GB2505198A

GB2505198A - Seal with a tubular net reinforcement

Info

Publication number: GB2505198A
Application number: GB201214898A
Authority: GB
Inventors: Steinar Wasa Tverlid; Nils Lennart Rolland
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2012-08-21
Filing date: 2012-08-21
Publication date: 2014-02-26
Anticipated expiration: 2032-08-21
Also published as: GB2505198B; GB201214898D0

Abstract

An apparatus (packer) 50 for sealing an annular space between concentrically arranged tubulars includes a sleeve of elastically deformable material and, at least partially embedded within the sleeve, a tubular net formed by a multiplicity of resiliently deformable segments 16 interconnected by means of flexible joints 20.

Description

Apparatus for Sealing an Annular Space between Concentrically Arranged Tu bu Ia rs

Field of the Invention

This invention relates to an apparatus for sealing an annular space between concentrically arranged tubulars. Particularly, but not exclusively, the invention relates to a sealing apparatus for use in deepwater riserless drilling for the extraction of oil and gas. Aspects of the invention can be considered to provide a dynamic annular seal.

Background to the Invention

When drilling in deep waters, it is advantageous to drill without a drilling riser since the additional construction of the riser adds to the time, effort, cost and complexity of the entire operation. Furthermore, many drilling locations (particularly deepwater locations) have been found to be un-drillable with conventional drilling riser systems. Drilling without a riser can also improve the pressure conditions in a well by reducing the pressure difference at the well head (usually referred to as the riser margin), making disconnection less risky.

The primary challenge in achieving riserless drilling is to provide an effective annular seal which allows the drill string, including the drill pipe and associated tools having a varying outer diameter, in and out of the borehole (which normally has an inner diameter of 18.75 inches, approximately 0.48m) at the sea bed while also separating drilling fluid from the sea and surrounding environment. A secondary challenge is to develop a seal that can be used in Managed Pressure Drilling (MPD) systems, where the aim is to better control the annular pressure profile throughout the wellbore, so as to allow MPD to be employed by floating drilling vessels in shallow to ultra deep water (e.g. 3000m true vertical depth).

There are to date no solutions developed for this purpose within the offshore drilling industry. Today's sealing solutions for land and shallow calm water MPD are typically not used subsea (i.e. below water level)! wear fast, have limited sealing ability (especially when worn) and require manual interference during drilling (e.g. to increase sealing pressure with wear or increasing overpressure).

It is therefore an aim of the present invention to provide a sealing apparatus which addresses at least some of the afore-mentioned problems.

Summary of the Invention

According to a first aspect of the present invention there is provided an apparatus for sealing an annular space between concentrically arranged tubulars, the apparatus comprising a sleeve of elastically deforrnable material and, at least partially embedded within the sleeve, a tubular net formed by a multiplicity of resiliently deformable segments interconnected by means of flexible joints.

Thus embodiments of the invention provide a flexible annular sealing apparatus which is deformable from a narrow sleeve to a wide sleeve and which comprises a robust and reliable construction having improved wear and sealing lifespan and no rotating parts.

The construction of the apparatus also provides a degree of flexibility ensuring that varying diameters of tubulars (e.g. associated with different tooling) can be securely accommodated, even within a single seal. As the deformation of each segment in the net will generally increase with increasing diameter, the inwardly directed restoring or sealing force of the apparatus will also tend to increase such that the apparatus will be easy to use as it will be biased towards contracting around an inner tubular. Thus, although it will be possible to park' the apparatus around a retainer pipe and to remove or insert the retainer pipe to effectively remotely activate or deactivate the apparatus (as explained below in more detail), it is important to note that, when in use, the apparatus will automatically contract around an inner tubular to seal there-against.

Furthermore, the apparatus will continue to provide good, possibly even improved, sealing characteristics in the case of an emergency well event such as a blowout which causes an increase in pressure surrounding the seal, resulting in an increased force being applied to the inner tubular.

The apparatus may be employed in a number of different wellbore applications, for example, between a drill string and a riser (e.g. at the sea bed), as a blowout prevention (BOP) annular seal, as a seal in riserless drilling, and in Managed Pressure Drilling (MPD), Underbalanced Drilling or Dual Gradient Drilling systems. The apparatus may further be suitable for sealing an annular space between non-concentrically arranged tubulars. The apparatus may be used as a single seal or employed to form a series of multiple seals, for example, to enable a lubricator function for a bottom hole assembly (BHA). In certain embodiments, the seal may be configured as a loose mud scraper provided on a rig floor to scrape mud from an inner tubular. Alternatively, the seal may be employed in well interventions such as snubbing operations or in any operation where a wireline, pipe or coiled tubing is required to be run through a stuffing box.

The flexible joints may be configured to allow the segments to fold over each other when the apparatus is in a collapsed configuration and to lever the segments apart when the apparatus is in an expanded configuration.

The segments may be interconnected by way of hinged joints having axes of rotation which are substantially radially aligned with respect to the sleeve.

Each segment of the net may be coupled at each of its ends to a set of neighbouring segments by a bolt having an axis aligned substantially radially with respect to the sleeve. Intermediate segments of the net may be coupled at each end to three neighbouring segments. Thus, the net may comprise a series of flexible quadrilateral elements.

The segments may be of metal (e.g. steel). Each segment may be substantially planar in its undeformed state, such that when the apparatus is expanded the segments are deformed, resulting in a radially inward force being exerted by the apparatus.

It is also contemplated that the segments may be formed of metal rope or the like.

Radially inwardly facing surfaces of the segments may be exposed and may project from the sleeve so that, in use, these surfaces of the segments come into contact with the inner tubular, thereby reducing the friction between the apparatus and the inner tubular. The surfaces may be provided with a relatively low friction coating to facilitate insertion and rotation of the inner tubular within the apparatus. The coating may comprise a ceramic or polymer coating but is not limited thereto.

It will be understood that both friction and wear between the apparatus and the inner tubular can be controlled through selective use of a material having the desired friction/wear and sealing properties at the interface between the segments and the inner tubular. However, the interface material need not be chosen for its elastic properties also, as is the case for traditional BOP annular seals, since in accordance with the present invention, the elastic properties are catered for by the provision of the deformable sleeve and flexible net.

The apparatus may be configured to have a large operating range, for example, by having an outer diameter which can flex from at least 6.625 inches (approximately 0.19m) to at least 18.75 inches (approximately 0.48m), thus making the apparatus suitable for use with drill pipes and slick drill collars.

According to a second aspect of the present invention there is provided a method of installing an apparatus for sealing an annular space between concentrically arranged tubulars, the method comprising: providing the apparatus according to the first aspect of the invention within an outer tubular; expanding the apparatus for receipt of a retainer pipe; and inserting the retainer pipe at least partially into the apparatus so as to hold at least one end of the apparatus open for subsequent receipt of an inner tubular.

An expansion member may be employed to expand the apparatus for receipt of the retainer pipe.

In order to allow insertion of the inner tubular through the apparatus, the retainer pipe may be arranged to hold just one end of the apparatus open or may expand along the entire length of the apparatus. Once the inner tubular is inserted, the retainer pipe may be fully or partially withdrawn from within the apparatus.

In certain embodiments, the retainer pipe may be constituted by a full bore pipe section such that the apparatus is pre-tensioned and "parked' around the full bore pipe section and wherein the retainer pipe can be moved axially to expose the apparatus to an inner tubular (e.g. drill pipe), which the apparatus will automatically clamp onto due to the restoring torces in the net. When the use of the apparatus is complete the full bore pipe section may be run back into the apparatus such that the apparatus will again be pre-tensioned and "parked" behind the full bore pipe, ready to be deployed around a subsequent inner tubular as and when required. Notably, the full bore pipe, which energises and offloads the apparatus by sliding up and down, may allow full access to the bore (the same as a BOP stack bore) when the apparatus is not required and is parked.

The apparatus is particularly suited to sealing an opening between a subsea riser and a tubular extending through the riser and out of an end of the riser. This tubular may be a drill string. A tubular retainer pipe can be inserted between the inner tubular and the apparatus in order to radially expand at least a portion of the apparatus and force its outer surface into sealing contact with the inner surface of the riser, whilst an unexpanded portion of the apparatus remains tightly sealed against the inner tubular.

The apparatus may also be used downhole to seal components other than a riser.

In a particular embodiment of the invention, the apparatus may be installed down hole and configured to seal automatically if an external annular pressure reaches a pre-determined level (i.e. becomes too high) relative to an internal string pressure. Such a configuration would stop a so-called kick at its infancy down where the formation can handle the pressures concerned. The apparatus will also make it easier to work through the kick and regain integrity since one can operate though a bore of the apparatus like normal (as long as the retainer pipe or inner tubular is not pulled out).

According to a third aspect of the present invention there is provided a method of manufacturing an apparatus for sealing an annular space between concentrically arranged tubulars, the method comprising: assembling a tubular net formed by a multiplicity of resiliently deformable segments interconnected by means of flexible joints; and at least partially embedding the net within a sleeve of elastically deformable material.

The elastically deformable material may comprise rubber, more specifically although not limited to, vulcanised rubber.

It will be understood that the provision of the flexible net will not only prime the apparatus so that it will try to latch onto an inner tubular but also serve to reinforce the sleeve of deformable material.

Brief Description of the Drawings

Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1A shows a plan view of a portion of a tubular net in accordance with an embodiment of the present invention, in both an expanded configuration and a contracted configuration; Figure 1 B shows a side perspective view illustrative of one segment of the tubular net illustrated in Figure 1A; Figure 1 C shows a side perspective view illustrative of two segments from the tubular net of Figure 1A, coupled togetherwith a flexible joint; Figure 2A illustrates a tubular net similar to that shown in Figure 1A, provided around an inner tubular; Figure 2B illustrates the forces causing elastic deformation of a segment of the net shown in Figure 2A, when it is wrapped around an inner tubular; Figure 2C illustrates the deformed shape of segments of the net as a result of the forces illustrated in Figure 2B; Figure 3 shows a deformed segment in the form it would adopt when in a net wrapped around an inner tubular as per Figure 2C; Figure 4A shows a side perspective view of a segment of a tubular net in accordance with another embodiment of the invention, comprising a low friction coating on its underside; Figure 4B shows a cross-sectional view taken along the dashed centre line shown in Figure 4A, when the segment is provided on an inner tubular; Figure 5 illustrates the sealing capacity of a tubular net in accordance with an embodiment of the present invention; Figure 6A illustrates a top and side view of an unexpanded tubular net in accordance with an embodiment of the present invention; Figure 6B illustrates the tubular net of Figure 6A once incorporated into a sleeve of elastically deformable rubber to form a sealing apparatus in accordance with an embodiment of the invention; Figure 6C shows the sealing apparatus of Figure 6B provided within an outer tubular housing in, for example, a wellbore; Figure 6D shows a retainer pipe prior to insertion into the sealing apparatus of Figure 6C; and Figure 6E shows the top of the sealing apparatus being held in an expanded configuration to allow insertion of the retainer pipe into the apparatus; Figure 7A shows the sealing apparatus of Figures 6B to 6E in stand-by mode with the retainer pipe provided through the sealing apparatus such that the sealing apparatus is expanded energized (pressing strongly towards the retainer pipe ready to seal if the retainer pipe is removed) and primed for use; Figure 7B shows the sealing apparatus of Figure 7A in use whereby the retainer pipe is withdrawn to allow the sealing apparatus to contract around a smaller inner tubular -the arrows also illustrate that if the apparatus is exposed to high external pressures, these pressures will contribute to a higher sealing force which is important for a good sealing; Figure 8A shows a transverse cross-sectional view of the apparatus when contracted around an inner tubular; Figure BB shows a side view of apparatus of Figure BA; Figure 9A shows the apparatus of Figure 8B adapted to seal around an inner tubular having a varying outer diameter; Figure 9B shows the apparatus of Figure 9A returning to seal the inner tubular as the varying outer diameter portion is extracted from the apparatus; and Figure 10 shows the apparatus of Figure BB fitted with an emergency closure pipe from below.

Detailed Description of Certain Embodiments

With reference to Figure 1A, there is illustrated a portion of a tubular net 10 in accordance with an embodiment of the present invention, in both an expanded configuration 12 and a contracted configuration 14. The net 10 comprises a multiplicity of resiliently deformable steel segments 16 interconnected by means of flexible joints 18. As will be illustrated in later figures, the net 10 will be partially embedded in a rubber sleeve to form a sealing apparatus in accordance with an embodiment of the present invention.

Each segment 16 of the net 10 is coupled at each of its ends to a set of neighbouring segments 16 by a bolt 20. As shown in Figure 1A, intermediate segments 16 of the net are coupled at each end to three neighbouring segments 16 so as to form a series of flexible quadrilateral elements 22.

In the expanded configuration 12, the segments 16 are each spaced relatively far apart such that the quadrilateral elements 22 are relatively short and wide. However, in the contracted configuration 14, the segments 16 are each spaced relatively close together such that the quadrilateral elements 22 are relatively tall and narrow. Similarly, the net 10 as whole is relatively short and wide in its expanded configuration 12 and becomes relatively tall and narrow in its contracted configuration 14.

As illustrated in Figure 1 B, each segment 16 is substantially planar in its undeformed state, with the plane of each segment 16 extending radially with respect to the tubular structure of the net 10. In addition, a first end of the segment 16 is provided with a first coupling 24 and a second end of the segment 16 is provided with a second coupling 26.

The first and second couplings 24, 26 are configured to engage with one another so that, as shown in Figure 1C, the second coupling 26 of one segment 16 can engage with the first coupling 24 of another segment 16 and the bolt 20 can pass through the engaged first and second couplings 24, 26 to hingably connect the two segments 16 together. Notably, the hinged joints 18 have an axis of rotation which is substantially radially aligned with respect to the tubular structure of the net 10. However, it will be understood that the couplings 24, 26 shown in Figures lB and 10 are simplified for illustrative purposes since, as drawn, they are only able to connect to one other segment while, in reality, at least one end of each segment 16 must connect to three other segments as shown in Figure 1A. Also, in certain embodiments, two aligned segments 16 need not be hinged together as shown in Figure 1C. However, in such a case, the two aligned segments must be hinged at their centre to two crossing aligned segments. In other words, each of the two continuous lines forming an "X" in the net may be stiff/not hinged, but the two lines themselves must be hinged to each other allowing the angle between the two lines to change unstrained.

Figure 2A illustrates a tubular net 10 similar to that shown in Figure 1A, provided around an inner tubular 30. Thus, it can be seen that, in use, each of the segments 16 will be deformed so as to allow the net 10 to encircle the inner tubular 30. More specifically, as shown in Figure 2B for a specific segment 16A (which is curving downwardly from left to right in Figure 2A), each segment 16 will be subject to opposed twisting forces. Thus, for segment 1 6A the top of the first coupling 24 will be forced in a first direction 32, the boftom of the first coupling will be forced in an opposite, second direction 34, the top of the second coupling 26 will be forced in the second direction 32 and the bottom of the second coupling 26 will be forced in the first direction 34. Of course, the segments 16 curving from downwardly from right to the left in Figure 2B would be subject to opposite twisting forces to those illustrated in Figure 2B. Figure 2C shows the resulting deformation of the segment iSA of the net 10, when it is wrapped around the inner tubular 30.

It should be noted that the elastic deformation of each segment 16 of the tubular net 10 will increase as the diameter of the net 10 is increased and this will set up a force that will try to collapse the net 10 and which, in turn, will serve to seal the net 10 against the inner tubular 30.

Figure 3 shows a single deformed segment 16 in the form it would adopt when part of the net 10 is wrapped around the inner (hollow) tubular 30. As illustrated, the first and second couplings 24, 26 (through which the bolts 20 pass) each have an axis 36 which is perpendicular to the surface of the inner tubular 30. Consequently, the forces between each segment 16 will be evenly distributed and each segment 16 will adopt a shape having an underside 38 which follows the surface of the inner tubular 30 tangentially. It should be noted that the length of each segment 16 (or each set of two adjacent stiff segments) will be restricted by the need for each segment 16 to deform sufficiently so that it follows and seals against the circumference of the inner tubular 30.

As shown in Figures 4A and 4B, in a particular embodiment of the present invention the underside 38 is provided with a low friction polymer coating 40 (or a coating of another material) that exhibits low friction and low wear characteristics on the inner tubular 30 (which may comprise steel), and which has the ability to seal one side of the segment 16 from the other -p. It will be noted that the cross-sectional configuration of the polymer coating 40 shown in Figure 4B is for illustrative purposes only and other cross-sections may be employed to achieve the desired sealing effect.

Figure 5 illustrates the sealing capacity of the tubular net 10. In this particular embodiment, the sealing capacity of the net 10 is determined by the sum of the force provided by each circumferential band of segments 16 and the sealing capacity of each joint 18 is determined as twice the restoring force associated with a single segment 16.

Thus, where the net 10 comprises six bands, each providing a pressure of 100 bar, the net 10 will have a total sealing capacity of 600 bar. Note, this means that each joint 18, as drawn in this illustration, needs to handle a Ap of 200bars (this can be seen by drawing a straight vertical line through the net along one set of nodes/joints 18 since this line will pass three quadrilateral elements 22 and 600/3=200). As explained previously, the restoring forces experienced by each segment 16 will increase as the diameter of the net 10 is increased and so the sealing capacity will also increase accordingly.

Figures 6A through 6E illustrate the assembly and installation of an apparatus 50 according to an embodiment of the present invention. Thus, a tubular net 10 as described above is first formed from a multiplicity of resiliently deformable segments 16 interconnected by means of flexible joints 18, as shown in Figure 6A. The net 10 is then partially embedded within the inner surface of a sleeve 52 of elastically deformable vulcanised rubber, as shown in Figure 6B, to form the apparatus 50.

The apparatus 50 is then inserted (in a relaxed or collapsed state) into an outer tubular which, in this case, is constituted by an expanded head of a wellbore as shown in Figure 6G. In order to insert a retainer pipe 62, as shown in Figure 6D, into the apparatus 50, it is necessary to expand at least the upper portion of the apparatus 50 as shown in Figure 6E. Although not shown, the apparatus 50 may be expanded by an expansion member in the form of a funnel which can be pulled through the apparatus allowing the retainer pipe 62 to follow the large end of the funnel such that the retainer pipe 62 is then partially inserted into the apparatus 50 so as to hold at least one end 64 of the apparatus 50 open for subsequent receipt of an inner tubular. The end 64 of the apparatus 50 may then be fixedly secured to the outer tubular 60 for subsequent operation. Alternatively, the retainer pipe 62 may be inserted into the apparatus 50 as a manufacturing step.

Figure 7A shows the apparatus 50 of Figures 6B to 6E in a stand-by mode with the retainer pipe 62 inserted along the entire length of the apparatus 50 such that the apparatus 50 is stretched and expanded against the inner surface of the outer tubular and is thereby provided with potential energy ready for use. Notably, in stand-by mode, the inner surface of the retainer pipe 62 will surround the inner, usable portion of the wellbore at full bore width. Figure 7B shows the apparatus 50 in use whereby the retainer pipe 62 has been partially withdrawn to allow the apparatus 50 to contract around and seal against a smaller inner tubular 66 in the form of a drill string which is provided through the retainer pipe 62. As illustrated, any increase in external pressure due to a wellbore issue will enhance the sealing capacity of the apparatus 50 such that it will more tightly seal against the inner tubular.

It should also be noted that, in the partially expanded configuration of Figure 7B, the upper end of the apparatus 50 is brought into sealing contact with the inner surface of the outer tubular 60 thereby preventing flow from passing around the apparatus 50 in a vertical direction. In certain embodiments, the upper end of the apparatus 50 may be held or fixed in sealing contact with the outer tubular 60. In other embodiments, the sealing contact with the outer tubular 60 may be provided at the lower end of the apparatus 50, or part-way along its length. It will be understood that, as illustrated in Figure 7B, the apparatus 50 is primarily configured to seal against external pressure acting on the apparatus from below. In order to seal against external pressure from above, the apparatus 50 may be inverted such that the sealing contact with the outer tubular 60 is downstream of the high pressure area. Consequently, in order to seal against external pressure from both directions (above and below), two oppositely orientated sets of apparatus 50 may be provided with the sealing contact of each with the outer tubular 60 provided in the centre. Of course, the two sets of apparatus described could also be integrated in a single apparatus configured for external sealing contact at its centre.

As shown in Figures 8A and 8B, when the apparatus 50 is contracted around the inner tubular 66, gaps 68 are provided between the outer surface of the inner tubular 66 and the rubber 52 due to the partially exposed ends of the segments 16, which are provided with the polymer coating 40. Thus, there is low friction between the apparatus 50 and the inner tubular 66 making it much easier to manoeuvre and rotate the inner tubular 66 within the apparatus 50.

Figure 9A shows the apparatus of Figure 8B adapted to seal around an inner tubular having a varying outer diameter. More specifically, the retainer pipe 62 has been partially withdrawn to expose the apparatus 50 to the inner tubular 70 which comprises a radially expanded portion 72 part-way along its length. Notably, the apparatus 50 has adapted to expand around the portion 72 but is still contracted around the remaining narrow regions of the inner tubular 70 to completely seal against the inner tubular 72. Figure 9B shows the apparatus 50 returning to seal a narrow region of the inner tubular 70 as the expanded portion 72 is extracted from the apparatus 50.

Accordingly, it will be clear that the apparatus 50 can easily adapt to different outer diameters (such as may be encountered with wellbore tooling) while continuously and firmly tightening around the tool surface and returning to a desired outer diameter when required. Notably, this process is reversible such that Figure 9B can also be interpreted to show how the apparatus 50 would behave when the larger portion 72 of the drill pipe is on its way upwards expanding the lower end of the apparatus 50.

In the event of an emergency situation, the apparatus 50 can be locked in place by providing an emergency closure pipe 80 forced around the apparatus 50 from below, as shown in Figure 10. The emergency closure pipe 80 in this example is constituted by a hollow steel pipe having an inwardly tapering (i.e. funnelled) leading edge 82 which forces the apparatus 50 inwardly such that the apparatus 50 adopts an outer diameter which matches the inner diameter of the emergency closure pipe 80.

As mentioned previously, the net 10 can ensure no contact between the inner tubular and the rubber 52 so that friction is low and, in certain embodiments, a metal-to-metal seal can be provided, in particular, where a metal funnel (e.g. constituted by the emergency closure pipe 80) is used to lock the seal.

It will be appreciated by persons skilled in the art that various modifications may be made to the above embodiments without departing from the scope of the present invention, as defined by the claims.

Claims

CLAIMS: 1. An apparatus for sealing an annular space between concentrically arranged tubulars, the apparatus comprising a sleeve of elastically deformable material and, at least partially embedded within the sleeve, a tubular net formed by a multiplicity of resiliently deformable segments interconnected by means of flexible joints.
2. The apparatus according to claim 1 configured for use in a wellbore application.
3. The apparatus according to either preceding claim wherein the flexible joints are configured to allow the segments to fold over each other when the apparatus is in a collapsed configuration and to lever the segments apart when the apparatus is in an expanded configuration.
4. The apparatus according to any preceding claim wherein the segments are interconnected by way of hinged joints having axes of rotation which are substantially radially aligned with respect to the sleeve.
5. The apparatus according to claim 4 wherein each segment of the net is coupled at each of its ends to a set of neighbouring segments by a bolt having an axis aligned substantially radially with respect to the sleeve.
6. The apparatus according to claim 5 wherein intermediate segments of the net are coupled at each end to three neighbouring segments.
7. The apparatus according to any preceding claim wherein the net comprises a series of flexible quadrilateral elements.
8. The apparatus according to any preceding claim wherein the segments comprise metal.
9. The apparatus according to any preceding claim wherein each segment is substantially planar in its undeformed state, such that when the apparatus is expanded the segments are deformed, resulting in a radially inward force being exerted by the apparatus.
10. The apparatus according to any one of claims 1 to 8 wherein the segments are formed of metal rope or the like.
11. The apparatus according to any preceding claim wherein radially inwardly facing surfaces of the segments are exposed and project from the sleeve so that, in use, these surfaces of the segments come into contact with the inner tubular.
12. The apparatus according to claim 11 wherein the surfaces are provided with a relatively low friction coating to facilitate insertion and rotation of the inner tubular within the apparatus.
13. The apparatus according to claim 12 wherein the coating comprises a ceramic and/or a polymer.
14. The apparatus according to any preceding claim configured to have an outer diameter which can flex from at least 6.625 inches (approximately 0.19m) to at least 18.75 inches (approximately 0.48m).
15.A method of installing an apparatus for sealing an annular space between concentrically arranged tubulars, the method comprising: providing the apparatus according to any preceding claim within an outer tubular; expanding the apparatus for receipt of a retainer pipe; and inserting the retainer pipe at least partially into the apparatus so as to hold at least one end of the apparatus open for subsequent receipt of an inner tubular.
16. The method according to claim 15 wherein an expansion member is employed to expand the apparatus for receipt of the retainer pipe.
17. The method according to claim 15 or 16 wherein the retainer pipe is arranged to expand along the entire length of the apparatus.
18. The method according to any one of claims l5to 17 wherein the retainer pipe is fully or partially withdrawn from within the apparatus once the inner tubular is inserted.
19. The method according to any one of claims 15 to 18 wherein the retainer pipe is constituted by a full bore pipe section which allows full access to the bore when the apparatus is not required.
20. The method according to any one of claims 15 to 19 wherein the inner tubular comprises a drill string.
21.A method of manufacturing an apparatus for sealing an annular space between concentrically arranged tubulars, the method comprising: assembling a tubular net formed by a multiplicity of resiliently deformable segments interconnected by means of flexible joints; and at least partially embedding the net within a sleeve of elastically deformable material.
22. The method of claim 21 wherein the elastically deformable material comprises rubber.
23. An apparatus for sealing an annular space between concentrically arranged tubulars, substantially as hereinbefore described with reference to the accompany drawings.
24. A method of installing an apparatus for sealing an annular space between concentrically arranged tubulars, substantially as hereinbefore described with reference to the accompany drawings.
25. A method of manufacturing an apparatus for sealing an annular space between concentrically arranged tubulars, substantially as hereinbefore described with reference to the accompany drawings.