GB2216965A - Energisation of sealing assemblies - Google Patents

Abstract

The invention is concerned with the energisation of wedge-type sealing devices 26, 28 of the type known as Cahn devices by applying compressive force in an axial direction to cause expansion in a radial direction. The method provides for inserting a housing 6, or energising ring (88), into the bore which may be part of a wellhead arrangement, rotating the housing 6 by means of a running tool so that it rotates within the bore wall 18 or a member 10 engaged in a recess in the bore wall until a stop position is reached, continuing rotation of the housing so as to produce relative movement with respect to the bore along a threaded interengagement zone to cause said sealing devices 26, 28 to be compressed within a gap provided between the housing 6 and a leading, nose portion 30 thereof, so as to cause radial expansion of the members of the wedge-type sealing device. <IMAGE>

Description

ENERGISATION OF SEALING ASSEMBLIES The invention relates to the energisation of sealing assemblies, for example, metal-to-metal seals.

Metal-to-metal seals are preferable to other types in many situations, for example, in the oil drilling industry where wellhead seals must withstand high temperatures and pressures, thermal cycling and chemical attack.

It is known that a metal-to-metal seal of the wedge type may successfully be used in connection with the packoff element of the well head drill assembly. This type c- edge seal, known as a Canh seal, may comprise two metal seal rings each have complementary frusto-conical confronting surfaces and are received one within the other. The outer ring may for example seal the inner surface of the wellhead wall and the inner ring seals against the outer peripheral surface of the casing or mandrel hanger.

n an alternative form, an intermediate ring of rhombic cross-section may be interposed between the two metal eal rings, the sealing action of the latter operating as before.

Axial compressive force applied to the seal rings produces controlled radial expansion so that contact is made between convex annular ribs on the seal rings and the wall surfaces to the sealed. These ribs comprise two pairs of ribs on each surface adapted to contact a wall surface.

However, some problems have arisen he method hitherto employed for the activation or energisation of the wedge seals. This method uses external hold-down screws which penetrate radially into the outer wall and impinge upon a frusto-conical surface of a suitable annular member which acts as a camming surface to exert pressure upon the rings to compress them. However, this arrangement has the obvious disadvantage that there is a potential leak path in the pressurised assembly.

The present invention therefore seeks to provide energisation of axially compressible seal members by means which minimises the above disadvantages The invention provides, in one of its aspects, a method of energising annular sealing devices by applying compressive force to at least two annular members thereof so as to produce increased radial diameter of the device, comprising the steps of inserting a housing into a bore to be sealed thereto, said housing being provided with an externally threaded portion and a nose portion, there being provided an adjustable axial gap between the housing and said noseportion, into which gap is received said sealing device, rotating said housing by means of a rotary running tool in an advancing movement until a stop position is reached by the nose portion of the housing, said stop position being capable of providing a reaction surface, continuing said rotation of the housing by means of said tool and causing said external thread to travel relative to a co-operating internal thread formed on or solid with the bore walls to cause said housing to continue to advance relative to the nose portion thereof to apply compressive force to the seal rings between said housing and the nose portion thereof.

In an example in which the device comprises three members, the force may be first applied to a peripheral annular member which moves with respect to a captive intermediate annular member of rhombic cross-section until level therewith, whereafter said members move together as if a single member in a movement relative to the other peripheral member in order to achieve said increased radial diameter.

The invention provides, in another of its aspects, a device for energising annular sealing devices comprising at least two annular members movable relative to one another comprising a housing adapted to be inserted into a bore to be sealed, said housing comprising a main body portion and an annular nose portion adapted to locate against a reaction surface, a sealing device located at a region intermediate said nose portion and said main body portion means to permit axial movement between the nose portion and the main body portion so as to compress said annular members of the sealing device to produce increased radial diameter of said device, an external thread being provided on said housing and adapted to co-operate with an internal thread provided on or solid with said bore walls, rotation of said housing causing the sa. -c advance within the bore until said nose portion locates against the reaction surface, and continued rotation then bringing about said axial movement to compress the seal device.

It may be convenient, for example, for the internal thread to be formed on the inner surface of the bore.

Advantageously, the internal thread may be provided on a ring encircling the main body portion of the housing, and the ring may be provided on an external surface thereof with means to engage firmly but releasably with the inner surface of the bore.

Conveniently said means may comprise spring-loaded engagement members, for example in the form of blocks, receivable in recesses formed in the bore walls.

Alternatively, an outer locking ring means is provided in association with the housing and adapted to be received within a recess or groove in the bore wall when the housing is inserted therein, a cam surface provided on said housing and adapted to contact frusto-conical surfaces of said locking ring means, the construction and arrangement being such that as the housing is rotated to advance within the bore, the locking ring means is forced outwardly with respect to the housing as so to enter the recess or groove.

In one example, a device according to the invention is used in a wellhead bore as a packoff element of the wellhead. It will be understood that devices according to the invention may be used in this context in conjunction with a mandrel or in an emergency situation.

In operation, the housing may be inserted by means of a running tool having releasable engagement means adapted to engage the main body of the housing.

Two examples of devices according to the invention will now be described in detail with reference to the drawings.

It will be understood that the description is given by way of example only and not by way of limitation.

In the drawings: Fig. 1 is an elevational view of a first example of a device, the left hancti portion being in section; Fig. 2 is a section on line II-II of Fig. 1; Fig. 3 is a fragmentary sectional view of a second, modified, device including a lock ring in an un-energised state; Fig. 4 is a similar view to that of Fig. 3 of the device in an energised state; and Fig. 5 is a fragmentary, perspective, view of a portion of the exterior of the device of Figs. 3 and 4.

In Fig. 1, a device according to the invention is shown secured to a T-slotted running tool 2 and positively retained by a lock ring 4. The device comprises a main head housing 6 having an external thread 8 on which is received an internally threaded ring 10. Recesses 12 in the outer surface of the ring 10 provide mounting for spring loaded blocks 14 engageable in recesses 16 in the wellhead bore casing 18.

Mounted for independent rotation on a lock-ball race 20, is a packoff follower ring 22 to which is attached so as to allow for relative axial movement therebetween, a rhombic cross-section ring 24 disposed between an outer wedge ring 26 and an inner wedge ring 28 of an annular wedge seal (Cahn seal).

The ring 26 is secured to a packoff nose member 30 which, when the device is run into the wellhead bore, abuts a shoulder 32 formed on the casing or a shoulder 32' formed on a casing hanger 33 shown in dotted line. The nose member 30 is rotatable relative to the ring 24 but is secured thereto by a lock race including rotary members 34 acting to reduce rotational friction under the application of torque.

In use, the packoff device is connected to the running tool 2 by engagement with T-slots 36 and secured by the ring 4. The whole assembly is rotated as it is lowered into the wellhead bore until the nose member 30 contacts the shoulder 32. The head housing 6, the ring 16 and the blocks 14 thus continue to rotate with the tool 1, aided by the provision of detent pins 48, until the blocks 14 run into the recesses 16 in the casing 18. These recesses are also shown in Fig. 2, and include an end wall 38 against which the blocks 14 abut when fully engaged. The blocks 14 can now no longer rotate and therefore continued rotation of the tool causes the external thread 8 on housing 6 to progress downwardly with respect to the ring 10.Continued rotation thus forces the lower portion of the follower ring 11 downwardly in contact with the inner wedge 28 which moves against the rhombic cross-section ring 24 until level therewith. The rings 24 and 28 then act as a solid ring to press on the outer ring 26 through adjacent, wedge, surfaces.

However, the ring 26 is prevented from moving axially downwards because of its abutment with the nose member 30. The ring 26 is therefore forced radially outward into sealing co-operation with the inner surface of the casing 18. Thus the energisation of the Canh seal is completed by the continued rotation of the tool 2 until no further turns are possible.

The running tool 2 may then readily be removed by imparting a turning movement of about 10 in the reverse direction which allows disengagement with the T-slots by the housing 6. The tool may then be withdrawn.

The device will then be firmly and sealingly positioned in the bore and, as desired, sealed against the outer wall of an inner member which may be a casing H shown in chain dot lines. However, the arrangement may also be utilised in an emergency situation in which only the outer sealing ring 26 is actually in sealing contact with a wall surface.

When it is desired to withdraw the packoff device the running tool is again rotated but not wLv ,awn until positive contact is made within the slot whereupon continued rotation causes each block 14 to move away from the end wall 38 of the recess 16 and then to ride an inclined surface 40 so as to leave the recess 16. The packoff device may then be pulled free.

When it is required to test the efficiency of wedge seal operation, this may be carried out by means of a pressure test involving applying pressure through a test port (not shown) in the housing 6. A back-up seal is provided for this purpose in the form of elastomeric seal means 44 on the nose member 30. In addition the presence of a seal ring of the means 44 on the exterior of the nose member 30 acts to wipe the bore of the casing hanger during assembly to ensure a clean sealing face for the wedge seal (Canh) seal.

A second example will now be described which illustrates a modified version.

A wellhead body 52 provides a bore 54 which is to be installed in a casing hanger 56.

The casing hanger 56 is shown in Fig. 3 in a position in which a lower portion thereof abuts a shoulder (not shown) in the bore 54 and requires to be sealed into the bore by means of a wedge Canh seal assembly comprising an outer ring member 58 and an inner ring member 60, the members having inner confronting, frusto-conical surfaces 62,64 and outer surfaces including sealing ridges 66,68 sealingly engageable with the bore wall 54 and the casing hanger 56 respectively.

Lower portions of the ring member 58 are provided with slots at 70 engageable with radially extending flutes 72 on the hanger 56 to prevent relative rotation. As may be seen most clearly from Fig. 5 extensions 74 are provided at upper portions of the member 58 which engage with castellations 76 in an internally threaded ring member 78. The member 78 has a number of apertures 80 therearound into each of which is received a locking member 82 to form a ring thereof.

The member 82 is provided with a frusto-conical surfaces 84 against which bears a confronting surface 86 of an energising ring member 88. The ring member 88 is provided with T-slots 90 adapted to receive a running tool (not shown) by which the member 88 is rotated so as to make it progress downwardly with respect to the internal thread of the ring member 78.

Downward movement of the energising ring member 88 therefore causes the locking ring members 82 to move radially outwards so as to engage in an annular groove 92 in the bore wall 54, thus securing the assembly in position within the bore.

However, it will also be observed that a leading edge portion 94 of the energising ring member 88 now comes into abutment with an upper surface of the wedge seal ring member 60 and exerts an axially directed force thereon resulting in relative movement between - @@e confronting surfaces 62,64 of the seal assembly and an increase in the radial dimension thereof so as to effect the desired seal.

Claims (10)

CLAIMS:

1. A method of energising annular sealing devices of the wedge type as herein defined by applying compressive force to at least two annular members thereof so as to produce increased radial diameter of the device, comprising the steps of inserting a housing into a bore to be sealed thereto, said housing being provided with an externally threaded portion and a nose portion, there being provided an adjustable axial gap between the housing and said nose portion, into which gap is received said sealing device, rotating said housing by means of a rotary running tool in an advancing movement until a stop position is reached by the nose portion of the housing, said stop position being capable of providing a reaction surface, continuing said rotation of the housing by means of said tool and causing said external thread to travel relative to a co-operating internal thread formed on or solid with the bore walls to cause said housing to continue to advance relative to the nose portion thereof to apply compressive force to the seal rings between said housing and the nose portion thereof.

2. A method as claimed in claim 1 wherein compressive force is applied to three members of an annular sealing device and wherein the force is first applied to a peripheral annular member which moves with respect to a captive intermediate annular member of rhombic cross-section until level therewith, whereafter said members move together as if a single member -n a movement relative to the other peripheral member in order to achieve said increased radial diameter.

3. A device for energising annular sealing devices comprising at least two annular members movable relative to one another comprising a housing adapted to be inserted into a bore to be sealed, said housing comprising a main body portion and an annular nose portion adapted to locate against a reaction surface, a sealing device located at a region intermediate said nose portion and said main body portion, means to permit axial movement between the nose portion and the main body portion so as to compress said annular members of the sealing device to produce increased radial diameter of said device, an external thread being provided on said housing and adapted to co-operate with an internal thread provided on or solid with said bore walls, rotation of said housing causing the same to advance within the bore until said nose portion locates against the reaction surface, and continued rotation then bringing about said axial movement to compress the seal device.

4. A device as claimed in claim 3 wherein the internal thread is formed on the inner surface of the bore.

5. A device as claimed in claim 3, wherein the internal thread is provided on a ring encircling the. main body portion of the housing, the ring being provided on an external surface thereof with means to engage firmly but releasably with the inner surface of the bore.

6. A device as claimed in claim 5, wherein the engagement means comprise spring-loaded engagement members receivable in recesses in the inner surface of the bore.

7. A device as claimed in claim 5, wherein the engagement means comprise an outer locking ring means provided in association with the housing and adapted to be received within a recess or groove in the bore wall when the housing is inserted therein, a cam surface provided on said housing and adapted to contact frusto-conical surfaces of said locking ring means the construction and arrangement being such that as the housing is rotated to advance within the bore, the locking ring means is forced outwardly with respect to the housing so as to enter the recess or groove.

8. A device as claimed in claim 7, wherein the outer lowing means comprises a-plurality of arcuate locking members comprising a locking ring.

9. A method of energising annular sealing devices of the wedge type and herein defined substantially as hereinbefore described with reference to a) Figures 1 and 2 b) Figures 3 - 5 of the drawings.

10. A device for energising annular sealing devices of the wedge type as herein defined constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as shown in a) Figures 1 and 2 b) Figures 3 - 5 of the drawings.