbore.

Bull Plug

A solid plug used as an isolation device in piping systems, conduits or wellbore tubulars.

Bias Weld

A technique used in the assembly of coiled tubing strings at the manufacturing plant. Prior to being formed, the string is assembled from flat steel strips joined by a bias weld that is angled across the strip joint at 45 degrees. When the tubing string is milled, the helical weld form provides enhanced characteristics of the tube at the weld site. These are significantly better than those achievable with the alternative butt weld technique

Bleed Off

To equalize or relieve pressure from a vessel or system. At the conclusion of high-pressure tests or treatments, the pressure within the treatment lines and associated systems must be bled off safely to enable subsequent phases of the operation to continue. The bleedoff process must be conducted with a high degree of control to avoid the effect of sudden depressurization, which may create shock forces and fluid-disposal hazards.

Bleed Off Line

A section of manifold containing the valves and piping necessary to bleed off pressure from a vessel or system. Bleedoff lines may be exposed to widely fluctuating pressures. They must be adequately secured, and consideration must be given to safe handling or disposal of the resulting fluids.

Barrel Pump      

A small pump with an extended suction duct that is designed to pump fluid from barrels. Barrel pumps are commonly used to decant liquid additives during the preparation of treatment fluids at the wellsite.

Blender

The equipment used to prepare the slurries and gels commonly used in stimulation treatments. The blender should be capable of providing a supply of adequately mixed ingredients at the desired treatment rate. Modern blenders are computer controlled, enabling the flow of chemicals and ingredients to be efficiently metered and requiring a relatively small residence volume to achieve good control over the blend quality and delivery rate.

Butt Weld

A welding technique used to join two tubes in which the squared and prepared ends are butted together in preparation for welding. The resulting circumferential weld has relatively good strength characteristics but has limitations where the tube is to be plastically deformed or bent, such as occurs on a coiled tubing string. Consequently, butt welds performed on a coiled tubing string should be checked carefully using hardness and radiographic testing methods and their locations detailed in the string record. The anticipated fatigue life in the butt-weld area must also be reduced to compensate for the weakness of the weld.

C pump

A type of pump commonly used in the handling and mixing of oilfield fluids. The rotary motion of a profiled impeller in combination with a shaped pump housing or volute applies centrifugal force to discharge fluids from the pump. Centrifugal pumps generally operate most efficiently in high-volume, low-output-pressure conditions. Unlike a positive-displacementpump, the flow from centrifugal pumps can be controlled easily, even allowing flow to be completely closed off using valves on the pump discharge manifold while the pump is running. This pump is known as a "centrifugal pump."

Closure Pressure

An analysis parameter used in hydraulic fracture design to indicate the pressure at which the fracture effectively closes without proppant in place.

Casing Patch     

A downhole assembly or tool system used in the remedial repair of casing damage, corrosion or leaks. Casing patches are most frequently used as short- to medium-term repairs that enable production to be resumed until a major workoveroperation is scheduled. In some cases, such as in depleted wells nearing the end of viable production, a casing patch may be the only economic means of safely returning the well to production.

Chrome Tubing

Tubing manufactured from an alloy containing a high proportion of chrome, typically greater than 13%. Chrome tubing is classified as a corrosion-resistant alloy (CRA) and is used where the wellbore conditions or reservoir fluid create a corrosive environment that conventional tubing cannot safely withstand. Wells that produce hydrogen sulfide, and similar corrosive fluids, typically require chrome tubing.

Coiled Tubing   

A long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool. Depending on the pipe diameter (1 in. to 4 1/2 in.) and the spool size, coiled tubing can range from 2,000 ft to 15,000 ft [610 to 4,570 m] or greater length.

Circulation Sub

A downhole tool typically used with motors or assemblies that restrict the allowable fluid-circulation rates. When operated, the circulation sub allows a higher circulation rate to be established by opening a path to the annulus in the top section of the tool string. This is especially useful in applications such as drilling in slim-diameter wells, where a higher circulation rate may be necessary to effect good cuttings transport and hole cleaning before the string is retrieved.

Coiled Tubing Connector            

The downhole device used to connect the tool string to the coiled tubing string. Several types of devices with varying principles of operation are commonly used. The primary requirement is provision of an adequate mechanical connection capable of withstanding the necessary tensile and compressive forces, while ensuring efficient hydraulic isolation of the connection between the tool string and the coiled tubing string.

Casing Scraper

A downhole tool incorporating a blade assembly that is used to remove scale and debris from the internal surface of a casing string. Generally run on tubing or drill pipe, casing scrapers are routinely used during work over operations to ensure that the wellbore is clean before reinstalling the completion string.

Circulation Valve

A downhole device that enables circulation through the tubing string and associated annulus. As a completion accessory, a circulation valve is included to circulate fluid for well kill or kickoff. Circulation valves typically are operated by slickline tools and are generally capable of several opening and closing cycles before requiring service.

Coiled Tubing String      

A continuous length of low-alloy carbon-steel tubing that can be spooled on a reel for transport, then deployed into a wellbore for the placement of fluids or manipulation of tools during workover and well-intervention operations. The process of spooling and straightening a coiled tubing string imparts a high degree of fatigue to the tube material. Therefore, a coiled tubing string should be regarded as a consumable product with a finite service life. Predicting and managing the factors that affect the safe working life of a coiled tubing string are key components of the string-management system necessary for ensuring safe and efficient coiled tubing operations.

Corrosion Inhibitor

A chemical additive used in acid treatments to protect iron and steel components in the wellbore and treating equipment from the corrosive treating fluid. Corrosion inhibitors generally are mixed with the treatment fluid and are formulated to be effective in protecting the metal components the fluid is likely to contact. This protection must remain effective under the anticipated pressure and temperature environment for the duration of the treatment.

Coiled Tubing Unit         

The package of equipment required to run a coiled tubing operation. Four basic components are required: the coiled tubing reel to store and transport the coiled tubing string, the injector head to provide the attractive effort to run and retrieve the coiled tubing string, the control cabin from which the equipment operator controls and monitors the operation, and the power pack that generates the necessary hydraulic and pneumatic power required by the other components. The dimensions and capacities of the coiled tubing unit components determine the size and length of coiled tubing string that can be used on the unit. Pressure-control equipment is incorporated into the equipment to provide the necessary control of well pressure fluid during normal operating conditions and contingency situations requiring emergency control.

Counter Balance Winch

The lifting device on a snubbing unit used to pick up and lay down the tool string and running-string tubulars.

Clean Out           

To remove wellbore-fill material such as sand, scale or organic materials, and other debris from the wellbore. Many reservoirs produce some sand or fines that may not be carried to surface in the produced fluid. Accumulations of fill material may eventually increase in concentration within the lower wellbore, possibly restricting production. Cleanouts using coiled tubing, snubbing or hydraulic workover techniques are performed routinely.

Collapse Pressure

The pressure at which a tube, or vessel, will catastrophically deform as a result of differential pressure acting from outside to inside of the vessel or tube. The collapse-pressure rating of perfectly round tubing is relatively high. However, when the tubing is even slightly oval, the differential pressure at which the tube will collapse may be significantly reduced. This is an important factor in determining the operating limits of coiled tubing strings since the action of spooling the string tends to induce some ovality.

Collector

The electrical device used on the axle of a spool or reel to provide electrical continuity between the rotating reel core and the stationary reel chassis. When using a coiled tubing string equipped with an electrical conductor, such as required during coiled tubing logging operations, a collector is fitted to the reel axle to allow connection of the surface data-acquisition equipment

Closing Unit

A generic term given to the hydraulic power pack and accumulators used to control the blowout preventers on a drilling or workover rig.

Combi BOP

A type of blowout preventer (BOP) in which each ram set combines two conventional ram functions, such as blind/shear and pipe/slip. The principal advantage of the combi-BOP is the reduced height required for rig up of the required ram functions.

CT

Another term for coiled tubing, a long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool. Depending on the pipe diameter (1 in. to 4 1/2 in.) and the spool size, coiled tubing can range from 2,000 ft to 15,000 ft [610 to 4,570 m] or greater length. 

Dart      

A device dropped or pumped through tubing or coiled tubing string to activate downhole equipment and tools.

Deployment System

An assembly of pressure-control equipment that enables the running and retrieval of long tool strings on a coiled tubing string in a live wellbore. The deployment system is configured to provide two barriers against well pressure as the tool string is assembled and run into the wellbore. Once fully assembled, the coiled tubing equipment is connected and the tool string is run into the wellbore. The process is reversed for tool retrieval.

Dummy Valve

A blank gas-lift valve placed in a gas-lift mandrel to isolate the tubing string from the annulus. Gas-lift valves frequently are replaced with dummy valves during intervention work on wells with gas-lift completions.

Equalizing Valve             

A device that is operated to equalize the pressure across a valve, plug or similar pressure or fluid isolation barrier. The operating mechanism on many pressure-sealing devices is rendered inoperable once the mechanism has been activated by pressure. In such cases, the pressure across the pressure barrier must be equalized before the barrier can be removed.

Flow Meter                                        

A device installed in a pump manifold or treating line to measure the fluid flow rate. Flowmeters can be used to measure the flow rates of liquid or gas and are available in various configurations and with differing operating principles.

Flow Meter

A device installed in a pump manifold or treating line to measure the fluid flow rate. Flowmeters can be used to measure the flow rates of liquid or gas and are available in various configurations and with differing operating principles.

Fishing Diagram

A diagram noting the major profiles and dimensions of tools and equipment run into a wellbore. A fishing diagram should be prepared for every tool operation, enabling contingency plans to be implemented efficiently if the tool string becomes stuck or lost.

Free Point

The depth at which tubing or coiled tubing string that is stuck in the wellbore is free to move. When the tubing string must be cut to enable recovery, the free point should be known to ensure retrieval of the cut tubing. This enables remedial action to be taken to resolve the sticking mechanism on the portion of the string below the cut.

Fishing Neck

The surface on which a fishing tool engages when retrieving tubing, tools or equipment stuck or lost in a wellbore. Tools and equipment that are temporarily installed in a wellbore are generally equipped with a specific fishing-neck profile to enable the running and retrieval tools to reliably engage and release.

Fluid Compatibility Test              

A test, or series of tests, performed to check that no undesirable reactions occur with a specific fluid. The testing process may include checks for compatibility with other treating fluids, wellbore fluids, reservoir fluids and the reservoir formation. In extreme cases, the mixing of seemingly benign fluids can create significant reactions that may damage the reservoir permeability permanently.

Fluid Level

The depth, or distance from surface, that the fluid in a well incapable of natural flow will reach under static conditions.

Free-Point Indicator

A wireline tool used to determine the free point on a stuck string. The free-point indicator operates by detecting stretch in the tubular when tension is applied at surface. If stretch is not detected, the string must be stuck above the tool; if stretch is detected, the string is free above the free-point indicator tool.

Gas Buster

A simple separator vessel used to remove free or entrained gas from fluids circulated in the wellbore, such as mud used during drilling operations. The gas buster typically comprises a vessel containing a series of baffles with a liquid exit on the bottom and a gas-vent line at the top of the vessel.

GooseNeck

An inverted "U" shaped section of rigid piping normally used as a conduit for high-pressure drilling fluid. In particular, the term is applied to a structure that connects the top of a vertical standpipe running up the side of a derrick or mast to a flexible kelly hose that in turn is connected to another gooseneck between the flexible line and the swivel.

Grapple              

A generic name given to tools that engage on the outer surface of a tubing string or tool assembly, generally for fishing purposes.

Grease-Injection System

An assembly of components used to contain wellhead fluids and pressure during braided-line or wireline operations. The wireline passes through a close-tolerance tube assembly as it leaves the wellbore. High-pressure grease is pumped into the surrounding annulus to effect a pressure-tight dynamic seal that is maintained during the operation by injecting more grease as required. A slight leakage of grease is normal, and the addition of fresh grease enables the consistency of the seal to be maintained at an effective level.

 Gripper Blocks

The profiled blocks attached to the drive chains of a coiled tubing injector head. The gripper blocks are arranged in opposing pairs to secure the coiled tubing string in the injector-head chains. As the hydraulic drive system rotates the chains, the gripper blocks feed the tubing string into, or out of the well.

Gin Pole

A lifting device, similar in function to a crane jib, that is used in a number of oilfield applications, such as for handling tubularson a snubbing unit, tool strings on a slickline unit or on a winch truck, and for general lifting at the wellsite.

Heavy Pipe        

An operating condition during a snubbing operation in which the force resulting from the weight of the pipe or tubing string is greater than the wellhead pressure and the buoyancy forces acting to eject the string from the wellbore. In the heavy-pipe condition, the string will drop into the wellbore if the gripping force is lost.

High-PressureSsqueeze

A squeeze-cementing technique involving the application of treatment pressure that is higher than the fracture pressure of the information. This procedure may be necessary to force the slurry into microcracks or annuli that surround the wellbore. The characteristics of a fracture are dependent on the fluid flow rate when the fracture is initiated; consequently, high-pressure squeeze operations must be conducted with a high degree of control to place the slurry in the desired location.

Hydraulic Release Tool           

A downhole tool designed to allow the lower and upper tool string sections to be parted to enable retrieval of the running string. Hydraulic disconnects rely on the application of a predefined pressure through the running string to activate a release mechanism. In some cases, a ball or dart is plugged to block circulation through the tool string and enable the application of the release pressure.

Hesitation Squeeze

A technique used in squeeze cementing whereby a portion of the slurry is pumped, then pumping stops to expose the slurry to differential pressure against the zone of interest in stages over a period from several minutes to several hours. This pressure, higher than necessary for fluid movement, is applied to force the cement slurry into the area requiring repair. This staged procedure is repeated until all the slurry has been pumped or until no further slurry can be placed into the treatment zone. The cement remaining in the zone forms an effective hydraulic seal with a high compressive strength.

Hydraulic Disconnect                                          

A downhole tool designed to allow the lower and upper tool string sections to be parted to enable retrieval of the running string. Hydraulic disconnects rely on the application of a predefined pressure through the running string to activate a release mechanism. In some cases, a ball or dart is plugged to block circulation through the tool string and enable the application of the release pressure

Injector Head   

One of the principal equipment components of a coiled tubing unit. The injector head incorporates special profiled chain assemblies to grip the coiled tubing string and a hydraulic drive system that provides the tractive effort for running and retrieving the string from the wellbore. The base of the injector head is secured to the wellhead pressure-control equipment by the stripper assembly mounting system. The gooseneck mounted on top of the injector head feeds the tubing string from the reel around a controlled radius into the injector head.

Intensifier

A downhole tool used with a jar to increase the impact force imparted as the jar is fired. Similar in function to an accelerator, intensifiers typically use compressed gas rather than a mechanical spring to store the energy released during operation.

Jacking Frame

A support structure used to stabilize the injector head and pressure-control equipment on some offshore, or special onshore, coiled tubing units. The jacking frame is hydraulically controlled to enable the injector head to be located at a safe and secure working height. Additional features, such as the ability to skid the injector head to the side for access to the wellbore are included in some of the more complex designs of jacking frame.

Junk Sub

A downhole tool with a profiled external surface designed to catch and retrieve junk or debris from the wellbore. The debris is carried up the tool-string annulus in the circulation fluid. An indented profile creating a larger annular area causes the fluid flow rate to drop and allows debris to drop into a basket or receptacle located at the base of the tool.

Jar

A mechanical device used downhole to deliver an impact load to another downhole component, especially when that component is stuck. There are two primary types, hydraulic and mechanical jars. While their respective designs are quite different, their operation is similar. Energy is stored in the drill string and suddenly released by the jar when it fires. The principle is similar to that of a carpenter using a hammer. Kinetic energy is stored in the hammer as it is swung, and suddenly released to the nail and board when the hammer strikes the nail. Jars can be designed to strike up, down, or both. In the case of jarring up above a stuck bottom hole assembly, the driller slowly pulls up on the drill string but the BHA does not move. Since the top of the drill string is moving up, this means that the drill string itself is stretching and storing energy. When the jars reach their firing point, they suddenly allow one section of the jar to move axially relative to a second, being pulled up rapidly in much the same way that one end of a stretched spring moves when released. After a few inches of movement, this moving section slams into a steel shoulder, imparting an impact load. In addition to the mechanical and hydraulic versions, jars are classified as drilling jars or fishing jars. The operation of the two types is similar, and both deliver approximately the same impact blow, but the drilling jar is built such that it can better withstand the rotary and vibrational loading associated with drilling.

Kill Pump

A high-pressure pump designated for well-kill purposes. Depending on the application, the kill pump may need to be connected to a ready supply of kill fluid should well control be required at short notice.

Lubricator

A long, high-pressure pipe fitted to the top of a wellhead or Christmas tree so that tools may be put into a high-pressure well. The top of the lubricator assembly includes a high-pressure grease-injection section and sealing elements. The lubricator is installed on top of the tree and tested, the tools placed in the lubricator and the lubricator pressurized to wellbore pressure. Then the top valves of the tree are opened to enable the tools to fall or be pumped into the wellbore under pressure. To remove the tools, the reverse process is used: the tools are pulled up into the lubricator under wellbore pressure, the tree valves are closed, the lubricator pressure is bled off, and then the lubricator may be opened to remove the tools.

Lifting Frame

A lifting device used when performing coiled tubing operations from a semisubmersible rig or drillship. The coiled tubing injector and pressure-control equipment are positioned within the lifting frame, which is attached to the flow head and running string and supported by the traveling blocks. This configuration enables the heave-compensation system of the rig to counteract the vessel motion.

Light Pipe

An operating condition during a snubbing operation in which the wellhead pressure and buoyancy forces are greater than the force resulting from the weight of the pipe or tubing string. In the light-pipe condition the string will be ejected from the wellbore if the gripping force of the slips is lost.

Load Cell

The sensor component in a weight-indicator system that detects the tensional or compression forces being imparted to the running string at surface. Load cells are hydraulically or electronically operated and are connected to the weight-indicator display system on the equipment operator's console.

Milling

The use of a mill or similar downhole tool to cut and remove material from equipment or tools located in the wellbore. Successful milling operations require appropriate selection of milling tools, fluids and techniques. The mills, or similar cutting tools, must be compatible with the fish materials and wellbore conditions. The circulated fluids should be capable of removing the milled material from the wellbore. Finally, the techniques employed should be appropriate to the anticipated conditions and the likely time required to reach the operation objectives.

Mast Unit

A well-servicing unit for slickline, wireline or coiled tubing operations that is equipped with a mast rather than a crane or gin pole. The mast provides a means of lifting and stabilizing tools, and running pressure-control and other equipment.

Mill       

A tool that grinds metal downhole. A mill is usually used to remove junk in the hole or to grind away all or part of a casing string. In the case of junk, the metal must be broken into smaller pieces to facilitate removal from the wellbore so that drilling can continue. When milling casing, the intent is to cut a window through the side of the casing or to remove a continuous section of the casing so that the wellbore may be deviated from the original well through the window or section removed. Depending on the type of grinding or metal removal required, the shape of the cutting structures of mills varies. Virtually all mills, however, utilize tungsten carbine cutting surfaces.

Mechanical Jar

A type of jar that incorporates a mechanical trip or firing mechanism that activates only when the necessary tension or compression has been applied to the running string. In slickline operations, the term is often used to describe any jar that does not contain a hydraulic trip mechanism, such as link and tubular jars that do not incorporate a firing mechanism.

Overshot

A downhole tool used in fishing operations to engage on the outside surface of a tube or tool. A grapple, or similar slip mechanism, on the overshot grips the fish, allowing application of tensile force and jarring action. If the fish cannot be removed, a release system within the overshot allows the overshot to be disengaged and retrieved.

Pack off

To plug the wellbore around a drillstring. This can happen for a variety of reasons, the most common being that either the drilling fluid is not properly transporting cuttings and cavings out of the annulus or portions of the wellbore wall collapse around the drill string. When the well packs off, there is a sudden reduction or loss of the ability to circulate, and high pump pressures follow. If prompt remedial action is not successful, an expensive episode of stuck pipe can result. The term is also used in gravel packing to describe the act of placing all the sand or gravel in the annulus.

Pill

Any relatively small quantity (less than 200 bbl) of a special blend of drilling fluid to accomplish a specific task that the regular drilling fluid cannot perform. Examples include high-viscosity pills to help lift cuttings out of a vertical wellbore, freshwater pills to dissolve encroaching salt formations, pipe-freeing pills to destroy filter cake and relieve differential sticking forces and lost circulation material pills to plug a thief zone.

Poppet Valve

A type of check valve often used in the lines or manifolds associated with kill and choke lines or pressure-control equipment.

Pipe Heavy        

An operating condition during a snubbing operation in which the force resulting from the weight of the pipe or tubing string is greater than the wellhead pressure and the buoyancy forces acting to eject the string from the wellbore. In the heavy-pipe condition, the string will drop into the wellbore if the gripping force is lost.

Pipe Light

An operating condition during a snubbing operation in which the wellhead pressure and buoyancy forces are greater than the force resulting from the weight of the pipe or tubing string. In the light-pipe condition the string will be ejected from the wellbore if the gripping force of the slips is lost.

Pulling Tool

A slickline or coiled tubing tool used to retrieve temporary devices, such as plugs and flow-control equipment, from the wellbore. Pulling tools are available in a range of sizes and profiles and must be compatible with the equipment to be retrieved. A contingency release system in the pulling tool allows the tool to be released and retrieved if the equipment to be retrieved cannot be released.

Reel Back Tension

The tension applied to a coiled tubing string as it passes between the reel and the injector head. An adequate back-tension must be maintained to ensure that the string spools correctly on or off the reel.

Running Tool

A generic name for a tool or device that is used in the placement or setting of downhole equipment such as permanent packers or plugs. The running tool can be retrieved after the operation or setting process. In some cases, the running tool also is used to retrieve the equipment or tool that has been set in the wellbore.

Reel      

The device used to store and transport a coiled tubing string ready for use at the wellsite. The coiled tubing reel incorporates a manifold and swivel arrangement to enable fluids to be pumped through the coiled tubing string at any time, a level wind assembly to ensure the string is correctly spooled and a treatment system to apply inhibitor or similar protective coatings to the coiled tubing string. The reel functions are hydraulically powered and controlled from the unit control cabin.

Shear Ram

A blowout preventer (BOP) closing element fitted with hardened tool steel blades designed to cut the drillpipe or tubing when the BOP is closed, and then fully close to provide isolation or sealing of the wellbore. A shear ram is normally used as a last resort to regain pressure control of a well that is flowing. Once the pipe is cut (or sheared) by the shear rams, it is usually left hanging in the BOP stack, and kill operations become more difficult. The joint of drill pipe or tubing is destroyed in the process, but the rest of the string is unharmed by the operation of shear rams.

Snubbing Basket             

The work area at the top of a snubbing unit that houses the unit controls and a means of handling the tubulars and tool string to be run or retrieved.

Safety Head      

Another term for shear-seal BOP, an item of pressure-control equipment often fitted to the wellhead during well-intervention operations on live wells. Most commonly associated with coiled tubing operations, the shear-seal BOP is a ram-type preventer that performs the dual functions of shearing or cutting the tubing string and then fully closing to provide isolation or sealing of the wellbore. Shear-seal BOPs are most commonly used in offshore or high-pressure applications where an additional contingency pressure barrier is required.

Shear Seal BOP

An item of pressure-control equipment often fitted to the wellhead during well-intervention operations on live wells. Most commonly associated with coiled tubing operations, the shear-seal BOP is a ram-type preventer that performs the dual functions of shearing or cutting the tubing string and then fully closing to provide isolation or sealing of the wellbore. Shear-seal BOPs are most commonly used in offshore or high-pressure applications where an additional contingency pressure barrier is required.

Snubbing Force               

The force required to insert a tool or tubing string into a live wellbore. Two main components act to determine the snubbing force: the force resulting from the wellhead pressure acting on the cross-sectional area of the tubing, or the outside diameter of the tool and the force required to overcome the friction resulting from the stripper or similar sealing device containing the wellbore pressure and fluids.

Stabbing Valve

A valve that is connected to the work string in the event that the well starts to flow when running or retrieving the string. A stabbing valve generally is kept on the rig floor as a contingency against unexpected well flow. On snubbing operations, a stabbing valve, or safety valve, is kept in the workbasket to protect against tubing plug or backpressure valve failure.

Snubbing Jack

The components of a snubbing unit that provide the vertical stroke or movement required to run or retrieve the work string. Snubbing jacks are hydraulically operated and can apply extremely high forces to the tubing string and the wellhead to which they are attached.

Stationary Slips

The slip set on a snubbing unit located at the base of the jack. Two sets of stationary slips are available, one set for pipe-heavy conditions and another for pipe-light conditions.

Sand Cleanout 

The process of removing sand or similar fill from a wellbore. Many wells produce sand that may accumulate and restrictproduction if not removed from the wellbore by the production fluid. Coiled tubing and snubbing units are routinely used for sand-cleanout operations, enabling the well condition to be treated without removing the completion equipment or even killing the well.

Shear-Seal BOP               

An item of pressure-control equipment often fitted to the wellhead during well-intervention operations on live wells. Most commonly associated with coiled tubing operations, the shear-seal BOP is a ram-type preventer that performs the dual functions of shearing or cutting the tubing string and then fully closing to provide isolation or sealing of the wellbore. Shear-seal BOPs are most commonly used in offshore or high-pressure applications where an additional contingency pressure barrier is required.

Spooler               

A device used to handle and temporarily store a coiled tubing string. Spoolers generally are configured with a removable drum that allows transport spools to be inserted, allowing a new string to be spooled onto a reel. The term is also occasionally used to describe the level wind assembly on a tubing reel.

Stationary Snubbers

The stationary slip set on a snubbing unit used when operating under light-pipe conditions. Under these conditions, the well head pressure is sufficient to eject the tubing string from the wellbore. Therefore, the slips are oriented in a hold-down position to grip with the force acting upward on the string.

Shifting Tool

A downhole tool, most commonly associated with slickline operations, that is used to open, close or shift the position of downhole flow control or circulation devices, such as sliding sleeves. The shifting tool generally features some means of engaging the components to be shifted and is typically run with upward or downward operating jars to deliver the necessary force or impact.

Spot      

To place a small volume or pill of fluid in a wellbore annulus to free differentially stuck pipe. Oil-base mud is the traditional stuck-pipe spotting fluid. Speed in mixing and placing the spot is of primary importance to successfully freeing pipe. Because of concern about mud disposal, spots used offshore are either synthetic-based emulsions or benign water-base formulations. Each type is supplied as prepackaged concentrate designed for rapid access and mixing at the rig. A spot frees pipe by covering the stuck region. It presumably breaks up the filter cake, allowing the spot to migrate into cracks in the cake and between the pipe and the cake, reducing the stuck area and allowing pipe to be pulled free.

Stem

The weight bar used in slickline operations to overcome the effects of wellhead pressure and friction at the surface seal where the wire enters the wellbore. In addition to a solid steel stem, a special high-density stem is available with internal cavities filled with lead, tungsten or mercury alloys.

Sand Line                                      

A long cable, installed on most drilling and work over rigs, used when swabbing or bailing in the production tubing or well bore tubulars. The sand line is typically stored and operated on a winch drum that is part of the rig draw works. The sand line is capable of significantly higher tensile forces than slickline or electric wireline.

Sand Out                                                                                    

A condition encountered during some hydraulic fracturing operations whereby the fracture cannot accept further sand orproppant and only the carrier fluid is injected into the formation. A sand out occurs when the concentration of proppant within the tubing string rapidly increases, creating a corresponding sudden increase in pump pressure.

Slickline

A thin nonelectric cable used for selective placement and retrieval of wellbore hardware, such as plugs, gauges and valves located in side pocket mandrels. Valves and sleeves can also be adjusted using slickline tools. Partially collapsed tubing can be repaired using a tubing swage on slickline.

Slug      

A volume of mud that is denser than the mud in the drill pipe and wellbore annulus. A slug is used to displace mud out of the upper part of the drill pipe before pulling pipe out of the hole and is mixed in the pill pit by adding additional weighting material (barite) to a few barrels of mud from the surface pits. The pill is pumped into the top of the drill string to push mud downward, out of the pipe, thus keeping the upper stands of pipe empty.

Stripper Rubber                                                           

The sealing element used in coiled tubing or snubbing stripper systems. The stripper element is a consumable product and generally should be replaced for each operation. Coiled tubing elements can be replaced with the tubing in place, enabling a worn or leaking element to be replaced during an operation. Snubbing stripper rubbers are of single-piece construction and cannot be changed with the work string in place.

Scraper

Also called a pig, a device with blades or brushes inserted in a pipeline for cleaning purposes. The pressure of the oil stream behind pushes the pig along the pipeline to clean out rust, wax, scale and debris. To clean downhole tubulars a similar device, called a casing scraper or paraffin scraper, may be used.

Stripping

The act of putting drill pipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. This is necessary when a kick is taken, since well kill operations should always be conducted with the drill string on bottom, and not somewhere up the wellbore. If only the annular BOP has been closed, the drill pipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then the ram closed again. This procedure is repeated whenever a tool joint must pass by a ram BOP. Rig crews are usually required to practice ram-to-ram and ram-to-annular stripping operations as part of their well control certifications. In stripping operations, the combination of the pressure in the well and the weight of the drill string is such that the pipe falls in the hole under its own weight, whereas in snubbing operations the pipe must be pushed into the hole.

Snub     

To put drillpipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. Snubbing is necessary when a kick is taken, since well kill operations should always be conducted with the drill string on bottom, and not somewhere up the wellbore. If only the annular BOP has been closed, the drill pipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram BOP or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then closing the ram again. This procedure is repeated whenever a tool joint must pass by a ram BOP. In snubbing operations, the pressure in the wellbore acting on the cross-sectional area of the tubular can exert sufficient force to overcome the weight of the drill string, so the string must be pushed (or "snubbed") back into the wellbore. In ordinary stripping operations, the pipe falls into the wellbore under its own weight, and no additional downward force or pushing is required.

Stripping Ram

A ram-type blowout preventer used to provide primary pressure control in high-pressure snubbing operations. Stripping rams are used when the wellhead pressure is higher than the limitations of a stripper bowl.

Secondary Cementing  

Another term for remedial cementing, cementing operations performed to repair primary-cementing problems or to treat conditions arising after the wellbore has been constructed. The two main categories of remedial cementing include squeeze cementing and the placement of cement plugs.

Snubbers            

The slips used to grip the pipe during a snubbing operation.

Swab Valve

The topmost valve on a Christmas tree that provides vertical access to the wellbore.

Snubbing            

The act of putting drillpipe into the wellbore when the blowout preventers (BOPs) are closed and pressure is contained in the well. Snubbing is necessary when a kick is taken, since well kill operations should always be conducted with the drill string on bottom, and not somewhere up the wellbore. If only the annular BOP has been closed, the drillpipe may be slowly and carefully lowered into the wellbore, and the BOP itself will open slightly to permit the larger diameter tool joints to pass through. If the well has been closed with the use of ram BOPs, the tool joints will not pass by the closed ram element. Hence, while keeping the well closed with either another ram BOP or the annular BOP, the ram must be opened manually, then the pipe lowered until the tool joint is just below the ram, and then closing the ram again. This procedure is repeated whenever a tool joint must pass by a ram BOP. In snubbing operations, the pressure in the wellbore acting on the cross-sectional area of the tubular can exert sufficient force to overcome the weight of the drill string, so the string must be pushed (or "snubbed") back into the wellbore. In ordinary stripping operations, the pipe falls into the wellbore under its own weight, and no additional downward force or pushing is required.

Tapered String 

A string of drill pipe or casing that consists of two or more sizes or weights. In most tapered strings, a larger diameter pipe or casing is placed at the top of the wellbore and the smaller size at the bottom. Note that since the pipe is put into the well bottom first, the smaller pipe is run into the hole first, followed by the larger diameter. Other than the different sizes, which are usually chosen to optimize well economics, there is nothing distinctive about the pipe sections. However, pipe-handling tools must be available for each pipe size, not just one size, as is the typical case.

Travelling Snubbers      

The travelling slip set on a snubbing unit that is used when operating under light-pipe conditions. Under these conditions, the wellhead pressure is sufficient to eject the tubing string from the wellbore. Therefore, the slips are oriented in a hold-down position to act against the upward force applied to the tubing string.

Wireline             

Related to any aspect of logging that employs an electrical cable to lower tools into the borehole and to transmit data. Wireline logging is distinct from measurements-while-drilling (MWD) and mud logging.

Work string

A generic term used to describe a tubing string used to convey a treatment or for well service activities. Both coiled and jointed tubing strings are referred to as work strings.

Wash Pipe         

A tool-string component used with a burn shoe for washover operations. The wash pipe is a relatively large internal-diameter tubular that can be washed over a fish in preparation for engaging and retrieving the fish.

Weight Indicator            

One of the instruments that the driller uses to monitor and improve the operating efficiencies of the drilling operation. The actual measurement of weight is made with a hydraulic gauge attached to the dead line of the drilling line. As tension increases in the drilling line, more hydraulic fluid is forced through the instrument, turning the hands of the indicator. The weight that is measured includes everything exerting tension on the wire rope, including the traveling blocks and cable itself. Hence, to have an accurate weight measurement of the drillstring, the driller must first make a zero offset adjustment to account for the traveling blocks and items other than the drillstring. Then the indicated weight will represent the drillstring (drillpipe and bottomhole assembly). However, the driller is only nominally interested in this weight for most operations. The weight of interest is the weight applied to the bit on the bottom of the hole. The driller could simply take the rotating and hanging off bottom weight, say 300,000 pounds [136,200 kg], and subtract from that the amount of rotating on bottom weight, say 250,000 pounds [113,500 kg], to get a bit weight of 50,000 pounds [22,700 kg]. However, most rigs are equipped with a weight indicator that has a second indicator dial that can be set to read zero ("zeroed") with the drillstring hanging free, and works backwards from the main indicator dial. After proper zeroing, any weight set on bottom (that takes weight away from the main dial), has the effect of adding weight to this secondary dial, so that the driller can read weight on bit directly from the dial.

Wireline Cutter               

A downhole tool used to cut slickline from a tool string that is stuck or jammed in a wellbore. The wireline cutter is attached to the slickline at surface and dropped down the wellbore. When the cutting tool impacts the tool string, a cutting mechanism cuts the slickline and enables recovery of the line in preparation for further fishing operations.

Workover

The repair or stimulation of an existing production well for the purpose of restoring, prolonging or enhancing the production of hydrocarbons.

Washover

A type of milling operation in which the outer surfaces of a plug or similar fish are milled with a circular hollow mill. By including wash pipe in the tool string, the mill face can reach over the body of the fish until it can be pushed to bottom, or until the slips or retaining device can be milled out and the fish retrieved.

Well Servicing 

The maintenance procedures performed on an oil or gas well after the well has been completed and production from thereservoir has begun. Well service activities are generally conducted to maintain or enhance the well productivity, although some slickline and coiled tubing applications are performed to assess or monitor the performance of the well or reservoir. Slickline, coiled tubing, snubbing and workover rigs or rod units are routinely used in well service activities.

Wireline Grab  

A fishing tool used for the retrieval of broken or cut slickline from the wellbore. Wireline grabs are intended to catch and engage wireline that has been bunched or nested in the wellbore. For that reason, they are often run after a blind box or similar fullbore tool has been used to nest the wireline.

Workover Fluid

A well-control fluid, typically a brine, that is used during workover operations. Since the wellbore is in contact with the reservoirduring most workover operations, workover fluids should be clean and chemically compatible with the reservoir fluids and formation matrix.

Wire Clamp       

A safety device attached to the slickline at surface between the hay pulley and stuffing-box pulley. The wire clamp generally is applied when the slickline is to be stationary for a period of time. This prevents the tool string from dropping down the wellbore if the winch unit fails or the slickline becomes damaged at surface.

Work Basket     

The work area at the top of a snubbing unit that houses the unit controls and a means of handling the tubulars and tool string to be run or retrieved.

Workover String

Another term for work string, a generic term used to describe a tubing string used to convey a treatment or for well service activities. Both coiled and jointed tubing strings are referred to as work strings.

A

abnormal pressure n: pressure outside the normal or expected range.

accumulator n: the storage device for nitrogen pressurized hydraulic fluid, which is used in operating the blowout preventers.API American Petroleum Institute n: a trade association and standards organization that represents the interests of the oil and gas industry. It offers publications regarding standards, recommended practices, and other industry related information. 

IADC International Association of Drilling Contractors n: a trade association that represents the interests of members of the drilling segment of the oil and gas industry. It offers publications regarding recommended industry practices and training materials. 

annular blowout preventer n: a well control device, usually installed above the ram preventers, that forms a seal in the annular space between the pipe and well bore or, if no pipe is present, over the well bore itself.

annular pressure n: pressure in an annular space.

annulus n: the space around a pipe in a well bore, sometimes termed the annular space.

ball-and-seat valve n: a device used to restrict fluid flow to one direction. It consists of a polished sphere, or ball, usually of metal, and an annular piece, the seat, ground and polished to form a seal with the surface of the ball. Gravitational force or the force of a spring holds the ball against the seat. Flow in the direction of the force is prevented, while flow in the opposite direction overcomes the force and unseats the ball.

barite n: barium sulfate, BaSO₄; a mineral frequently used to increase the weight or density of drilling mud. Its relative density is 4.2 (meaning that it is 4.2 times denser than water). See barium sulfate, mud.

barium sulfate n: a chemical compound of barium, sulfur, and oxygen (BaSO₄), which may form a tenacious scale that is very difficult to remove. Also called barite.

barrel (bbl) n: 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).

bit n: the cutting or boring element used in drilling oil and gas wells.

bit sub n: a sub inserted between the drill collar and the bit.

bleed v: 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.

blowout n: an uncontrolled flow of gas, oil, or other well fluids from the well.

blowout preventer (BOP) n: one or more valves installed at the wellhead to prevent the escape of pressure either in the annular space between the casing and the drill pipe or in open hole (for example, hole with no drill pipe) during drilling or completion operations. Seeannular blowout preventer and ram blowout preventer.

blowout preventer control panel n: controls, opens and closes the blowout preventers. See blowout preventer.

blowout preventer control unit n: a device that stores hydraulic fluid under pressure in special containers and provides a method to open and close the blowout preventers.

blowout preventer stack (BOP stack) n: the assembly of well control equipment including preventers, spools, valves, and nipples connected to the top of the wellhead.

BOP abbr: blowout preventer.

BOP stack n: the assembly of blowout preventers installed on a well.

bore n: 1. the inside diameter of a pipe or a drilled hole. v: to penetrate or pierce with a rotary tool. Compare tunnel.

bottomhole n: the lowest or deepest part of a well.

bottomhole assembly n: the portion of the drilling assembly below the drill pipe. It can be very simple, composed of only the bit and drill collars, or it can be very complex and made up of several specialty components.

bottomhole plug n: a bridge plug or cement plug placed near the bottom of the hole to shut off a depleted, water-producing, or unproductive zone.

bottomhole pressure n: 1. the pressure at the bottom of a borehole. It is caused by the hydrostatic pressure of the wellbore fluid and, sometimes, by any backpressure held at the surface, as when the well is shut in with blowout preventers. When mud is being circulated, bottomhole pressure is the hydrostatic pressure plus the remaining circulating pressure required to move the mud up the annulus. 2. the pressure in a well at a point opposite the producing formation, as recorded by a bottomhole pressure measuring device.

brake n: The braking device on the drawworks or airhoist to stop a load being lifted. It is a device for arresting the motion of a mechanism, usually by means of friction, as in the drawworks and airhoist brakes.
brine n: water that has a quantity of salt, especially sodium chloride, dissolved in it; salt water.

bushing n: 1. a pipe fitting on which the external thread is larger than the internal thread to allow two pipes of different sizes to be connected. 2. a removable lining or sleeve inserted or screwed into an opening to limit its size, resist wear or corrosion, or serve as a guide. 

C

cable n: 1. a rope of wire, hemp, or other strong fibers. 2. braided wire used to conduct electricity, often called power cable.
a back-in type or a drive-in type.

casing n: 1. steel pipe placed in an oil or gas well to prevent the wall of the hole from caving in, to prevent movement of fluids from one formation to another and to aid in well control.

cased hole n: a wellbore in which casing has been run.

casing head n: 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 casing spool.

casing point n: the depth in a well at which casing is set, generally the depth at which the casing shoe rests.

casing pressure n: the pressure in a well that exists between the casing and the tubing or the casing and the drill pipe.

casing string n: the entire length of all the joints of casing run in a well.

casing shoe n: see guide shoe.

casing tongs n pl: large wrench used for turning when making up or breaking out casing. See tongs.

casing-tubing annulus n: in a wellbore, the space between the inside of the casing and the outside of the tubing.
cement n: 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.

cement casing v: to fill the annulus between the casing and wall of the hole with cement to support the casing and prevent fluid migration between permeable zones.

cementing n: the application of a liquid slurry of cement and water to various points inside or outside the casing.

cement plug n: 1. a portion of cement placed at some point in the wellbore to seal it. 2. a wiper plug. See cementing.

cementing pump n: a high-pressure pump used to force cement down the casing and into the annular space between the casing and the wall of the borehole.

choke n: a device with an orifice installed in a line to restrict the flow of fluids. Surface chokes are part of the Christmas tree on a well and contain a choke nipple, or bean, with a small-diameter bore that serves to restrict the flow. Chokes are also used to control the rate of flow of the drilling mud out of the hole when the well is closed in with the blowout preventer and a kick is being circulated out of the hole. See choke manifold.

choke line n: a line, or pipe, that runs from the blowout preventer stack to the choke manifold through which fluid from the hole is flowed when the well is shut in with the blowout preventer.

choke manifold n: the arrangement of piping and special valves, called chokes, through which drilling mud is circulated when the blowout preventers are closed to control the pressures encountered during a kick.

circulate v: to pass from one point throughout a system and back to the starting point. For example, drilling fluid is circulated out of the suction pit, down the drill pipe and drill collars, out the bit, up the annulus, and back to the pits while drilling proceeds.

circulating pressure n: the pressure generated by the mud pumps and exerted on the drill stem.

circulation n: the movement of drilling fluid out of the mud pits, down the drill stem, up the annulus, and back to the mud pits. See normal circulation, reverse circulation.

circulation valve n: an accessory employed above a packer, to permit annulus-to-tubing circulation or vice versa.

collar n: 1. a coupling device used to join two lengths of pipe, such as casing or tubing. A combination collar has left-hand threads in one end and right-hand threads in the other. 2. a drill collar.

come out of the hole v: 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, tripping out (TOH).

completion fluid n: 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.

conductor casing n: 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). 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, drive pipe.

conductor pipe n: the largest diameter casing and the topmost length of casing. It is relatively short and encases the topmost string of casing.


connection n: 1. a section of pipe or fitting used to join pipe to pipe or to a vessel. 2. a place in electrical circuits where wires join. 3. the action of adding a joint of pipe to the drill stem as drilling progresses.

coring n: the process of cutting a vertical, cylindrical sample of the formations encountered as a well is drilled.

crank n: an arm keyed at right angles to a shaft and used for changing radius of rotation or changing reciprocating motion to circular motion or circular motion to reciprocating motion. On a beam pumping unit, the crank is connected by the pitman to the walking beam, thereby changing circular motion to reciprocating motion.

crew n: 1. the workers on a drilling or workover rig, including the driller, the derrickhand, and the rotary helpers. 2. any group of oilfield service workers.

crossover sub n: a sub that allows different sizes and types of drill pipe or other components to be joined.

cuttings n pl: the fragments of rock dislodged by the bit and brought to the surface in the drilling mud. Washed and dried cuttings samples are analyzed by geologists to obtain information about the formations drilled. 

D

deck n: (nautical) floor.

degasser n: the equipment used to remove unwanted gas from a liquid, especially from drilling fluid.

density n: the mass or weight of a substance per unit volume. For instance, the density of a drilling mud may be 10 pounds per gallon, 74.8 pounds/cubic foot, or 1,198.2 kilograms/cubic meter. Specific gravity, relative density, and API gravity are other units of density.

derrick n: a large load-bearing structure, usually of bolted construction. In drilling, the standard derrick has four legs standing at the corners of the substructure and reaching to the crown block. The substructure is an assembly of heavy beams used to elevate the derrick and provide space to install blowout preventers, casingheads, and so forth.

derrick floor n: also called the rig floor.

derrickhand n: the crew member who handles the upper end of the drill string as it is being hoisted out of or lowered into the hole. On a drilling rig, he or she may be responsible for the circulating machinery and the conditioning of the drilling or workover fluid.

derrickman n: see derrickhand.

diamond bit n: a drill bit that has small industrial diamonds embedded in its cutting surface.

directional drilling n: 1. intentional deviation of a wellbore from the vertical. Although wellbores are normally drilled vertically, it is sometimes necessary or advantageous to drill at an angle from the vertical. Controlled directional drilling makes it possible to reach subsurface areas laterally remote from the point where the bit enters the earth.

dissolved gas n: natural gas that is in solution with crude oil in the reservoir.

downhole adj, adv: pertaining to the wellbore.

drawworks n: the hoisting mechanism on a drilling rig. It is essentially a large winch that spools off or takes in the drilling line and thus lowers or raises the drill stem and bit.

drawworks brake n: the mechanical brake on the drawworks that can slow or prevent the drawworks drum from moving.

drill v: to bore a hole in the earth, usually to find and remove subsurface formation fluids such as oil and gas.

drill ahead v: to continue drilling operations.

drill bit n: the cutting or boring element used in drilling oil and gas wells. Most bits used in rotary drilling are roller-cone bits. The bit consists of the cutting elements and the circulating element. The circulating element permits the passage of drilling fluid and utilizes the hydraulic force of the fluid stream to improve drilling rates.

drill collars n: a heavy, thick-walled tube, usually steel, used between the drill pipe and the bit in the drill stem, used to stiffen the drilling assembly an put weight on the bit so that the bit can drill.

drill collar sub n: a sub made up between the drill string and the drill collars that is used to ensure that the drill pipe and the collar can be joined properly.

driller n: the employee normally in charge of a specific (tour) drilling or workover crew. The driller’s main duty is operation of the drilling and hoisting equipment, but this person may also be responsible for downhole condition of the well, operation of downhole tools, and pipe measurements.

drill floor n: also called rig floor or derrick floor. See rig floor.

drilling engineer n: an engineer who specializes in the technical aspects of drilling.

drilling fluid n: circulating fluid, one function of which is to lift cuttings out of the wellbore and to the surface. It also serves to cool the bit and to counteract downhole formation pressure.

drilling mud n: a specially compounded liquid circulated through the wellbore during rotary drilling operations. See drilling fluid, mud.

drill pipe n: the heavy seamless tubing used to rotate the bit and circulate the drilling fluid. Joints of pipe are generally approximately 30 feet long are coupled together by means of tool joints.

driller's console n: the control panel, where the driller controls drilling operations.

drill string n: the column, or string, of drill pipe with attached tool joints that transmits fluid and rotational power from the kelly to the drill collars and the bit. Often, the term is loosely applied to include both drill pipe and drill collars.

F

flow line n: the surface pipe through which oil or gas travels from a well to processing equipment or to storage.

flow rate n: the speed, or velocity, of fluid or gas flow through a pipe or vessel.

fluid loss n: the unwanted migration of the liquid part of the drilling mud or cement slurry into a formation, often minimized or prevented by the blending of additives with the mud or cement.

formation fluid n: fluid (such as gas, oil, or water) that exists in a subsurface formation.

formation gas n: gas initially produced from an underground reservoir.

formation pressure n: the force exerted by fluids or gas in a formation, recorded in the hole at the level of the formation with the well shut in. Also called reservoir pressure or shut-in bottomhole pressure.

formation water n: 1. the water originally in place in a formation. 2. any water that resides in the pore spaces of a formation.

fracture pressure n: the pressure at which a formation will break down, or fracture.

friction n: resistance to movement created when two surfaces are in contact. When friction is present, movement between the surfaces produces heat.

G

gas cap n: a free-gas phase overlying an oil zone and occurring within the same producing formation as the oil. See reservoir.

gas-cut mud n: a drilling mud that contains entrained formation gas, giving the mud a characteristically fluffy texture. Gas cut mud may cause a lowering of mud weight.

gas well n: a well that primarily produces gas. Legal definitions vary among the states.

gel n: a semisolid, jellylike state assumed by some colloidal dispersions at rest.

geologist n: a scientist who gathers and interprets data pertaining to the formations of the earth’s crust.

H

hex kelly n: see kelly.

hoist n: 1. an arrangement of pulleys and wire rope used for lifting heavy objects; a winch or similar device. 2. the drawworks. v: to raise or lift.

hoisting components n pl: drawworks, drilling line, and traveling and crown blocks. Auxiliary hoisting components include catheads, catshaft, and air hoist.

horizontal drilling n: deviation of the borehole from vertical so that the borehole penetrates a productive formation in a manner parallel to the formation.

hydraulic adj: 1. of or relating to water or other liquid in motion. 2. operated, moved, or effected by water or liquid.

hydraulic fluid n: a liquid of low viscosity (such as light oil) that is used in systems actuated by liquid (such as the brake system in a car).

hydrocarbons n pl: organic compounds of hydrogen and carbon whose densities, boiling points, and freezing points increase as their molecular weights increase. Although composed of only two elements, hydrocarbons exist in a variety of compounds, because of the strong affinity of the carbon atom for other atoms and for itself. The smallest molecules of hydrocarbons are gaseous; the largest are solids. Petroleum is a mixture of many different hydrocarbons.

hydrogen sulfide cracking n: a type of corrosion that occurs when metals are exposed to hydrogen sulfide gas; it is characterized by minute cracks that form just under the metal’s surface.

hydrostatic pressure n: 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 many different units, including pounds per square inch or kilopascals. 

I

IADC abbr: International Association of Drilling Contractors.


impermeable adj: preventing the passage of fluid. A formation may be porous yet impermeable if there is an absence of connecting passages between the voids within it. See permeability.

induction log n: an electric well log in which the conductivity of the formation rather than the resistivity is measured. Because oil-bearing formations are less conductive of electricity than water-bearing formations, an induction survey, when compared with resistivity readings, can aid in determination of oil and water zones.

intermediate casing string n: the string of casing set in a well after the surface casing but before production casing is set to keep the hole from caving and to seal off formations. In deep wells, one or more intermediate strings may be required.

K

kelly n: the heavy square or hexagonal steel member suspended from the swivel through the rotary table and connected to the topmost joint of drill pipe to turn the drill stem as the rotary table turns.

kelly bushing n: a device fitted to the rotary table through which the kelly passes and the means by which the torque of the rotary table is transmitted to the kelly and to the drill stem. Also called the drive bushing.

kelly cock n: a valve installed at one or both ends of the kelly. When a high-pressure backflow occurs inside the drill stem, the valve is closed to keep pressure off the swivel and rotary hose.

kelly drive bushing n: see kelly bushing.

kick n: 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 prompt action is not taken to control the kick, or kill the well, a blowout may occur.

kick fluids n pl: oil, gas, water, or any combination that enters the borehole from a permeable formation.

kickoff point (KOP) n: the depth in a vertical hole at which a deviated or slant hole is started; used in directional drilling.

kill v: 1. in drilling, to control a kick by taking suitable preventive measures (for example, to shut in the well with the blowout preventers, circulate the kick out, and increase the weight of the drilling mud). 2. in production, to stop a well from producing oil and gas so that reconditioning of the well can proceed. 

L

land rig n: any drilling rig that is located on dry land.
liner n: 1. a string of pipe used to case open hole below existing casing. A liner extends from the setting depth up into another string of casing, usually overlapping about 100 feet (30.5 meters) above the lower end of the intermediate or the oil string. Liners are nearly always suspended from the upper string by a hanger device. 2. a relatively short length of pipe with holes or slots that is placed opposite a producing formation. Usually, such liners are wrapped with specially shaped wire that is designed to prevent the entry of loose sand into the well as it is produced. They are also often used with a gravel pack. 3. in jet perforation guns, a conically shaped metallic piece that is part of a shaped charge. It increases the efficiency of the charge by increasing the penetrating ability of the jet. 4. a replaceable tube that fits inside the cylinder of an engine or a pump. See cylinder liner.

location n: the place where a well is drilled. Also called well site.

log n: a systematic recording of data, such as a driller’s log, mud log, electrical well log, or radioactivity log. Many different logs are run in wells to discern various characteristics of downhole formation. v: to record data.

log a well v: to run any of the various logs used to ascertain downhole information about a well.

logging devices n pl: any of several electrical, acoustical, mechanical, or radioactivity devices that are used to measure and record certain characteristics or events that occur in a well that has been or is being drilled.

lost circulation n: the quantities of whole mud lost to a formation, usually in cavernous, pressured, or coarsely permeable beds. Evidenced by the complete or partial failure of the mud to return to the surface as it is being circulated in the hole.

lubricator n: a specially fabricated length of casing or tubing usually placed temporarily above a valve on top of the casinghead or tubing head. It is used to run swabbing or perforating tools into a producing well and provides a method for sealing off pressure and thus should be rated for highest anticipated pressure. 

M
make a connection v: to attach a joint or stand of drill pipe onto the drill stem suspended in the wellbore to permit deepening the wellbore by the length of the pipe.

make up a joint v: to screw a length of pipe into another length of pipe.

mandrel n: a cylindrical bar, spindle, or shaft around which other parts are arranged or attached or that fits inside a cylinder or tube.

manifold n: 1. an accessory system of piping to a main piping system (or another conductor) that serves to divide a flow into several parts, to combine several flows into one, or to reroute a flow to any one of several possible destinations.

master bushing n: a device that fits into the rotary table to accommodate the slips and drive the kelly bushing so that the rotating motion of the rotary table can be transmitted to the kelly.

master valve n: 1. a large valve located on the Christmas tree and used to control the flow of oil and gas from a well. Also called master gate.

mechanical rig n: a drilling rig in which the source of power is one or more internal-combustion engines and in which the power is distributed to rig components through mechanical devices (such as chains, sprockets, clutches, and shafts). Also called a power rig. Compare electric rig.

mixing tank n: any tank or vessel used to mix components of a substance (as in the mixing of additives with drilling mud).

mix mud v: to prepare drilling fluids.

monitor n: an instrument that reports the performance of a control device or signals if unusual conditions appear in a system.

mud n: the liquid circulated through the wellbore during rotary drilling and workover operations.

mud engineer n: an employee of a drilling fluid supply company whose duty it is to test and maintain the drilling mud properties that are specified by the operator.

mud-gas separator n: a device that removes gas from the mud coming out of a well when a kick is being circulated out.

mud logging n: 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 site.

mud pit n: originally, an open pit dug in the ground to hold drilling fluid or waste materials discarded after the treatment of drilling mud. For some drilling operations, mud pits are used for suction to the mud pumps, settling of mud sediments, and storage of reserve mud. Steel tanks are much more commonly used for these purposes now, but they are still usually referred to as pits.

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

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

N

natural gas n: a highly compressible, highly expansible mixture of hydrocarbons with a low specific gravity and occurring naturally in a gaseous form.

night toolpusher n: an assistant toolpusher whose duty hours are typically during nighttime hours. Also known as a tourpusher.

nipple n: a tubular pipe fitting threaded on both ends used for making connections between pipe joints and other tools.

nipple up v: in drilling, to assemble the blowout preventer stack on the wellhead at the surface.

normal circulation n: the smooth, uninterrupted circulation of drilling fluid down the drill stem, out the bit, up the annular space between the pipe and the hole, and back to the surface.

nozzle n: 1. a passageway through jet bits that causes the drilling fluid to be ejected from the bit at high velocity. 

oil n: a simple or complex liquid mixture of hydrocarbons that can be refined to yield gasoline, kerosene, diesel fuel, and various other products.

oil-base mud n: a drilling or workover fluid in which oil is the continuous phase and which contains from less than 2 percent and up to 5 percent water. This water is spread out, or dispersed, in the oil as small droplets. See oil mud.

oilfield n: the surface area overlying an oil reservoir or reservoirs. The term usually includes not only the surface area, but also the reservoir, the wells, and the production equipment.

oil mud n: a drilling mud, such as, oil-base mud and invert-emulsion mud, in which oil is the continuous phase. It is useful in drilling certain formations that may be difficult or costly to drill with waterbase mud. Compare oil-emulsion mud.

oilwell n: a well from which oil is obtained.

oil zone n: a formation or horizon of a well from which oil may be produced. The oil zone is usually immediately under the gas zone and on top of the water zone if all three fluids are present and segregated.

open hole n: 1. any wellbore in which casing has not been set. 2. open or cased hole in which no drill pipe or tubing is suspended. 3. the portion of the wellbore that has no casing.

O-ring n: a circular seal common in the oil field. O-rings may be made of elastomer, rubber, plastic, or stainless steel. To seal properly, they all require enough pressure to make them deform against a sealing surface. 

P

packer n: a piece of downhole equipment that consists of a sealing device, a holding or setting device, and an inside passage for fluids.

penetration rate n: see rate of penetration.

permeability n: 1. a measure of the ease with which a fluid flows through the connecting pore spaces of a formation or cement. The unit of measurement is the millidarcy. 2. fluid conductivity of a porous medium. 3. ability of a fluid to flow within the interconnected pore network of a porous medium.

pick up v: 1. to use the drawworks to lift the bit (or other tool) off bottom by raising the drill stem. 2. to use an air hoist to lift a tool, a joint of drill pipe, or other piece of equipment.

pipe ram n: a sealing component for a blowout preventer that closes the annular space between the pipe and the blowout preventer or wellhead.

pipe ram preventer n: a blowout preventer that uses pipe rams as the closing elements. See pipe ram.

pit level n: height of drilling mud in the mud tanks, or pits.

pit-level indicator n: 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 may sound to warn the driller of lost circulation or a kick.

porosity n: 1. the condition of being porous (such as a rock formation). 2. the ratio of the volume of empty space to the volume of solid rock in a formation, indicating how much fluid a rock can hold.

preventer n: shortened form of blowout preventer. See blowout preventer.

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

pump rate n: the speed, or velocity, at which a pump is run. In drilling, the pump rate is usually measured in strokes per minute.

pusher n: shortened form of toolpusher. 

R
ram n: the closing and sealing component on a blowout preventer. One of three types—blind, pipe, or shear—may be installed in several preventers mounted in a stack on top of the wellbore. Blind rams, when closed, form a seal on a hole that has no drill pipe in it; pipe rams, when closed, seal around the pipe; shear rams cut through drill pipe and then form a seal.

ram blowout preventer n: a blowout preventer that uses rams to seal off pressure on a hole that is with or without pipe. It is also called a ram preventer. Ram-type preventers have interchangeable ram blocks to accommodate different O.D. drill pipe, casing, or tubing.

rate of penetration (ROP) n: a measure of the speed at which the bit drills into formations, usually expressed in feet (meters) per hour or minutes per foot (meter).


remote BOP control panel n: a device placed on the rig floor that can be operated by the driller to direct air pressure to actuating cylinders that turn the control valves on the main BOP control unit, located a safe distance from the rig.

remote choke panel n: a set of controls, usually placed on the rig floor, or elsewhere on location, that is manipulated to control the amount of drilling fluid being circulated through the choke manifold. This procedure is necessary when a kick is being circulated out of a well. See choke manifold.

reserve pit n: 1. (obsolete) a mud pit in which a supply of drilling fluid is stored.

reserves n pl: the unproduced but recoverable oil or gas in a formation that has been proved by production.

reserve tank n: a special mud tank that holds mud that is not being actively circulated. A reserve tank usually contains a different type of mud from that which the pump is currently circulating. For example, it may store heavy mud for emergency well-control operations.

reservoir n: a subsurface, porous, permeable or naturally fractured rock body in which oil or gas are stored. Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. The four basic types of hydrocarbon reservoirs are oil, volatile oil, dry gas, and gas condensate. An oil reservoir generally contains three fluids—gas, oil, and water—with oil the dominant product. In the typical oil reservoir, these fluids become vertically segregated because of their different densities. 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. Volatile oil reservoirs are exceptional in that during early production they are mostly productive of light oil plus gas, but, as depletion occurs, production can become almost totally completely gas. Volatile oils are usually good candidates for pressure maintenance, which can result in increased reserves. In the typical dry gas reservoir natural gas exists only as a gas and production is only gas plus fresh water that condenses from the flow stream reservoir. In a gas condensate reservoir, the hydrocarbons may exist as a gas, but, when brought to the surface, some of the heavier hydrocarbons condense and become a liquid.

reservoir pressure n: 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.

reverse circulation n: the course of drilling fluid downward through the annulus and upward through the drill stem, in contrast to normal circulation in which the course is downward through the drill stem and upward through the annulus. Seldom used in open hole, but frequently used in workover operations.

rig n: the derrick or mast, drawworks, and attendant surface equipment of a drilling or workover unit.

rig floor n: the area immediately around the rotary table and extending to each corner of the derrick or mast—that is, the area immediately above the substructure on which the rotary table, and so forth rest.

rotary n: the machine used to impart rotational power to the drill stem while permitting vertical movement of the pipe for rotary drilling. Modern rotary machines have a special component, the rotary or master bushing, to turn the kelly bushing, which permits vertical movement of the kelly while the stem is turning.

rotary bushing n: see master bushing.

rotary drilling n: a drilling method in which a hole is drilled by a rotating bit to which a downward force is applied. The bit is fastened to and rotated by the drill stem, which also provides a passageway through which the drilling fluid is circulated. Additional joints of drill pipe are added as drilling progresses.

rotary table n: The principal component of a rotary, or rotary machine, used to turn the drill stem and support the drilling assembly. It has a beveled gear arrangement to create the rotational motion and an opening into which bushings are fitted to drive and support the drilling assembly.

roughneck n: see rotary helper.

S

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

set pipe v: see set casing.

shaker n: shortened form of shale shaker. See shale shaker.

shale n: a fine-grained sedimentary rock composed mostly of consolidated clay or mud. Shale is the most frequently occurring sedimentary rock.

shale shaker n: a vibrating screen used to remove cuttings from the circulating fluid in rotary drilling operations. Also called a shaker.

shear ram n: the component in a blowout preventer that cuts, or shears, through drill pipe and forms a seal against well pressure.

shear ram preventer n: a blowout preventer that uses shear rams as closing elements.

shut in v: 1. to close the valves on a well so that it stops producing. 2. to close in a well in which a kick has occurred.

slips n: wedge-shaped pieces of metal with teeth or other gripping elements that are used to prevent pipe from slipping down into the hole. Rotary slips fit around the drill pipe and wedge against the master bushing to support the pipe. Power slips are pneumatically or hydraulically actuated devices. Packers and other down hole equipment are secured in position by slips that engage the pipe by action directed at the surface.

slug n: a quantity of fluid injected into a reservoir to accomplish a specific purpose, such as chemical displacement of oil. 

slurry n: 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. a mixture in which solids are suspended in a liquid.

spud v: 1. to begin drilling a well; such as, to spud in. 2. to force a wireline tool or tubing down the hole by using a reciprocating motion.

spud in v: to begin drilling; to start the hole.
stabilizer n: 1. a tool placed on a drill collar near the bit that is used, depending on where it is placed, either to maintain a particular hole angle or to change the angle by controlling the location of the contact point between the hole and the collars.

stack n: 1. a vertical arrangement of blowout prevention equipment. Also called preventer stack. See blowout preventer. 2. the vertical chimney-like installation that is the waste disposal system for unwanted vapor such as flue gases or tail-gas streams.

standpipe n: a vertical pipe rising along the side of the derrick or mast, which joins the discharge line leading from the mud pump to the rotary hose and through which mud is pumped going into the hole. 

string n: the entire length of casing, tubing, sucker rods, or drill pipe run into a hole. 

string up v: to thread the drilling line through the sheaves of the crown block and traveling block. One end of the line is secured to the hoisting drum and the other to the drill-line anchor.

stuck pipe n: 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.

surface casing n: see surface pipe.

surface pipe n: 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 (meters).

surface stack n: a blowout preventer stack mounted on top of the casing string at or near the surface of the ground or the water.

swab n. a hollow mandrel fitted with swab cups used for swabbing. v. to operate a swab on a wireline to lower the pressure in the well bore and bring well fluids to the surface when the well does not flow naturally. Swabbing is a temporary operation to determine whether the well can be made to flow. If the well does not flow after being swabbed, a pump is installed as a permanent lifting device to bring the oil to the surface.

T

tertiary recovery n: 1. the use of improved recovery methods that not only restore formation pressure but also improve oil displacement or fluid flow in the reservoir. 2. the use of any improved recovery method to remove additional oil after secondary recovery. Compare primary recovery, secondary recovery. 

tight formation n: a petroleum- or water-bearing formation of relatively low porosity and permeability. 

tight sand n: sand or sandstone formation with low permeability. 

tight spot n: a section of a borehole in which excessive wall cake has built up, reducing the hole diameter and making it difficult to run the tools in and out. Compare keyseat. 

tongs n pl: the large wrenches used for turning when making up or breaking out drill pipe, casing, tubing, or other pipe; variously called casing tongs, rotary tongs, and so forth according to the specific use. Power tongs or power wrenches are pneumatically or hydraulically operated tools that serve to spin the pipe up and, in some instances, to apply the final makeup torque.

toolpusher n: an employee of a drilling contractor who is in charge of the entire drilling crew and the drilling rig. Also called a rig superintendent, drilling foreman, or rig supervisor. 

top drive n: a device similar to a power swivel that is used in place of the rotary table to turn the drill stem.

torque n: the turning force that is applied to a shaft or other rotary mechanism to cause it to rotate or tend to do so. Torque is measured in foot-pounds, joules, newton-metres, and so forth.

total depth (TD) n: the maximum depth reached in a well.

trip n: the operation of hoisting the drill stem from and returning it to the wellbore. v: to insert or remove the drill stem into or out of the hole. Shortened form of "make a trip."

trip in v: to go in the hole. 

trip out v: to come out of the hole. 

tripping n: the operation of hoisting the drill stem out of and returning it into the wellbore.

tubing n: relatively small-diameter pipe that is run into a well to serve as a conduit for the passage of oil and gas to the surface.
U

unconsolidated formation n: a loosely arranged, apparently unstratified section of rock.

upper kelly cock n: 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. 

V

valve n: 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.

W

water pump n: on an engine, a device, powered by the engine, that moves coolant (water) through openings in the engine block, through the radiator or heat exchanger, and back into the block.

water tank n: the water tank is used to store water that is used for mud-mixing, cementing, and rig cleaning. 

water well n: a well drilled to obtain a fresh water supply to support drilling and production operations or to obtain a water supply to be used in connection with an enhanced recovery program.

weight indicator n: an instrument near the driller’s position on a drilling rig that shows both the weight of the drill stem that is hanging from the hook (hook load) and the weight that is placed on the bottom of the hole (weight on bit).

weight indicator n: a device for measuring the weight of the drill string.

weight on bit (WOB) n: the amount of downward force placed on the bit.

well n: the hole made by the drilling bit, which can be open, cased, or both. Also called borehole, hole, or wellbore.

wellbore n: 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.

well control n: the methods used to control a kick and prevent a well from blowing out. Such techniques include, but are not limited to, keeping the borehole completely filled with drilling mud of the proper weight or density during operations, exercising reasonable care when tripping pipe out of the hole to prevent swabbing, and keeping careful track of the amount of mud put into the hole to replace the volume of pipe removed from the hole during a trip.

well fluid n: the fluid, usually a combination of gas, oil, water, and suspended sediment, that comes out of a reservoir. Also called well stream. 

wellhead n: 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.

well logging n: 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.

WOB abbr: weight on bit.