There are many different designs and configurations of CTunit. Most have evolved over a relatively short period as theunderstanding of criteria critical to the reliability of CTservices have become better understood. In addition, theoperating conditions in many geographical areas oftendetermine the most appropriate CTU design.
Regardless of manufacturer, model and design, every CTUcomprises the following principal items.
• Injector head
• CT reel
• Power pack
• Control cabin
• Pressure control equipment
The following section provides an overview of these itemsof CT equipment, describing their function and principalcomponents or subsystems.
1 COILED TUBING INJECTOR HEAD
1.1 Description
The coiled tubing injector head provides the effort andtraction necessary to run and retrieve the CT string into andout of a wellbore. Several hydraulic systems are used toenable the coiled tubing unit (CTU) operator to exercise ahigh degree of control over any CT string movement. Athorough understanding of the injector head control andmonitoring systems is essential to ensure the equipment isoperated efficiently, safely and without risk of damage tothe well equipment, pressure control equipment, CT stringor the CTU.
1.1.1 Principal Functions
The basic functions required of all CT injector headsincludes safely pulling, pushing and holding the CT stringunder the specific wellbore and treatment conditions.However, there are several secondary or support functionsthat are vital to ensure safe and reliable CT operations.
The following functions apply to the majority of injectorheads.
• Pull the CT string
• Push the CT string
• Hold the CT string
• Guide and support the CT string
• Secondary/support functions include:
• Weight indicator mount
• Depth system mount
• Stripper mount
Pull (Tensile Force)
The injector head pull capacity should be compatible withthe weight of the CT string in use plus:
• Effect of fluid density inside/outside the CT string
• Overpull (tension) to be applied at the BHA
• Effect of drag (friction) caused by the string or BHA
• Friction or drag created by the stripper(s)
Push (Snubbing Force)
The injector head snubbing capacity should be compatiblewith:
• The force required to overcome the wellhead pressure
• Acting on the cross-sectional area of the CT string
• Friction or drag created by the stripper(s)
Hold
The injector head should be capable of safely holding theCT string stationary. This holding function should beavailable with the hydraulic systems or power pack in both
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normal operating conditions and disabled modes. In addi-tion, the transition from stationary to in-hole and out-of-holemodes should be smooth and easily controlled.
Guide the tubing
Components of the injector head (guide-arch or gooseneck)serve to support and guide the CT string from the delivery(fleet) angle of the reel into the wellbore.
Weight indicator mount
Injector heads are typically configured with the traction anddrive components mounted on a “floating” inner chassis.This is contained within a fixed outer frame with the weightindicator sensor(s) connected between the two frames.
Depth system sensor
The injector head provides a convenient mounting positionfor friction wheel depth measurement systems. At least twoindependent sensors are typically required on every CToperation, e.g., one reel mounted and one injector headmounted system.
Stripper mount
The primary stripper is generally permanently mounted tothe injector head. Unless the injector head is otherwisesupported, the mounting point bears all of the forcesnecessary to run and retrieve the CT string. The strippermount also provides a reference point with which the drivechains and guide-arch are ultimately aligned.
1.2 Features
The design and configuration of injector heads have devel-oped over several years to meet specifications whichreflect the evolving nature of CT applications. The trendtoward larger tubing sizes which enable greater circulationrates, requires the injector head be capable of handling awider range of tubing. Similarly, since CT has commonlybecome the preferred intervention method in extendedreach or horizontal wells, the “average string” length hasincreased in recent years. These factors, especially incombination, demonstrate the increased demands beingplaced on injector heads and other key items of CT handlingequipment.
The global CTU fleet includes several injector head models,the most common of which are shown below.
The explanation of systems and components in this manualsection will be generic although some of the more signifi-cant variations in design, specification and operation maybe outlined.
The principal features and components of injector headsare illustrated in Figures 1 through 5.
The capacity (maximum pull) of an injector head is themajor factor in determining the operating capability of theCTU. The table in Figure 5 summarizes the key perfor-mance data and specifications of common injector headmodels
The principal components of an injector head can becategorized in the following systems or major assemblies.
• Drive and brake system
• Chain assembly
• Traction and tension system
• Guide-arch assembly
In addition, secondary or support systems, include:
• Weight indicator
• Depth sensor mounts
• Stripper mount
1.2.1 Drive and Brake Systems
Note: The injector head drive and brake systems arecapable of exerting high forces on the CT string, wellboretubulars or wellhead equipment. Significant damage mayresult if the systems are not operated, controlled or moni-tored correctly. Therefore, it is vital that the CTU operatoris aware of the design and layout of the specific system inuse. The operator must be familiar with the location andsetting of the system control and relief valves. In addition,the limitations of the CT string must be understood whenadjusting system pressures etc. to avoid the application ofexcessive force to the string.
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Figure 1. Typical injector head.
Stripper assembly
Injector drive motor
Gooseneck
Accumulator
Stripper assembly
Lubricant reservoir
Inside chaintension system
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Figure 3. - Hydra-Rig HR 440. Figure. 4 Stewart and Stevenson SS 400.
Figure 2. - Hydra-Rig HR 480.
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Figure 6. Injector head specification table.
Figure 5. Stewart and Stevenson SS 800.
Injector Model Approximate Dimensions Snub Pull CT Size RangeHeight(in.)
Width(in.)
Weight(lb)
Depth(in.)
(in.)
HR240
HR260
HR440
HR480
SS 400
SS 800
164
180
80
109
82
82
52
52
52
60
42
42
7,800
9,200
6,750
11,200
5,700
6,125
55
55
55
60
58
58
40
60
60
100
40
80
1 to 1-3/4
1 to 2-3/8
1 to 2-3/8
1-1/4 to 3-1/2
3/4 to 3-1/2
3/4 to 3-1/2
Capacity(x1,000 lbs)
20
20
20
40
20
20
R T- 20
M A R I TI M E H YD R AU L I CS ( CA N) L TD .CA LG AR Y, ALB ERTA, CANA DA
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All injector heads currently in common use are hydraulicallydriven using either two or four hydraulic motors. The motorsare typically connected and synchronized through a gearsystem located at the top of the injector head. Drive isdirected to the chain drive sprockets (one for each injectorchain set) via the drive shafts located at the top of theinjector head.
The direction of rotation and speed of the motors iscontrolled and shifted by a four-way hydraulic control valvelocated on the CTU power pack. The functions of thehydraulic valve, plus the hydraulic system pressure andrate, are remotely controlled from the CTU control console.
Protection devices, such as pressure relief valves andcrossover relief valves, are installed in the system toprotect the tubing and hydraulic components from damagedue to operator error or component failure.
The injector-head brake is generally mounted integral to themotor assembly and is hydraulically controlled. Hydraulicpressure is required to release the brake so the system isconsidered fail-safe in operation. Application of the brake istypically automatic and controlled by the drive systemhydraulic pressure, i.e., the brake is applied when the drivesystem hydraulic pressure falls below a preset value.
Some early injector heads are equipped with hydraulicbrakes controlled manually from the control console. Onearly models of Uniflex injector heads, external pneumati-cally operated disc brakes were fitted.
Several injector head hydraulic motors are equipped with aninternal speed shift facility which provides a high/low gearoption that can be selected remotely from the CTU thecontrol console. Two speed capability allows the injectorhead to operate more efficiently with the available hydraulicpower supply, i.e. supply pressure and rate. When set in lowspeed mode the injector drive motors can apply maximumtorque or pulling force. In high speed mode, available pullingforce is typically halved and the running speed doubled.
The injector head drive system includes several compo-nents necessary for control and safety purposes. Almostall injector heads are equipped with two pilot-operatedcounterbalance valves, located on the injector drive sys-tem lines between the drive motors and the pressure filters.The valves function as load holding valves by closing themotor outlet line until a pilot pressure, obtained from themotor inlet line, is sufficient to open the valve. Thisarrangement enables a smooth transition between station-ary and operating modes. In addition, it enables the weightof the CT string to be supported by the hydraulic fluidtrapped by the counterbalance valve, effectively providing
Figure 7. CT chain assembly on tubing
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a fail-safe facility in the event of brake failure.
The hydraulic lines between the counterbalance valves andthe motor are high-pressure welded steel pipe. This is asafety feature since the line can contain hydraulic fluid athigh-pressure while the string load is held by the counter-balance valve.
High pressure filter assemblies are fitted on the injectorhead to protect the motor from extraneous materials whichmay be trapped during rig-up of the drive hose connections.
Hydraulic Supply System Overview
Coiled tubing units are designed with two basic options forthe primary injector drive hydraulic system, i.e., open orclosed loop. Actual operation of the injector head and CTUdiffers little between the two systems, however, eachsystem has associated advantages and disadvantages.
System pressure is controlled by pilot operated reliefvalves located on each circuit. The maximum pressure foreach circuit is preset by adjusting the relief valve (typicallylocated on the power pack). The system pressure can thenbe controlled from zero up to the preset maximum by
operating the pilot valve on the control console. Thesesystems enable the operator to preset the maximum forcethat can be applied to the tubing.
Some injector heads are offered with auto-driller controloptions. The purpose of auto driller control systems is toincrease the operator’s ability to control the injector head atvery slow speeds, such as may be encountered duringdrilling operations. Most systems also enable finer controlof the force exerted on the tubing.
1.2.2 Chain Assembly
The majority of injector heads are configured with two setsof opposing endless chains on which are mounted a seriesof gripper blocks. The gripping profile of each block isprecisely shaped to suit a specific tubing size. To facilitatelarger tubing sizes and the increasing range of sizescommonly used, chain designs with removable gripperinserts are commonly specified on most new injectorheads. The gripper insert enable a range of tubing sizes tobe run without the need to remove and replace the entirechain assembly. This facility reduces the time and effortrequired to reconfigure the injector head when running adifferent size of CT string. In addition, gripper inserts
Figure 8. HR240/260 chain assembly
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reduce the inventory items (quantity and cost) required forreplacement when the gripper contact area becomes worn,or redressing when another tubing size is to be run.The force required for the chain to provide adequate grip onthe tubing string is provided by the inside chain tensionersystem (also known as the skate system or tractiontensioner system). This force is applied to the back of thechain assembly. To enable the chains to rotate easily withrelatively high loads applied, the chains are fitted withbearings which roll smoothly over the tensioner systemcomponents while transmitting the load.
Some special applications may require tapered OD stringto be run, e.g., 1-1/2-in. and 1-3/4-in strings joined and hungoff in a velocity string installation. The ability to change thechain gripper inserts as the tubing join passes through theinjector head provides a clear advantage in such applica-tions.
The entire CT string load is held by the face of the gripperblock or insert. This is often achieved under significantforce. Therefore, the selection, operation and maintenanceof chain components should be undertaken with a view tominimizing the risk of damage to the CT string andoptimizing the life expectancy of consumable components.Recent studies indicate that even relatively light damageon the string surface can have a significant effect on the
predicted fatigue life of the string. Consequently, the effectof any components and equipment in contact with the stringsurface should be understood and carefully monitored.
The majority of chain systems are assembled from stan-dard ANSI chain components and custom built partsenabling relatively easy replacement of worn or damageditems. The principal chain components and assembliescommonly found on injector heads are shown below. Arelatively recent chain design featuring a single chaintraction system is also included.
HR 240/260 Chain Assembly
The HR 240/260 chain assembly incorporates a singlepiece gripper block design which is compatible with onlyone tubing size. This design was generally regarded as theindustry standard until the introduction of chain with re-placeable inserts. With the introduction of larger tubingsizes, a limitation of the single piece gripper resulted fromthe limited space afforded by the relatively small chainpitch used in early injector heads. Larger pitch chains wereintroduced on some injector head models, However, theflexibility of the insert chain system brought obviousadvantages.
The HR 480 chain assembly incorporates carrier blockseach of which contains two gripper inserts. The inserts aresupported by elastomeric elements which help ensure aneven application of the gripping force transmitted to the CTstring. This system is designed to reduce the risk ofdistorting the CT string when high loads are applied in deepor heavy-duty applications. The gripper block contact faceis machined with a smooth surface and profile to minimizethe risk of damaging the CT string surface. Gripper insertsare available in a range for 1-1/4-in. to 3-1/2-in.
Gripper inserts are secured to the carrier block by a detentprofile and held in place by a locking pin which locatesthrough the side of the carrier block.
SS 800 Chain
Stewart and Stevenson injector heads are equipped withthe Varia-Block chain system which can be fitted withgripper inserts to suit a range of CT string sizes from 1-in.through to 3-1/2-in. The gripper insert is secured within thegripper block by a detent profile and locked in place by a
spring loaded locking pin which protrudes from the carrierblock into the back surface of the insert.
The Varia-Block chain system is designed so the as-sembled chain has a flat back which rides on the rollersmounted on the chain tension or traction system, i.e.,unlike conventional chains the Varia-Block chain assemblyhas no roller bearings.
DRECO Chain
The DRECO chain and drive system features a uniquesingle chain system. A hinged gripper assembly is housedin a carrier assembly (bucket) which in turn is attached tothe drive chains. The chain assembly is aligned with thetubing axis thereby reducing eccentric loading on the chainand gripper components. In addition, the hinged gripperarrangement ensures that the gripping force is isolated fromthe drive chain components. These features are intendedto provide smooth operation and long component life.
Gripping force is applied to the tubing through the action ofthe hinged gripper block. The cam rollers on the griper blockarms are forced closed by pressure beams which are ineffect the equivalent of conventional skates or tensionerbars. Hydraulic rams are used to control the force appliedby the pressure beams using a control and monitoringsystem similar to convention hydraulic tensioners.Chain Lubrication
Injector head chains are submitted to significant forces anda high degree of movement during operation. To ensure thecomponents function efficiently over an optimized chainlife, efficient lubrication of moving components is required.This should be achieved without jeopardizing the essentialfriction between the tubing and the gripper block or insert.The lubricating oil is typically SAE 30, or equivalent.
The fluid reservoir and control manifold are typically mountedon the injector head enabling the system to be remotelyactivated from the CTU control cabin. In addition to lubricat-ing the chain components, the lubrication system is alsosometimes used to lubricate the timing gears which syn-chronize the multiple motor and chain drive train.
1.2.3 Traction and Tension Systems
The injector head traction or inside chain tensioner system,(also known as the skate system) provides the forceFigure 13. HR240/260 chain tension assembly.
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required to securely grip the tubing in the chain gripperblocks. The necessary force is provided by a hydraulicsystem which is typically split into three distinct sub-systems, i.e., top, middle and bottom traction systems.This enables some flexibility in operation and provides ahigh degree of contingency or back-up for one of the mostimportant injector head functions.
The inside chain tensioner pressure required during a CToperation is a function of the tubing load, size, condition,gripper-block condition and presence of oil or similarbetween the tubing and block. Since the consequences ofattempting to run CT with too little inside tension on thechains can be catastrophic, the natural tendency of theoperator is to apply excessive pressure to the system.While in operating terms this should ensure adequatecontrol over the tubing slip, it will almost certainly besufficient to significantly affect the life span of the injectorchain bearings and the CT.
The force is hydraulically applied through three separatesets of hydraulic cylinders. Each set is independentlycontrolled and monitored from the control cabin. The use ofthree separate sets reduces the risk of a major operatingfailure should a component in the system fail.
To ensure adequate tension is maintained in the chainsection outside the vertical drive plane, the injector head isfitted with an outside chain tensioner system. Currentproduction injector-head models are equipped with a hy-draulic tensioner system which is controlled and monitoredfrom the control console. Hydraulic rams provide thetension by acting on the external idler gears. The idler gearsare allowed to float horizontally allowing both chains to betensioned with a single set of rams. Early injector headdesigns required that the tension be checked and adjustedmanually through a mechanical adjustment mechanism.
The chain tension applied is based on the injector-headmanufacturer’s recommendations for the specific operat-ing conditions. The outside chain tension is critical whilethe tubing is being injected with a negative load on theinjector chains (while snubbing against high wellheadpressures). Damage to the CT string and chain drivecomponents may result if outside chain tension is notproperly applied under these conditions.
Figure 14. Comparison of guide arch sizes and recommended guide arch radii.
The gooseneck and pipe straightener (where fitted) act asa guide, turning the tubing through the angle between thewellhead and the CT reel. The CT string is supported byrollers located at ±10-in. intervals around the gooseneckcircumference. The top rollers used to restrain the tubingare removable to enable easier installation and removal oftubing from the injector head. The guide arch rollers aretypically profiled with a “V” of 120° and may be manufac-tured from steel, aluminum or polyurethane. Most guidearch designs incorporate a flared end which reduces therisk of damage to the tubing caused by misalignment whenthe tubing is being spooled to the edges of the reel drum.This is especially noticeable when the reel is located closeto the injector head.
The guide arch radius has a significant influence on thefatigue induced in the CT string, e.g., a 50 in. radius guidearch will have a more detrimental effect on tubing life thana 72-in. radius guide arch. Guidelines extracted from APIRP 5C7 are shown in Figure 14 for various tubing sizes.
The pipe straightener, where fitted, is located immediatelyabove the injector head. It performs two main functions.
Figure 15. Weight indicator equipment.
Figure 16. Depth measurement equipment.
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• Ensures the tubing is as straight as possible beforeentering the injector-head chains.
• Guides the tubing cleanly into the injector-head chains,thereby reducing damage caused by misalignment.
The pipe straightener generally consists of one adjustableroller located between two fixed opposing rollers.
1.2.5 Weight Indicator
The weight-indicator load cell (or strain gage on electronicweight indicators) is typically located on the lower frontedge of the injector head. The weight or load information istransmitted, from the load cell to the weight-indicator dial ordisplay, either electronically or hydraulically.
The injector-head frame is typically constructed in twodistinct assemblies comprising the inner and outer frames(see Stripper Mount section). Pivot points between theframes enable the weight-indicator load cell to accuratelymeasure the force between the assemblies. Such forcemay act up or downward, resulting from the weight of the CTstring (tension) or action of high wellhead pressure (com-pression).
1.2.6 Depth Measurement Equipment
Depth measuring equipment, electronic or mechanical, isfrequently mounted on the injector head. Depth informationis commonly gathered by two methods.
• Mounting a friction-wheel-type counter assembly betweenthe injector chains and stripper, or
• Mounting an encoder assembly to the injector-head chaindrive shaft.
1.2.7 Stripper Mount
The outer frame of the injector head is equipped with astripper mount facility which secures the injector head tothe pressure control stack. The stripper is generally perma-nently bolted in place. With the injector head outer framefixed to the pressure control stack and the inner injectorhead assembly supporting the tubing string, some limitedmovement is allowed to ensure correct alignment andoperation of the weight indicator load cell.
In some larger models of injector head, the stripper ismounted on a subassembly which can be removed duringtransportation.
Figure 17. Typical CT reel configuration.
Reel drum
Tubingmeasurementand coatingaccessories
Levelwindassembly
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2 COILED TUBING REEL
2.1 Description
The primary function of the coiled tubing reel is to safelystore and protect the CT string. This should be achievedwhile avoiding excessive damage to the string throughfatigue (bending) or mechanical damage from spooling. Inaddition, the reel typically incorporates several featureswhich, although less obvious, are equally important to thesuccessful operation of the CTU. Most significant of whichis the swivel facility which enables fluids to be pumpedthrough the tubing string while the reel drum rotates.
Almost all reels rely totally on hydraulic power to operatethe drive, braking and spooling guide (levelwind) systems.Previous reel designs have used pneumatics, or a combi-nation of pneumatics and hydraulic power, to control someof the brake and levelwind systems.
The reel levelwind is frequently used as a mounting positionfor a variety of tubing protection, monitoring and measuringequipment.
Figures 17 identifies the principal components of a typicalCT reel.
Figure 20. Skid mounted reel. Figure 21. Special application reel.
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2.2 Features
CT Reels are commonly available in a number of configu-rations and can be categorized as shown below. Localconditions and the nature of the CT operations will deter-mine the type of reel required.
• Truck mounted (fixed) - permanently fixed to the truckchassis (Figure 18)
• Truck mounted (skid) - may be changed out (Figure 19)
• Skid mounted - for offshore operations (Figure 20)
• Trailer mounted - for large capacity (length) or heavyweight strings
• CT logging reel - fitted with electrical swivel/collector
• Special application reel - typically for completion applica-tions (Figure 21)
With the advent of larger CT sizes, that are installed ascompletion tubulars, there is increased use of special reelsand spooling stands designed to handle large tubulars.These structures typically enable the shipping spool to befitted in place of the drum assembly, thereby avoidingunnecessary spooling, which in large tubing sizes can bedifficult and hazardous.
The evolution of CT string sizes and the general trendtoward longer CT work strings has resulted in manydifferent reel designs, many of which are still in commonuse. However, the facilities and components identifiedbelow are found on almost all reels:
• Reel drum
• Reel drive and brake systems
• Reel swivel and manifold
• Levelwind assembly
• Depth measurement accessories
• Tubing lubrication equipment
• Crash protection frame
2.2.1 Reel Drum
The reel drum assembly typically consists of a reel drum,axle, flanged connection on the axle to allow the swivel tobe connected, and chain sprocket on the axle by which thedrum is driven. A second chain sprocket on the axle is oftenused to drive the levelwind leadscrew. Direct drive reelshave a motor and gearbox mounted directly on the axle. Thereel axle bearings are mounted and secured on supportposts which form part of the reel chassis.
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Figure 22. Reel drum capacity.
A facility to lock the reel drum while being transported isrequired on all reels. This is commonly achieved bysecuring with a chain and binder between the reel drum rimand a point on the reel chassis. This must be in addition toany hydraulic or pneumatic brake which is operated fromthe control cabin. Reels that have wireline installed requirea modified axle to allow an electrical collector to be fitted tothe axle.
The theoretical tubing capacity (Figure 22) of any drum canbe calculated using the procedure shown below. Thismethod of calculation assumes perfect spooling across thewidth of the drum. Since in practice this is difficult toachieve, an allowance must be made to maintain the reelcapacity within its practical limitations.
L = (A+C) (A) (B) (K)
where:L = tubing capacity (ft)A = tubing stack height (in.)B = width between flanges (in.)C = reel drum core diameter (in.)K = K value for different tubing sizes.
Figure 23. Reel back tension.
A
B
C
Freeboard
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The K values for different tubing sizes are:
Tubing OD (in.) K value1 0.262
1-1/4 0.1681-1/2 0.1161-3/4 0.086
2 0.0662-3/8 0.0462-7/8 0.0323-1/2 0.021
The freeboard is the amount of clearance between the ODof the reel flanges and the OD of the wrapped tubing atmaximum capacity (L). The minimum recommended free-board varies with the tubing size:
Tubing OD (in.) Freeboard (in.)1 and 1-1/4 1.5
1-1/2 and 1-3/4 2.02 3.0
>2 10.0
2.2.2 Reel Drive/Brake Systems
All reels are hydraulically driven, although the controlsystem and type of motor vary between manufacturers andreel models. Most reels can be powered in an “in-hole” and“out-hole” direction. However, during normal operations,only the out-hole option should be selected, since it is theaction of the reel drive motor in this direction that providesthe back tension applied to the CT string while running inand out of the well.
The hydraulic pressure in the drive system can be varied tocontrol the torque output of the motor which allows thetension on the tubing (between the injector head and reel)to be varied. Generally, only sufficient tension to keep thetubing straight between the reel and injector head should beapplied (Figure 23). Applying excessive tension may resultin premature failure of the hydraulic and drive componentsor damage to the tubing. This combined with incorrectspooling will almost certainly result in some tubing damage.
The amount of hydraulic pressure required to achieve asatisfactory tension will depend on the amount of tubingcontained on the reel and the distance from the injector
Figure 24. Typical reel manifold configuration.
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head. The distance from the reel axle to the top tubing wrapmay be regarded as a lever through which the drive systemtorque must be transmitted to tension the tubing string. Thegreater the distance, the more torque will be required tomaintain a constant tension. To increase the torque outputof the drive system, the hydraulic pressure must beincreased. Therefore, while pulling out of the well, thedistance from the reel axle to the top wrap is increased,requiring that the hydraulic pressure in the drive systemmust be increased to keep a constant tubing tension. Whilerunning in the hole (RIH), the pressure required to maintainsufficient back tension will reduce as the number of wrapson the drum is reduced.
In addition to the torque changes with varying reel capacity,the change in weight will also affect the pressure requiredto drive the reel. This is particularly noticeable whenstarting from rest especially when the reel contains high-density fluids or electric cable.
The reel drive motor is either mounted on the base of thereel chassis, or mounted directly on the axle. If mounted onthe reel chassis, it is connected by a chain and sprocket tothe reel axle.
Reel brake systems may be air or hydraulically operated.Most current models have a hydraulic reel brake incorpo-
rated within the motor assembly. This is set/released by adedicated hydraulic circuit which is controlled from thecontrol cabin.
Generally, the reel brake is applied whenever the tubing isstationary. However, consideration must be given to theconsequences of actions or operations which may affectthe stability of the CT string in the injector head, e.g. if high-density fluid is to be pumped through the CT at depth, theincrease in weight may cause the CT to slip through theinjector chains. With the reel brake applied, the resultingforce/tension would then be applied to the reel.
2.2.3 Reel Swivel and Manifold
The design and configuration of reel swivels and manifoldsvary according to the manufacturer and model of the reel.Early models were of simple design and often containedthreaded connections on the swivel or manifold. It is arequirement many organizations that all treating equipmentbe of integral or of non-pressure union construction. Thisrestriction also prevents the use of Swagelok fittings toconnect the tubing end within the reel core. Therefore, theCT string is typically terminated with a 1502 Weco unionwhich has been welded in place and has undergone therequired quality control procedures.
Figure 25. Reel levelwind assembly.
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All reels should have a valve fitted as close as practical tothe end of the CT string. This valve can be closed in theevent of a swivel seal failure while the CT is being run,thereby isolating the contents of the string. Reels that havewireline installed require a modified manifold to enablewireline access (pressure bulkhead) downstream of theisolation valve.
The reel fluid manifold is generally considered in two parts- the external manifold which consists of treating ironoutboard of the swivel, and the internal manifold which ismounted within the reel core.
2.2.4 Levelwind Assembly
Accurate and even spooling of the CT onto the reel drum isimportant for several reasons:
• Badly spooled damage is liable to damaged at the contactpoints. Even apparently minor surface damage can affecttubing life or performance.
• For the reel drum to achieve maximum capacity the CTmust be properly spooled.
Figure 26. UTIM device mounted on CT reellevelwind.
Figure 27. CTL reel configuration.
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• Poorly spooled tubing may shift and slacken on the reelwhile being transported. This may result in damage orproblems when the tubing is drawn from the reel for thenext operation.
• Corrosion protection of the external surface is moreeffective if the tubing is closely and evenly spooled.
To help achieve a satisfactory spooling standard, thelevelwind assembly guides the tubing onto the reel drumand automatically follows the progress of the spoolingtubing. A manual override facility allows minor adjustmentsto be made to the position of the levelwind head whenrequired. In addition, some vertical adjustment of thelevelwind assembly is necessary to allow the fleet angle oftubing to suit the equipment rig-up.
2.2.5 Tubing Measurement Accessories
The levelwind travelling head provides an ideal mountingposition for friction wheel depth counters or encoders.Back-up mechanical counters that display large-sizeddigits can, in most cases, be read from the operator’sconsole. The travelling head also provides the mountingposition for tubing monitoring equipment such as the DowellUniversal Tubing Integrity Monitor (UTIM) device.
2.2.6 Tubing Lubrication Equipment
Current reel designs include a fixed tubing lubrication/inhibition system, part of which is permanently mounted onthe reel chassis, with the control system located on theoperator’s console.
2.2.7 Crash Protection Frame
The degree of protection required depends on anticipatedapplication and use of the CTU (e.g. offshore skid-mountedor truck-mounted reel). In addition to the practical efficiencyof the crash frame, consideration must be given to therequirements of certifying or regulatory authorities. Forexample, a DNV certified unit for offshore use must havea fitted reel roof, coated with a non-slip material, to assistthe seamen in attaching the load to the crane hook.
2.2.8 Wireline Reels
Wireline reels are used in CT logging operations andincorporate a logging cable installed inside the CT string
which is used to transmit power and data between the BHAand surface equipment.
The following items are required to complete the surfaceequipment hook-up associated with the CT reels to be usedon coiled tubing logging operations:
Pressure Bulkhead (PBH)
The pressure bulkhead is used to allow electrical connec-tion of the reel mounted electrical components to thelogging cable inside the CT string. This must be achievedwhile maintaining the pressure integrity of the reel manifold.
Reel Collector
The reel connector is used to allow an electrical connectionto be made between the cable in the rotating reel core andthe surface electrical equipment.
3 CT POWER PACK
3.1 Description
The function of the power pack may be simply stated asproviding the hydraulic power to operate the coiled tubingunit (CTU) and pressure control equipment, e.g., BOPsystem. To perform this function satisfactorily under var-ied conditions and for the duration of any coiled tubing (CT)operation, current generation power packs are designed tooperate independently of exterior power or air supplies oncestarted.
In addition to the hydraulic power supplied when running,the power pack incorporates an accumulator facility toallow limited operation of pressure control equipment fol-lowing engine shutdown.
A compressor mounted on the engine provides an airsupply for operation of the engine controls and pneumaticsystems on the CTU, e.g., the stripper air-operated pump,injector-head chain lubrication, lights and transfer pumps.The power-pack air receiver will provide sufficient storageto allow an engine restart shortly after shutdown, providedthe unit pneumatic systems are isolated.
The environment in which the CTU is to operate willdetermine the engine protection facilities required by therelevant local and national authorities. For example, off-
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shore skid units operating in the North Sea are required tobe fitted with an engine (and electrical, where fitted)protection package that allows the unit to be operated inZone II areas, hence the designation of Zone II unit.
The CTU configuration will determine the location of thepower pack and corresponding control equipment.
• Truck or trailer mounted using the truck engine as a powersource.
• Truck or trailer mounted with an independent powersource.
• Skid mounted with the control cab and power packincorporated on one skid, designated a three-piece unit,i.e., control cab/power pack, reel and injector-head/BOPtransport basket.
• Skid mounted with the control cab mounted separatelyfrom the power pack, designated as a four piece unit.
Regardless of the type of unit to which the power pack isfitted, the function and facilities contained within the powerpack will be similar.
Successful operation of the CTU requires the delivery ofprecisely controlled hydraulic power on demand. Mainte-nance checks performed on the CTU, such as thoseidentified in the CT STEM program, are designed to ensure
continuing satisfactory operation of all CTU functions. Theimportance of the relevant power-pack checks being thor-oughly and regularly completed is obvious. In addition thecompletion of the required reports will provide a usefulrecord of the power unit performance, identifying possibleproblems before the operation of the CTU is affected.
3.2 Features
The majority of CTUs in use are assembled by Hydra-Rig.The evolution of CTU design to the current standards hasresulted in several different designs of the power packbeing supplied. Figure 28 shows the power pack/controlcab skid from a three-piece Hydra-Rig CTU.
In general, all power packs will include the following majorcomponents:
• Engine
• Hydraulic pumps
• Pressure Control Valves
• Hydraulic Reservoir
• Filters and Strainers
• Hydraulic Fluid
Figure 28. CT power pack.
Lay er 1Hig h Coola ntTem p eratu re
High Exhau stTem pe ratu re
Low OilPre ssure
Lo ss of C oola nt
Coo lant Te mper atur e
OilPr essu re
En gine Tach omet er
AirPr essur e
Per missive star t
Eng ineKill
Em ergen cyKill
St art
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• Heat Exchanger and Thermostatic Valve
• Accumulator
Operation, or even start-up of the CTU power pack, mustnot be attempted until a series of maintenance and opera-tional checks has been completed. Failure to follow theprestart-up procedure may expose equipment and person-nel to unacceptable risks.
The prestart-up operational checks will vary with thelocation and application of the CTU but should include thefollowing points as a minimum requirement.
• Ensure any location requirements, such as a permit towork systems, are complied with fully and that actionsneed for such requirements have been completed, e.g.,positioning of gas detecting and fire-fighting equipment.
• Ensure operating and associated personnel are aware ofthe above requirements, and that only qualified personnelare authorized to operate the equipment.
3.2.1 Power-Pack Engine
Almost all engines fitted to CTU power packs are of theGeneral Motors Detroit series. They may be of 8V, 6V or(more recently), six cylinder, in-line configuration. Coiledtubing units manufactured after 1990 are likely to be fittedwith Caterpillar engines. This is primarily due to the superiorengine noise and emission control specifications achievedby the Caterpillar engine.
Engine controls are likely to be remotely operated from thecontrol console and from the engine control panel locatedon the power pack. Some three-piece units may only beequipped for single-station operation, i.e., all engine con-trols are located on the operator’s console.
The following engine controls are found on standard enginesets.
• Engine Start
• Engine Stop
• Emergency Kill
• Engine Throttle
Engine instrumentation will generally include the following.
• Oil Pressure Gauge
• Coolant Temperature Gauge
• Air Pressure Gauge
• Ammeter (where applicable)
3.2.2 Hazardous Area Designation
Engines and electrical equipment are often required to bespecially protected or isolated before their use is permittedin certain environments.
The identification of designated hazardous areas or zonesin and around wellhead and process plant areas is theprincipal basis upon which equipment suitability is as-sessed. The extent of the zoned area is generally deter-mined by the relevant national authorities. Consequently,international variations exist both in terminology of areasand in the extent to which they apply; however, zoned areaswill generally be based on relevant API guidelines.
The inspection and certification of equipment as being incompliance with the operator’s standards are often con-ducted by third-party inspection companies. Examples areDet Norske Veritas (DNV) and the American Bureau ofShipping (ABS).
3.2.3 Zone II Engine Protection Equipment
Diesel engine driven equipment that is intended for usewithin Zone II areas and which is in compliance with themost rigorous standards set by operating companies willtypically be fitted with the following engine protectionequipment.
• Air-inlet shutoff valve - designed to shut down the enginewhen an overspeed condition is detected by increasedairflow through the shutdown valve or by the overspeedgovernor, where fitted.
• Liquid-cooled exhaust gas manifold/heat exchanger.Designed to maintain engine surface temperatures below392°F (200°C)
• Exhaust gas spark arrestor and flame trap
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• Engine breather and air-box breather flame traps
• Screw-secured oil-filler cap and dipstick
• Heavy-duty radiator
• Plastic blade fan
The protection package will initiate engine shutdown in twoways.
• In the case of engine overspeed, by closing the air-inletshutoff valve.
• In the case of high exhaust temperature, high watertemperature and low engine oil pressure, by cutting off thefuel supply, generally by an actuator moving the enginefuel rack.
3.2.4 Hydraulic Pumps
The hydraulic pump array will vary with the model andmanufacturer of the CTU. The hydraulic systems on mostCTUs consist of balanced vane type pumps operating in anopen-loop system (Figure 29).
Balanced vane-type hydraulic pumps for this applicationare commonly supplied by Abex Denison. Most of themodels used are high-performance double pumps, therebyallowing two separate hydraulic systems to be run from onepump assembly. In this case, the pump contains twoseparate pump cartridges supplied by a common suctionline but having separate discharge ports. The constructionof the pump body allows cartridges of a different size, andtherefore output, to be fitted. Consequently, the outputcapability of the hydraulic pump array is tailor made to therequirement of the system it supplies.
3.2.5 Pressure Control Valves
Each hydraulic circuit must be fitted with a device to controlthe maximum pressure within the system. On Hydra-RigCTU hydraulic circuits, this is achieved in several ways.
• Preset relief valves
• Pilot-operated relief valves
• Unloader valves
Figure 29. Open and closed loop hydraulic systems.
Injector headdrive motors
Injector headdrive motors
Return flow to reservoir
Fixeddisplacement
pump
Variabledisplacement
pump
Directional,pressure andflow control
valves
Load holding(counterbalance)
valves
Directionalcontrolvalves
Crossoverreliefvalve
Open loop:
Closed loop:
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Preset Relief Valves
This type of valve is manually adjusted and set to themaximum desired pressure in the system. Once thispressure is reached, the relief valve lifts allowing excessflow to be directed back to the hydraulic reservoir. Thisaction imparts considerable energy to the hydraulic fluid,causing the system temperature to rise if the valve relievesover a prolonged period.
Pilot-Operated Relief Valves
Pilot operated relief valves are similar to preset reliefvalves, but have the additional facility of allowing the reliefpressure to be remotely controlled by a pilot control valveconnected to the relief valve by a pilot control line. Thepressure may be remotely varied up to the preset maximumsetting of the relief valve.
Unloader Valve
Unloader valves are similar to relief valves, but differ in thatwhen the preset maximum pressure is reached, the valvereacts to isolate the system and direct the flow to thereservoir under no load. When the system pressure isreduced, the valve opens to recharge the system, closingagain when the desired pressure is reached. Unloadervalves are commonly fitted to systems that require littleflow during operation and that are also fitted with accumu-lators. Hydraulic circuits that supply BOP operating pres-sure are generally fitted with an unloader-type valve.
3.2.6 Hydraulic Fluid Reservoir
The hydraulic fluid reservoir performs several functions.
• Stores the hydraulic fluid
• Allows the fluid to cool
• Allows settling of dirt and metal particles
• Allows entrained air to be released.
The reservoir is generally mounted high in the power packto provide a positive head of pressure at the hydraulic pumpsuction port. Suction lines from the reservoir to the pumpsare commonly fitted with strainers and isolation valves.
3.2.7 Filters and Strainers
The hydraulic fluid and system are kept clean by passingthe fluid through filters and strainers as it flows through thecircuits.
A strainer is a coarse filter, commonly made from wiremesh, which is generally fitted to the suction line inside thereservoir. The strainer is generally specified by a meshnumber or standard sieve number.
Filters retain much smaller particle sizes than strainers andare commonly located on the reservoir return lines. Filtersare generally specified by a micron number and as beingeither nominal or absolute. A nominal filter rated at 10micron will trap most of the particles of that size; however,an absolute filter will trap all particles of that size andgreater.
In addition to the filters placed in the reservoir return lines,some circuits have an in-line filter installed upstream of thevalve gear, particularly where there is a limited flow throughthe system, e.g., on the priority supply line to the MonsunTison valve, the main control valve of the injector head.
Many filter assemblies incorporate a filter condition indica-tor. This simply gives some indication of the differentialpressure being applied across the filter. A filter which ispartially plugged will create a larger differential, the indica-tion of which is commonly displayed by a colored indicatorsystem. A green display during operation is normal; a reddisplay indicates the filter requires changing. In addition tothis feature, or as an alternative, a bypass system may alsobe incorporated into the filter assembly. This allows fluid tobypass the filter should the back pressure caused by ablocked, or partially blocked filter, become too severe.
3.2.8 Hydraulic Fluid
The hydraulic fluid has four main functions
• Power Transmission - to transmit power efficiently, thefluid must flow easily through lines and components.Resistance to flow caused by friction will result in powerloss. The fluid should also be as incompressible aspossible to transmit power immediately on start-up.
• Lubrication - most hydraulic components are lubricated bythe fluid; therefore, for a long component life, the fluid
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should contain the necessary additives to ensure highantiwear characteristics.
• Sealing - in many cases, the close mechanical fit andhydraulic fluid provide the only seal against leakagewithin the hydraulic component. Therefore, the mechani-cal fit and fluid viscosity will determine the leakage rate.
• Cooling - heat generated by the components in the systemis dissipated by the fluid as it passes through the lines andreservoir.
In addition to the four main functions of the fluid, a numberof other quality requirements are desirable.
• Prevent rust, corrosion or pitting.
• Prevent sludge formation.
• Depress foaming.
• Maintain stability over a wide temperature range.
• Separate out water.
• Be compatible with seal and gasket materials.
The excess generation of heat and associated problems isa relatively common problem in incorrectly designed oroperated hydraulic systems. To combat this potentialproblem and to assist with heat dissipation during periodsof high load or high ambient temperature, most CTUs areequipped with a heat exchanger.
Heat exchangers may rely on air or water to cool the fluid,and are generally located on a main reservoir return line.This ensures that the majority of the fluid passing throughthe system goes through the heat exchanger.
3.2.9 Accumulator
Hydraulic systems that operate at a static pressure andhave a low fluid flow rate are commonly fitted with accumu-lators. In this application, the accumulator performs twofunctions.
Accumulators fitted to the power pack generally contain aninternal bladder which is precharged with nitrogen. Theprecharge pressure is dependent on the application andvolume of the accumulator. For example, the BOP circuitis fitted with a large-capacity accumulator which, when fullycharged, will allow limited operation of the BOP followingshutdown of the power pack.
4 CONTROL CABIN
4.1 Description
The control cabin contains all of the controls and instru-ments necessary to allow the CT operation to be run fromone control station. The location of the control cabin willvary depending on the configuration and type of the coiledtubing unit; however, the cabin is generally situated behindthe CT reel, in line with the wellhead/injector head. To helpachieve maximum visibility from the control station, thecabin is commonly elevated.
The level of control and instrumentation fitted will greatlydepend on the model and version of the CTU. However,typical design objectives include ability to:
• Control and monitor the operation of all of the CTUoperating functions.
• Control and monitor the operation of well pressure controlequipment.
• Monitor and record the principal well and CT stringparameters of wellhead pressure, circulating pressure,tubing weight at the injector head and tubing depth.
The principal benefit of this comprehensive control andinstrument package is that it provides the operator with anincreased awareness of the CTU operating conditions. Thisin turn provides three important prerequisites that arecrucial to achieving adequate service quality:
• The CTU can be operated safely and efficiently.
• Potential problems can be identified and rectified beforethey interfere with the operation of the CTU.
• An accurate CT string work record is developed, basedon the primary factors which influence the useful life of thetubing.
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Figure 30. Typical control panel layout - flat panel.
Figure 31. Typical control panel layout - split panel.
OPEN
STRIPPER#2
LEVELWIND ARM
UP
DOWN
EMERGENCYTRACTION SUPPLY
INJECTOR INSIDE TRACTION PRESSURE
1500 PSI MAX
TOP
ON
OFF
ON
OFF
ON
OFF
MIDDLE
BOTTOM
INSIDE TRACTION
PRESSURE ADJUST
INSIDE TRACTIONSUPPLY PRESSURE
BLEEDPRESSURE
INJECTOR OUTSIDETENSION PRESSURE
150 PSI MAX
PRESSURE
PRESSURE
PRESSURE
STRIPPER#1
RETRACT NEUTRAL PACKRETRACT NEUTRAL PACK
STRIPPER SYSTEM PRESSURE5000 PSI MAX
STRIPPERPRESSURE ADJUSTAIR REG. CONTROL
#2STRIPPER
#1STRIPPER
BOP SUPPLYBOP PRESSURE BOP SUPPLY PRESSURE
ON
OFF
CLOSE OPEN CLOSE OPEN
CLOSE OPEN CLOSE OPEN
BLIND RAM
PIPE RAM
SHEAR RAM
SLIP RAM
B
O
P
HIGH
LOW
INJECTORSPEED
REEL BRAKE
OFF
REEL PRESSURE
REEL PRESSURE ADJUST
REEL CONTROLLEVELWINDOVERRIDE
INSIDE TRACTIONPRESSURE DRAIN
CLOSE
INJECTORMOTOR PRESSURE
INJECTOR MOTOR PRESSURE ADJUST
INJECTORCONTROL
INJECTOR DIRECTIONALCONTROL VALVEPILOT PRESSURE
PRIORITY PRESSURE2,000 PSI MAX
IN
OUT
ON
OFF
ON
OFF
AIP SUPPLYPRESSURE
30 GPMPUMP
60 GPMPUMP
THROTTLE
ENGINESTOP
EMERGENCYSTOP
AIR HORN
INJECTOR CHAINLUBRICATION
REEL TUBINGLUBRICATION
WELLHEAD PRESSURECIRCULATING PRESSURE
TUBING WEIGHT INDICATOR
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EMERGENCYTRACTION SUPPLY
TOP TRACTION
MIDDLE TRACTION
BOTTOM TRACTION
STRIPPERBLEED
PRESSURE BLEED
STRIPPER#1
STRIPPER#2
STRIPPER #2PRESSURE
INSIDE TRACTIONSUPPLY PRESSURE
CHARGEPRESSURE
PRIORITYPRESSURE
SYSTEMAIR PRESSURE
DEPTH SYSTEMBOP SYSTEMPRESSURE
STRIPPERPRESSURE ADJUST
INSIDE TRACTION
PRESSURE ADJUST
BOP SUPPLY
BOP PRESSURE STRIPPER #1PRESSURE
STRIPPER SYSTEMPRESSURE
STRIPPER SYSTEMPRESSURE
ON
OFF
CLOSE OPEN CLOSE OPEN
CLOSE OPEN CLOSE OPEN
BLIND RAM
RETRACT PACK
NEUTRAL
RETRACT PACK
NEUTRAL
PIPE RAM
SHEAR RAM
SLIP RAM
CLOSE OPEN
AUX BOP
B
O
P
REEL BRAKEPRESSURE
REEL CONTROLLEVELWINDARM
LEVELWINDOVERRIDE
INSIDE TRACTIONPRESSURE DRAIN
OUTSIDE TENSIONINJECTOR
CLOSE OPEN
REEL PRESSURE ADJUST
INJECTORPRESSURE ADJUST
INJECTORCONTROL
IN
OUT
ON OFF
ON OFF
INJECTOR2 SPEED
HIGH LOW ON OFF
REEL BRAKE
ON OFF
ON OFF
INJECTOR TOPTRACTION CYL.
INJECTOR MIDDLETRACTION CYL.
INJECTOR BOTTOMTRACTION CYL.
INJECTOR CONTROLPILOT PRESSURE
INJECTOR MOTORPRESSURE
REEL PRESSURE
ENGINESTOP
EMERGENCYSTOP
AIR HORN
INJECTOR SLOWSPEED CONTROL
INJECTOR LUBE REEL LUBE
WELLHEAD PRESSURE CIRCULATING PRESSURE
TUBING WEIGHT INDICATOR
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THROTTLE
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4.2 Features
Controls and instruments can be grouped by function asfollows.
The illustrations in Figure 30 and Figure 31 show typicalconsole layouts.
The explanations given below summarize the function ofeach control or instrument group.
4.2.1 Injector Inside Chain Tension
This system is served by the following controls andinstruments.
Emergency Traction Supply
A three-way valve that is used to apply full priority pressurein the event of an emergency (runaway) situation. In thenormal operating position, the pressure to each of the threetensioner cylinder ram sets is determined by the pressureadjust valve.
Inside Traction Pressure Adjust
This is a pressure reducing valve used to adjust thehydraulic pressure to the cylinders (increase and decreasepressure). The hydraulic supply is from the priority circuit(2,000 psi); the maximum chain tension pressure shouldnot exceed 1,500 psi.
Inside Traction Supply Pressure Gauge
Displays system pressure as determined by the pressureadjust valve.
Control Valve (3)
May be used to isolate each of the three inside chaintension cylinder sets.
Pressure Gauges (3)
Displays the hydraulic pressure downstream of the controlvalves.
Inside Traction Pressure Drain
This valve is used to bleed pressure from the system whenthe control valves are open. Caution must be exercisedwhen opening this valve when tubing is suspended in theinjector chains because a sudden drop in the cylinderpressure will result. Fine pressure adjustment should bemade by the pressure adjust valve.
4.2.2 Injector Outside Chain Tension
This system is served by the following controls andinstruments.
Injector Outside Tension Pressure Gauge
Displays the current hydraulic pressure within the outsidetension cylinders.
Pressure Valve
A needle valve which isolates the supply pressure from thesystem.
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Bleed Valve
A needle valve used to bleed pressure from the system.
4.2.3 Injector-Head Drive
This system is served by the following controls andinstruments.
Injector Motor Pressure Adjust Valve
A remote pilot valve used to control the injector drivepressure.
Injector Control Pilot Pressure Gauge
Displays the pilot control pressure, which is equal to thedischarge pressure of the Husco valve.
Injector Control Valve
Provides directional and speed control of the injector- headmotors by controlling the output of the Husco valve. Pullingthe valve handle backward selects the out-hole direction;pushing the handle forward selects an in-hole direction.
Injector Speed High/Low
Valve used to control injector-head motor speed selection.
Injector Motor Pressure
Displays the injector motor hydraulic pressure.
30-GPM Pump/60-GPM Pump
These two valves are used to control the injector-headmotor speed. One or more of the pumps must be selectedin order to operate the injector head. For high injector headspeeds both pumps may be selected.
Priority Pressure Gauge
Displays the priority system pressure. The priority systempressure is used to operate several of the remote pilotfunctions associated with the other controls.
4.2.4 Reel Controls
This system is served by the following controls andinstruments.
Reel Control
The reel directional control valve. Should be locked in theout-hole direction for all normal operations.
Reel Pressure Adjust
A remote pilot valve used to adjust the reel drive systemrelief valve from zero to the preset maximum.
Reel Pressure Gauge
Displays the hydraulic pressure to the reel motor.
Reel Brake
A valve used to apply/release the reel brake.
Levelwind Override
Advances or retards the position of the levelwind travelinghead.
Levelwind Raise/Lower
Control to raise or lower the levelwind assembly.
4.2.5 Lubrication Controls
This system is served by the following controls andinstruments.
Reel Tubing Lubrication
A pilot valve used to control (on/off) the reel tubinglubrication system.
Injector Chain Lubrication
A pilot valve used to control (on/off) the injector-head chainlubrication system.
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4.2.6 Engine Controls
This system is served by the following controls andinstruments.
Emergency Stop
A valve which operates the engine’s air inlet shutoff valve.Should only be used in an emergency. The shutoff valvemust be manually reset at the power pack to allow furtheroperation.
Engine Stop
A valve which remotely shuts off the diesel fuel supply tothe engine.
Throttle
Used to control the engine speed.
Air-Supply Pressure Gauge
Displays the pneumatic system pressure.
4.2.7 Blowout Preventers (BOP)
This system is served by the following controls andinstruments.
BOP-Supply Pressure Gauge
Displays the BOP’s hydraulic supply pressure.
BOP Pressure
Displays the hydraulic pressure in the BOP circuit down-stream of the BOP supply valve.
BOP Supply Valve
Valve used to isolate the BOP circuit from the hydraulicsupply.
Ram Control Valve (4)
Used to open/close each of the four ram sets (blind, shear,slip and pipe rams).
4.2.8 Strippers
This system is served by the following controls andinstruments.
Stripper Selection Valve
Three-way valve which directs the hydraulic supply to theappropriate stripper.
Stripper-System Pressure Gauge
Displays the discharge pressure of the stripper supplypump.
Stripper Pressure Adjust
Air regulator control which controls the operation of thestripper supply pump. Stripper pressure decrease cannotbe achieved by this control.
Retract/Neutral/Pack Valve (2)
Control valve for each stripper selecting the desired func-tion. The neutral position bleeds stripper pressure.
Stripper Pressure Gauge (2)
Displays the hydraulic pressure of the selected function, asselected by the retract/neutral/retract valve.
4.2.9 Principal Gauges
Wellhead Pressure Gauge
Displays wellhead pressure at the BOP pressure port,generally located at the center of the BOP stack.
Circulating Pressure Gauge
Displays pressure at the reel-manifold pressure sensor.
Weight Indicator
Displays the weight exerted by the tubing on the injectorhead.
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4.2.10 Emergency Hydraulic Supply
The emergency pump console contains the pressure gaugeand valves to allow the selection and monitoring of emer-gency hydraulic supply to the stripper, BOP and chaintensioner systems, as selected. Control of pressure is thenby manual effort.
4.2.11 Electronic Equipment
The following electronic equipment may be fitted or in-stalled to monitor and record the CTU, tubing, and well data.
• Electronic Depth Sensors
• Electronic Pressure Sensors
• Tubing Monitoring Equipment
4.3 Operating Technique
The controls and systems of any CTU must be operated ina manner which ensures that the following general require-ments are met:
• The safety of personnel associated with the operation andmaintenance of the CTU and ancillary equipment mustnot be jeopardized by the actions of the CT operator.
• Operation or maintenance of any controls or system of theCTU must not compromise the efficiency of the wellcontrol barriers. The operation of primary, secondary andtertiary (where required) well control barriers must beunderstood. In addition, the consequences of their opera-tion must be understood.
• The operating limits of key components and systemsassociated with the CTU or ancillary equipment shouldnot be exceeded.
• The operating limits defined by appropriate CT softwaremodels should not be exceeded. In the event that thisinformation is not available, the operation should beconducted within the operating limits identified during thejob design phase.
• Applicable safety and environmental policies must beunderstood and complied with.
The equipment operator should coordinate the control andinstrumentation functions to affect a high level of controlover the CTU. Good control, together with smooth operationwill help to improve the reliability and longevity of thecomponents, system controls, tools and tubing used.
During operation, consideration must be given to the speedand levels of force applied to the CT. These must beconsistent with the well conditions and equipment limita-tions.
Starting/Stopping
The process of starting and stopping the movement of theCT must be conducted by applying or reducing the drivingforce slowly and smoothly. Sudden changes may exertunacceptably high forces to the tubing, reel, injector head,power pack and pressure control equipment components.
NOTE: If any of the defined operating limits are met, orexceeded, the injector-head drive must be disengaged asquickly as possible. Operation may commence only whenthe appropriate course of action has been determined.
Changes in the injector head direction must only beattempted after the tubing has been brought to a completehalt.
Several precautions must be taken when the injector-headdrive is to be engaged. These may include, but not belimited to:
• Check that the BOP rams and wellhead valves are open(including the subsurface safety valve, where appli-cable). Ensure that all pressure control systems areappropriately energized.
• Ensure that parking devices such as BOP slips, reelbrakes, etc., are released and that the appropriate reelback tension is applied.
• Note (reset if applicable) the depth system readout.
• The weight indicator reading at the maximum allowabletension (T
max), as determined during the job planning
phase, must be known and noted by the operator prior tocommencing the operation.
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Running the CT
The location of the CT BHA in relation to the wellboretubulars and restrictions should be a constant consider-ation. Appropriate precautions must be taken as the CTBHA passes restrictions or variations in the wellborediameter. These may include, but not be limited to, thefollowing.
• Close observation of the weight indicator display.
• A reduction in the running speed.
• Coordination with operators of a specialist tool string, e.g.,CT Logging company.
• Checking the actual vs predicted weight/depth plots.
• The operator must, at all times, be prepared to quicklydisengage the injector-head drive should abnormal condi-tions be observed.
Pressure Control Equipment
With the exception of strippers and equipment designed tobe operated while the tubing is in motion, operation ofpressure control equipment must only be attempted whenthe tubing is stationary.
The operation of BOP functions which may damage the CT,e.g., the blind rams or shear rams, must only be attemptedafter considering the implications of such action. Lockoutdevices should be fitted to all BOP controls that may initiatesevere damage to the CT if unintentionally actuated.
4.4 Instrument Scanning
To ensure that unusual circumstances during a CT opera-tion are detected as early as possible, it is necessary for theoperator to constantly scan the CTU instrument array.
The priorities assigned to each instrument group areintended to initiate a regular scanning sequence whichshould become habitual to the operator during normaloperations. However, during special or emergency opera-tions, some instrument groups may require extra attention.
The control and operation of the CTU should be consistentwith any conditions, known or suspected, which may affectthe CT operation.
The following instruments and gauges are generally vari-able throughout a CT operation and are assigned an “A”priority.
• Weight indicator display
• Wellhead pressure gauge
• Circulating pressure gaugeIn addition, the following locations are assigned an “A”priority.
• Injector head and wellhead area
• CT reel
The following instruments and gauges are generally lesslikely to change rapidly and are assigned a “B” priority.
• Depth measurement system
• Stripper pack pressure
• Inside chain tensioner system
In addition, the following locations are assigned a “B”priority.
• Pump and choke parameters
• Auxiliary equipment
The following instruments are generally static throughoutthe operation. They do not normally require adjustment andare assigned a "C" priority.
• Power-Pack Engine Gauges
• Priority Circuit Pressure Gauge
• BOP Circuit Pressure Gauge
• Stripper System Supply Pressure Gauge
• Injector Motor Pressure and Direction Pressure Gauges
COILED TUBING SERVICES MANUALCOILED TUBING UNIT
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• Outside Chain Tension Pressure Gauge
• Inside Chain Tension Supply Pressure Gauge
• Reel Back Tension Pressure Gauge
The frequency of scanning should ensure that all of thesystems and locations are checked every four to fiveminutes.
The B priority items should be checked every two to threeminutes.
Attention should be maintained on the A priority items at alltimes other than when B and C items are being checked.
5 CTU COMPONENTS - APPOROXIMATE SIZES
Figure 32 shows approximate sizes for the following CTUcomponents:
