WO2014038956A1

WO2014038956A1 - Seal assembly

Info

Publication number: WO2014038956A1
Application number: PCT/NO2013/050154
Authority: WO
Inventors: Viktor GRENNBERG; Lars Timberlid LUNDHEIM; Daniel Vik SKOGEN; Ernst Folke Leif CEDERSTRÖM; Hongzhou HU
Original assignee: Aker Subsea As
Priority date: 2012-09-07
Filing date: 2013-09-06
Publication date: 2014-03-13
Also published as: NO20130153A1; NO339186B1

Abstract

Seal assembly comprising a seal ring (3) sealing between an inner and outer tubular element. Inner or outer surface (7, 5) has an inclined element surface (9) against which the seal ring (3) moves, thereby altering its circumference (C). An activation arrangement (2) exerts actuation force onto the seal ring, forcing an inclined seal ring surface (11) of the seal ring (3) against the inclined element surface. The activation arrangement maintains said actuation force along a function path of the seal ring, as a result of radial expansion or reduction of the inner or outer surface. When radial distance between inner and outer surface increases, the activation arrangement moves the seal ring along the inclined element surface in one direction. When radial distance decreases, the activation arrangement is compressed, and the seal ring moves along the inclined element surface in a second opposite direction.

Description

Seal assembly

The present invention relates to a seal assembly according to the introductory part of claim 1 , as well as methods of sealing. In particular it relates to a seal assembly which adapts to variations of dimensions of the tubular elements against which it seals.

Background

In the technical field of subsea wells for production of hydrocarbons, many components exhibit a tubular shape, such as tubing hangers, Xmas tree spools, and well heads. The components are heavy and large, and are designed to bear large mechanical forces, such as from external influence and well pressures. Despite their large sizes, some sections need to accommodate functional components in limited spaces. For instance, when coaxially connecting two pressure-containing tubular elements one needs to arrange high pressure seals between them in order to provide a pressure barrier for possible well pressures.

This task has existed for a long time in the field of subsea hydrocarbon production and various solutions have been presented. Some seals are ring seals with a U-shaped cross section. It is known to force a wedge element between the legs of the U-shape in order to force the "legs" into sealing contact with the facing sealing surfaces of respective side of an annulus within which the ring seal is arranged. It is also known to have a present pressure increasing the sealing contact force, such as with the U-shaped cross section. Patent publication US5174376 describes a metal seal adapted for sealing between coaxially tubular elements. A wedging ring is forced in between the "legs" of a V- or U-shaped sealing ring, thereby forcing the legs into sealing contact with the inner surface of the outer tubular element and the outer surface of the inner tubular element.

Solutions like the ring seal having U-shaped cross section are able to adapt to some, however small variations of the distance between an inner and outer sealing surface. Such variations will arise typically due to varying pressure within the tubular elements, varying temperature, or external forces. Patent publication US8104769 describes a seal ring (20) which is adapted to twist about its cross section in order to increase or decrease the radial distance between its sealing surfaces. The seal ring is arranged in the annulus between an inner and outer tubular element. Axially below the seal ring there is arranged a spring ejector (22) which exerts an axial force onto the seal ring. The axial compression makes the seal ring twist. When the compression force is removed, the spring ejector makes sure that the seal ring is ejected from its sealing position, i.e. it twists back into its original or resting position.

Another solution is described in patent publication US4384730. This sealing ring (10) exhibits an inclined face that faces an inclined face of the inner tubular element, against which it seals. There is a 5 degree misalignment between the two facing inclined faces, resulting in a deformation of the seal ring when it is compressed between the inclined face of the inner tubular member and a lower shoulder of the outer tubular member. When compressed into the sealing mode, the seal ring carries the load of a tubing hanger.

Patent application publication US20120285676 discloses a sealing assembly having an inner (24) and outer (32) seal ring which slide against one another on facing inclined faces (tapered faces). A spring assembly exerts an axial force onto the inner seal ring. When moved from the non-sealing mode into the sealing mode, the outer seal ring is forced into the annulus between the inner and outer tubular element. This movement compresses the spring assembly. One should note that if the radial distance of the annulus increases, the tension in the outer seal ring decreases. Moreover, since two seal rings are used, the seal assembly needs to seal along three possible leakage paths. That is between the two seal rings in addition to between respective seal ring and the inner and outer tubular element. The circumference and hence the tension forces or compression forces in the inner seal ring remains constant.

Patent publication US7861789 shows a wedge seal (cf. Fig. 4). A seal ring (55) has a metal seal (57) of another metal on it. The seal ring is forced axially into a sealing engagement with inner and outer coaxially arranged surfaces. Fingers (59) forces the seal ring into sealing mode when a drive ring moves the upper end of fingers against a tapered surface (71 ).

Hence, a vast variety of metal seals exist, adapted for sealing the annulus between two coaxially arranged tubular elements. However, the seal assemblies of the prior art fail to adapt to large variations of radial distance of the annulus. That is, it is known to force a seal ring into sealing action, but such force is neither maintained if the seal ring needs to seal an increasing radial distance of the annulus, nor is such force compliant if the seal ring needs to permit this radial distance to decrease. Thus, if variations of the radial distance between the coaxially arranged surfaces between which the seal ring shall seal becomes too large, the seal assemblies of the prior art are not able to maintain their sealing function. An object of the present invention is to provide a sealing assembly that will provide a sealing function over a larger range of such distance variation.

The invention

According to a first aspect of the present invention there is provided a seal assembly comprising a seal ring comprising metal. The seal ring seals between an inner tubular element having an outer surface and a coaxially arranged outer tubular element having an inner surface. The inner surface or the outer surface has an inclined element surface against which the seal ring moves when moving in an axial direction, thereby altering its circumference. An activation

arrangement exerts an actuation force onto the seal ring, thereby forcing an inclined seal ring surface of the seal ring against the inclined element surface. According to the present invention, the activation arrangement maintains said actuation force along a function path of the seal ring between an inner sealing position and an outer sealing position. Furthermore, when the sealing ring is between the inner and outer sealing positions ,as a result of radial expansion or radial reduction of the inner surface or the outer surface, whichever is opposite of the inclined element surface;

- in a case where the radial distance between the inner surface and outer surface increases, the activation arrangement moves the seal ring along the inclined element surface in a first direction, thereby increasing the difference between the circumference of the seal ring and the original circumference of the seal ring; and

- in a case where the radial distance between the inner surface and the outer surface decreases, the activation arrangement is compressed in an axial direction by the seal ring as the seal ring is forced against the inclined element surface by radial force from the inner surface or the outer surface, resulting in a movement of the seal ring along the inclined element surface in a second direction which is opposite of the first direction, thereby reducing the difference between the circumference of the seal ring and the original circumference of the seal ring.

The inclined element surface is a portion of the inner surface or outer surface which is tapered, so that when the seal ring moves along it, the circumference of the seal ring will change. The inner surface and the outer surface are coaxially arranged.

The said radial expansion or radial reduction of the inner surface or the outer surface means an increase or reduction of the diameter of the inner or outer surface.

The term original circumference of the seal ring shall be construed as the circumference of the seal ring when it is not exposed to tension or compression forces. The same applies for an original circumference of a centre ring, an upper ring, a lower ring or a spring ring, as will be discussed below.

The function path of the seal ring is the course or track along which it moves along the inclined element surface, along which it is able to maintain sealing function against the inner surface and the outer surface. The function path extends between an inner sealing position and an outer sealing position, wherein the seal ring exhibits a smaller circumference in the inner sealing position than in the outer sealing position. The actuation force may vary along the function path. It shall however be within sufficient upper and lower thresholds, so that the sealing function of the seal ring is maintained along the function path. An essential feature of the present invention is that the activation arrangement makes the seal ring adapt to an increasing or decreasing radial distance of the annulus in which it seals, namely the distance between the inner surface of the outer tubular element and the outer surface of the inner tubular element. Many solutions of the prior art simply thrusts the seal ring into a sealing mode, without taking account for variation of the annulus dimension. Compression of the seal ring in the solution according to the present invention, as a result of the radial distance between the inner and outer surface being reduced, makes the seal ring circumference move towards its resting state/original state.

According to an embodiment of the invention, the activation arrangement can comprise a spring ring in the form of an endless ring with an inclined ring sliding face that abuts an opposite sliding face. In a case where the radial distance between the inner surface and the outer surface increases, the endless spring ring will then slide on the opposite sliding face in such direction that the circumference of the spring ring changes towards the original circumference of the spring ring. Moreover, in a case where the radial distance between the inner surface and the outer surface decreases, the endless spring ring slides on the opposite sliding face in such direction that the circumference of the spring ring changes away from the original circumference of the spring ring.

When the seal assembly according to the invention is activated, the activation arrangement becomes axially compressed, thereby providing the actuation force onto the seal ring. In the embodiment introduced above involving the endless spring ring, the spring ring may be moved from a resting or original state before the seal assembly is activated, to a tensioned or compressed state when it is activated. In this embodiment it is these tension forces or compression forces in the endless spring ring that provide for the actuation force onto the seal ring. The activation arrangement may even comprise a plurality of endless spring rings that are coaxially arranged with respect to each other. Adjacent spring rings may then be adapted to slide against each other along their facing inclined sliding faces and opposite sliding faces in such manner that the circumference of adjacent spring rings changes in opposite directions. I.e. if the circumference of one spring ring increases, the circumference of its one or two adjacent ring(s) is reduced, and vice versa.

The seal ring comprises an actuation surface which is adapted to receive said actuation force from the activation arrangement. The actuation surface may be inclined with respect to the axial and radial direction, wherein a spring ring or an intermediate ring which is arranged between the activation arrangement and the seal ring, can abut the actuation surface of the seal ring with an inclined actuation force surface, thereby transmitting said actuation force between two facing inclined surfaces. The inclination of the actuation surface of the seal ring will contribute in providing a twisting movement of the seal ring as it moves along the inclined element surface.

Preferably the actuation surface together with an opposite seal ring surface, which is adapted to seal against the inner surface or the outer surface, forms a tip in the cross section through the seal ring. The tip can be at an axial and radial end portion of said cross section and closer to the activation arrangement than the inclined seal ring surface of the seal ring is. In the described examples of embodiment below, the seal ring is provided with only one such tip and the tip is arranged adjacent to either the inner surface or outer surface.

According to an embodiment of the seal assembly according to the present invention,

- in a case where the radial distance between the inner surface and outer surface increases, the activation arrangement is adapted to, with the activation force, twist the seal ring in a first twisting direction thereby moving a contact line between the inclined element surface and the inclined seal ring surface in such direction that the difference between the twist angle of the seal ring and the original twist angle of the seal ring increases; and - in a case where the radial distance between the inner surface and the outer surface decreases, the activation arrangement is adapted to be

compressed in an axial direction by the seal ring as the seal ring is forced against the inclined element surface by radial force from the inner and outer surface, resulting in a twisting movement of the seal ring in a second twisting direction opposite of the first direction, thereby reducing the difference between the twist angle of the seal ring and the original twist angle of the seal ring. Advantageously, the above mentioned inclination of actuation surface of the seal ring and/or upper inclined actuation face ensures both twisting of the seal ring and a change of circumference of the seal ring.

Advantageously a wedge seal is arranged coaxially with respect to the seal ring and on the axial side of the seal ring which is opposite of the activation arrangement. A wedge seal actuation force is then transmitted from the seal ring onto the wedge seal. In such an embodiment, the wedge seal can be adapted to slide on an inclined wedge seal surface which is arranged on the same inner surface or outer surface as the inclined element surface.

When the seal ring moves against the inclined element surface, the movement may involve sliding and/or a rolling movement as the seal ring twists.

According to a second aspect of the present invention, there is provided a method of sealing between an inner tubular element having an outer surface and a coaxially arranged outer tubular element having an inner surface, the method comprises the following steps:

a) arranging a seal ring radially between the outer surface and the inner surface and axially between an activation arrangement and an inclined element surface on the outer surface or the inner surface;

b) activating the seal ring into sealing mode by moving the inclined element surface and the activation arrangement axially towards each other, thereby compressing the seal ring between the inclined element surface and the activation arrangement, thereby providing a mutual force between the seal ring and the activation arrangement, and with this mutual force

- moving the seal ring along the inclined element surface, thereby

increasing the difference between the circumference of the seal ring and the original circumference of the seal ring; and

- axially compressing the activation arrangement; c) maintaining a sealing function of the seal ring upon a change of the radial distance between the outer surface of the inner tubular element and the inner surface of outer tubular element with the following steps:

i) when the change is an increase of said radial distance as a result of a change in diameter of the outer surface or inner surface which is opposite of the one provided with the inclined element surface, increasing further the difference between the circumference of the seal ring and the original circumference of the seal ring with said mutual force; ii) when the change is a reduction of said radial distance as a result of a change in diameter of the outer surface or inner surface which is opposite the one provided with the inclined element surface, reducing the difference between the circumference of the seal ring and the original circumference of the seal ring by letting force from the seal ring axially compress the activation arrangement.

According to a third aspect of the present invention there is also provided a method of adapting a seal ring arranged in an annulus between an outer surface of an inner tubular element and an inner surface of a coaxially arranged outer tubular element to variations of radial distance between said outer and inner surfaces. The method comprises the following steps:

a) activating the seal ring into sealing mode by compressing an activation arrangement axially between the seal ring and an abutment shoulder, thereby reducing the axial extension of the activation arrangement, wherein an axial force is transmitted through the seal ring from an inclined element surface on the outer or inner surface to the activation arrangement;

and, when said radial distance increases

i) moving the seal ring along the inclined element surface and away from the position of the abutment shoulder with a force from the activation arrangement exerted onto the seal ring; and

when said radial distance decreases

ii) compressing the activation arrangement by movement of the seal ring along the inclined element surface and towards the position of the abutment shoulder. Advantageously, step i) or ii) of this method may include twisting the seal ring about a contact line between the inclined element surface and the seal ring surface, thereby moving the contact line along the inclined element surface, as at least one of the inclined element surface and the inclined seal ring surface exhibits a curved shaped cross section along a radially extending cross section plane.

Characteristic to the assembly and methods according to the invention is that the activation arrangement is compressed upon activation of the seal ring. The activation arrangement functions like a spring which, when within the function path may be further compressed. It will also apply sufficient force onto the seal ring when the latter may be moved axially away from the position of the activation arrangement, due to an increase of the radial distance between the inner and outer surfaces. In other words, along the function path it exhibits sufficient force onto the seal ring to maintain the sealing function of the seal ring.

Example of embodiment

While the invention has been described in general terms above, a more detailed and non-limiting example of embodiment will be described in the following with reference to the drawings, in which

Fig. 1 is a cross section view of a subsea internal tree cap (ITC), illustrating one possible application of the seal assembly according to the present invention;

Fig. 2 is an enlarged cross section view of a part of the ITC of Fig. 1 , however with its lock ring in a locked position;

Fig. 3 is an enlarged cross section view through a portion of a seal ring which is part of the seal assembly;

Fig. 4 is a cross section view through the entire seal ring;

Fig. 5 is a principle cross section view through a part of the seal assembly

according to the invention in an non-activated mode, showing parts of the inner and outer tubular elements, the seal ring, and the activation arrangement; Fig. 6 is a cross section view corresponding to Fig. 5, however showing the seal assembly in an activated mode;

Fig. 7 is a cross section view corresponding to Fig. 6, however with an

increased distance between the inner and outer tubular elements;

Fig. 8 is a cross section view corresponding to Fig. 7, however showing a

situation where a well pressure exerts a force onto the seal ring;

Fig. 9 is a principle view of the embodiment shown in the previous drawings; Fig. 10 is a principle view of another embodiment of the seal assembly according to the present invention;

Fig. 1 1 is a principle top view of a seal ring in a resting or original configuration; Fig. 12 is a principle view according to Fig. 1 1 , illustrating the seal ring in an expanded configuration;

Fig. 13 is a principle cross section view of a portion of a seal ring abutting an inclined element surface;

Fig. 14 is a view corresponding to Fig. 13, showing the seal ring in a twisted position;

Fig. 15 is a cross section view of a seal assembly according to the invention, having a wedge seal arranged axially onto the seal ring;

Fig. 16 to Fig. 20 are enlarged cross section views through alternative

embodiments of the seal ring;

Fig. 21 to Fig. 23 are principle cross section views through yet an alternative embodiment in a non-activated state, wherein the seal ring is split into a seal ring part and a seal stop ring;

Fig. 24 is an enlarged cross section view through the seal ring part of the

embodiment shown in Fig. 21 to Fig. 23;

Fig. 25 is a cross section view through the entire seal ring part of the seal ring part shown in Fig. 24;

Fig. 26 is an enlarged cross section view of a portion of the seal ring in an

alternative embodiment; and

Fig. 27 is view corresponding to Fig. 26, showing yet an alternative embodiment.

Fig. 1 illustrates an internal tree cap (ITC) 100 which is adapted to be installed within the spool of a subsea Xmas tree (not shown in Fig. 1 ). The ITC 100 is provided with a seal assembly 1 according to the invention, which will be described further below. In order to lock the ITC 100 to internal locking profiles of the XT spool, the ITC 100 comprises a lock ring 103 which is actuated in the radially outward direction by means of an actuation sleeve 105. This method of locking an internal tubular element to the inner bore of an outer element is well known to the skilled person in the art. It should be understood that the ITC 100 and the XT spool are only examples of inner and outer tubular elements between which the seal assembly 1 according to the invention may seal. It is noted, however, that the seal assembly 1 according to the invention is particularly useful in the field of subsea wells, which involves a plurality of tubular metal

components between which reliable sealing is needed.

Fig. 2 is a segment of the right portion of the cross section of Fig. 1 , however with the lock ring 103 in the locked position (radially outward position). In Fig. 2 an activation arrangement 2, here in the form of a spring assembly, and a seal ring 3 are indicated, which are both parts of the seal assembly 1 according to the present invention. The activation arrangement 2 provides an actuation force on the seal ring 3 and is able to do so along a varying axial distance. That is, the seal ring 3 is adapted to move a certain axial distance and the activation arrangement 2 will follow the axial movement of the seal ring 3 and exhibit an actuation force through this entire distance. It should be appreciated by the person skilled in the art that the activation arrangement 2 can be of another type than the one shown in the example embodiment. For instance, the activation arrangement could be a stack of Belleville washers. The activation arrangement 2 shown herein is however advantageous as it provides a sufficient yet not excessive actuation force along an appropriate axial distance without need of excessive axial space to accommodate the activation arrangement.

The seal ring 3 extends about an inner tubular element 105 which in this embodiment is the actuation sleeve.

Above the seal ring 3 is arranged a wedge seal 31 . The wedge seal 31 is arranged about and surrounds an inclined wedge seal surface 33 of the inner tubular element, which in this embodiment is the actuation sleeve 105 of the ITC 100. As will be described further below, the seal ring 3 is adapted to move in a substantial axially direction in the annulus 19. Since the wedge seal 31 lands on the top of the seal ring 3, the wedge seal 31 is adapted to move with the seal ring 3.

Fig. 3 is an enlarged cross section view through a portion of the seal ring 3, corresponding to the right portion of the cross section through the entire seal ring 3 in Fig. 4.

Fig. 5 is an enlarged cross section showing the seal ring 3 arranged in the annulus 19 between an inner tubular element 105 and an outer tubular element 107. In this embodiment the inner tubular element is the actuation sleeve of the ITC 100 and the outer tubular element 107 is a spool of a Xmas tree. The annulus 19 is between an inner surface 7 of the outer tubular element 107 and an outer surface 5 of the inner tubular element 105. In this embodiment the outer surface 5 of the inner tubular element 105 is provided with an inclined element surface 9. The seal ring 3 comprises an inclined seal ring surface 1 1 that abuts and faces the inclined element surface 9. The inclined seal ring surface 1 1 and the inclined element surface 9 form together a sealing engagement when the seal ring 3 is activated.

On an end of the cross section through a portion of the seal ring 3 which is opposite the inclined seal ring surface 1 1 , , as shown in Fig. 3 and Fig. 5, the seal ring 3 exhibits an opposite seal surface 13. The opposite seal ring surface 13 is adapted to form a sealing engagement with the inner surface 7 of the outer tubular element 107.

Below the seal ring 3 is arranged an activation arrangement 2 which will now be described. The purpose of the activation arrangement 2 is to provide an actuation force on the seal ring 3. If the radial distance D (Fig. 5) between the inner surface 7 and the outer surface 5 (of the outer and inner tubular element 107, 105, respectively) changes, the seal ring 3 will also change its position and/or orientation, thereby adapting to such change. The actuation force of the activation arrangement 2 provides for this change if the said radial distance D of the annulus 19 increases. In this embodiment, the activation arrangement 2 has a centre ring 201 with an upper inclined face 207 and a lower inclined face 209. Abutting the upper and lower inclined faces 207, 209 are an upper ring 203 and a lower ring 205, respectively. The upper and lower ring 203, 205 are adapted to slide on the upper and lower inclined faces 207, 209 with their respective opposite sliding faces 213, 215.

Referring again to Fig. 1 and Fig. 2, when the actuation sleeve 105 is moved downwards, the activation arrangement 2 is axially compressed between an abutment shoulder 103, which in this embodiment is the lock ring 103. During this compression, the centre ring 201 is elastically compressed as it is forced radially inwards by the upper and lower rings 203, 205 sliding on the upper and lower inclined faces 207, 209. Contrary to this, the upper and lower rings 203, 205 are elastically expanded. As a result, the axial extension of the activation

arrangement 2 is reduced. The activation arrangement 2 maintains a significant force onto the seal ring 3, pushing it upwards towards the inclined element surface 9. Fig. 6 shows the activation arrangement 2 in a compressed state. It should be appreciated by the person skilled in the art, that the type of activation arrangement is not essential for the function of the seal ring 3. Thus other arrangements that are able to bias the seal ring 3 through the required axial varying distance will be applicable. However, the activation arrangement 2 shown in this embodiment has proven to fulfill this technical task in a reliable and satisfactory manner. Advantages of such an embodiment of the activation arrangement 2 is that it maintains an appropriate actuation force onto the seal ring 3 along a sufficient function path, and that it needs a limited axial and radial space. In addition to bias the inclined seal ring surface 1 1 towards the inclined element surface 9, the activation arrangement 2 also bias the opposite seal ring surface 13 against the inner surface 7 (i.e. the inwardly facing surface of the outer tubular element 107 in this embodiment). An actuation force surface 21 1 is in this embodiment inclined and situated on the upper ring 203. The actuation force surface abuts a facing actuation surface 15 of the seal ring 3. Due to the inclination of the actuation force surface 21 1 as well as the position of

engagement between the actuation force surface 21 1 and the actuation surface 15 of the seal ring 3, this abutment provides a twisting movement of the seal ring 3, in addition to an axial movement of the seal ring 3, when the radial distance D between the outer surface 5 of the inner tubular element 105 and the inner surface 7 of the outer tubular element 107 changes. This will be described further below. The twisting movement can be about a contact line 23 (indicated in Fig. 13 and Fig. 14) at which the inclined seal ring surface 1 1 of the seal ring 3 contacts the inclined element surface 9. Thus the contact line 23 extends circumferentially about the seal ring 3, parallel to a circumferential axis of the seal ring 3. When the seal ring 3 moves along the inclined element surface 9, the contact line 23 will also move along the inclined element surface. In the following, various situations will be described with reference to Fig. 5 to Fig. 8.

Fig. 5 shows the seal assembly 1 according to the present invention in a non- activated state. The seal ring 3 rests freely between the inclined element surface 9 above it and the activation arrangement 2 below it. The actuation element 2 is in a non-compressed mode. Thus, there is a free space radially within the centre ring 201 so that it may move radially inwards. Correspondingly, there is space on the radial outside of the upper and lower ring 203, 205 so that they may move radially outwards.

Fig. 6 shows a situation where the seal assembly 1 has been actuated. The activation arrangement 2 has been axially compressed so that it exerts an actuation force onto the seal ring 3. More precisely, the actuation force is exerted onto the actuation surface 15 of the seal ring 3 from the actuation force surface 21 1 of the upper ring 203. The centre ring 201 has moved radially into contact with the outer surface 5 of the inner tubular element 105. The upper and lower ring 203, 205 have moved slightly radially outwards and still have the possibility to move further. Due to the force exerted onto the actuation surface 15 of the seal ring 3 by the activation arrangement 2, the seal ring 3 is in sealing contact with the inclined element surface 9 as well as the inner surface 7.

It should be noted that in lieu of having the actuation force surface 21 1 on the upper ring 203 of the activation arrangement 2, one could also arrange for instance an intermediate ring between the activation arrangement 2 and the seal ring 3 for transmitting the actuation force from the activation arrangement 2 to the seal ring 3. The activation arrangement 2 could also comprise more or less spring rings 201 , 203, 205 than what is shown in the embodiment described here.

Fig. 7 shows a situation similar to that shown in Fig. 6. However, in Fig. 7 the radial distance D (Fig. 5) has increased. This may for instance be due to internal pressure, thermal expansion or removal of mechanical forces that previously was exerted onto the external face of the outer tubular element 107 (the XT spool in this embodiment). Due to this larger annulus 19, the seal ring 3 may move along the inclined element surface 9 to expand radially, and it may also twist as the activation arrangement 2 exerts a force from it from below ("below" with respect to the drawing of Fig. 7). The cross section shown in the drawings of Fig. 5 to Fig. 8 rotates or twists in an anti-clockwise direction as a result of increase of the radial dimension of the annulus 19, as indicated with the curved arrow in Fig. 7. As a result, the opposite sealing surface 13 of the seal ring moves after (i.e.

follows) the inner surface 7 of the outer tubular element 107 and ensures continuing sealing. It should be noted that in the situations shown in Fig. 6 and Fig. 7 (also Fig. 8), the circumference of the seal ring 3 has been increased by forcing it to move along the inclined element surface 9. Hence, tension in the seal ring 3 will ensure an appropriate contact force between the inclined seal ring surface 1 1 and the facing inclined element surface 9, which will provide a sealing between these surfaces.

In Fig. 8 the situation corresponds in many ways to the one in Fig. 7. However, a significant pressure, such as a well pressure, exerts an additional force onto the lower side of the seal ring 3. This additional force makes the seal ring 3 slide an additional distance along the inclined element surface 9. Since the opposite seal ring surface 13 abuts the inner surface 7 of the outer tubular element 107, the seal ring 3 now twists in the other direction (i.e. the clockwise direction in the depiction of Fig. 8). In order to limit this twisting movement, an upper shoulder 17 of the seal ring 3 abuts the inner surface 7 at an upper portion of the seal ring 3. The upper shoulder 17 may also exhibit a surface adapted for sealing against the inner surface 7 of the outer tubular element 107.

If the radial distance D of the annulus 19 now decreases, the seal ring 3 will be forced downwards by the inclined element surface 9, thereby compressing the activation arrangement 2. Also, if the pressure is relieved the seal ring 3 will also move downwards along the inclined element surface 9. In these cases, the seal ring 3 will also twist in the opposite direction, towards its original configuration. Thus, the seal assembly 1 according to the invention comprises a seal ring 3 arranged between an inner tubular element and an outer tubular element, which will continue to exhibit sealing performance both during varying pressure conditions, as well as during varying sizes of the inner and outer tubular elements. That is, when the annulus size increases and/or the pressure increases, the seal ring is able to move along the inclined element surface and twist, thereby adapting to the new annulus size. Correspondingly, when the annulus size decreases, the seal ring is able to move back along the inclined element surface and twist in the opposite direction, thereby adapting to the reduced annulus size. During these movements of the seal ring, i.e. changing circumference and configuration (by twisting), the activation arrangement continues to exhibit an actuation force onto the seal ring to ensure a proper sealing action against both the inner and outer surface.

The activation arrangement 2 functions like an axially moving spring that maintains an actuation force on the seal ring 3 over a function path of the seal ring 3, along which the seal ring 3 will provide sufficient sealing function against both the inner surface 7 of the outer tubular element 107 and the outer surface 5 of the inner tubular element 105. When the radial distance between the inner surface 7 and the outer surface 5 increases, the centre ring 201 slides on the opposite sliding face 21 3 of the lower ring 205 in such direction that the circumference CR of the centre ring 201 changes towards the original

circumference of the centre ring C_R0. This change may either be a change towards less tension or a change towards less compression of the centre ring 201 . Moreover, when the radial distance between the inner surface 7 and the outer surface 5 decreases, the centre ring 201 slides on the opposite sliding face 21 3 in such direction that the circumference CR of the spring ring 201 changes away from the original circumference C_R0 of the spring ring 201 . It is again referred to Fig. 3, which shows an enlarged cross section view through a portion of the seal ring 3 of a seal assembly 1 according to the invention. The inclined seal ring surface 1 1 , which is adapted to abut the inclined element surface 9, advantageously exhibits a curved shape. This curved shape makes the seal ring 3 suitable for the twisting movement described above, while still maintaining sealing performance. The curved shape also reduces the risk of damage to the facing seal surfaces, such as by scratching, denting and deformation. The curved shape of the inclined seal ring surface 1 1 results in that the contact line 23, at which the inclined seal ring surface 1 1 contacts the inclined element surface 9, will move when the seal ring 3 twists (cf. Fig. 1 3 and Fig. 1 4)

As appears from Fig. 3, the opposite seal ring surface 1 3 also advantageously exhibits a curved shape. This is advantageous since the radial distance D varies, as described above. Thus, the seal ring 3 is adapted to seal in various twist positions, with both the inclined seal ring surface 1 1 and the opposite seal ring surface 1 3.

Fig. 9 and Fig. 1 0 are principle drawings to show how the principle of the seal assembly 1 according to the present invention functions when the inner surface 7 of the outer tubular element 1 07 comprises the inclined element surface 9, in lieu of the outer surface 5 of the inner tubular element, as shown in Fig. 1 to Fig. 8.

Fig. 9 corresponds to the embodiment shown with reference to Fig. 1 to Fig. 8, in which the inclined element surface 9 is on the inner tubular element 1 05, that is on the outer surface 5 of the inner tubular element 105, which faces radially outwards.

Fig. 10 shows an embodiment where the inclined element surface 9 is arranged on the inwardly facing inner surface 7 of the outer tubular element 107. The cross section of a portion of the seal ring 3 is mirrored so that the inclined seal ring surface 1 1 faces the inclined element surface 9. Moreover, when the activation arrangement 2, here only indicated with an arrow, exerts the actuation force on the seal ring 3, the circumference C of the seal ring 3 is reduced elastically. This is in contrast to the embodiment shown in Fig. 1 to Fig. 8, wherein the

circumference C was increased. Due to the reduction of circumference C, the seal ring 3 will exert a force onto the inwardly facing inclined element surface 9. The opposite seal ring surface 13 will, on the other hand, be forced radially against the outer surface 5 of the inner tubular element 105.

As described above, when the seal ring 3 moves in an axial direction and slides along the inclined element surface 9, its circumference C will change. Fig. 1 1 and Fig. 12 principally illustrate such a change. It should be noted that these drawings are merely principle drawings for illustration. In Fig. 1 1 a seal ring 3 is shown in its resting or original configuration. In such a state its circumference C is equal to its original circumference Co, as indicated with the circle shaped line encircling the seal ring 3. Fig. 12 illustrates the same seal ring 3 in a mode where it has been moved along the inclined element surface 9, such as shown in Fig. 6 to Fig. 8. As a result of the movement its circumference C has increased an amount of AC. Hence, its circumference C is now C₀ + AC. It should be noted that the difference between these figures is greatly exaggerated for the purpose of illustration.

If the inclined element surface 9 is arranged on the inner surface 7 of the outer tubular element 107, such as illustrated in Fig. 10, the circumference C would be reduced when the activation arrangement 2 forces the seal ring 3 along the inclined element surface 9. The seal ring 3 would then become compressed. In both cases, the circumference C of the seal ring 3 is altered from its original state having a circumference C equal to Co to a new circumference which is either compressed or expanded to C = C₀ + AC. The change in circumference, AC, can thus be positive or negative.

Fig. 13 and Fig. 14 are enlarged principle cross section drawings through a portion of the seal ring 3 and the inclined element surface 9, illustrating the twisting of the seal ring 3. Fig. 13 illustrates the seal ring 3 in a sealing mode in which it has been forced a distance up along the inclined element surface 9. Compared to the situation in Fig. 13, in the situation shown in Fig. 14 the radial distance between the outer surface 5 and the inner surface 7 (not indicated in these drawings) of the outer tubular element 107 has increased. As a result, the seal ring 3 has moved an additional distance along the inclined element surface 9 and also twisted an angle corresponding to the indicated angle a (Fig. 14). As can be appreciated by comparing the two drawings of Fig. 13 and Fig. 14, the opposite seal ring surface 13 is substantially further to the right in Fig. 14 than in Fig. 13, as a result of a combination of altered circumference C and the twisting corresponding to the indicated angle a. One should also note that the contact line 23 has changed its position both on the inclined element surface 9 as well as on the inclined seal ring surface 1 1 . Some features shown in Fig. 13 and Fig. 14 are exaggerated for the purpose of illustration.

Fig. 15 is a cross section view of the seal assembly 1 according to the invention. In this embodiment the seal assembly 1 further comprises a wedge seal 31 which is arranged coaxially with respect to the seal ring 3. Moreover, it is arranged on the axial side of the seal ring 3 which is opposite of the activation arrangement 2. As can be appreciated from Fig. 15, the wedge seal 31 is arranged onto the seal ring 3, so that a wedge seal actuation force is transmitted from the seal ring 3 onto the wedge seal 31 . Thus, when the seal ring 3 is moved in the axial direction, sliding up or down along the inclined element surface 9, the wedge seal 31 will move along with it. When the wedge seal 31 moves in the axial direction, it slides along an inclined wedge seal surface 33 on the inner tubular element 105, i.e. on the outer surface 5 of the inner tubular element 105. It should be noted, however, that in a case where the inclined element surface 9 is arranged on the inner surface 7 of the outer tubular element 107 (cf. the principle illustration of Fig. 10), the inclined wedge seal surface 33 would also be arranged on the inner surface 7. The wedge seal 31 can advantageously be made of a polymer. Moreover, it may contain a pressure side (on the axially lower side in Fig. 15) which is made of one type of polymer, and a sealing side (on the axially opposite side with respect to the pressure side) made of another polymer. The wedge seal 31 constitutes an additional pressure barrier and operates simultaneously with the seal ring 3. Moreover the wedge seal 31 may function to prevent impurities, such as dust or small particles, from entering past the wedge seal and being compressed between the inclined element surface 9 and the inclined seal ring surface 1 1 .

Fig. 16 to 20 show enlarged cross sections through different alternative embodiments of a seal ring 3 which could be part of other embodiments of the seal assembly according to the invention. All the illustrated seal rings 3 have an inclined seal ring surface 1 1 adapted to seal against the inclined element surface 9 (cf. Fig. 5). Common to them all is also that they have an actuation surface 15 adapted to be engaged by an activation arrangement 2 and an opposite seal ring surface 13 adapted to seal against the inner surface of the outer tubular element 107 or the outer surface 5 of the inner tubular element 105, against which the inclined seal ring surface 1 1 does not seal. Furthermore, the axial position of the inclined seal ring surface 1 1 is offset with respect to the axial position of the opposite seal ring surface 13. Or at least the point of engagement between the inclined seal ring surface 1 1 and an abutting inclined element surface 9 is axially offset with respect to the point of engagement between the opposite seal ring surface 13 and an abutting inner surface 7 or outer surface 5. This axial offset brings about the desired varying radial distance between the inclined seal ring surface 1 1 and the opposite seal ring surface 13 when the seal ring 3 twists.

Common to all the embodiments of a seal ring 3 shown in Fig. 16 to Fig. 20 (as well as the one shown in Fig. 3) is that the actuation surface 15 exhibits an inclination and faces in a partial radial direction which is opposite of the radial direction which the opposite seal ring surface 13 faces. This inclination of the actuation surface 15 contributes in bringing about the rotational movement of the seal ring 3 when adapting to varying distances of the annulus 19.

In the shown embodiments, the actuation surface 15 of the seal ring 3 forms together with the opposite seal ring surface 13 a tip 21 in the cross section through the seal ring 3. The tip 21 is at an axial and radial end of the cross section shape and also closer to the activation arrangement than the inclined seal ring surface 1 1 is. Furthermore, in the embodiments shown in Fig. 3 and Fig. 16 to Fig. 19, there is an angle of at least 20 degrees between the general direction of the actuation surface 15 and the general direction of the opposite seal ring surface 13. This angle results in a pointed tip in a cross section of a portion of the seal ring 3.

One should also note that the point of engagement between the actuation surface 15 of the seal ring 3 and the activation arrangement 2 (or an intermediate ring transferring the actuation force from the activation arrangement 2 to the seal ring 3) is radially offset towards the opposite seal ring surface 13 with respect to an axial centre line between the radially outermost portions of the seal ring 3 (with respect to the enlarged cross sections shown in Fig. 3 and Fig. 16 to Fig. 20). This feature also contributes in bringing about said rotational movement.

As shown with the embodiments illustrated in Fig. 17 and Fig. 19, the part of the seal ring 3 that exhibits the opposite seal ring surface 13 and the actuation surface 15 may have a slim shape (i.e. this part of the cross section of the seal ring 3) that will allow for some bending of the seal ring 3 about a circumferential axis extending parallel to the seal ring 3. Thus, for such embodiments the seal ring 3 will adapt to the varying dimensions of the annulus 19, as described above, by movement along the inclined element surface 9, twisting of the entire seal ring cross section (such as shown in Fig. 3), as well as some degree of bending in the seal ring 3. This bending may allow for an even further variation of annulus distance without loosing the sealing capability of the seal ring 3. In one possible embodiment of the seal ring 3, as shown in Fig. 18, the seal ring 3 is not provided with the upper shoulder 17 which is arranged in the other embodiments to limit the amount of rotation. It should be noted that the shown cross sections of various embodiments of the seal ring 3, as shown in Fig. 3 and Fig. 16 to Fig. 20, may be employed both on a radially inwardly and outwardly facing inclined element surface 9, such as described with reference to Fig. 9 and Fig. 10. Fig. 21 is a principle cross section view through yet an alternative embodiment of a seal assembly 1 ' according to the invention. In Fig. 21 the assembly is shown in a non-activated state. In this embodiment the seal ring 3 is split into a seal ring part 3a and a seal stop ring 3b. The function of this seal assembly 1 ' is substantially corresponding to the function of the seal assembly 1 described above. The seal ring part 3a exhibits an inclined seal ring surface 1 1 , an opposite seal ring surface 13, and an actuation surface 15. The seal stop ring 3b is arranged directly axially adjacent and abutting the seal ring part 3a. The seal stop ring 3b serves to limit the axial movement of the seal ring part 3a. Without the seal stop ring 3b, the seal ring part 3a could also be prone to twist in the "wrong" direction, as the inclined seal ring surface 1 1 could be allowed to slide an excessive distance along the inclined element surface 9. Thus, one of the radially facing sides of the seal stop ring 3b is comparable to the upper shoulder 17 shown in the embodiments above. Fig. 22 shows the same cross section as Fig. 21 , however with the seal assembly 1 ' in an activated state. Fig. 23 is a cross section view according to Fig. 22, however in a state where well pressure exerts a force onto the seal ring part 3a.

Fig. 24 is an enlarged cross section view through the seal ring part 3a of the embodiment shown in Fig. 21 to Fig. 23. Fig. 25 is a cross section view through the entire seal ring part 3a of the seal ring part shown in Fig. 24.

Both the seal ring 3, and the inner and outer tubular elements 105, 107 are preferably of metal, such as common in a subsea well application. Fig. 26 shows an alternative embodiment of the invention. Here the inclined seal ring surface 1 1 is not curved. Rather, its cross section shows a straight line, while the abutting inclined element surface 9 is curved in order to make it possible for the seal ring 3 cross section to rotate with respect to the inclined element surface 9.

Fig. 27 is yet an alternative, somewhat similar to the one shown in Fig. 26. Here both the inclined element surface 9 and the inclined seal ring surface 1 1 exhibit a curved cross section. The curving of each surface may then be less.

In all the embodiments described above, both the seal ring 3, and the inner and outer tubular elements are preferably of metal, such as in a subsea well application.

Claims

1 . Seal assembly comprising

- a seal ring (3) comprising metal, which seals between an inner tubular element (105) having an outer surface (5) and a coaxially arranged outer tubular element (107) having an inner surface (7), wherein the inner surface (7) or outer surface (5) is provided with an inclined element surface (9) against which the seal ring (3) moves when moving in an axial direction, thereby altering its circumference (C); and

- an activation arrangement (2) exerting an actuation force onto the seal ring, thereby forcing an inclined seal ring surface (1 1 ) of the seal ring (3) against the inclined element surface (9);

characterized in that

the activation arrangement (2) maintains said actuation force along a function path of the seal ring (3) between an inner sealing position and an outer sealing position, wherein, when the sealing ring (3) is between the inner and outer sealing positions, as a result of radial expansion or radial reduction of the inner surface (7) or the outer surface (5), whichever is opposite of the inclined element surface (9),

- in a case where the radial distance between the inner surface (7) and outer surface (5) increases, the activation arrangement (2) moves the seal ring (3) along the inclined element surface (9) in a first direction, thereby increasing the difference between the circumference (C) of the seal ring and the original circumference of the seal ring (Co); and

- in a case where the radial distance between the inner surface (7) and the outer surface (5) decreases, the activation arrangement (2) is compressed in an axial direction by the seal ring (3) as the seal ring is forced against the inclined element surface (9) by radial force from the inner surface (7) or the outer surface (5), resulting in a movement of the seal ring (3) along the inclined element surface (9) in a second direction which is opposite of said first direction, thereby reducing the difference between the circumference (C) of the seal ring (3) and the original circumference (Co) of the seal ring (3).

2. Seal assembly according to claim 1 , characterized in that the activation arrangement (2) comprises a spring ring (201 ) in the form of an endless ring with an inclined ring sliding face (209) that abuts an opposite sliding face (213), wherein

- in the case where the radial distance between the inner surface (7) and the outer surface (5) increases, the endless spring ring (201 ) slides on the opposite sliding face (213) in such direction that the circumference (CR) of the spring ring (201 ) changes towards the original circumference of the spring ring (CRO); and that

- in the case where the radial distance between the inner surface (7) and the outer surface (5) decreases, the endless spring ring (201 ) slides on the opposite sliding face (213) in such direction that the circumference (C_R) of the spring ring (201 ) changes away from the original circumference of the spring ring (C_R0).

3. Seal assembly according to claim 2, characterized in that the activation arrangement (2) comprises a plurality of endless spring rings (201 , 203, 205) that are coaxially arranged, wherein adjacent spring rings (201 , 203, 205) are adapted to slide against each other along their facing inclined sliding faces and opposite sliding faces (207, 209, 213, 215) in such manner that the circumference of adjacent spring rings () changes in opposite directions.

4. Seal assembly according to claim 2 or 3, characterized in that the seal ring (3) comprises an actuation surface (15) which is adapted to receive said actuation force from the activation arrangement (2).

5. Seal assembly according to claim 4, characterized in that the actuation surface (15) is inclined with respect to the axial and radial direction, wherein a spring ring (203) or an intermediate ring which is arranged between the activation arrangement (2) and the seal ring (3), abuts the actuation surface (15) of the seal ring (3) with an inclined actuation force surface (21 1 ), thereby transmitting said actuation force.

6. Seal assembly according to claim 4 or 5, characterized in that the actuation surface (15) together with an opposite seal ring surface (13) forms a tip (21 ) in the cross section through the seal ring (3), said tip (21 ) being at an axial and radial end of said cross section and closer to the activation arrangement (2) than the inclined seal ring surface (1 1 ) of the seal ring is.

7. Seal assembly according to one of the preceding claims, characterized in that - in a case where the radial distance between the inner surface (7) and outer surface (5) increases, the activation arrangement (2) is adapted to, by means of the activation force, twist the seal ring (3) in a first twisting direction thereby moving a contact line (23) between the inclined element surface (9) and the inclined seal ring surface (1 1 ) in such direction that the difference between the twist angle (a) of the seal ring and the original twist angle (α₀) of the seal ring

(3) increases; and that

- in a case where the radial distance between the inner surface (7) and the outer surface (5) decreases, the activation arrangement (2) is adapted to be compressed in an axial direction by the seal ring (3) as the seal ring is forced against the inclined element surface (9) by radial force from the inner and outer surface (5, 7), resulting in a twisting movement of the seal ring (3) in a second twisting direction opposite of the first direction, thereby reducing the difference between the twist angle (a) of the seal ring (3) and the original twist angle (¾) of the seal ring (3);

as at least one of the inclined element surface (9) and the inclined seal ring surface (1 1 ) exhibits a curved shaped cross section along a radially extending cross section plane.

8. Seal assembly according to one of the preceding claims, characterized in that a wedge seal (31 ) is arranged coaxially with respect to the seal ring (3) and on the axial side of the seal ring (3) which is opposite of the activation arrangement (2), wherein a wedge seal actuation force is transmitted from the seal ring (3) onto the wedge seal (31 ).

9. Seal assembly according to claim 8, characterized in that the wedge seal (31 ) is adapted to slide on an inclined wedge seal surface (33) which is arranged on the same inner surface (7) or outer surface (5) as the inclined element surface (9).

10. Method of sealing between an inner tubular element (105) having an outer surface (5) and a coaxially arranged outer tubular element (107) having an inner surface (7), the method comprising the following steps:

a) arranging a seal ring (3) radially between the outer surface (5) and the inner surface (7) and axially between an activation arrangement (2) and an inclined element surface (9) on the outer surface (5) or the inner surface (7);

characterized in that the method further comprises the following steps:

b) activating the seal ring (3) into sealing mode by moving the inclined element surface (9) and the activation arrangement (2) axially towards each other, thereby compressing the seal ring between the inclined element surface (9) and the activation arrangement (2), thereby providing a mutual force between the seal ring (3) and the activation arrangement (2), and with this mutual force

- moving the seal ring (3) along the inclined element surface (9), thereby increasing the difference between the circumference (C) of the seal ring (3) and the original circumference (C₀) of the seal ring (3); and

- axially compressing the activation arrangement (2);

c) maintaining a sealing function of the seal ring (3) upon a change of the radial distance between the outer surface (5) of the inner tubular element (105) and the inner surface (7) of outer tubular element (107) with the following steps: i) when the change is an increase of said radial distance as a result of a change in diameter of the outer surface (5) or inner surface (7) which is opposite of the one provided with the inclined element surface (9), increasing further the difference between the circumference (C) of the seal ring (3) and the original circumference (C₀) of the seal ring (3) with said mutual force; ii) when the change is a reduction of said radial distance as a result of a change in diameter of the outer surface (5) or inner surface (7) which is opposite the one provided with the inclined element surface (9), reducing the difference between the circumference (C) of the seal ring and the original circumference of the seal ring (Co) by letting force from the seal ring (3) axially compress the activation arrangement (2).

1 1 . Method of adapting a seal ring (3) arranged in an annulus between an outer surface (5) of an inner tubular element (105) and an inner surface (7) of a coaxially arranged outer tubular element (107) to variations of radial distance between said outer and inner surfaces (5, 7),

characterized in that the method comprising the following steps:

a) activating the seal ring (3) into sealing mode by compressing an activation arrangement (2) axially between the seal ring (3) and an abutment shoulder

(103), thereby reducing the axial extension of the activation arrangement (2), wherein an axial force is transmitted through the seal ring (3) from an inclined element surface (9) on the outer or inner surface (7) to the activation arrangement (2);

and, when said radial distance increases

i) moving the seal ring (3) along the inclined element surface (9) away from the position of the abutment shoulder (103) with a force from the activation arrangement (2) exerted onto the seal ring (3); and

when said radial distance decreases

ii) compressing the activation arrangement (2) by movement of the seal ring (3) along the inclined element surface (9) towards the position of the abutment shoulder (103).

12. Method according to claim 1 1 , characterized in that step i) or ii) includes twisting the seal ring (3) about a contact line (23) between the inclined element surface (9) and the seal ring surface (1 1 ), thereby moving the contact line (23) along the inclined element surface (9), as at least one of the inclined element surface (9) and the inclined seal ring surface (1 1 ) exhibits a curved shaped cross section along a radially extending cross section plane.