GB2222858A - Sealing assemblies - Google Patents

Abstract

The invention relates to a metal-to-metal sealing device suitable for use in the oil-drilling industry. The device is of the wedge or Canh seal kind, and is provided with means to prevent over-energisation of such a seal device and consequent jamming when the seal is required to be demounted. The device comprises two annular sealing members (16, 14) with third, intervening member (22). Each member has confronting frusto-conical surface(s) with its neighbouring member, the member (16) having a surface (36), member (14) having a surface (20) and member (22) two opposed surface (18, 24). The member (22) has a further, lower, portion with a second frusto-conical surface (26) at a less steep angle than surface (18) which is confronted by a split-ring, anti-impaction member (44). A gap in the circumference of the member (44) closes as the seal is energised and a surface (50) forms a shoulder preventing further movement of the members (16 and 14). <IMAGE>

Description

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

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

One type of seal which is suitable in such a situation is the wedge type which may successfully be used in the packoff element of the wellhead drill assembly. This type of wedge seal, known as a Canh seal, comprises two metal seal rings each having complementary frustoconical confronting surfaces and which are received one within the other. The outer ring may for example seal the inner surface of the wellhead bore and the inner ring seals against the outer peripheral surface of the casing or mandrel hanger.

Axial compressive force applied to the 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.

A modification to the above described Canh seal is the inclusion of an intermediate ring member between the inner and outer rings of the seal. This member may have parallel frustoconical surfaces the'inner one of which is in confronting contact with the frustoconical surface of the inner ring and the outer one of which is in confronting contact with the frustoconical surface of the outer ring.

It may occasionally be found, however, that where the outer and inner annular members are successfully wedged in their operative position with respect to an intermediate annular member usually provided in such a sealing device, difficulty is encountered in releasing the device when the packoff element is to be demounted.

Whatever the situation is in which the sealing device is used, it is an object of the invention to provide a means whereby to facilitate release of the elements comprising the device.

The invention therefore provides an annular sealing device comprising two annular sealing members movable relative to one another in which an energising mechanism is used to provide operating force effective in a direction axially of the annular members, wherein a first one of said annular sealing members is adapted to make a sealing contact with a surface radially outward thereof and a second one of said annular sealing members is adapted to make a sealing contact with a surface arranged radially inwards thereof, there being interposed between said members a frustoconical member having an outer surface complementary to a confronting surface of one of said annular members and a inner surface complementary to a confronting surface of the other of the members, there being further provided a further annular, anti-impaction, member having a closable gap in its circumference adapted to prevent over-energisation of the sealing device in its operative condition.

The invention further provides an annular sealing device according to the previous paragraph in which said first one of the annular sealing members is provided with its confronting surface tapering at a predetermined oblique angle, said second one of the annular members is provided with its confronting surface tapering at the same oblique angle, wherein the outer and inner surfaces of said frustoconical member taper at substantially the same oblique angle, there being provided on said frustoconical member a further annular surface spaced from its first mentioned surface and tapering at a second oblique angle less steep with respect to the axis of the sealing device than the first-mentioned angle, wherein the anti-impaction member is provided with an annular surface tapering at said second oblique angle and confronting the further annular surface on said frustoconical member, so that sliding movement is permitted between the confronting surfaces as the seal device is energised, a gap being provided in the circumference of the anti-impaction member which gap is reduced in size during said sliding movement until it is closed and prevents further, excess, energisation of the sealing device.

There will now be described an example of a device according to the invention. 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 a section view taken in a longitudinal plane through a device according to the invention and Fig. 2 is an exploded view of the components of the device of Fig. 1.

The device illustrated may be used in a wellhead bore as a packoff element of the wellhead. Such a device may be used in conjunction with a casing or a mandrel casing hanger.

Fig. 1 shows a male sleeve 2 adapted to be operated by means of a tool (not shown) to energise the device. The male sleeve 2 is externally threaded to engage with an internally threaded sleeve 4. As the male sleeve 2 descends, a surface 6 thereof, co-operating with a split lock ring 8, acts to force the ring 8 outwardly to engage the wellhead bore casing (not shown). Continued downward movement of the tool 2 then brings it into contact through a thrust bearing 10 with the top surface of an inner energising ring 12 which is thus moved downwardly against an upper surface of an inner ring 14 of an annular wedge seal (Canh seal) device. The wedge seal device also comprises an outer wedge ring 16, each ring 14,16. having a frustoconical surface 18 and 24 respectively.The surface 18 on the ring member 14 is at the same oblique angle to the lengthwise axis of the device as the surface 24 on the ring member 16 and the surfaces are separated by a frustoconical member 22 having two opposed oblique surfaces 20 and 36 which, when the member 22 is received between the ring members 14,16, confront surfaces 18 and 24 respectively. The lower end portion 28 of the ring 22 is secured to a packoff nose member (not shown) through a guide ring 30. Contact with a reaction surface provided in the wellhead bore casing prevents the nose member and therefore the rhombic ring from partaking of further downward movement.

However, the provision of a retainer ring 32 around the inner circumferential surface of the rim portion 34 of the ring 22 positions the inner energising ring 12 which, when contacted by the thrust bearing 10 acts to press downwardly against the inner wedge ring 14 of the annular wedge seal (Canh seal). The inner ring 12, the wedge ring 14 and the rhombic ring 22 therefore are all under axial downward pressure and act as if integrally formed.

Thus the outer surface 24 of the rhombic ring is formed as a frustoconical, downwardly and inwardly tapering cam surface confronted by the complementary.

tapering surfaces 36 of the outer annular wedge ring 16 of the Canh seal. Relative movement between the surfaces 24 and 36 causes the outer wedge ring 16 to move outwardly into sealing contact with the wellhead bore casing, since downward movement of the ring 16 is prevented by the presence of an outer energising ring 38 interengaged with castellations provided on the guide ring 30.

Thus the sealing device is operated so that firm sealing contact is made with both the wellhead internal bore on the outside and with the external diameter of the mandrel hanger on casing (not shown) on the inside of the annular seal device. The device is located with respect to the casing or mandrel hanger by means of the split lock ring 8. This lock ring provides both the reaction point for any axial energisation and also the means by which any annular blowout is prevented.

A series of keyed members 40,42 are utilised to provide in effect a single-piece packoff mechanism. These keys also provide anti-rotation with the packoff.

However, when the seal device is to be released it is possible that the wedging action between the two surfaces 24 and 36 might be so great that the rings are effectively jammed together and cannot easily be freed.

The member 22 is therefore provided, at a lower portion thereof as viewed in Fig. 1, with a further frustoconical surface 40 spaced from the surface 20 and arranged at a less steep oblique angle with respect to the lengthwise axis of the sealing device.

Received immediately below the inner ring member 14 is an anti-impaction member in the form of an anti-wedge ring 44 adapted to lie adjacent the surface 26 of the member 22. The ring 44 has a frustoconical surface 46 which is at the same, less steep, angle as that of the surface 26.

The ring 44 is circular, having a gap 48 (Fig. 2).

As the ring 44 is forced downwardly by the seal member 41, the surfaces 26 and 46 slide relatively to one another and the gap 48 is closed. Once the gap closes, no further downward movement of the ring can take place. The upper surface 50 of the ring 32 thus acts as a shoulder to prevent further excessive downward movement of the seal member 14 and thus to prevent over-energisation of the seal device, and a situation in which the seal device is jammed cannot readily be de-mounted.

Repeated application and release of the seal requires the surfaces of the mandrel and of the casing to be relatively free of any build-up which would reduce the efficiency of the seal. It may therefore be found convenient to provide wiper rings 52 and 54 in the outer energising ring 30 and at the upper rim portion of the ring 38 respectively to clean the surfaces as the device is raised or lowered.

Various modifications may be made within the scope of the invention as defined in the following claims.

Claims (4)

1. An annular sealing device comprising two annular sealing members movable relative to one another in which an energising mechanism is used to provide operating force effective in a direction axially of the annular members, wherein a first one of said annular sealing members is adapted to make a sealing contact with a surface radially outward thereof and a second one of said annular sealing members is adapted to make a sealing contact with a surface arranged radially inwards thereof, there being interposed between said members a frustoconical member having an outer surface complementary to a confronting surface of one of said annular members and a inner surface complementary to a confronting surface of the other of the members, there being further provided a further annular, anti-impaction, member having a closable gap in its circumference adapted to prevent over-energisation of the sealing device in its operative condition.

2. A device as claimed in claim 1, wherein said first one of the annular sealing members is provided with its confronting surface tapering at a predetermined oblique angle, said second one of the annular members is provided with its confronting surface tapering at the same oblique angle, wherein the outer and inner surfaces of said frustoconical member taper at substantially the same oblique angle, there being provided on said frustoconical member a further annular surface spaced from its first mentioned surface and tapering at a second oblique angle less steep with respect to the axis of the sealing device than the first-mentioned angle, wherein the anti-impaction member is provided with an annular surface tapering at said second oblique angle and confronting the further annular surface on said frustoconical member, so that sliding movement is permitted between the confronting surfaces as the seal device is energised, a gap being provided in the circumference of the anti-impaction member which gap is reduced in size during said sliding movement until it is closed and prevents further, excess, energisation of the sealing device.

3. A device as claimed in claim 2, wherein the anti-impaction ring is provided with a generally radially extending surface adapted to be in contact with an end face of the second, inner, annular sealing members, so that when the gap in said ring becomes closed, said generally radially extending surface forms a shoulder to prevent further movement between the two annular sealing members.

4. An annular sealing device constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as shown in the drawings.