WO2015128217A1

WO2015128217A1 - Compact compensating cylinder

Info

Publication number: WO2015128217A1
Application number: PCT/EP2015/053248
Authority: WO
Inventors: Lars PØHNER
Original assignee: Mhwirth As
Priority date: 2014-02-27
Filing date: 2015-02-17
Publication date: 2015-09-03
Also published as: GB2538673A; NO339752B1; GB201616277D0; US20170009537A1; NO20140255A1

Abstract

The invention concerns a compensating cylinder 100 unit suitable for compensating relative movements between a stationary frame 40 and a compensated frame 50 constituting parts of a coiled tubing compensation system 30, where the compensated frame 50 is connected to the compensating cylinder 1. All the necessary tools for the coiled tubing system may be arranged on the compensated platform in order to ensure compensation of vertical movements during operation. The cylinder unit 100 comprises a compensating cylinder 1 suitable for connection to the compensated frame 50 and a fluid reservoir 5 suitable for connection to the stationary frame, wherein the compensating cylinder 1 is in fluid communication with the fluid reservoir 5 to allow for an axial displacement of the compensating cylinder 1 relative to the fluid reservoir 5. Furthermore, the compensating cylinder 1 is partly enclosing the fluid reservoir. The invention also concerns a method for altering a compensating cylinder unit from an operational configuration to a transport configuration.

Description

Title:

Compact compensating cylinder

Technical field:

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

Background of the invention

Coil tubing gives the rig crew 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 the coil tubing. Any abruption in the active compensation when the coil tubing is fixed to seabed may easily destroy the coil tubing. In such cases, the coil tubing frame itself must have a compensating feature.

Recently there have been some proposals to address the challenge of obtaining active compensation while ensuring satisfactory low risk of abruption. One example is found in WO 2005/061803 (Devin International) disclosing an inline compensator with two passive cylinders on a frame replacing the vertical beams. Another example which discloses a similar solution may be found in US 2012/0227976 Al.

Common for the prior art compensation systems is that the pressure vessels are not located on the compensating unit itself. Furthermore, the supply of compressed air in order to drive the compensation motion is performed by one or two relatively large size hoses, which for safety reasons are highly unfavorable.

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

Summary of the invention

The above-identified objects are achieved by a compensating cylinder unit in accordance with claim 1. The invention also concerns a method for altering a compensating cylinder unit from an operational configuration to a transport configuration in accordance with claim 17 and a coiled tubing compensation system in accordance with claim 19. Further beneficial features are defined in the remaining dependent claims.

In particular, the invention concerns 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 ensure 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. Furthermore, the compensating cylinder is characterized in that it at least partly encloses the fluid reservoir.

In a preferred embodiment the cylinder unit further comprises 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. Furthermore, the connection element may comprise a 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 another preferred embodiment a first fluid reservoir end of the fluid reservoir comprises an outward protruding fluid reservoir flange.

In another preferred embodiment the cylinder unit further comprises 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, creating 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 another preferred embodiment the cylinder unit further comprises 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. Furthermore, 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 another preferred embodiment the cylinder unit further includes 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, creating an axial interconnection between the gas reservoir and the fluid reservoir. Further, the fluid guiding feeding tube may 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 another preferred embodiment the axial walls of the compensating cylinder slidingly surrounds the connection element, the second gas reservoir end and the first fluid reservoir end, forming a fluid tight first cylinder chamber bounded by at least inner walls of the cylinder, 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 filed in question. The first fluid reservoir end may comprise a outwardly protruding fluid reservoir flange creating a second cylinder chamber bounded by at least the inner walls of the cylinder, 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 may advantageously be less than the volume of the first cylinder chamber. Furthermore, the second cylinder chamber may be connected to a pressure control means enabling pressure adjustments within the second cylinder chamber, for example an external accumulator and/or an active control system. In another preferred embodiment the cylinder unit further comprises 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 concerns 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 following steps: - 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 mentioned above. The present invention also concerns a coiled tubing compensation system comprising a stationary frame, a compensated frame and a compensating cylinder unit in accordance with the cylinder unit mentioned 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 hereinafter stationary relative to a underlying platform or vessel.

In the following description, numerous specific details are introduced to provide a thorough understanding of, and enabling description for, embodiments of the claimed apparatus and method. One skilled in the relevant art, however, will recognize 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.

Brief description of the drawings

Preferred embodiments of the present invention will now be described with reference to the attached drawings, in which:

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

Figures 2A-D show cross sectional side views of a compact compensating cylinder unit in accordance with the invention in an operational mode, where the accumulator assembly is stroked in an intermediate position relative to the surrounding compensating cylinder, Figures 3A and 3B show side views of a compact compensating cylinder unit in accordance with the invention in an operational mode, the accumulator assembly is stroked in an upper position relative to the surrounding compensating cylinder,

Figures 4A and 4B show side views of a compact compensating cylinder unit in accordance with the invention in an operational mode, the accumulator assembly is stroked in a lower position relative to the surrounding compensating cylinder, and

Figures 5A, 5B and 5C show side views of a compact compensating cylinder unit in accordance with the invention in a retracted transport mode.

Detailed description of the drawings

Figure 1 shows the main components of a coiled tubing system 30 in accordance with the invention. The 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 machine 31 has a curved guide beam 32 on top often called a guide arch or gooseneck which threads the pipe 34 into the machine body 31. A Blowout Preventer (BOP) 33 may be arranged to form an intermediate component between the machine 31 and the pipe 34. The BOP 33 may cut the pipe 34 with subsequent sealing. These components 31-34 are supported on a compensated frame 50 where each of its longitudinal ends are 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 latter 100 thus form an integral part of the coiled tubing system 30. The two longitudinal ends 10a,5b of each 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. Hence, there is 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 in that the latters must be lifted well clear of the drill floor (not shown). Figure 2A shows a principal side view sketch of the compensating cylinder unit 100 in accordance with the 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 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 said end 5a by pressure or other suitable means. Furthermore, the fluid accumulator 5 and the pressure vessel 10 are slidingly journaled into a common compensating cylinder or barrel 1 , forming a closed annulus cylinder chamber between the inner wall of the 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 , ' are bounded by an upper axial cylinder end la and a lower axial cylinder end lb, respectively. In order to ensure fluid communication between the interior of the pressure vessel 10 and the interior of the fluid accumulator 5 one or more through-going axial drillings 6 are provided into the piston 2. Furthermore, a fluid channel 8 (figure 2B) is provided running from the interior of the fluid accumulator 5 to the upper annulus chamber 1 ' . This fluid channel 8 comprises

- a lower end accumulator drilling 12 penetrating a lower axial accumulator end 5b,

- a suitable feeding tube 1 1 comprising upper and lower longitudinal ends 1 1 a, l ib 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 end 1 1a of the feeding tube 1 1 providing fluid communication between the interior of the feeding tube 1 1 and the upper annulus chamber .

Figure 2B provides further operational details of the compensating cylinder unit 100 indicating by arrow the pathway of the fluid channel 8. The fluid accumulator 5 is in figure 2B 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 annulus chamber via the axial feeding tube 1 1 and the radial bores 20. As a result the pressure in the fluid 22 is converted to a force within the upper chamber 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 l a 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 (figure 1). For example, if the axial (or vertical) force components (F_a) within the upper cylinder chamber 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 la. Likewise, if the axial (or vertical) force components (F_a) within the upper cylinder chamber 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 la. Consequently a compensating effect similarly to the effect of the prior art compensating cylinders is 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 is in general larger than the forces acting in the lower cylinder chamber 1 " . The latter chamber 1 " may be connected to a low pressure accumulator to keep the chamber volume oil-filled and lubricated. However, it may 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 near neutralized, by means of 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 figure 2C and 2D, respectively. The valve device 13 providing controlled fluid communication between the lower accumulator drilling 12 and the feeding tube 1 1 is partly illustrated in figure 3D.

Figures 3 A and 3B show side view drawings of the same operational compensating cylinder unit 100 as in figures 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 . Furthermore, figures 4A and 4B show side view drawings as in figures 2C, 3 A and 2D, 3B, respectively (figure 4B seen along C-C of figure 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 .

Figure 5 A shows a principal side view sketch of the compensating cylinder unit 100 in accordance with the 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 by means of various mechanically releasable coupling devices. An about 1 :22 scale side view drawing of a compact compensating cylinder unit 100 as in figure 5, i.e. retracted transport mode, and a corresponding sectional drawing along line A-A is shown in figure 5B and 5C, respectively.

In the preceding description, various aspects of the system and method according to the 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 list:

F_a Axial force component

1 Compensating cylinder / barrel

1 ' First cylinder chamber / upper cylinder chamber

1 ' ' Second cylinder chamber / upper cylinder chamber

1 a Upper cylinder end / first cylinder end

lb Lower cylinder end / second cylinder end

2 Central piston / connection element

5 Fluid accumulator / fluid reservoir

5a Protruding upper axial accumulator end / first fluid reservoir en<

5b Lower axial accumulator end / second fluid reservoir end

6 Axial drilling / pressure equalizing channel

8 Fluid channel

10 Pressure vessel / gas reservoir

10a Upper axial vessel end / first gas reservoir end

10b Lower axial vessel end / second gas reservoir end

1 1 Fluid guiding feeding tube / feeding tube

11a Upper longitudinal end / first longitudinal end

l ib Lower longitudinal end / second longitudinal end

12 Lower end accumulator drilling / Through-going accumulator p;

13 Valve device

14 Protruding piston flange

16 Protruding accumulator flange / protruding fluid reservoir flang

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 B lowout 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

PATENT CLAIMS

1. A compensating cylinder unit (100) for compensating relative movements between a stationary frame (40) and a compensated frame (50) constituting parts of a coiled tubing compensation system (30), characterized in that the compensating cylinder unit (100) comprises

- a compensating cylinder (1) for connection to the compensated frame (50) and

- a fluid reservoir (5) for connection to the stationary frame (40),

wherein the compensating cylinder (1) is in fluid communication with the fluid reservoir (5) to allow for an axial displacement of the compensating cylinder (1) relative to the fluid reservoir (5) and

wherein the compensating cylinder (1) at least partly encloses the fluid reservoir (5).

2. The cylinder unit (100) according to claim 1, characterized in that

the cylinder unit (100) further comprises

- a gas reservoir (10) having a second gas reservoir end (10b) and

- a connection element (2) fixed to the second gas reservoir end (10b) and arranged into an opening within a first fluid reservoir end (5a) of the fluid reservoir (5), creating an axial interconnection between the gas reservoir (10) and the fluid reservoir (5),

wherein the compensating cylinder (1) is slidingly arranged around the circumference of the connection element (2).

3. The cylinder unit (100) according to claim 2, characterized in that the connection element (2) displays at least one pressure equalizing channel (6) enabling fluid communication between the fluid and gas reservoirs (5,10).

4. The cylinder unit (100) according to one of claims 2-3, characterized in that the connection element (2) comprises

a protruding piston flange (14), wherein the connection element (2) releasably interconnects the second gas reservoir end (10b) to the first fluid reservoir end (5a) through abutment of

an outer radial surface of the protruding piston flange (14) against an inner radial surface of the first fluid reservoir end (5a).

5. The cylinder unit (100) according to one of the preceding claims, characterized in that a first fluid reservoir end (5a) of the fluid reservoir (5) comprises a protruding fluid reservoir flange (16).

6. The cylinder unit (100) according to one of the preceding claims, characterized in that the cylinder unit (100) further comprises a gas reservoir (10), wherein the cylinder (1), the gas reservoir (10) and the fluid reservoir (5) are mutually displaceable in the axial direction, the displacements being confined between

an operational configuration where the gas reservoir (10) is locked to the fluid reservoir (5) and

a transport configuration where the outer surface of a first fluid reservoir end (5a) of the fluid reservoir (5) abuts the inner surface of a first cylinder end (la) of the cylinder (1), and where the gas reservoir (10) is axially released from the fluid reservoir (5).

7. The cylinder unit (100) according to claim 6, characterized in that the cylinder unit (100) further comprises

- a connection element (2) fixed to a second gas reservoir end (10b) of the gas reservoir (10) and arranged into an opening within a first fluid reservoir end (5a) of the fluid reservoir (5), creating an axial interconnection between the gas reservoir (10) and the fluid reservoir (5),

and where the transport configuration includes abutment of the surface of the connection element (2) towards the inner surface of a second fluid reservoir end (5b) of the fluid reservoir (5).

8. The cylinder unit (100) according to one of the preceding claims, characterized in that the cylinder unit (100) further comprises a fluid channel (8) enabling fluid communication between the fluid reservoir (5) and a volume within the cylinder (1) situated outside the fluid reservoir (5).

9. The cylinder unit (100) according to claim 8, characterized in that the fluid channel (8) extends from a second fluid reservoir end (5b) of the fluid reservoir (5) to the volume within the cylinder (1) situated outside the fluid reservoir (5).

10. The cylinder unit (100) according to claim 9, characterized in that the fluid channel (8) further comprises a through-going accumulator passage (12) penetrating the second fluid reservoir end (5b).

11. The cylinder unit (100) according to one of claims 8- 10, characterized in that the fluid channel (8) further comprises

- a fluid guiding feeding tube (11) extending from a second fluid reservoir end (5b) of the fluid reservoir (5) within the fluid reservoir (5).

12. The cylinder unit (100) according to claim 1 1, characterized in that the cylinder unit (100) further comprises

- a gas reservoir (10) comprising a second gas reservoir end (10b) and

- a connection element (2) fixed to the second gas reservoir end (10b) comprising a radial channel (23), the connection element (2) being arranged into an opening within a first fluid reservoir end (5a) of the fluid reservoir (5) creating an axial interconnection between the gas reservoir (10) and the fluid reservoir (5),

wherein

the fluid guiding feeding tube (11) comprises at least one radial bore (20) being alignable to the at least one radial channel (23) to enable fluid communication between the fluid guiding feeding tube (1 1) and a volume within the cylinder (1) situated outside the fluid reservoir (5) and the gas reservoir (10).

13. The cylinder unit (100) according to one of claims 2- 12, characterized in that the axial walls of the compensating cylinder (1) slidingly surrounds

- the connection element (2),

- the second gas reservoir end (10b) and

- the first fluid reservoir end (5a),

forming a fluid tight first cylinder chamber ( ) bounded by at least

- inner walls of the compensating cylinder (1),

- outer walls of the gas reservoir (10) and

- an outer radial surface of the first fluid reservoir end (5a) facing a first axial cylinder end (la) of the compensating cylinder (1).

14. The cylinder unit (100) according to claim 13, characterized in that the first fluid reservoir end (5a) comprises a protruding fluid reservoir flange (16) creating a second cylinder chamber (1 ") bounded by at least - the inner walls of the cylinder (1),

- outer walls of the fluid reservoir (5) and

- an outer radial surface of the protruding fluid reservoir flange (16) of the first fluid reservoir end (5a) facing away from the first fluid reservoir end (5a).

15. The cylinder unit (100) according to claim 14, characterized in that the second cylinder chamber (1 ") is connected to a pressure control means enabling pressure adjustments within the second cylinder chamber (1 ").

16. The cylinder unit (100) according to one of claims 13-15, characterized in that the cylinder unit (100) further comprises a fluid channel (8) enabling fluid communication between the fluid reservoir (5) and the first cylinder chamber ( ),

the fluid channel (8) comprising

a through-going accumulator passage (12) penetrating a second fluid reservoir end (5b) of the fluid reservoir (5),

a valve device (13) arranged outside the fluid reservoir (5) in fluid communication with the through-going accumulator passage (12) and

a fluid guiding feeding tube (11) comprising

a first longitudinal end (11a) arranged in fluid communication with the first cylinder chamber ( ) during operation and

a second longitudinal end (l ib) arranged in fluid communication with the valve device (13).

17. A method for altering a compensating cylinder unit (100) from an operational configuration to a transport configuration, characterized in that said compensating cylinder unit (100) comprises

- a compensating cylinder (1),

- a fluid reservoir (5) and

- a gas reservoir (10) interconnected in fluid communication with the fluid reservoir (5),

the compensating cylinder (1) being in fluid communication with the fluid reservoir (5) to allow for an axial displacement of the compensating cylinder (1) relative to the fluid reservoir (5),

wherein the method comprises the following steps:

- venting the volumes within the compensating cylinder (1) and both reservoirs (5,10) to an ambient pressure, - applying an external contraction force on one or both axial sides of the cylinder unit (100) to axially displace the gas reservoir (10) relative to the fluid reservoir (5).

18. The method according to claim 17, characterized in that the compensating cylinder unit (100) is in accordance with one of claims 1- 16.

19. A coiled tubing compensation system (30) comprising

- a stationary frame (40),

- a compensated frame (50) and

- a compensating cylinder unit (100) in accordance with one of claims 1-16, wherein the stationary frame (40) connects to the fluid reservoir (5) and the compensated frame (50) connects to the compensating cylinder (1).

20. A coiled tubing compensation system (30) according to claim 19, characterized in that the system (30) comprises at least two compensating cylinder unit (100) having their longitudinal axes arranged in parallel.