COMPACT COMPENSATING CYLINDER

Abstract

A compensating cylinder unit for compensating relative movements between a stationary frame and a compensated frame which includes parts of a coiled tubing compensation system. The compensating cylinder unit includes a fluid reservoir configured to connect to the stationary frame, and a compensating cylinder configured to connect to the compensated frame, to at least partly enclose the fluid reservoir, and to be in a fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir.

Description

FIELD

The present invention relates generally to the field of floating offshore platforms or vessels for the exploitation of undersea deposits of petroleum and natural gas. The present invention more specifically relates to compensating cylinders for compensating relative movements within a coiled tubing compensation system.

BACKGROUND

Coil tubing provides a rig crew with a quick and easy access to live wells in order to perform various well intervention operations. The coil tubing equipment generally consists of a coiled tube, a drive unit, and a control cabinet. The equipment is normally not fixed to one rig, but can be transported between various locations. The coil tubing has a long track record for onshore land drilling, where the implementation is fairly simple. When used offshore on floating drilling units, it must also have some sort of compensation. With a traditional derrick with a drill string compensator or a ram rig system, the drive unit of the coil tubing is supported in a fixed coil tubing unit. This is hung up in either the elevator or the bails. Many of the latest rigs have substituted the regular drill string compensator with an active compensated drawwork. This is, however, not suitable for the more fragile operations like coil tubing. Any abruption of the active compensation when the coil tubing is fixed to seabed may easily destroy the coil tubing. The coil tubing frame itself must have a compensating feature in such cases.

There have been some recent proposals to address the challenge of obtaining active compensation while providing a satisfactory low risk of abruption. WO 2005/061803 describes an inline compensator with two passive cylinders on a frame replacing the vertical beams. US 2012/0227976 A1 describes a similar solution.

Common for the previously-described compensation systems is that the pressure vessels are not located on the compensating unit itself. The supply of compressed air to drive the compensation motion is furthermore performed by one or two relatively large size hoses, which is highly unfavorable for safety reasons.

SUMMARY

An aspect of the present invention is to provide a less space demanding yet secure compensating cylinder when installed in a system such as in a coil tubing system. Another aspect of the present invention is to provide a less space demanding compensating cylinder also after decoupling from the operational system, for example, during transport.

In an embodiment, the present invention provides a compensating cylinder unit for compensating relative movements between a stationary frame and a compensated frame which includes parts of a coiled tubing compensation system. The compensating cylinder unit includes a fluid reservoir configured to connect to the stationary frame, and a compensating cylinder configured to connect to the compensated frame, to at least partly enclose the fluid reservoir, and to be in a fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basis of embodiments and of the drawings in which:

FIG. 1 shows a cross sectional side view of a compensated coil tubing frame in accordance with the present invention, including a support structure and a coiled tubing rigup;

FIG. 2A shows a cross sectional side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, where the accumulator assembly is stroked in an intermediate position relative to the surrounding compensating cylinder;

FIG. 2B shows a cross sectional side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, where the accumulator assembly is stroked in an intermediate position relative to the surrounding compensating cylinder;

FIG. 2C shows a cross sectional side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, where the accumulator assembly is stroked in an intermediate position relative to the surrounding compensating cylinder;

FIG. 2D shows a cross sectional side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, where the accumulator assembly is stroked in an intermediate position relative to the surrounding compensating cylinder;

FIG. 3A shows a side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, the accumulator assembly being stroked in an upper position relative to the surrounding compensating cylinder;

FIG. 3B shows a side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, the accumulator assembly being stroked in an upper position relative to the surrounding compensating cylinder;

FIG. 4A shows a side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, the accumulator assembly being stroked in a lower position relative to the surrounding compensating cylinder;

FIG. 4B shows a side view of a compact compensating cylinder unit in accordance with the present invention in an operational mode, the accumulator assembly being stroked in a lower position relative to the surrounding compensating cylinder;

FIG. 5A shows a side view of a compact compensating cylinder unit in accordance with the present invention in a retracted transport mode;

FIG. 5B shows a side view of a compact compensating cylinder unit in accordance with the present invention in a retracted transport mode; and

FIG. 5C shows a side view of a compact compensating cylinder unit in accordance with the present invention in a retracted transport mode.

DETAILED DESCRIPTION

The present invention in particular relates to a compensating cylinder unit suitable for compensating relative movements between a stationary frame and a compensated frame constituting parts of a coiled tubing compensation system, where the compensated frame is connected to the compensating cylinder. All the necessary tools for the coiled tubing system may be arranged on the compensated platform in order to provide compensation of vertical movements during operation. The cylinder unit comprises a compensating cylinder suitable for connection to the compensated frame and a fluid reservoir suitable for connection to the stationary frame, wherein the compensating cylinder is in fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir. The compensating cylinder is furthermore characterized in that it at least partly encloses the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, for example, further comprise a gas reservoir having a second gas reservoir end and a connection element fixed to the second gas reservoir end and arranged into an opening within a first fluid reservoir end of the fluid reservoir, creating an axial interconnection between the gas reservoir and the fluid reservoir, wherein the cylinder is slidingly arranged around the circumference of the connection element. The connection element may display at least one pressure equalizing channel enabling fluid communication between the reservoirs. The connection element may furthermore comprise an outward protruding piston flange, wherein the connection element releasably interconnects the second gas reservoir end to the first fluid reservoir end through abutment of an outer radial surface of the protruding piston flange against an inner radial surface of the first fluid reservoir end.

In an embodiment of the present invention, a first fluid reservoir end of the fluid reservoir can, for example, comprise an outward protruding fluid reservoir flange.

In an embodiment of the present invention, the cylinder unit can, for example, further comprise a gas reservoir, wherein the cylinder, the gas reservoir and the fluid reservoir are mutually displaceable in the axial direction, the displacements being confined between an operational configuration where the gas reservoir is locked to the fluid reservoir and a transport configuration where the outer surface of a first fluid reservoir end of the fluid reservoir abuts the inner surface of a first cylinder end of the cylinder, and where the gas reservoir is axially released from the fluid reservoir. The term “locked” is defined as the situation where the gas reservoir is immovable or almost immovable relative to the fluid reservoir. The cylinder unit may further comprise a connection element fixed to a second gas reservoir end of the gas reservoir and arranged into an opening within a first fluid reservoir end of the fluid reservoir so as to create an axial interconnection between the gas reservoir and the fluid reservoir, and where the transport configuration includes abutment of the surface of the connection element towards the inner surface of a second fluid reservoir end of the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, for example, further comprise a fluid channel enabling fluid communication between the fluid reservoir and a volume within the cylinder situated outside the fluid reservoir. The fluid channel may extend from a second fluid reservoir end of the fluid reservoir to the volume within the cylinder situated outside the fluid reservoir. The fluid channel may further comprise a through-going accumulator passage penetrating the second fluid reservoir end. The fluid channel may further comprise a fluid guiding feeding tube extending from a second fluid reservoir end of the fluid reservoir within the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, for example, further comprise a gas reservoir comprising a second gas reservoir end and a connection element fixed to the second gas reservoir end comprising a radial channel, where the connection element is arranged into an opening within a first fluid reservoir end of the fluid reservoir so as to create an axial interconnection between the gas reservoir and the fluid reservoir. The fluid guiding feeding tube may further comprise at least one radial bore being alignable to the at least one radial channel to enable fluid communication between the feeding tube and a volume within the cylinder situated outside the fluid reservoir and the gas reservoir. Note that there is no fluid communication between the pressure equalizing channel(s) and the radial channel(s).

In an embodiment of the present invention, the axial walls of the compensating cylinder can, for example, slidingly surround the connection element, the second gas reservoir end, and the first fluid reservoir end, so as to form a fluid tight first cylinder chamber bounded by at least inner walls of the cylinder, the outer walls of the gas reservoir, and an outer radial surface of the first fluid reservoir end facing a first axial cylinder end of the cylinder. Note that “fluid tight” must be interpreted in accordance with the prevailing requirements of the technical field in question. The first fluid reservoir end may comprise an outwardly protruding fluid reservoir flange creating a second cylinder chamber bounded by at least the inner walls of the cylinder, the outer walls of the fluid reservoir, and an outer radial surface of the protruding fluid reservoir flange of the first fluid reservoir end facing away from the first fluid reservoir end. The volume of the second cylinder chamber can be less than the volume of the first cylinder chamber. The second cylinder chamber can furthermore be connected to a pressure control device which enables pressure adjustments within the second cylinder chamber, for example, an external accumulator and/or an active control system.

In an embodiment of the present invention, the cylinder unit can, for example, further comprise a fluid channel enabling fluid communication between the fluid reservoir and the first cylinder chamber, where the fluid channel comprises a through-going accumulator passage penetrating a second fluid reservoir end of the fluid reservoir, a valve device arranged outside the fluid reservoir in fluid communication with the through-going accumulator passage, and a fluid guiding feeding tube comprising a first longitudinal end arranged in fluid communication with the first cylinder chamber during operation and a second longitudinal end arranged in fluid communication with the valve device.

The present invention also provides a method for altering a compensating cylinder unit from an operational configuration to a transport configuration, which compensating cylinder unit comprises a compensating cylinder, a fluid reservoir, and a gas reservoir interconnected in fluid communication with the fluid reservoir. The compensating cylinder is in fluid communication with the fluid reservoir in order to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir. The method comprises the steps of:

venting the volumes within the compensating cylinder and both reservoirs to an ambient pressure;

optionally releasing the interconnection between the gas reservoir and the fluid reservoir; and

applying an external contraction force on one or both axial sides of the cylinder unit to axially displace the gas reservoir relative to the fluid reservoir.

The compensating cylinder unit used in the method may be in accordance with the compensation cylinder described above.

The present invention also provides a coiled tubing compensation system comprising a stationary frame, a compensated frame, and a compensating cylinder unit in accordance with the cylinder unit described above, wherein the stationary frame connects to the fluid reservoir and the compensated frame connects to the compensating cylinder. The system may comprise at least two compensating cylinder unit having their longitudinal axes arranged in parallel. The term “stationary” means stationary relative to an underlying platform or vessel.

Numerous specific details are introduced in the following description to provide a thorough understanding of, and an enabling description for, embodiments of the claimed apparatus and method. One skilled in the relevant art will recognize, however, that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

FIG. 1 shows the main components of a coiled tubing system 30 in accordance with the present invention. The coiled tubing system 30 comprises a coiled tubing machine (injector head) 31 containing the mechanism to push and pull a coiled tubing pipe or string 34 in and out of a well (not shown). The coiled tubing machine 31 has a curved guide beam 32 on top, often called a guide arch or gooseneck, which threads the coiled tubing pipe 34 into the body of the coiled tubing machine 31. A blowout preventer (BOP) 33 may be arranged to form an intermediate component between the coiled tubing machine 31 and the coiled tubing pipe 34. The BOP 33 may cut the coiled tubing pipe 34 with subsequent sealing. Components 31-34 are supported on a compensated frame 50 where each longitudinal end is connected to a compensating cylinder 1 of an inventive compensating cylinder unit 100 having the ability to compensate for environmentally induced forces such as sea current or sea waves. The compensating cylinder unit 100 thus forms an integral part of the coiled tubing system 30. The two longitudinal ends 10a, 5b of each compensating cylinder unit 100 are connected to a common top frame 60 and a common lower support frame 40, respectively. As will be apparent from the description below, the accumulator and pressure vessels 5,10 are included into the compensating cylinder 1. There is thus no need for large hydraulic or pneumatic hoses to external sources. The top frame 60 interfaces the lifting equipment in the derrick, and the lower support frame 40 may rest on deck. The structure that bonds the two cylinder tubes together will now function as a compensated platform for where to place all the necessary tools for the coil tubing system. This particular configuration separates this arrangement to a large degree from similar prior art systems which must be lifted well clear of the drill floor (not shown).

FIG. 2A shows a principal side view sketch of the compensating cylinder unit 100 in accordance with the present invention. A pressure vessel 10 and a fluid accumulator 5 are interconnected via a central piston 2, forming an accumulator assembly. The central piston 2 is fixed to a lower axial vessel end 10b of the pressure vessel 10 and is releasably fixed to a protruding upper axial accumulator end 5a of the fluid accumulator 5. The latter connection may be obtained by maintaining a protruding piston flange 14 pushed towards the inner surface of protruding upper axial accumulator end 5a by pressure or other suitable means. The fluid accumulator 5 and the pressure vessel 10 are further slidingly journaled into a common compensating cylinder or barrel 1, forming a closed annulus cylinder chamber between the inner wall of the compensating cylinder 1 and the outer wall of the journaled accumulator assembly 5,10. The cylinder chamber is divided into an upper cylinder chamber 1′ and a lower cylinder chamber 1″ by the protruding upper axial accumulator end 5a. The other longitudinal ends of the upper and lower cylinder chambers 1′,1″ are bounded by an upper axial cylinder end la and a lower axial cylinder end lb, respectively. One or more through-going axial drillings 6 are provided into the central piston 2 in order to provide fluid communication between the interior of the pressure vessel 10 and the interior of the fluid accumulator 5. A fluid channel 8 (FIG. 2B) is further provided to run from the interior of the fluid accumulator 5 to the upper cylinder chamber 1′. This fluid channel 8 comprises:

• • a lower end accumulator drilling 12 penetrating a lower axial accumulator end 5b;
  • a suitable feeding tube 11 comprising upper and lower longitudinal ends 11a,11b arranged from the lower axial accumulator end 5b to at least near the lower axial vessel end 10b;
  • a valve device 13 providing a controllable fluid communication between the lower accumulator drilling 12 and the feeding tube 11; and
  • one or more radial oriented bores 20 arranged at an upper longitudinal end 11a of the feeding tube 11 providing fluid communication between the interior of the feeding tube 11 and the upper cylinder chamber 1′.

FIG. 2B provides further operational details of the compensating cylinder unit 100 indicating by arrows the pathway of the fluid channel 8. The fluid accumulator 5 in FIG. 2B is illustrated as partly filled with pressurized fluid 22, while the pressure vessel 10 is illustrated as filled with pressurized gas 21 (for example, air). Due to the through-going axial drillings 6, the pressures in the pressure vessel 10 and the fluid accumulator 5 are equalized. If the valve device 13 is opened, the pressurized fluid 22 is forced through the fluid channel 8 into the upper cylinder chamber 1′ via the axial feeding tube 11 and the radial bores 20. As a result, the pressure in the pressurized fluid 22 is converted to a force within the upper cylinder chamber 1′ of the cylinder 1 that equals the effective chamber or annulus area times the fluid pressure. The axial force components (F_a) acting on the inner surface of an upper axial cylinder end la of the cylinder 1 and the outer surface of the protruding upper axial accumulator end 5a cause a vertical motion of the cylinder 1 when the fluid accumulator 5 is fixed to a rigid support such as a compensated frame 50 (FIG. 1). For example, if the axial (or vertical) force components (F_a) within the upper cylinder chamber 1′ increases due to increased pressure within the fluid channel 8, the accumulator assembly 5,10 moves along the axial direction of the cylinder 1 away from the upper cylinder end 1a. Likewise, if the axial (or vertical) force components (F_a) within the upper cylinder chamber 1′ decreases due to decreased pressure within the fluid channel 8 and the fluid accumulator 5, the accumulator assembly moves along the axial direction of the cylinder 1 towards the upper cylinder end 1a. A compensating effect similarly to the effect of the prior art compensating cylinders is consequently achieved, but with a more compact compensating cylinder unit 100.

Due to the different outer diameters of the pressure vessel 10 and the fluid accumulator 5, the forces acting in the upper cylinder chamber 1′ is in general larger than the forces acting in the lower cylinder chamber 1″. The lower cylinder chamber 1″ may be connected to a low pressure accumulator to keep the chamber volume oil-filled and lubricated. It may, however, also (or alternatively) be used to actively control the compensation in a similar way as, for example, in low pressure accumulator of prior art dual acting type cylinders. By adding an active control loop such as a hydraulic control loop to the lower cylinder chamber 1″, the force of the overall cylinder tensioning may be controlled by use of active means. The nature of a regular passive cylinder is that the pressure in the pressure vessel often varies with the position of the compensator stroke, which in general is undesired. The effect can be neutralized, or nearly neutralized, via the mentioned control loop, resulting in a cylinder providing a more stable compensating force throughout the stroke length compared with cylinders without active control loops.

An about 1:22 scale side view drawing of an operational compact compensating cylinder unit 100 in an intermediate stroke position and a corresponding sectional drawing along line B-B is shown in FIGS. 2C and 2D, respectively. The valve device 13 providing controlled fluid communication between the lower accumulator drilling 12 and the feeding tube 11 is partly illustrated in FIG. 3D.

FIGS. 3A and 3B show side view drawings of the same operational compensating cylinder unit 100 as in FIGS. 2C and 2D (the latter along D-D) but where the accumulator assembly 5,10 is stroked in an upper position relative to the surrounding compensating cylinder 1, i.e., a position where the outer radial surface of the protruding upper axial accumulator end 5a abuts the inner radial surface of the upper cylinder end la due to increased pressure force (F_a) within the first cylinder chamber 1′. FIGS. 4A and 4B also show side view drawings as in FIGS. 2C, 3A,2D, and 3B, respectively (FIG. 4B seen along C-C of FIG. 4A), but where the accumulator assembly 5,10 is stroked in a lower position relative to the surrounding compensating cylinder 1, i.e., a position where the outer radial surface of the protruding upper axial accumulator end 5a facing towards the lower axial accumulator end 5b abuts the inner radial surface of the lower cylinder end lb due to decreased pressure force (F_a) within the first cylinder chamber 1′.

FIG. 5A shows a principal side view sketch of the compensating cylinder unit 100 in accordance with the present invention and arranged in a retracted transport mode, i.e., a position where the outer radial surface of the protruding upper axial accumulator end 5a abuts the inner radial surface of a first cylinder end la, while the radial surface of the central piston 2 abuts the inner radial surface of the lower axial accumulator end 5b. This transport configuration or mode may be obtained by axially releasing the pressure vessel 10 from the fluid accumulator 5, for example, by venting the volumes within the compensating cylinder 1, the fluid accumulator 5 and the pressure vessel 10 to an ambient pressure and/or imparting an axial force on the cylinder unit 100, thereby enforcing an axial movement of the fluid accumulator 5 into the pressure vessel 10. Note that the central piston 2 on the pressure vessel 10 may be releasably connected to the fluid accumulator 5 by means other than, or in addition to, pressure induced connection, for example, via various mechanically-releasable coupling devices. An about 1:22 scale side view drawing of a compact compensating cylinder unit 100 as in FIG. 5A, i.e., retracted transport mode, and a corresponding sectional drawing along line A-A is shown in FIGS. 5B and 5C, respectively.

In the preceding description, various aspects of the system and method according to the present invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations are set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention. Reference should also be had to the appended claims.

LIST OF REFERENCE NUMERALS

• F_a Axial/vertical force component/pressure force
• 1 Compensating cylinder/barrel
• 1′ First cylinder chamber/upper cylinder chamber
• 1″ Second cylinder chamber/lower cylinder chamber
• 1 a Upper cylinder end/upper axial cylinder end/first cylinder end
• 1 b Lower cylinder end/lower axial cylinder end
• 2 Central piston/connection element
• 5 Fluid accumulator/fluid reservoir
• 5 a Protruding upper axial accumulator end/first fluid reservoir end
• 5 b Lower axial accumulator end/second fluid reservoir end
• 6 Axial drilling/pressure equalizing channel
• 8 Fluid channel
• 10 Pressure vessel/gas reservoir
• 10 a Upper axial vessel end/first gas reservoir end
• 10 b Lower axial vessel end/second gas reservoir end
• 11 Fluid guiding feeding tube/feeding tube
• 11 a Upper longitudinal end/first longitudinal end
• 11 b Lower longitudinal end/second longitudinal end
• 12 Lower end accumulator drilling/Through-going accumulator passage
• 13 Valve device
• 14 Protruding piston flange
• 16 Protruding accumulator flange/protruding fluid reservoir flange
• 20 Radial bore
• 21 Pressurized gas
• 22 Pressurized fluid
• 23 Radial channel
• 30 Coiled tubing system/Coiled tubing compensation system
• 31 Coiled tubing machine/injector head
• 32 Curved Guide beam/Guide Arch/Gooseneck
• 33 Blowout Preventer (BOP)
• 34 Coiled tubing pipe/Coiled tubing string
• 40 Lower support frame/stationary frame
• 50 Compensated frame
• 60 Upper support structure/Top frame
• 100 Compensating cylinder unit

Claims

1-20 (canceled)

21. A compensating cylinder unit for compensating relative movements between a stationary frame and a compensated frame comprising parts of a coiled tubing compensation system, the compensating cylinder unit comprising: a fluid reservoir configured to connect to the stationary frame; anda compensating cylinder configured to connect to the compensated frame, to at least partly enclose the fluid reservoir, and to be in a fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir.

22. The compensating cylinder unit as recited in claim 21, wherein, the fluid reservoir comprises a first fluid reservoir end which comprises an opening, andfurther comprising:a gas reservoir comprising a second gas reservoir end; anda connection element attached to the second gas reservoir end and arranged into the opening of the first fluid reservoir end of the fluid reservoir so as to provide an axial interconnection between the gas reservoir and the fluid reservoir,wherein, the compensating cylinder is further configured to slide around a circumference of the connection element.

23. The compensating cylinder unit as recited in claim 22, wherein the first fluid reservoir end of the fluid reservoir further comprises a protruding fluid reservoir flange.

24. The compensating cylinder unit as recited in claim 22, wherein the connection element comprises at least one pressure equalizing channel configured to enable a fluid communication between the fluid reservoir and the gas reservoir.

25. The compensating cylinder unit as recited in claim 22, wherein, the first fluid reservoir end further comprises an inner radial surface,the connection element comprises a protruding piston flange which comprises an outer radial surface, andthe connection element is configured to releasably interconnect the second gas reservoir end to the first fluid reservoir end through abutment of the outer radial surface of the protruding piston flange against the inner radial surface of the first fluid reservoir end.

26. The compensating cylinder unit as recited in claim 25, wherein, the first fluid reservoir end further comprises an outer surface,the compensating cylinder comprises a first axial cylinder end which comprises an inner surface,the compensating cylinder, the gas reservoir, and the fluid reservoir are each configured to be axially displaceable, the axial displacements being confined between, an operational configuration where the gas reservoir is locked to the fluid reservoir, anda transport configuration where the outer surface of the first fluid reservoir end abuts the inner surface of the first axial cylinder end of the compensating cylinder (1), and where the gas reservoir is axially released from the fluid reservoir.

27. The compensating cylinder unit as recited in claim 26, further comprising: a connection element comprising a surface, the connection element being fixed to the second gas reservoir end of the gas reservoir and arranged into the opening of the first fluid reservoir end of the fluid reservoir so as to provide an axial interconnection between the gas reservoir and the fluid reservoir,wherein,the fluid reservoir further comprises a second fluid reservoir end which comprises an inner radial surface, andthe transport configuration includes an abutment of the surface of the connection element towards the inner radial surface of the second fluid reservoir end of the fluid reservoir.

28. The compensating cylinder unit) as recited in claim 27, wherein, the compensating cylinder comprises a volume, andfurther comprising:a fluid channel configured to provide a fluid communication between the fluid reservoir and the volume within the cylinder arranged outside of the fluid reservoir.

29. The compensating cylinder unit as recited in claim 28, wherein the fluid channel is further configured to extend from the second fluid reservoir end) of the fluid reservoir to the volume within the cylinder situated outside the fluid reservoir.

30. The compensating cylinder unit as recited in claim 29, wherein the fluid channel comprises a through-going accumulator passage which is configured to penetrate the second fluid reservoir end.

31. The compensating cylinder unit as recited in claim 28, wherein the fluid channel further comprises a fluid guiding feeding tube configured to extend from the second fluid reservoir end of the fluid reservoir.

32. The compensating cylinder unit as recited in claim 31, wherein, the connection element further comprises at least one radial channel, the connection element being arranged into the opening of the first fluid reservoir end of the fluid reservoir so as to provide an axial interconnection between the gas reservoir and the fluid reservoir,wherein,the fluid guiding feeding tube comprises at least one radial bore which is alignable to the at least one radial channel to provide a fluid communication between the fluid guiding feeding tube and the volume within the cylinder situated outside the fluid reservoir and the gas reservoir.

33. The compensating cylinder unit as recited in claim 26, wherein, the gas reservoir further comprises outer walls,the first fluid reservoir end further comprises an outer radial surface which is arranged to face the first axial cylinder end of the compensating cylinder, andthe compensating cylinder further comprises inner walls and axial walls which are configured to slidingly surround the connection element, the second gas reservoir end and the first fluid reservoir end so as to form a fluid tight first cylinder chamber which is bounded by at least the inner walls of the compensating cylinder, the outer walls of the gas reservoir, and the outer radial surface of the first fluid reservoir end facing the first axial cylinder end of the compensating cylinder.

34. The compensating cylinder unit as recited in claim 33, wherein, the fluid reservoir further comprises outer walls, andthe first fluid reservoir end further comprises a protruding fluid reservoir flange comprising an outer radial surface which is arranged to face away from the first fluid reservoir end, the protruding fluid reservoir flange being configured to provide a second cylinder chamber which is bounded by at least, the inner walls of the compensating cylinder,the outer walls of the fluid reservoir, andthe outer radial surface of the protruding fluid reservoir flange of the first fluid reservoir end facing away from the first fluid reservoir end.

35. The compensating cylinder unit as recited in claim 34, further comprising: a pressure control device configured to provide pressure adjustments within the second cylinder chamber,wherein, the second cylinder chamber is connected to the pressure control device.

36. The compensating cylinder unit as recited in claim 34, further comprising: a fluid channel configured to provide a fluid communication between the fluid reservoir and the fluid tight first cylinder chamber, the fluid channel comprising, a through-going accumulator passage configured to penetrate the second fluid reservoir end of the fluid reservoir,a valve device arranged outside the fluid reservoir to be in a fluid communication with the through-going accumulator passage, anda fluid guiding feeding tube comprising a first longitudinal end arranged to be in a fluid communication with the fluid tight first cylinder chamber during operation, and a second longitudinal end arranged to be in a fluid communication with the valve device.

37. A method for altering a compensating cylinder unit from an operational configuration to a transport configuration, the compensating cylinder unit comprising: a compensating cylinder comprising a first axial side and a second axial side,a fluid reservoir, anda gas reservoir interconnected in a fluid communication with the fluid reservoir,the compensating cylinder being in fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir,the method comprising:venting each of a first volume within the compensating cylinder, a second volume in the fluid reservoir, and a third volume in the compensating cylinder to an ambient pressure; andapplying an external contraction force on at least one of the first axial side and the second axial side of the compensating cylinder unit to axially displace the gas reservoir relative to the fluid reservoir.

38. The method as recited in claim 17, wherein that the compensating cylinder unit comprises: a fluid reservoir configured to connect to the stationary frame; anda compensating cylinder configured to connect to the compensated frame, to at least partly enclose the fluid reservoir, and to be in a fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir.

39. A coiled tubing compensation system comprising: a stationary frame;a compensated frame; andthe compensating cylinder unit as recited in claim 21,wherein,the stationary frame is configured to connect to the fluid reservoir, andthe compensated frame is configured to connect to the compensating cylinder.

40. The coiled tubing compensation system as recited in claim 19 comprising at least two compensating cylinder units arranged so as to have their respective longitudinal axes arranged in parallel.