WO2008051092A1

WO2008051092A1 - Telescopic joint

Info

Publication number: WO2008051092A1
Application number: PCT/NO2007/000382
Authority: WO
Inventors: Brede Torkildsen; Halvdan Tore ANDERSEN
Original assignee: Fmc Kongsberg Subsea As
Priority date: 2006-10-27
Filing date: 2007-10-29
Publication date: 2008-05-02
Also published as: GB2456706A; GB2456706B; NO327932B1; NO20064917L; GB0907894D0

Abstract

The present invention relates to a telescopic joint (1) for use in a riser (2) extending between a floating structure (3) and a subsea installation (4), comprising an outer element (100) and an inner element (101) slidably arranged within the outer element (100), forming an internal flow passage (102) for well fluids, the inner and outer element having sealing elements (135, 138) between them defining an annular chamber (123,124,125) separated from the well fluid by the sealing element (135,138) and adapted for a barrier fluid, where the telescopic joint comprises arrangements for introducing a barrier fluid into said chamber (123) such that the well fluids are prevented from entering into the chamber (123).

Description

Telescopic joint

The present invention relates to a telescopic joint for use in a riser between a floating structure and a subsea installation, where the telescopic joint will compensate for vertical movement between the floating structure and the subsea installation.

A marine riser connects a subsea installation, as for instance a wellhead, which is in a steady position relative the seabed, with a movable floating structure. The floating structure will as a consequence of the weather conditions and how this influences the floating structure, move relative to the seabed. Because of this there is a need for a tensioning system onboard the floating structure connected between the floating structure and the riser, which system is regulated to keep a steady tension in the rise independent on the movement of the floating structure. With a mainly vertical riser there is also a need to keep a given tension in the riser to prevent the riser to collapse and/or buckle. The marine riser serves as a conduit between the surface and the wellhead. When used for drilling purposes it is called a drilling riser. When performing workover or intervention work on a well it has been customary to use a workover riser that is inserted into the marine riser. The reason for this is that the marine riser is not designed to withstand the high pressures that it encountered when working on a "live" well. In workover situations there is at times a need to introduce equipment into the workover riser. Since the upper end of the riser is kept in relative position to the seabed and the floating structure is moving there is a safety risk for personnel performing the work, and a limited weather window to perform any work. One solution to such a system is to provide a telescopic joint in the riser. With such a solution a bottom part of the riser may be kept under a constant tension while an upper part of the riser may be regulated to follow the movement of the floating structure and thereby giving a safer working environment for the personnel. There are known several telescopic joint configurations for use in a riser.

In NO 169027 and NO 322172 there is described a volume- and pressure/ axial force compensating telescopic joint. These telescopic joints are adapted to be operated with an internal pressure within the riser. The dynamic sealing systems in these publications have to be able to operate with a particle containing fluid and drilling mud in an annular chamber formed between the two parts of the telescopic joint. There is a potential risk for wear of seals and sealing surfaces when these are subjected to operation in a particle contaminated environment, and the added length caused by the volume compensated section can also be a disadvantage. The latter related to drilling rigs where space for handling and crane capacities are limiting factors. In patent NO 315807 Bl there is described the use of a telescopic joint in a workover riser, which telescopic joint is telescoping and regulating a top of the riser together with a working platform, when there is no pressure within the riser but where the telescopic joint will be fully stretched out when there is a pressure within the riser. In NO 317295 Bl there is described another telescopic joint for a riser, where the telescopic joint is locked in a collapsed position for handling high pressures within the riser.

An aim with the present invention is to improve working environment for the seals in a telescopic joint in a riser, reduce the overall size and length envelope of a telescopic joint while maintaining the functionality in operation for the applicable operating modes. It is another aim to provide a telescopic joint where particles and aggressive fluid has less influence on the service life of the seals and sealing surfaces in the telescopic joint. Another aim is to provide a telescopic joint which may in a better way handle side loads and pressure differential across the seals in the joint. It is also an aim to provide a telescopic joint where on may test the seal barriers in order to establish if the telescopic joint is leak tight. It is also an aim to provide a telescopic joint where an upper part of the joint may be regulated in relation to the movement of the floating structure while keeping tension in the lower part of the riser. There is also an aim to provide a telescopic joint which is volume compensating.

These aims are achieved with a telescopic joint according to the invention as defined in the following claims.

The present invention relates to a telescopic joint for use in a riser extending between a floating structure and a subsea installation, comprising an outer element and an inner element slidably arranged within the outer element forming an internal flow passage for well fluids within the and through the telescopic joint. A riser may be any elongated element with an internal chamber stretching in a mainly vertical direction between the subsea installation and the floating structure. The subsea installation may be a wellhead, a manifold or other equipment position on the seabed. There is also the possibility that the subsea installation is positioned in a distance from the seabed, but then kept in a steady position relative the seabed. The floating structure may be any kind of floating structure, a semi submersible platform, a production and or storage vessel. The outer element may be arranged in connection with an upper or lower part of the riser, i.e. it is envisaged that the telescopic joint may be turned around.

According to the invention the inner and outer elements are formed with sealing elements between them defining at least one annular chamber between the inner and outer element in different states of the telescopic joint, as telescoping, fully extended and or fully collapsed. There might one of or any combinations of an annular chamber in an extended state, an annular chamber in a collapsed state, an annular chamber in a telescoping state. At least one of the at least one annular chambers is adapted for a barrier fluid having several functions where one of the being as working as a barrier fluid for the sealing elements. At least one of the sealing elements is separating a well fluid within the internal flow passage from this annular chamber. And according to the invention the joint may also comprise arrangements for preventing the well fluids from entering into the barrier fluid.

Particles and aggressive fluids within the internal flow passage of the telescopic joint can significantly reduce the service life for seals and sealing surfaces in a telescopic joint. This is aggravated if the pressure differential across the seal is high with the aggressive side having the higher pressure. According to an aspect of the invention this is solved by having an arrangement preventing the well fluid from entering into the barrier fluid, which arrangement comprises means for regulating the pressure of the barrier fluid within the annular chamber. By having a pressure difference between the well fluids and the barrier fluid at a given value, where the barrier fluid is kept at a higher pressure than the well fluid one achieves an improved working environment for the sealing elements. When a telescopic joint is subjected to a flow of a well fluid stream, seal wear must not cause leakage of the well fluid to the environment and it must be possible to test the seal barriers in order to establish if the telescopic joint is leak tight. This is solved by the invention by the pressure difference between the barrier fluid and the well fluid and one may monitor the barrier fluid to monitor the condition of the sealing elements in the telescopic joint.

According to one aspect of the invention the arrangement may comprise a fluid circuit comprising means to circulate the barrier fluid within the annular chamber. This circulation may be achieved by having a system with a pipeline and one-way valves where the telescoping effect of the telescopic joint gives the pumping action within the fluid circuit; another possibility is to have specific means as a pump to provide circulation. One may even have a system adapted for both such means for providing circulation. According to another aspect the fluid circuit may comprise means cooling the barrier fluid within the annular chamber of the telescopic joint. This circuit may also comprise means for filtering the barrier fluid within the annular chamber of the telescopic joint. The telescopic joint will during its operation experience side loads and pressure differential across the sealing elements in the telescopic joint, these situations causes friction between relative movable parts as for instance sealing elements and sealing surfaces when subjected to axial movement during telescopic motion. The friction generates heat and depending on the velocity, cooling and lubrication is necessary in order to avoid seal damage and scouring, potentially jamming of relative moveable parts in the telescopic joint, which is solved by the aspect of the present invention as stated above. According to another aspect of the invention the telescopic joint comprises means to provide the possibility of regulating the upper part of the telescopic joint in a given position relative the floating vessel, and at the same time keep the tension in the lower part if the riser. By this one achieves a system where personnel working on the on the vessel with equipment that should be introduced into the riser may work on a platform in a fixed position relative the vessel and the upper part of the riser. This will reduces the risk for personnel damage when working on the equipment. The same system may also be used to maintain a relative position between a "down- hole" tool and the well, by regulating the upper part of the riser in relation to the weather induced motions of the vessel. This may be achieved by regulating the pressure from the barrier fluid on surfaces formed by the elements forming the telescopic joint, where these surfaces are working together with surfaces affected by the pressure in the well fluid. By controlling the pressure from the barrier fluid on the different surfaces on may regulate the positioning of the upper part of the telescopic joint to follow the movement to the vessel, move in a different way or be kept in a fixed position relative the seabed. The surfaces may be within the telescopic joint and or arranged in parts of the telescopic joint arranged outside the inner and outer element.

The telescopic motion of the inner and outer element of the telescopic joint will causes volume changes in the riser. In order to avoid pressure fluctuations, which can be damaging to seals and the reservoir, it is necessary that the riser is connected to a buffering volume. This buffering volume can either be inline with the riser as described in the applicants own patent NO 322172 or as according to an aspect of the invention connected through an aperture in riser wall and or one of the elements forming the telescopic joint, joining the internal bore with a tank or device with a buffering functionality.

According to an aspect of the invention this buffering volume may be solved by the telescopic joint further comprising a control cylinder comprising a first and second chamber each comprising a piston head, which piston heads are connected by a piston rod and thereby mechanically linked to each other. The first chamber on a side of the first piston head facing away from the second piston head or the piston rod is in contact with the annular chamber and the other side of the piston head is in contact with a first fluid source. This first fluid source is preferably a fluid source of a barrier fluid. The second chamber on a side of the second piston head facing away from the first piston head or the piston rod is in fluid contact with the internal flow passage thereby forming a buffering functionality for the well fluid. The other side of the second piston head is in contact with a second fluid source. The areas of the two piston heads facing away from each other may have different values and thereby giving the possibility of regulating the positioning of the upper part of the telescopic joint relative the floating vessel, as to follow it, have a given movement or be steady in relation to the seabed, at the same time as one keeps a tension in the lower part of the riser.

According to an aspect the piston rod is intersecting an intermediate chamber arranged between the first and second chamber and the intermediate chamber is in fluid contact with a third fluid source. This third fluid source may be the barrier fluid, the same fluid source as the fist fluid source or another source. This intermediate chamber may have a barrier fluid at a set or regulated pressure preventing any well fluid from mixing with the barrier fluid.

According to another aspect of the invention the part of the first chamber in fluid contact with the annular chamber is connected to at least one accumulator forming a buffering functionality for the barrier fluid within the annular chamber. This control cylinder arrangement may be formed by a separate cylinder or included in the inner and outer elements or formed between them.

According to a still further aspect the inner element is formed with an end section, where a part of the outer wall of the end section is in abutment against a first inner wall of the outer element. There are arranged dynamic sealing elements in this connection between the inner and outer element. The end section further comprises a graduated part. The graduated part is formed with a smaller diameter compared with the outer wall of the end section. An outer wall of the graduated part is in abutment against a second wall in a collapsed position of the telescopic joint where there are arranged static sealing elements in this connection. The graduation is formed to prevent the static seals from being in a sealing contact when the telescopic joint is in a normal telescoping mode. In a collapsed and or a fully extended position of the telescopic joint there may be formed a second annular chamber between the inner element and outer element between the first and second wall, which in an embodiment is formed by the outer element. This second annular chamber is sealed off from the surroundings by dynamic sealing elements between the inner and outer element and static sealing elements between the inner element and the second wall. The dynamic sealing elements being the sealing elements separating the well fluids from the barrier fluid during telescoping movements of the joint and the static sealing elements separating the well fluid from the second annular chamber in a collapsed state of the joint. The telescopic joint further comprises means for supplying barrier fluid to this second annular chamber, preferably at a pressure higher than the well fluid, preventing well fluids from entering the second annular chamber in a collapsed state of the joint.

According to another aspect the second wall may be formed by a separate head element arranged movable relative the outer element and which forms a third annular chamber between the head element and the outer element with sealing elements around this third annular chamber, and the outer element comprises means for adding a fluid to the third annular chamber. This gives the possibility of keeping the static sealing elements between the graduated part of the inner element and the second wall, as true static sealing elements, by regulating the pressure within the third annular chamber and thereby moving the head element in relation to the eventual movement of the inner element in a collapsed state of the joint. Such movements may occur due to temperature changes of the elements in the joint.

According to a further aspect of the invention the outer element may comprise means for limiting the movement of the head element relative the outer element, this may for instance be shoulders within the outer element of the telescopic joint. According to another further aspect of the invention the telescopic joint may be locked so that the inner and outer elements are kept in a relative position to each other. This may be done according to one aspect in any position between a fully extended and retracted position. This may be done by locking an incompressible barrier fluid within the annular chamber, and thereby preventing any further movement between the inner and outer element of the joint. According to another aspect a locking function may be achieved by having a locking mechanism at one end of the telescoping joint preventing relative movement between the parts.

A telescopic joint according to the invention may comprise some of or all of the different aspects of the invention as described above. The invention will now be explained with an embodiment with reference to the accompanying drawings, where;

Fig. 1 is a schematic view of a riser connection between the subsea installation and the floating vessel,

Fig. 2 shows one embodiment of a telescopic joint according to the invention, Fig. 3 shows a second embodiment focusing on different elements of the invention,

Fig. 4 A-B shows a detail of a third embodiment of a telescopic joint, in a collapsed state of the joint,

Fig. 5 shows a detail in an extended state of the joint, and

Fig. 6 shows a possible configuration for locking the telescopic joint. In fig. 1 there is shown a possible configuration with a telescopic joint 1 arranged in a riser 2 extending between a floating structure 3 and a subsea installation 4. The subsea installation 4 comprises of a subsea tree 7 attached at wellhead. The riser 2 is attached to the subsea tree 7 with a lower riser package 8 and an emergency disconnect package 9. There is also arranged a stress joint 10 in this connection. Further up in the riser 2 there is arranged a riser weak link 11. Closer to a cellar deck 13 of the floating structure 3 there is arranged a tension joint 12, which may be used to provide tension in the riser 2. The telescopic joint 1 is arranged close to a drill floor 14. Above the telescopic joint there is arranged a speed lock connector 15, a swivel 16, an adapter 17 below a surface flow tree 18 arranged in a tension frame 19.

In fig. 2 there is shown an embodiment of a telescopic joint according to one aspect of the invention. The telescopic joint may be positioned in an arrangement as the one shown in fig. 1. The telescopic joint comprises an outer element 100 and an inner element 101 defining an internal flow passage 102 within. The telescopic joint being so configured that the outer element may be connected to the lower part of the riser and the inner element may be connected to a surface flow tree. However, the arrangement may be reversed, i.e. with the inner element connected to the riser and the outer element connected to the surface flow tree.

The inner element 101 comprises a main section 130 with an outer wall 131 and an end section 132 with a larger diameter than the main section 130. The transition from the main section 130 to the end section 132 is formed by a radial end surface 133. The end section 132 has an outer wall 134 and is formed with a graduated section 136 with an outer wall 137 having a smaller diameter then the outer wall 134 of the rest of the end section 132. There is within the inner element formed an inner bore 139, which in one end has a funnel shaped part 139b. The outer element is formed with a cylindrical housing 140 which has a first inner wall 141 with an internal diameter. One end of the cylinder house 140 is formed with an end flange 142. The housing 140 is further formed with a narrow section 144, with a second inner wall 145 with an internal diameter smaller than the diameter of the first internal wall 141.

The inner element 101 is movable arranged within the outer element 100 and shown in a collapsed position in fig. 2. There are arranged dynamic sealing elements 135 A in the connection between the end flange 142 and the main section 130, and dynamic sealing elements 135B between the end section 132 and the first inner wall 141, forming an inner chamber 123 between the end flange 142, the first inner wall 141, the radial end surface 133 and outer wall 131 of the main section 130 of the inner element 101. This inner annular chamber 123 can be filled with a barrier fluid through a first port 143 connected to a control cylinder 103.

The control cylinder 103 comprises a first chamber 104. Within this chamber 104 there is arranged a first piston head 105 connected to a piston rod 116. One side of the piston head 105, facing away from the piston rod 116 is in fluid contact with the annular chamber 123 through a first fluid line 114 from the first chamber through the first port 143. The other side of the piston head 105 is in fluid contact with a first fluid source 106. There is in the control cylinder 103 a second chamber with a piston head 120 connected to the same piston rod 116. The part of the chamber on the side of the piston head 120 facing away from the piston head 120 is in fluid contact with the fluid within the internal flow passage 102 within the telescopic joint through a second fluid line 122 and a third port 147 through the wall of the cylinder house 140 leading into the flow passage 102. The other side of the piston head 120, with the piston rod 116, is in contact with a second fluid source 121. There is in addition in this embodiment an intermediate chamber 115 between the first 104 and the second 118 chamber. This intermediate chamber 115 is in contact with a third fluid source 117 and is intersected by the piston rod 116. There are sealing elements between the piston rod and the walls forming the intermediate chamber 115 keeping the barrier fluid within the first chamber 104 and the well fluid within the second chamber 118 from the fluid in the intermediate chamber 115 and thereby also separating the barrier fluid from the well fluid. There is in addition connected an accumulator 107 to the first chamber 104 on the side of the piston head 105 which is in fluid contact with the annular chamber 123. The piston head 105 and the piston head 120 are shown to have a similar area, this is however not necessary and in some applications it would be desirable to have different areas of the sides of the two piston heads facing away from each other.

The telescopic joint is in fig.2 shown in a collapsed position. In this position there is formed a second annular chamber 124 between the inner and outer elements, limited by the dynamic sealing elements 135B between the first inner wall 141 and the outer wall 134 of the end section 132 and the static sealing elements 138 between the outer wall 137 of the graduated part 136 and the second inner wall 145 of the narrow section 144 of the cylinder house 140. This second annular chamber 124 is in contact with a source of a barrier fluid through a second port 146 in the cylindrical housing 140.

In fig. 3 there is shown other aspects of the invention. Similar elements are given the same reference numerals and only differences will be explained. The annular chamber 123 is through at least two ports 143a, 143b connected to a fluid circuit 119 for the barrier fluid within the annular chamber 123. The fluid circuit 119 comprises pumping means 110 for possibly forced circulating the barrier fluid, one- way valves 112,113 preventing fluid from flowing the wrong way through the fluid circuit 119 and a cooler 109 and filtering means 108. There is also connected a controller 111 to the circuit for regulating the flow. There fluid circuit 119 may be connected the first fluid source 106 for supply of fluid into the circuit. There are also other valve arrangements for regulating the flow operated by the controller 111.

In fig. 4 A and 4B there is shown a detail of another aspect of the invention with a third embodimentof a telescopic joint In this embodiment where the telescopic joint in shown in a fully collapsed position one has static sealing elements 138 in a connection between an outer wall 137 of the graduated section 136 of the inner element 101. The second inner wall 145' in this embodiment for abutment against these static sealing elements 138 is formed by a head element 150 arranged movable within the outer element 100. The head element 150 is formed with a mainly cylindrical first part 151 , a radial transition part 152 and a mainly cylindrical second part 153. These parts have mainly the same wall thickness, and the first part 151 is formed with a main diameter which is larger than a main diameter of the second part 153. There are arranged dynamic sealing elements 135' between an outer surface of the first part 151 and the outer element 100 and dynamic sealing elements 135" between a part connected to the outer element 100 and the second part 153 of the head element 150. There is between a surface of the transition part 152, a section of the second part 153 and the outer elements 100 formed a third annular chamber 125. This third annular chamber 125 is also in fluid contact with a fluid source through a third fluid port 126. A barrier fluid is added to this third annular chamber 125 with a pressure, and this pressure is regulated so that the head element 150 is moved relative the outer element 100 but kept in a relative position in relation to the inner element 101, thereby giving true static conditions for the static sealing elements 138. The head element 150 is movable relative the outer element 100 but limited in its movement in one direction by a first stopping shoulder 127 formed in connection with the second annular chamber 124. The head element 150 is limited in its movement in the opposite direction by a second stopping shoulder 128 formed as a surface of the third annular chamber 125.

The purpose of the head element 150 is to ensure that the static sealing elements 138 towards the telescopic inner element 101 remain static. The telescopic inner element 101 and telescopic outer element 100 will be subjected to small relative movements caused by differences in length due to temperature, axial forces and bending moments. The size of the relative movement can be in the order of several millimetres depending on the applied loads and thermal transients. The head element 150 is such designed that the application of the pressure to the third annular chamber 125 actuates the head element 150 while the stroke is limited to significantly less than the travel needed to expose the dynamic seals 135', 135". This effectively ensures that the static sealing elements 138 remains true static while the dynamic sealing elements 135', 135" will always remain within a non exposed sealing area. The annular chamber 124 may as in the previous explained embodiments be in connection with a source of a barrier fluid.

A fully extended position is shown in fig. 5. In this embodiment one may see that it is a possibility to form the inner element with a graduated section 136' at the opposite end of the inner element 101 compared with the end section. This graduated section 136' has a slightly smaller outer diameter compared with the main section of the inner element 101. The graduated section 136' is formed with an outer wall 137' wherein there is arranged static sealing elements 138' between the outer wall 137' and a second inner wall 145'. The movement of the inner element in one direction along the longitudinal axis is prevented by a stopping surface 127' formed by a shoulder of a part forming a part of the outer element 100. The different aspects of the invention have now been explained with reference to several drawings. A telescopic joint may comprise one, some or all of the different aspects. With a telescopic joint according to the invention one may achieve that the hydraulic system for the barrier fluid maintains hydraulic pressure above the well bore pressure in order to prevent ingress of particles and well fluids. In addition the telescopic motion will provide a pumping action towards the barrier fluid such that it is circulated through a cooler without the use of a pump in the lubrication system. The cooling of the barrier fluid is beneficial because high axial velocity in combination with high bending loads causes heat generated due to friction.

The hydraulic system can as stated be connected to an external high pressure unit (HPU) which enables inline tensioning of the telescopic joint and helping to provide a closing force when moving the telescopic joint to collapsed (closed) position. With this one has to relate the different surfaces exposed to the different fluid in relation to each other to achieve the specific effect. Passive compensation can be provided by charging the hydraulic system with pressure. An accumulator will allow for volume compensation in the hydraulic system during telescopic motion. The hydraulic system can be controlled by a governing/regulating system or controlled in sequence by the thus providing the ability to provide active (forced) compensating movement. This can then be used in conjunction with wire-line tools / drilling equipment and coiled tubing in order to maintain a fixed position (relative to well) down-hole for the "tools" by compensating for the rig movement. The active compensating mode may automatically revert to passive mode in case there is a malfunction in the regulating system.

The hydraulic system can be furnished with a particle filter integral with the fluid chamber and a cooler which can be located inside the telescopic joint assembly. The accumulator will dampen a recoil motion in the riser.

When operating in extreme aggressive environments (high particle content or subjected to substances with severe degradation of seal materials i.e. chemicals) it may be a disadvantage if the volume compensation is located in the riser. By allowing volume compensation to take place outside the telescopic joint, seals are more readily accessible and the design of the volume compensator can have facility for flushing of debris, multiple chambers for protection of the hydraulic lubrication and seals. The elimination of volume compensation as an inline chamber located on the telescopic joint also significantly reduces the length of the telescopic joint. This is advantageous on rigs/vessels where space and crane capacity for handling are the limiting factors. Especially as retrofit to existing systems can this be of significance.

The telescopic joint according to the invention may be locked in any position, either by closing in the barrier fluid within the first annular chamber or by having an external locking mechanism.

The invention has now been explained with embodiments, but the skilled person will understand that one may perform alterations or modifications to the system that are within the scope of the invention as defined in the following claims. A skilled person will also understand than it is possible to combine some or all elements from the different embodiments to form an new embodiment of a telescopic joint.

Claims

1. Telescopic joint (1) for use in a riser (2) extending between a floating structure (3) and a subsea installation (4), comprising an outer element (100) and an inner element (101) slidably arranged within the outer element (100), forming an internal flow passage (102) for well fluids, the inner and outer element having sealing elements (135,138) between them defining at least one annular chamber (123,124,125) separated from the well fluid by the sealing elements (135,138) and adapted for a barrier fluid, characteri zed in that it comprises arrangements for introducing a barrier fluid into at least one of said chambers (123,124,125) such that the well fluids are prevented from entering into the at least one chamber (123,124,125) where at least one of the annular chambers (123) is connected to a fluid circuit comprising means (110, 111,112,113) to circulate a fluid within the annular chamber (125).

2. Telescopic joint according to claim 1, ch aracte ri z e d i n that the fluid circuit comprises means for cooling (109) a fluid within the annular chamber

(123,124,125)

3. Telescopic joint according to claim 1 or 2, charact e ri ze d i n th at the arrangements comprise means for regulating the pressure in the barrier fluid for preventing the well fluid from entering the annular chamber (123).

4. Telescopic joint (1) according to one of the claims 1 -3, charact e ri z ed i n that the telescopic j oint further comprises a control cylinder (103) comprising a first (104) and second (118) chamber each comprising a piston head (105,120), which piston heads (105,120) are connected by a piston rod (116), where the first chamber (104) on a side of the first piston head (105) facing away from the second piston head (120) is in contact with the annular chamber (123) and the other side of the piston head is in contact with a first fluid source (106), the second chamber (118) on a side of the second piston head (120) facing away from the first piston head (105) is in fluid contact with the internal flow passage (102) and the other side of the second piston head (120) with a second fluid source (121).

5. Telescopic joint according to claim 4, charact e ri z e d i n that the piston rod ( 116) is intersecting an intermediate chamber (115) arranged between the first (104) and second (118) chamber and the intermediate chamber (115) is in fluid contact with a third fluid source (117).

6. Telescopic joint according to claim 4, c haract eri ze d in that the part of the first chamber (104) in fluid contact with the annular chamber (123) is connected to at least one accumulator (107).

7. Telescopic joint according to one of the previous claims 1, c haract e ri ze d i n that the fluid circuit comprises means for filtering (108) a fluid within the annular chamber (123).

8. Telescopic joint (1) for use in a riser (2) extending between a floating structure (3) and a subsea installation (4), comprising an outer element (100) and an inner element (101) slidably arranged within the outer element (100), forming an internal flow passage (102) for well fluids, the inner and outer element having sealing elements (135,138) between them defining at least one annular chamber (123,124,125) separated from the well fluid by the sealing elements (135,138) and adapted for a barrier fluid, characteri ze d i n that it comprises arrangements for introducing a barrier fluid into at least one of said chambers (123,124,125) such that the well fluids are prevented from entering into the at least one chamber (123,124,125) where the inner element (101) is formed with an end section (132), where a part of the outer wall (134) of the end section (132) is in abutment against a first inner wall (141) of the outer element (100), with dynamic sealing elements (135) in this connection, the end section (132) further comprises a graduated part (136) where an outer wall (138) of the graduated part (136) is in abutment against a second wall (145) in a collapsed position of the telescopic joint where there are arranged static sealing elements (138) in this connection.

9. Telescopic joint according to claim 8, characterized in that the joint in a collapsed position forms a second annular chamber (124) between the inner element (101) and outer element (100) between the first (141) and second (145) wall of the outer element (100), and that it further comprises means (146) for supplying fluid to this second annular chamber (124).

10. Telescopic joint according to claim 8, charact e ri z e d i n that the second wall (145) is formed by a separate head element (150) arranged movable relative the outer element (100) and which forms a third annular chamber (125) between the head element (150) and the outer element (100) with sealing elements around this third annular chamber (125), and the outer element (100) comprises means (149) for adding a fluid to the third annular chamber (125).

11. Telescopic joint according to claim 10, characteri ze d in that the outer element (100) comprises means (148) for limiting the movement of the head element (150) relative the outer element (100).