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.
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