A list of these corresponding documents: API Standard ISO Document API Title or Topic & Comments RP 17A 13628-1 Design & Operation of Subsea Production Systems RP 17B n/a Flexible Pip
Terms and definitions
3.1.1 bend radius radius of curvature as measured to the centreline of a conduit
3.1.2 circulation control valve valve normally placed across the circulation point to allow isolation of the tubing strings or tubing/casing during production
3.1.3 circulation point location where communication is established between supply and return fluids for TFL servicing
3.1.4 diverter device used to direct tools at a branch connection
NOTE Used generically, it refers to that category of equipment which includes deflectors, diverters and selectors.
3.1.5 drift gauge used to check the minimum radius of curvature and minimum ID of loops, flowline and nipples
H-member nipple assembly that provides fluid communication and circulation between strings of tubing in the wellbore
3.1.7 loop curved section of pipe allowing change in direction of TFL flowlines
3.1.8 lubricator tube and valve assembly that permits tool-strings to be inserted into and removed from a pressurized system
The parking system is a method that allows tools and equipment designed for a specific tubing size to be transported through a larger flowline This is achieved using a transport piston string, which remains outside the well, or "parked," while the other equipment continues its journey into the tubing.
3.1.10 profile internal conduit configuration (receptacle) used to engage tools
3.1.11 recess enlargement in conduit bore, normally concentric with the bore
3.1.12 sealing bore polished section of conduit that receives a packing element
3.1.13 flowline service line line from a platform or land facility to a subsea facility used for TFL servicing
NOTE It may also be used for production or other testing of the well.
The flowline signature service involves a specific set of pressure pulses, or spikes, that are recorded at the surface These pressure signatures help identify particular points in the service or flowline, as well as in the well, when tools are pumped past these locations.
3.1.15 subsea tree christmas tree placed at the seabed
TFL piping system all piping from the surface lubricator through the flowline and tubing to the deepest point in the well to which TFL tools can be circulated
3.1.17 tubing-retrievable safety valve downhole safety valve run in the well on tubing
NOTE It is normally surface-controlled and has an ID close to the size of the tubing bore, thereby providing an almost unrestricted bore.
3.1.18 wye spool piping section of a subsea tree where the loop joins the vertical tubing bore
Abbreviated terms
SCSSV surface-controlled subsurface safety valve
SVLN safety valve landing nipple
TRSV tubing-retrievable safety valve
Description of system
The TFL method enables efficient well servicing by using fluid to transport tools through flowlines and loops into and out of tubing strings The differential pressure of the transport fluid across the tool-string generates the necessary force to carry out various operations.
TFL components
A typical TFL system, as illustrated in Figure 2, consists of essential components such as surface equipment, flowlines, subsea trees, TFL service tools, and downhole equipment This system is designed to facilitate the transport and control of TFL tools, with pumping equipment responsible for transportation and the control managed through pumping rates, instrumentation, and the TFL control manifold Key criteria for an effective TFL system include maintaining an appropriate pressure rating, ensuring sufficient fluid volumes for TFL operations, and controlling equipment within specified operating parameters.
System/equipment design
TFL tools are specifically designed to function with various tubing sizes used in subsea wells, with their design influenced by the tubing's internal diameter (ID) and the minimum radius of curvature for bends It is crucial for the TFL piping system to consider the internal diameters of conduits and receptacles, as well as the pressure ratings of the pipes and tubing The service line's ID must match that of the downhole tubing strings; otherwise, a parking system should be implemented An oversized ID can lead to fluid bypassing the tool-string piston units, diminishing their force capability and compromising tool position measurements Conversely, an undersized ID may obstruct tool passage, increase drag, or cause damage to the tool, seals, and piston units.
Annex A specifies the requirements for TFL pipe and Table A.1 lists pipe ID dimensions that are compatible with tubing sizes.
Pressure rating
The pressure rating of a TFL system must exceed the maximum pressure expected during its operational lifespan Key factors to consider include the maximum static bottom-hole pressure of the well, adjusted for the hydrostatic pressure of the fluids in the TFL system, the pressure needed to overcome frictional losses during fluid circulation and tool-string operations, and the pressure necessary to operate all TFL devices, including service tools and downhole isolation equipment Additionally, it is essential to account for hydraulic shocks or surges that may occur during operations like jarring, as well as the pressure required to effectively kill the well if the TFL system is utilized for pumping kill fluids into the producing formation.
Multiple-well systems shall consider the effect of the higher pressure wells in the system.
Additional information about the system pressure rating and TFL fluids is provided in clause 9 and annex B.
General
The TFL surface equipment comprises essential components such as a service pump, control manifold, control console, lubricator, fluid storage, separator, and piping system It is crucial that the pump's pressure and flow ratings align with the system's design, considering tool transport speeds, actuation pressures, and potential fluid bypass during operations Adequate volume in tanks and tubing strings is necessary to ensure effective handling of all operations The surface facility must be designed to accommodate TFL facilities, with careful arrangement of equipment to facilitate easy access to the control console, pump, manifolding, and lubricator, as well as to allow for the insertion and removal of extended-length tool-strings If situated on a drilling or production platform, utilizing existing high-volume mud or kill pumps may negate the need for dedicated equipment.
2 Threaded quick connection with plug
8 High pressure/high volume triplex pump
11 From platform saltwater system (optional)
13 From dry oil tank (optional)
21 To well a Recommended minimum straight level section.
12 To other wells in system
Figure 5 — Typical surface equipment arrangements for installations
Table 1 — Recommended flow rates for TFL tools
Nominal tubing ID mm (in)
Flow rate l/min (bbl/min)
Service pump
Triplex-type positive displacement pumps are commonly utilized for TFL operations, although some operators have successfully employed slow-speed duplex and high-pressure multi-stage centrifugal pumps Key recommendations for these pumps include ensuring that pressure and flow rate capabilities align with clause 9, incorporating a relief valve on the pump discharge to safeguard against over-pressure and hydraulic shocks, providing connections in the pump suction piping for auxiliary tanks or mixing facilities, and designing the TFL pump drive to facilitate smooth adjustments across the specified operating conditions in clause 9.
TFL control manifold
Valving arrangements must be designed to effectively manage pump flow and fluid return to service lines, tanks, and separators for TFL operations It is essential that piping and valves can withstand the system's maximum working pressure Additionally, valves and actuators should enable rapid line switching, ideally within 2 seconds The system should include provisions for fluid return through an adjustable back pressure regulator or choke, along with flow meters This setup is crucial for regulating back pressure on the return line, thereby controlling inflow from the well and minimizing fluid loss to the formation during downhole TFL operations.
TFL control console and instrumentation
A typical TFL instrumentation/control console, as shown in Figure 6, facilitates the monitoring of tool progress, operation, and well fluid changes This setup typically includes pressure gauges with strip chart recorders, pressure transducers on the lubricator or manifold, and flow rate meters with volume totalizers on both pump discharge and return lines It is crucial for the instrumentation to be robust enough to endure vibrations and pressure surges To protect turbine flow meters from debris, high-pressure screens or filters should be installed upstream, although other meter types may not require such filters.
Pressure transducers with surface readout can be installed at the wellhead to enhance monitoring of tool location, alongside control console instrumentation Additionally, specialized tool detection systems may be implemented for effective monitoring.
1 Dual flow meters and totalizers
4 Two-pen strip-chart recorder
5 Chart recorder on/off switch
7 Monitoring gauges (engines, pumps and transmission)
8 Hydraulic choke and manifold – control valves
9 Engine – start, stop and emergency kill
Figure 6 — Typical TFL instrumentation control console
Lubricator
A lubricator facilitates the insertion and removal of tool-strings in a pressurized system Typically, a TFL lubricator features a horizontal launch tube that ranges from 6 m to 18 m (20 ft to 60 ft) in length, equipped with quick-connecting unions at both ends, a full-opening block valve, bleed valves, and a fluid pumping connection.
In certain fishing and remedial operations requiring long tool-strings, it may be essential to utilize the service line to the subsea tree as part of the lubricator system It is important to bleed off the line pressure before each use.
7 Bull plug assembly with quick union
Figure 7 — Typical lubricator skid 5.5.2 Design
When designing a TFL lubricator, it is crucial to prevent internal diameter (ID) reductions or misalignments that could hinder tool passage and lead to seal or tool damage The lubricator's ID must be significantly larger than the flowline ID to facilitate easy loading and removal of tools, yet not excessively large to avoid requiring a high pump rate for tool movement Typically, an increase of 1.6 mm to 4.8 mm (1/16 in to 3/16 in) over the nominal ID of the service line will meet these essential criteria.
To enhance safety, pressure bleed-off valves must be installed at both ends of the lubricator launch tube, ensuring pressure is released on either side of the tool-string before tool removal The design should facilitate the collection of excess fluids from the lubricator Additionally, branch connections should be strategically placed to prevent the tool-string from slamming into the lubricator end upon surfacing Incorporating a power-assisted tool feeder for push/pull operations and work tables may be essential for efficient loading and removal processes.
The lubricator piping shall be designed and fabricated in accordance with API RP 14E and clause 6.
Fluid storage and working tank
A working tank or fluid storage vessel is essential in surface facilities, with a storage capacity that should match or exceed the volume of flowlines and tubing strings In cases where space is limited, smaller tanks may be utilized if make-up liquid is accessible and excess fluids can be safely disposed of A split 6.3 m³ (40 bbl) tank is effective for monitoring allowances for lost circulation or well fluid influx The type of working fluid can vary, including diesel, dead crude, inhibited water, or brine, and appropriate connections must be available for these sources It is crucial to implement special precautions to comply with area classification standards when handling crude oil or fluid returns.
Separator
A separator is essential for eliminating gas from the return stream, ensuring consistent performance in tool operations and accurate tool positioning, as detailed in clause 9.
The separator must be appropriately sized and pressure-rated to manage well fluids, accommodate the maximum pumping rate, and handle fluid surges that occur during flow path transitions in TFL operations.
Testing
The entire TFL platform facility assembly (see Figure 4) should be pressure tested in accordance with API RP 14E.
In addition, the ID of the piping through which TFL tools are to pass should be gauged using the tests described in clause 6.
General
The TFL piping system includes several key components: the surface piping connecting the lubricator to the top of the riser, the riser extending from the seabed, a straight flowline section, preformed TFL loops or bends for directional changes in confined areas, the subsea tree, and the tubing string along with downhole accessories and their end connections.
All piping connectors and connection methods must ensure an unobstructed passage for tools, preventing any damage to both metallic and non-metallic seals on TFL tools, TFL pistons, and other components of the TFL tool-string.
Design
TFL pipe shall be either a rigid metallic tubular or a flexible tubular, the latter being constructed of composites of metallic and non-metallic materials.
Various metal grades have been used for TFL piping, including carbon steel (ISO 3183-1 and ISO 3183-2 [6]), austenitic-ferritic ("duplex") stainless steel, martensitic stainless steel ("13-chrome"), and others.
More detailed information on the appropriate materials can be found in API RP 17A [4] and ISO 13628-1 [8] for subsea production control systems and in ISO 10420 [7] for flexible pipe.
The flowline and straight sections of the piping system should generally match the minimum and maximum inner diameters (ID) of the well tubing string to minimize fluid bypassing and enhance TFL tool-positioning control However, in cases where flowlines are particularly long, a larger ID may be necessary to reduce pressure drop In such instances, a parking system, as illustrated in Figure 9, is recommended This system utilizes a large diameter TFL tool carrier to transport the downhole service tool-string to the subsea wellhead, allowing for the release or retrieval of the smaller diameter downhole tool-string.
TFL piping systems must maintain a working pressure that aligns with the design pressure of the TFL system The selection of wall thickness and material strength is crucial to ensure that all components of the piping system adhere to the relevant design codes of the operating country or those specified by the operator.
In straight sections of the piping system, side-entry ports must intersect the TFL flowline at a 90° angle; if this is not possible, the angle should be no less than 45° to the flowline's longitudinal axis to reduce the size of the exposed side-port opening Additionally, the intersection should be positioned above the longitudinal axis of the TFL flowline, and all corners of the intersecting bore must be bevelled to avoid interference with the TFL tool and prevent damage to its components.
Figure 10 — Bore junction configuration for a non-TFL pipe intersecting TFL piping
Restrictions in flowlines or tubing that lead to temporary pressure spikes during the movement of TFL pistons are effective for identifying the TFL service string These restrictions can be intentionally created, such as with specially designed, short, heavy-walled pipe sections, or they may occur naturally in any flowline, known as the flowline signature Typically, these restrictions result in a pressure increase of 1.4 MPa to 2.1 MPa (200 psi to 300 psi) at standard tool transport speeds Blast joints and flow couplings have proven to be effective for this application.
To effectively identify the tool-string location with downhole restriction devices, it is crucial to maintain adequate distance between these devices and any landing nipple This spacing allows for proper tool positioning and deceleration before reaching the landing nipple, with the required distance influenced by factors such as pumping rate, fluid volume, and flow rate response time Additionally, the speed of pressure pulse detection is impacted by fluid properties, temperature, pressure, and the distance from the pressure detector to the restriction device Proper spacing is essential to ensure that piston elements are not within the device during actuation, thereby avoiding complications in fishing operations caused by reduced fluid bypass.
Installation methods shall consider the effects of installation forces and stresses causing ovality that would restrict drifting and tool passage.
Bend loops must maintain a minimum bend radius of 1,524 mm (60.0 in) Whenever possible, a larger bend radius is recommended to minimize fabrication and operational issues This minimum bend radius requirement is applicable to both rigid and flexible piping.
Table 2 specifies, for some typical tubing sizes, the maximum ID of loop material prior to bending and the minimum
ID of loop material after bending Minimizing the pipe ID in the bend should be considered in order to increase the efficiency of the TFL tool.
ID before bending mm (in)
Minimum ID after bending mm (in)
See Figure 11 for a description of terms.
Avoid using tangent-coupled bends that create significant directional changes in multiple planes unless compound bending is essential Regardless, the bend geometry must permit the passage of the TFL drift as outlined in section 6.4.1.
Two 90° bends can be connected at their tangents to create a 180° turn in a single plane due to their shared center of curvature However, if the bends are rotated at the tangent coupling, causing the centers of curvature to be misaligned, certain TFL tool-strings may encounter issues passing through To resolve this, it is typically effective to install a straight section that is at least nine pipe IDs long between the tangent ends of the bends.
A slight change in direction, like the continual helix or "ram's horn" configuration at the entrance of a subsea tree, can allow the tool to pass successfully It is crucial during the design phase to consider the worst-case TFL tool-strings to ensure the tool-string can navigate effectively For additional details, refer to the footnotes in Figure 11.
Compound bends in one plane, known as coplanar "S" bends, should have a minimum radius of curvature of 1,524 mm (60 in) throughout the tube's length Utilizing a larger internal diameter for the compound bend, along with a bend radius that surpasses the minimum recommendation, can enhance its effectiveness However, the implementation of these bends often requires a trial-and-error approach based on the tools being used, with adequate drifting being essential to ensure the successful passage of the TFL tool-string.
For non-planar bends, the typical joining length is 9 pipe IDs, while for connectors to bends with unlimited space, it is usually 6 pipe IDs Bends joined at the tangent point are considered tangent-coupled, with coplanar bends generally acceptable for F/TFL use However, tangent-coupled non-planar bends may not meet acceptance criteria For further details, refer to section 6.2.2.
Bend materials must possess adequate strength and wall thickness to ensure that, post-formation, the bend's rated working pressure meets or exceeds that of the flowline and adheres to relevant design codes.
6.2.2.5 Position of connections at ends of bends
In field installations with limited space, successful connections have been made using tangential attachments that accommodate bend curvature while ensuring smooth internal connections These connections must be designed to facilitate the appropriate TFL drift as outlined in section 6.4.1.
All connections should meet service and pressure rating(s) of the associated piping.
Support bracing for wellhead bends must accommodate thermal variations Flexible pipes should be supported to maintain a minimum radius of curvature of 1,524 mm (60 in) along the centerline For additional information on flexible pipes, refer to ISO 10420.
Fabrication
To ensure compatibility with TFL tools, flowline pipe must be produced according to annex A Additionally, each pipe joint should be drifted using the ID drift specified in ISO 3183-1 to detect and remove any damaged or undersized joints.
Flowlines created through welding must undergo drifting post-welding with both the sharp-shouldered drift and the TFL flowline drift, as outlined in section 6.4 This process is essential to guarantee the passage of TFL tools, which is typically carried out manually, as detailed in section 6.4.1.
To ensure acceptable connections for TFL operations, follow the guidelines for joining techniques, which require that connections be concentric within 0.76 mm (0.03 in) of true position, with a maximum gap of 4.8 mm (0.19 in) Joints with a recess must adhere to the specifications illustrated in Figure 14 Additionally, valves, unions, and other connections should be aligned concentrically to the piping within the same tolerance of 0.76 mm (0.03 in) All piping connections must be drifted using both the sharp-shouldered drift and the TFL flowline drift, as outlined in section 6.4 It is also essential that internal surfaces are free from weld slag, mill scale, or significant surface imperfections.
Drift dimensions a Nominal tool size
OD Length mm (in) mm (in) mm (in)
2 Segments pinned and oriented at 45° to provide 360°of key clearance
4 OD at shoulder = pipeline/loop ID plus 1,6 mm (1/16 in) minimum
5 Length, centreline swivel to swivel a Dimensions based on minimum loop IDs of Table 2 with 1 524 mm (5 ft) radius to centreline.
Nom size Tubular drift OD Flowline drift OD Shaft OD
A1 A2 B D E mm (in) mm (in) mm (in) mm (in) mm (in) mm (in)
Nom size Overall length Inner loop radius Outer loop radius Centre distance Centre distance
F G H J K mm (in) mm (in) mm (in) mm (in) mm (in) mm (in)
Figure 13 — TFL drift mandrel dimensions
Typical end preparations for welding are shown in Figure 15 This figure shows the U-shaped preparation. However, the V-shaped preparation shown in API Std 1104 may also be used.
When choosing between U-shaped and V-shaped weld preparations for TFL applications, it's important to consider that V-shaped configurations are more prone to slag inclusions and excessive penetration into the pipe bore, which typically necessitates post-weld broaching or reaming In contrast, U-shaped preparations facilitate the entry of a gas-tungsten-arc welding tip into the weld groove for the root pass, often reducing the need for post-weld clean-up Both configurations can be utilized for subsea tree or surface equipment welds, depending on the manufacturer's efficiency assessment or purchaser specifications However, U-shaped preparations are recommended for flowline connections to minimize post-weld work.
Welding must adhere to relevant codes and standards, primarily API Std 1104 or ASME Boiler and Pressure Vessel Code, Section IX These standards align with additional piping specifications like ANSI/ASME B31.3, B31.4, or B31.8 Alternative welding standards may also be utilized if they are suitable and properly documented.
After welding, it is essential to pass a sharp-shouldered drift through each joint in both directions to check for restrictions and ensure the TFL tool can pass To achieve a smooth-bore internal diameter, broaches and/or grinders may be required to eliminate slag, excess weld metal, and any eccentricities or distortions resulting from the welding process.
Non-destructive examination of welds shall be as specified in 6.4.5.
Dimensions in millimetres (inches) a 0,25 mm to 0,50 mm (0,01 in to 0,02 in) chamfer 43°to 47°
Figure 15 — TFL pipe U-shaped weld configurations 6.3.3.3 Threaded-and-coupled connections
To ensure ID concentricity in threaded-and-coupled connections, it is crucial to fabricate them correctly In cases where eccentricity arises, rotating API EUE type connections can often mitigate the issue, but care must be taken to avoid over-torquing, which may lead to ID reduction Additionally, the gap between threaded pipes should not exceed 25.4 mm (1.0 in) in a properly torqued connection, and each threaded pipe end must be bevelled as illustrated in Figure 16.
When economically appropriate, the use of a premium (proprietary) type of thread, with a flush or near-flush ID at the joint preparation, should be considered.
Dimensions in millimetres (inches) a Root diameter at tip
Figure 16 — Reduced-entry profile dimensions 6.3.3.4 Flanged or clamped connections
Flanged or clamped connections must ensure that the piping inner diameter (ID) remains concentric within 0.76 mm (0.03 in) of the true position Proper welding of the end fitting is essential to prevent ID reductions; otherwise, sharp shoulders must be eliminated for smooth transitions It is important to minimize gaps between mating flanges and chamfer the edges of each flange opening to reduce damage to TFL tools For further details, refer to Figure 14.
Flanged or clamped connections must include a metal seal-ring to ensure proper concentric alignment It is advisable to avoid flat, gasket-type flanged connections Innovative techniques, such as tongue-and-groove features and alignment jigs placed in the inner diameter, can be utilized to achieve concentricity, which is also applicable for welded connections.
TFL tool designs adhere to a minimum bend radius of 1,524 mm (60 in), typically measured at the inside surface of the bend for practical purposes This approach maintains the same minimum radius while ensuring a slightly conservative bend radius Bends must be drifted using the TFL flowline drift as outlined in section 6.4.
Table 2 highlights the essential measurements of bends taken before and after the forming process It is crucial to conduct "test" bends using spare, duplicate pipe material prior to executing production bends.
The internal surface of a bent pipe must be smooth and free from imperfections such as mill scale, significant wrinkles, buckles, and weld slag, as these flaws can obstruct tool movement and negatively impact tool efficiency.
Metallurgical tests should be performed after bending to ensure that the material still meets the minimum design requirements of the manufacturer.
Testing
TFL flowline and tubing drifts are essential tools designed to verify the minimum bend radius and internal diameter (ID) of pipes These drifts, detailed in Figure 13, include a sharp-shouldered, spring-loaded drift (Figure 12) that identifies internal restrictions at flowline connections The drift must be collapsible to a diameter smaller than that of the pipe, with the shoulder maintained within a maximum radius of 0.76 mm (0.03 in) to effectively locate any undesirable shoulders or impediments It is crucial for the drift to be passed through the joint in both directions The assembly features two segments arranged at a 45° angle to ensure 360° coverage A "worst-case" drift refers to the tool-string that encompasses the largest or most critical envelope recommended by the TFL equipment manufacturer for the TFL system.
For flowline drifts, tubing drifts, or "worst case" tool-strings, the applied force for pushing or pulling the drift should not exceed 445 N (100 lbf) above the drift's weight This limit is crucial for sharp-shouldered drifts as well.
890 N (200 lbf) above the weight of the TFL tools shall be applied.
In addition to the drifting described in 6.3, all assembled piping shall be re-drifted using the flowline drift and the
Flowlines shall be re-drifted after installation using the flowline drift and the "worst case" tool-string.
TFL piping shall be tested in accordance with 7.2.2 and ISO 13628-4:1999, 7.16.
TFL piping shall be examined in accordance with ISO 11960 and API Std 1104.
7 Subsea tree, tubing hanger, diverters and selectors
Subsea tree design
The subsea tree is a critical component of the TFL system, situated between the tubing hanger and the flowline It comprises specialized valves, completion hardware, and wellhead equipment essential for underwater well completion Key elements of the subsea tree include the connector, master and wing valves, wye spool, tree loop, and flowline connector.
The article discusses various configurations of TFL (Tree Flowline) trees and wellhead completions, including a typical TFL tree schematic, an alternative design featuring a crossover valve upstream of wing valves, a TFL tree with separate annulus access, and a "partial" TFL tree.
2 Swab valves or crown plugs
9 TFL tools pass only through this line
Figure 18 — Various TFL tree configurations
The bore diameter of the subsea tree must align with the specifications for the valve outlined in Table 3 Internal profile recesses are required to comply with clause 8 Additionally, mechanical connections to other subsea tree components must feature conical transition surfaces and adhere to the minimum gap lengths illustrated in Figure 19 or Figure 20 Furthermore, all welded connections must satisfy the criteria set forth in clause 6.
Tubing Production bore Valve Tubing hanger
OD ID min max Bore Plug bore a mm (in) mm (in) mm (in) mm (in) mm (in) mm (in)
The data presents various measurements, including sizes such as 60.3 mm (2 3/8 in), 73.0 mm (2 7/8 in), and 114.3 mm (4 1/2 in), along with their corresponding values in inches Additional sizes like 139.7 mm (5 1/2 in) and optional sizes are available, provided they meet the overall TFL system requirements The specifications also include features like face-to-face bore recess and bore transition profiles for face-to-face flange connections.
1 Valve bore a 0,25 mm to 0,50 mm (0,01 in to 0,02 in) chamfer at 43°to 47°
Figure 19 — Face-to-face flange connection profiles
3 Valve bore a 0,25 mm to 0,50 mm (0,01 in to 0,02 in) chamfer 43°to 47°
7.1.3 Valve and valve block bores
The bores of blocks with valve assemblies and individual valve bodies must meet the tubing hanger specifications outlined in Table 3 Additionally, the interface between the valve gate and valve seat should adhere to the recess dimensions depicted in Figure 21 It is essential that the bore of the valve body, valve gate, and valve seats are concentric within 0.76 mm (0.03 in) of true position.
Figure 21 — Bore transition profiles between a gate and seats in a valve
Mechanical connections to valves or wellhead bores must feature conical transition surfaces and a minimum gap length, as illustrated in the referenced figures It is essential that all bores are concentric within 0.76 mm (0.03 in) of true position to prevent valve damage during tool passage Aside from the transition surface specifications, all other requirements of ISO 13628-4 remain applicable.
4 Tree tubing stab a See Figure 16 b 0,25 mm to 0,50 mm (0,01 in to 0,02 in) chamfer 43°to 47°
TFL trees are equipped with a wye spool that facilitates both vertical and TFL access to the well, featuring a deflector designed to guide TFL tools effectively The wye spool ensures smooth transition IDs to prevent any obstruction during the passage of TFL tools, with the deflector providing a seamless cross-section transition from the cylindrical to the curved passageway Both vertical and TFL-access bores must maintain a minimum ID after bending, as specified in Table 2, while the bend radius of the TFL-access bore must comply with clause 6 requirements Additionally, mechanical connections for TFL access should include conical transition surfaces and adhere to the minimum gap length outlined in Figures 19 and 20, with welded connections also meeting the standards set forth in clause 6.
Incorporating TFL tree loops into subsea tree design is essential for ensuring effective supply and return paths for circulating TFL tools in and out of the well These tree loops must be fabricated following the recommended practices outlined in clause 6 Additionally, mechanical connections to other tree components that facilitate TFL access should feature conical transition surfaces and maintain a minimum gap length.
Non-TFL piping that connects to a TFL tree loop must intersect the loop at an angle of at least 45°, ideally at 90°, to reduce interference with the TFL tool's movement Additionally, corners at these intersections should feature bevelled transitions as outlined in clause 6.
The subsea tree design must incorporate a crossover valve between the TFL tree loops to facilitate circulation when opened, allowing for the circulation and filling of flowlines with TFL fluids before operations This valve also serves as a transport point for TFL tools to reach the tree prior to entering the well Ideally, the crossover valve should be positioned near the wye spool, unless TFL-retrievable chokes or plugs are utilized, in which case it should be placed on the outboard side of the choke/plug nipple Additionally, the crossover valve must be designed and pressure tested in accordance with ISO 13628-4 standards.
Flowline connectors and their design considerations are outlined in API RP 17A For connectors designed for TFL service, the following criteria must be met: the TFL passageway must have a bore that meets the minimum internal diameter after bending as specified in Table 2, and any loops and bends at the connector must adhere to clause 6 Additionally, flowline connectors should feature conical transition surfaces and minimum gap lengths as illustrated in Figures 19 and 20 Welded flowline connections must comply with the requirements detailed in clause 6, and end connections between the bores of the flowline, flowline connector, and tree loops must be concentric within 0.76 mm (0.03 in) of true position.
Piping in the subsea tree that incorporates a landing nipple profile shall have straight sections, each at least 0,3 m
(12 in) long, above and below the landing nipple.
Subsea tree testing
During drift testing, it is essential to ensure that the bores containing valves and valve block assemblies are drifted using the appropriate bore drift as outlined in ISO 13628-4 before the final assembly of the subsea tree Additionally, vertical runs of the fully-assembled subsea tree must be drifted with the specified tubing drift according to ISO 11960 Furthermore, all TFL-access bores of the fully-assembled subsea tree should be thoroughly tested with the appropriate drifts as specified in section 6.4.
The subsea tree and tree loops, fully assembled, will undergo testing as per ISO 13628-4:1999, section 7.16 Additionally, the piping located downstream of the first wing valve will be tested according to the relevant pipeline code.
Tubing hanger design
The tubing hanger is a crucial component of the TFL system, situated between the subsea tree and the downhole tubing strings It offers essential structural support for the tubing string, ensures pressure containment, and facilitates access between the tubing string and the subsea tree.
The hanger must feature a profile designed to accommodate tubing hanger plugs, with a sealing bore diameter that aligns with the specifications in Table 4 Additionally, any internal profile recesses should adhere to clause 8 The top recesses of the tubing hanger, intended for tree tubing-stabs, should include conical transition surfaces and a minimum gap length as illustrated in Figure 22 Furthermore, the thread preparations at the bottom of the tubing hanger also require conical transition surfaces and a minimum gap, as depicted in Figure 22.
Table 4 — Landing nipple sealing bore dimensions
Tubing size OD mm (in)
Sealing bore diameter mm (in)
Tubing hanger testing
Tubing hanger bores shall be drifted with the appropriate tubing drift as specified in ISO 11960.
All TFL access to the tubing hanger shall be tested throughout with the appropriate drifts in 6.4.
The tubing hanger should be tested in accordance with ISO 13628-4.
Diverters, deflectors and selectors
Diverters, deflectors, and selectors are essential components for directing TFL tools at branch connections Diverters are active devices operated by a TFL operator, allowing tools to navigate between two possible passageways In contrast, deflectors are passive devices that guide tools along a single passageway Selectors, also active devices, enable tools to be directed through multiple passageways.
There are two types of deflector, as follows: a) wedge (or wireline) deflector
The wedge deflector is a wireline-installed device designed with a contoured bottom that fits the curved passageway of a wye spool Once positioned in the vertical bore, it acts as a passive barrier, preventing further vertical access and guiding tools through the TFL-access bore During workover operations, the deflector can be removed from the tree using wireline techniques to restore vertical access to the well.
2 Wireline internal profiles and recesses for orienting and locking wedge in wye spool
Figure 23 — Wye spool with wedge deflection b) paddle (or detent) deflector
The paddle deflector is a device integrated into a wye spool featuring a "paddle" gate, designed to fit both the vertical bore and the TFL access bore It includes a detent mechanism that secures the paddle in one of two positions As a passive device, it is activated by the movement of the tool-string; when a tool approaches from the vertical bore, the paddle shifts to allow passage and then redirects the tool on its return Conversely, when a tool enters from the TFL access bore, the paddle moves to accommodate this entry, remaining in place for the return journey.
Figure 24 — Wye spool with flapper deflection 7.5.3 Diverters
There are two types of diverter which typify the various options available: a) paddle diverter
The paddle diverter is an active device integrated into a branch connection, featuring a paddle gate It utilizes a rotary or manual actuator to rotate the paddle between two positions, allowing for efficient flow direction control.
The plug diverter is a specialized device integrated into a branch connection, featuring a cylindrical "plug" with one or two holes designed to match the shape of the passageway This active device utilizes either a linear or rotary actuator to adjust the position of the plug, aligning the holes with the designated passageway as needed.
A TFL selector is an active device integrated into a multi-branched piping system that channels TFL tools from a single entry point to multiple outlets It comprises a moving section, a fixed section, and an indexing mechanism that aligns the two sections to a specific orientation.
Diverter design
Diverters intended for TFL service must adhere to specific design criteria, including ensuring that any straight or curved TFL-access bore matches the minimum internal diameter after bending as outlined in Table 2, with bends conforming to clause 6 Additionally, mechanical end connections at the entry or exit ports should feature conical transition surfaces and a minimum gap length as depicted in Figure 19 Welded connections at these ports must also comply with clause 6 Furthermore, selectors with reverse bends (S-bends) must include a straight section between the tangent of the bends that is long enough to accommodate the appropriate TFL drift and tools specified in clause 6.
Diverter testing
The bores of a diverter shall be tested while connected to the piping, using the appropriate drifts specified in 6.4.
The diverter shall be tested in accordance with the piping test code appropriate to its location and function within the TFL system.
General
The completion equipment and tools form a crucial part of the TFL system, connecting the wellhead to the production zone It is essential to design well completions to minimize tool manipulations during servicing An example of a completion setup includes production casing, tubing, landing nipples, circulating valves, and packers Additionally, the design must account for temperature and pressure variations from cold fluid circulation, as well as the jarring and water hammer effects associated with pumping operations.
TFL completions utilize a circulation member to establish a circulation path, distinguishing them from wireline completions To enhance TFL service capability and reduce fluid loss to the formation, standing valves are typically installed Additionally, the design of the completion significantly influences TFL service capabilities and procedures, with more complex designs enabling a wider range of services while simplifying the service procedures.
When designing completions, it is essential to determine production and service requirements to tailor the design accordingly The depth of the circulation member significantly influences service potential; deeper circulation members enhance serviceability by allowing tool circulation to the well's lowest point and minimizing the need for reach-rod or spacer-bar work Additionally, incorporating isolation and production devices, such as foot valves and sliding side-doors, facilitates the retrieval of standing valves for maintenance while preserving the integrity of the TFL service system It is also advisable to consider alternative TFL service procedures in case of issues with primary methods Lastly, maintaining consistent tubing and flowline inner diameters is crucial for optimizing piston unit compatibility and performance.
Injection wells require careful attention as standing valves must be removed during the injection process Expendable standing valves can be installed prior to TFL service and removed before injection resumes It is crucial to design completions with access for the installation and proper removal of these valves, especially in dual-string completions.
Wireline and TFL equipment differ significantly, particularly in their component design and functionality TFL wells utilize moulded seals for packing bores instead of traditional V-packing, enhancing sealing efficiency Additionally, TFL tools are engineered to facilitate continuous fluid circulation, even after being positioned in the downhole nipple.
Completion design
Annex C presents four fundamental completion designs: the single string, single zone, annular circulation type (Figure C.1), the single string, single zone, side string circulation type (Figure C.2), the dual string, single zone type (Figure C.3), and the dual string, dual zone type (Figure C.4).
The selection of completion design should be determined with considerations given to ắ economics; ắ production and injection requirements; ắ service requirements; ắ secondary recovery requirements.
Annex C may be consulted for further details regarding completion concepts.
Tubing
Standard tubing sizes ranging from 60.3 mm to 114.3 mm (2 3/8 in to 4 1/2 in) are commonly utilized in TFL installations These installations have effectively employed API and various premium thread joints It is essential that joint transitions meet the requirements outlined in clause 6 and Figure 16.
Surface-controlled subsurface safety system
Appropriate consideration shall be given to the design of the surface-controlled subsurface safety system These are: ắ valve selection
TRSVs are more efficient than TFL-retrievable valves, as they eliminate the need for retrieval and rerunning before and after service work, thereby reducing service times The long TFL flowlines make it possible to save on both time and costs by avoiding two service trips It is advisable to consider TFL-retrievable insert valves as backup options for TRSVs to maintain control system pressure.
TFL wells, often located subsea, require careful evaluation of control system pressure capabilities Unlike wireline-serviced wells, these systems must manage not only shut-in well pressures but also keep the safety valve open during peak TFL service pressures If single line type valves are utilized, the control system pressure must meet or exceed the greater of the maximum tubing pressure or maximum TFL service pressure, in addition to the valve hold-open pressure Employing balanced type (dual-line) or nitrogen-charged safety valves can lower control system pressure requirements, as they are less affected by tubing pressure It is crucial that the hold-open force of any TRSV is adequate to counteract TFL-piston drag forces during the upward movement of the TFL tool A TRSV with a larger piston area enhances hold-open force, preventing inadvertent valve closure Consultation with the TFL equipment manufacturer is essential to ensure the compatibility of safety valves and control systems.
Maintaining circulation is essential for TFL servicing When utilizing a TRSV with a TFL-retrievable SVLN back-up capability, it is crucial to implement special control line routing The control line should be directed to the TRSV via a lockout isolation/redirection feature before reaching the SVLN This design ensures that control line access to the SVLN is restricted until the TRSV is securely locked out of service, thereby preventing any loss of control pressure in the TRSV due to unintended shifting of the SVLN sleeve.
The design and procedures must ensure that the TFL-retrievable safety valve remains open until the hold-open hydraulic pressure is achieved, as neglecting this feature may lead to a loss of TFL circulation Additionally, an emergency shear feature should be included in the running tool to facilitate retrieval while the valve is mechanically held open, thus enabling continued circulation.
When designing a safety system, it is crucial to assess the total depth, which includes the water depth In single-line installations, the minimum tubing pressure at the safety valve must be taken into account, as it can enable a reduction in control system pressure while still maintaining the fail-safe functionality of the safety valve.
Packers
Full-bore packers are typically utilized in suitable conditions, with any shoulders or internal profiles featuring chamfers as shown in Figures 16 and 28 For TFL completions, packers are often specially designed to withstand the elevated pressures associated with TFL operations It is essential to set hydraulic packers at the maximum anticipated TFL operating pressure to ensure optimal packer movement, including stroking, seal compression, and slip movement, which should be thoroughly tested during the initial completion phase.
1 ID orR 1 a 0,25 mm to 0,50 mm (0,01 in to 0,02 in) chamfer 43°to 47° b See Table 4. t=R 2 –R 1 wheret= wall thickness
Telescoping joints
In TFL completions, tubing strings experience significant temperature fluctuations, ranging from heating during production to cooling during operations To manage these temperature extremes, telescoping joints are incorporated into the completion design.
Telescoping joints designed for TFL completions have specific requirements due to their operational conditions The stroke length is limited to less than 1.0 m (3 ft) to ensure that TFL piston units can effectively traverse the joint while spanning the enlarged inner diameter when fully expanded Additionally, given the higher operating pressures, potential water-hammer effects, and temperature fluctuations in TFL operations, it is crucial to assess the movable sealing mechanism in the telescoping joint for high reliability under these challenging conditions.
Multiple telescoping joints are typically necessary in a tubing string due to the recommended stroke limitation of 1.0 m (3 ft) To ensure efficient transport of the piston unit, these joints should be spaced with at least one tubing joint between them It is also important to position the telescoping joints away from nipples and other service work areas In dual-string completions, adjacent placement of telescoping joints should be avoided to prevent potential interference during stroking.
Landing nipples
Landing nipples are tubular members that allow TFL retrievable equipment to be located, locked and sealed downhole.
Landing nipple internal profiles facilitate the transition to the nominal tubing internal diameter, allowing piston units and retrievable tools to pass through It is essential that the entry and exit surfaces are designed to reduce seal element damage and ensure smooth tool passage.
Design practices for TFL landing nipples require internal profile entry and exit angles of 30° or smaller to ensure smooth tool passage, reduce tool wear, and prevent damage to seals and pistons For no-go shoulders and locking profile recess angles, a minimum of 45° is acceptable on load-bearing surfaces, while non-load-bearing surfaces should maintain angles of 30° or smaller, with sharp corners chamfered Location-type profiles must adhere to specified entry and exit angles, with square shoulders allowed but corners needing a defined chamfer Additionally, sealing bores used in TFL operations should feature entry and exit angles of 15°, as detailed in industry standards.
Circulation members
A circulation member is essential for enabling the pumping of TFL tools into and out of the well, as well as for displacing well fluid with TFL service fluids before service operations It should be positioned close to the deepest anticipated service point to facilitate the circulation of tools to the lowest well points without the need for long reach rods or spacer bars The circulation member can be installed below the packer or at any suitable location within the tubing string, and it comes in various standard designs.
A double-bored block facilitates the passage of tools and features a communication port between the bores Typically, no-go or selective landing nipples are positioned above the block, while polished subs are connected below the H-member block This configuration enables the installation of a CCV (refer to section 8.9) or a pack-off across the communication port, effectively isolating the tubing string.
The tool functions like a side-pocket mandrel but includes an additional side string that connects to the mandrel's pocket section By adjusting a CCV in the mandrel pocket, communication between the two strings can be effectively managed This design is beneficial for emergency circulation or as a primary circulation member when a through tubing bore is necessary while the CCV remains in position.
A single tubing string can be utilized with a straight-through bore for TFL service, featuring a smaller side-string offset that connects to the main tubing bore The offset string serves solely to establish the circulation path, without providing access to TFL.
The design of the nipple features uniform upper and lower connections, facilitating TFL access from either string to a point below the wye This configuration is typically utilized in dual-string completions alongside a single packer.
Provides for circulation between the tubing and casing for annular circulation completions (see Figure C.1).
A landing nipple is installed above the ports, while a polished bore is located below the ports, facilitating the isolation of the annulus during production or injection through a CCV in a side-pocket mandrel.
A side-pocket mandrel featuring an enlarged port area serves as an effective circulation member, akin to the functionality of a ported nipple This design enables the installation of a CCV within the side-pocket while maintaining an unrestricted through-bore for optimal performance.
Up-hole or alternate circulation members facilitate fluid communication for operations like gas-lifting, emergency circulation, and sand-washing These members must include a mechanism for isolating communication to enable tool-string operation with the primary circulation member Various retrievable devices, including SDCs, check valves, and dummy plugs, are utilized to isolate the circulating port effectively.
To prevent damage to passing seals and reduce the risk of pressure-differential-induced lock-up of tools, it is essential to prepare the exposed side outlets of a circulation crossover in accordance with clause 6.
Circulation controls
A circulation control device (CCV) is essential in certain completion designs to facilitate communication during TFL service and to isolate tubing strings or tubing/casing during production or injection The CCV can be installed either concentrically or in a side-pocket and is initially set in the open position to enable circulation for the retrieval of the TFL-service tool-string The valve is closed after TFL service and reopened for subsequent services by adjusting the system pressure CCVs are particularly important in multi-zone completions where the mixing of zones is not allowed or is undesirable.
Emergency circulation devices (ECDs) can be installed in circulation members as pressure-manipulated valves that operate in a closed position These devices are strategically placed in an up-hole or alternate circulation member to ensure emergency circulation when the primary circulation member is obstructed by debris or sand.
Standing valves and isolation/production devices
TFL-retrievable standing valves, also known as check valves, are integral components in TFL production completions These valves facilitate the entry of production fluids into the tubing while effectively blocking TFL service fluids from entering the formation, thereby ensuring accurate pressure response at the TFL control console They can be installed in various types of landing nipples, including selective landing nipples, no-go nipples, or isolation/production devices, and may feature shear-out capabilities to enable pumping into the formation.
An isolation/production device is designed to be tubing-retrievable, opening when the standing valve is set and closing upon retrieval, effectively isolating the well formation There are two main types of these devices: one permits production through annular access below the packer, while the other allows production through the bottom of the tubing and can be positioned anywhere in the tubing string The latter type should be installed close to a circulation member to facilitate TFL service.
TFL tools are engineered to accommodate a bend radius of 1,524 mm (60 in) The minimum loop bore IDs for the various tool sizes can be found in Table 2 under the "minimum ID after bending" column.
In the design of tools, it is essential to maximize segment length to avoid excessive tool-string articulation, thereby minimizing handling issues Tools should be designed for running, activation, and setting with minimal system manipulation Additionally, provisions must be made for tool manipulations and dynamic loads, including impact loads, cyclic pressures, and water-hammer encountered during TFL operations Shear pins should be designed to retain all pieces within the tool to prevent loose metal from interfering with operations or entering the flowline system Furthermore, all threaded connections should incorporate a mechanical locking device, such as a roll pin, set-screw, or jam nut, to counteract the loosening effects of impact and vibration on the tool-string.
General
This article outlines essential requirements and recommendations for operating TFL equipment and tools in subsea satellite wells and template/manifold production systems These guidelines have been developed through practical experience and effective methodologies Operators may also utilize their own preferred techniques tailored to specific well applications For additional recommendations, refer to API RP 17A [4].
Personnel and training
Effective planning of all aspects of the TFL project from the initial stages is crucial for successful maintenance operations This planning must encompass training provisions for personnel engaged in well-maintenance tasks TFL operators should possess experience in maintenance, be well-versed in well completion processes, wireline maintenance operations, hydraulic parameters of TFL services, and have a solid understanding of general offshore and subsea operations.
9.2.2 TFL operators shall be trained in the subsea control system, emergency shutdown procedures and pressure readings being received from different points.
Operators must receive training on the TFL equipment in use and the well completion being serviced This training should cover the equipment's functionality, including tool setting pressures, sliding sleeve shift pressures, and shear pin shear pressures for different tool operations.
Completion equipment
Key considerations include TFL piping, subsea trees, and downhole equipment During the project planning phase, TFL piping, as outlined in clause 6, along with tree and tubing hangers discussed in clause 7, must be designed to accommodate TFL tools to reduce service issues Essential planning elements involve the positioning of in-line chokes, the placement of blast joint indicators, and the arrangement of valving, diverters, and plug bore recesses.
Downhole equipment shall be planned and checked for the following: ắ tool passage
All downhole equipment shall be checked for compatibility with TFL tools. ắ spacing of the completion
To prevent tubing buckling during the landing of completions and setting of packers, it is essential to properly space the tubing above the top packer and between packers in multi-zone completions, especially due to the significant temperature fluctuations experienced in TFL operations.
Certain components in the completion can be influenced by differential or system pressures Incorrect pressure application or improper tool setup may lead to unintended tool activation, adversely affecting the completion's serviceability It is essential to design tool operating pressures with adequate spacing to prevent accidental operation, particularly during the shifting of lockout profiles.
Consideration should be given to items which could cause accidental location with selective keys If different manufacturers' profiles are involved, they should be assessed for compatibility.
Satellite well and template well control systems
9.4.1 The control systems for TFL satellite and template wells are usually complex The TFL operator shall be knowledgeable of the control system basics and response times.
The subsea control system must be designed to allow the TFL operator to take control of specific valve functions during maintenance operations on the well This includes managing in-line valves and diverters that impact TFL operations, such as riser isolation valves, flowline isolation valves, tree master valves, and downhole safety valves Additionally, these control functions should be integrated with emergency shut-down systems, enabling the TFL operator to temporarily override them to safely pump tools away from valves, thereby preventing any potential closure on the tool-string.
Service planning and documentation
The TFL operator must examine the current well history file before commencing TFL operations A comprehensive service procedure should be developed and assessed The operator is accountable for preparing and setting up the equipment, which includes determining the appropriate shear pin size and material for running and pulling tools, configuring the shear up/down mode of the pulling tool, ensuring shear pins are locked, and setting the shear pressures for prongs and kickover tool activation It is advisable to test the equipment prior to use to verify its operational condition.
The TFL operator must thoroughly document all activities and maintain the well history file This documentation should encompass reports that include relevant sections of strip-chart recordings when necessary or applicable.