DK2041392T3 - sealing - Google Patents

Description

DESCRIPTION

[0001] The present invention relates to a sealing device to be used in tough conditions, such as conditions with strongly varying pressure, conditions with strongly varying temperature and conditions with an chemically stressing environment. In addition the sealing device according to the present invention shall fullfil the requirement of a reliable and maintenancefree function in the long run.

[0002] The oil industry uses a great variety of sealing device in all stages of the processes which lead to the conduction of oil and gas from a subterranean reservoir, up to the surface and on to the end user. The present invention particularly relates to sealing devices to be used underground, but the advantages of the sealing devices according to the present invention may also find their use in other context where there is a need for robust sealing devices.

[0003] When completing oil and gas wells so-called cementing valves are used in the cementing work. The cementing valves form parts of the production tubing and is arranged in such a way that they can be opened and closed as needed during the cementing work. Cementing valves are subjected to large and varying loadings, such as large pressure differentials, elevated temperatures and/or large temperature variations, strong physical loadings and also a very tough chemical environment.

[0004] One kind of cementing valves comprises an inner sleeve which can be slid back and forth to close and open radial valve openings or -ports in a base tube, respectively, an open cementing valve form communication between the inside and outside of production tubing. The base tube is screwed in as a part of the production tubing, the cementing valve thereby form a tubing section of the production tubing.

[0005] In order to ensure that the cementing valve is sealed when the inner sleeve is located in its closing position, ring shaped sealing devices are arranged between the outside of the inner sleeve and the inside of the base tube. These ring shaped sealing devices are usually situated in encircling grooves which are milled out or in another way are arranged in the sleeve. Althoug the sealing device which in this way encircle the sleeve is of a very robust and resistant kind, it has turned out that the great differential pressure which arise at the cementing valves contribute to stretching and deforming the sealing devices in such a way that the sealing devices are pulled out of their grooves, are squeezed between the sleeve and the valve ports in the base pipe, and thereby cut totally or partly when the cementing valve is opened or closed. This again leads to a considerable reduction of the sealing capability of the sealing devices, since they in certain cases also can be washed totally out through the valve ports.

[0006] Another shortcoming with conventional sealing devices is that they are subjected to so-called scouring. When the valves are opened, i.e. the sleeve is slid relatively to the base tube, and the sealing is exposed by the valve port, and intense liquid flow over the exposed sealing may lead to a complete or partly wearing down of the sealing, and the sealing will thereby totally or partly loose its sealing function.

[0007] There is a limited range of materials which are suitable for use in sealings of this kind. One way to arrange the sealing ring in the sealing groove is to heat expand the sealing ring when it is threaded over the sleeve and into the sealing groove. When the sealing ring is cooled down, it will tighten into place in the sealing groove. This method does, however, limit the material choice with a view to strenghts and temperature resistance, chemical resistance and tolerance to pressure.

[0008] Some of the chemicals the sealing can be exposed to down in the well comprise formic acid, hydrochloric acid, saline solutions, acid gases such as Ffø, etc. It is a known problem that elevated temperatures can make the sealings brittle. Futher gas may penetrate into the sealing material and form gas bobbles which cause the sealing to "blow up". Depending of the composition of the mud and the material in sealings, sealings can be dissolved in mud. The combination of these factors, which sometimes also occure concurrently, make the choice of sealing material difficult. When the sealing in addition must have certain mechanical qualities in order to enable installation, the choice is further limited.

[0009] Conventional sealings usually comprise Teflon. Teflon has a tendency to expand and get softer at elevated temperatures, but will again retract when the temperature falls. In order to avoid thermal expansion a material called Devlon V has inter alia been used. Devlon V is mechanically stronger than Teflon and will endure higher differential pressures than e.g. Teflon. Although Devlon V also expands at elevated temperatures, it does not expand to the same extent as Teflon. Devlon V has a melting point of 216°C. If the sealings shall be used in environments with even higher temperatures, there is a material called Peek which endure up to 333°C. If Teflon or Peek is used in environments with H2S, the sealings will swell and get brittle over time. There are other materials which can be used, but this may be at the expence of other qualities. Price is also a factor which of course is taken into consideration: Devlon V is considerably more expensive than Teflon and Peek is considerable more expensive than Devlon V, etc.

[0010] The sealings must be flexible enought to be threaded over the cementing valve sleeve and down into a groove arranged for that purpose. If the requirements to mechanical strenghts of the sealing are particularly strict, the sealing of the preferred sealing material will be too hard to be threaded over the sleeve.

[0011] With the limitations which exist with respect to mechanical construction and selection of materials, today's conventional sealing systems do not endure a greater differential pressure than approximately 100 bar. In addition the various unfavourable well conditions mentioned above cause today's conventional sealing systemes to quickly deteriorate, and that the above mentioned tolerance to a differential pressure of approximately 100 bar is quickly reduced to unacceptable low levels. Sliding sleeve cementing valve sealing devices according to the preamble of claim 1 are known from the following documents: [0012] US patent annlication US2003/0056951A1 Kaszuba. "Sliding sleeve valve", discloses a sliding sleeve valve and method for assembly. The valve comprises a segmented main body that is assembled from a top, middle and bottom segments. The middle segment has flow apertures. A closing sleeve is co-axially mounted in the assembled main body. The closing sleeve has flow apertures that are intended to communicate with the flow apertures of the middle section when the valve is open. The closing sleeve is sealed by seal means within the main body to prevent undesired fluid flow across the valve. The seal means comprise primary, secondary and tertiary seals acting in cooperative combinations.

[0013] US patent US4131287 to Gunderson. "Annular seal", discloses a pressure energized seal to seal an annulus between two concentric cylindrical members, particularly well suited to be used as an annular casing seal in oil and gas well. A circular sealing ring has both its upper and lower surfaces channeled to leave two upper sealing lips and two lower sealing lips which effect the seal by being forced against the sealing surfaces of the cylindrical members. Two circular setting rings can be used to spread the sealing lips into sealing engagement with the sealing surfaces of the cylindrical members. The setting rings would be partially disposed within the channels of the sealing ring and adapted to spread the sealing lips when the setting rings are moved toward the sealing ring.

[0014] It is therefore an object with the present invention to provide a sealing device which to a much less extent than de above mentioned conventional sealing devices is encumbered with said drawbacks. According to the present invention this object is achieved with a sealing device which is characterized by the features which appear from the independent claim 1. Futher advantageous features and embodiments appear from the independent claims.

[0015] The following is a detailed description of a preferred embodiment with refrence to the appended figures, where Fig. 1 illustrate a conventional sealing system,

Fig. 2 and 3 illustrate longitudinal sections of a cementing valve provided with the sealing device according to the present invention, and

Fig. 4 and 5 illustrate in closer detail the sealing device according the present invention.

[0016] Fig. 1 illustrates a conventional sealing system in conjunction with a sleeve 20 in a cementing valve. A sealing in the shape of an O-ring 21 is arranged in a groove 22 which encircles the sleeve 20. The groove 22 in the sleeve 20 is big enough to contain additional rings 23, 24 which purpose is to protect the O-ring 21, but these additional rings 23, 24 does not contribute to support and retain the O-ring in place by radially outwardly directed forces. The rings 23, 24 are similar to the O-ring 21 preferably manufactured from Teflon, and must similar to the O-ring 21 as a rule be heated and threaded over the sleeve 20 in order to get them in place.

[0017] The present invention provides a sealing device 10 (see fig. 2 to 5) which comprises a sealing 1, e.g. in the form of a sealing ring, which is held in place by support rings 2. The support rings 2 functions as shape-adapted keys which both contribute to clamping around the sealing 1 and which themselves are keyed or clamped into position by outer locking rings 3. The outer locking rings 3 are in turn shaped to fit into suitable locking grooves 6 in sleeve 7. Sleeve 7 comprises a threaded portion 8 and also possibly a recessed portion 9 which contribute to reducing the diameter 11 of the sleeve. When assembling the sealing device 10, first one outer locking ring 3 is threaded over the recessed portion of sleeve 7, bringing this outer locking ring 3 into abutment and engagement with the locking groove 6. Then a support ring 2 is threaded over the recessed portion of sleeve 7, bringing support ring 2 into abutment and engagement with the outer locking ring 3. Then sealing ring 1 is threaded over the recessed portion of sleeve 7, bringing sealing ring 1 into abutment and engagement with locking groove 6. Then follows the other support ring 2 and the other locking ring 3, before a locking nut 5 comprising suitable locking grooves 6 is screwed over the sleeves 7 threaded portion 8 and tightened sufficiently to hold the locking rings 3, support rings 2 and the sealing 1 in place, and possibly apply the sealing ring 1 a predetermined pressure / prestress / compression. The sealing device 10 according to the present invention is arranged in such a way that an applied differential pressure will cause the sealing 1, the support rings 2 and the locking rings 3 to interlock and thereby protect against scouring.

[0018] The sealing device 10 according to the present invention gives much greater freedom in choice of materials for the sealing 1. Because the support rings 2 and the locking rings 3 are arranged to take up many of the mechanical loadings, and since the sealing 1 in itself can be put in place without the need to heat expand it in advance or forcibly threaded over the sleeve 1 and down in a locking groove, materials may be chosen for the sealing 1 which to a much larger extent have good sealing, thermal, chemical, pressure and abrasion properties. The material which the support rings 2 are manufactured from may also be adapted to the use and the material which the sealing 1 is made from, and may also be manufactured from the same material as the sealing 1. The locking rings 3 will preferably be manufactured from the same material as sleeve 7, but may also be manufactured from another material, e g. a material which has properties which can be said to be between the material which sleeve 7 is manufactured from and the material the support ring 2 are manufactured from with respect to hardness, toughness, expansibility, etc. The locking nut 5 is as a rule manufactured from the same or equivalent material as sleeve 7.

[0019] According to the present invention it is an important feature that the sealing device 10 is allowed to expand when pressure and temperature increase. The sealing device 10 is arranged in such a way that the sealing 1 gets better support the higher pressure the sealing device 10 is subjected to. At higher pressure the support rings 2 will press harder against the sealing, the sealing 1 is thereby squeezed together and expand in radial direction. This again will contribute to an increase in pressure from the sealing 1 against the inside of the base tube 11, which contributes to an improvement of the sealing. The support rings 2 and the shaping between the support rings 2 and the sealing 1 prevents, however, the sealings from being squeezed, scoured or sucked out of the groove the sealing 1 is located in and through the valve openings 12 when the sealing 1 is exposed to these. In addition the support rings 2 and the shaping between the support rings 2 and the sealing 1 will prevent the sealing 1 from being displaced relative to or being twisted out of the groove the sealing 1 lies in.

[0020] According to a preferred embodiment of the present invention the sealing and the support rings 2 are provided with a tongue-and-groove configuration, e.g. in the form of elevations 13 or “wings” on each side in axial direction of the sealing 1 which match corresponding grooves in the support rings 2 (see fig. 4 and 5), which contribute to holding the sealing 1 in correct location between the support rings 2, both with a view to prevent sucking out and vwth a view to preventing the sealing 1 from twisting relative to the support rings 2. Other configurations comprise dovetail 2, U-shaped groove, V-shaped groove, drop-shaped groove, etc., depending on what is regarded being optimal for every single case.

[0021] According to another advantageous embodiment of the present invention, the support rings 2 are provided with a lip which partly overlies the sealing 1 (see tig. 4 and 5). The support rings 2 can possibly be shaped in such a way that the support rings 2 partly encircles the sealing 1. Such designs contribute to an even greater extent to holding the sealing 1 in place between the support rings 2.

[0022] According to a further advantageous embodiment of the present invention, the support rings 2 and the locking rings 3 are designed such that the support rings 2 are held in place between the locking rings 2, e g. by the locking rings 3 comprising keyshaped lips which project partly over the support rings 2 and thereby prevent the support ring 2 in bulging too much or bouncing out of its allocated position between the locking rings 3 (see fig. 4 and 5).

[0023] According to a further advantageous embodiment of the present invention, the sealing device 10 vil function as a scraper against the inside of the base tube 11, to thereby ensure that the sealing surface between the sealing device 10 and the base tube 11 stay free from cement and other unwanted particles. I saline environments salt may crystallize out and settle around the sealing. In such cases the sealing device will also function as a scraper, without the sealing itself being cut or get damaged from the salt crystals.

[0024] According to another further aspect of the present invention, the strenght and durability of the sealing device 10 may further be improved by providing the cementing valve with oval ventilation ports 12 (see fig. 2-4). By giving the valve port 12 an oval shaping, the distribution of tension in the base tube 11 vil be improved, something which result in considerably improved tensile strength. The most significant advantage of providing oval ports 12 is nevertheless that the opening as the sealing 1 "sees" is considerably smaller, it thereby has a smaller and finer opening to expand into, even if the area of the valve port in practice become almost twice as big as for conventional round ports. It is understood that the sealing device 10 is subjected to the greatest mechanical loading during opening or closing of the cement valve and exposing the sealing device 10 for the valve ports 12. I addition the valve port 12 may with advantage be designed as an embrasure, so that the edge the sealing 1 bends around get less sharp. Afavourable taper angle has turned out to be approximately 20°. In addition the inside of the valve port 12 is somewhat rounded.

[0025] The sealing device 10 according to the present invention can be adapted to the environment and the loadings the cementing valve shall be subjected to, by adapting the support rings 2 and the sealings 1 materials and possibly also design to the individual instances of use and conditions of use.

[0026] According to the present invention the sealing device 10 may also be retrofit on existing equipment which need robust and maintenancefree sealings.

[0027] Tests have shown that the sealing device 10 according to the present invention easily endure differential pressures of 250 bar, more than twee as much as todays conventional sealing systems. By choosing other materials it's possible to further increase the strengths considerably.

[0028] The present invention provides a stronger, maintenancefree and durable sealing device. By the fact that the support rings 2 and the locking rings 3 are configured in such a way that they can take up more of the mechanical forces the sealing 1 is subjected to, by the fact that the configuration with support rings 2 and locking rings 3 ensures that the sealing 1 is held better in place, and by the fact that the sealing 1 may be threaded of the sleeve 7 without the sealing 1 need to be flexible, far more materials can be used for the sealing 1. I addition the sealing device 10 in any case configured in such a way that the strenghts, service life and usefulness is radically improved relative to todays conventional solutions.

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • US20030056951A1 [00121 • US4131287A ΓΟΟΙ .η

Claims (11)

A sealing device for a sliding sleeve cementing valve for an oil or gas wellbore bottom tube, said sealing device comprising a seal (1) screwed onto the sliding sleeve (7), wherein the sliding sleeve (7) is located in a bottom tube (11) with valve openings (12), the sealing device sealing between the sliding sleeve (7) and the bottom tube (11), characterized in that the sealing (1) is secured with support rings (2), the support rings (2) being secured with locking rings (3) where the locking rings (3) fit into an inner suitable locking nut (6) in the sliding sleeve (7), wherein the sliding sleeve (7) comprises a threaded part (8), wherein a locking nut (5) comprising an outer suitable locking nut (6) is arranged so that be screwed onto the threaded part (8) of the sleeve (7) to secure the locking rings (3), the supporting rings (2) and the seal (1) outside the sliding sleeve (7). A sealing device according to claim 1, wherein the support rings (2) are arranged as form-fitting fit springs clamped around the seal (1), wherein the support rings (2) are wedged or clamped with the outer locking rings (3). A sealing device according to claim 2, wherein the molded fit spring support rings (2) comprise a feather and groove configuration, a swan tail note, a U-shaped groove, a V-shaped groove and / or a drop shaped groove. A sealing device according to any one of the preceding claims, wherein the support rings (2) are made from the same or similar materials as the seal (1). A sealing device according to any one of the preceding claims, wherein the locking rings (3) are made from the same or a similar material as the sliding sleeve (7). A sealing device according to any one of the preceding claims, wherein the securing nut (5) is made from the same or a similar material as the sliding sleeve (7). A sealing device according to any one of the preceding claims, wherein the inner locking note (6) is either milled in the sliding sleeve (7) or screwed into place outside the sliding sleeve (7). A sealing device according to claim 7, wherein the inner locking nut (6), the locking rings (3), the supporting rings (2), the seal (1) and also the securing nut (5) are all arranged to be screwed onto the sliding sleeve (7). A sealing device according to claim 7, wherein the inner locking note (6), the locking rings (3), the supporting rings (2), the seal (1) and also the locking nut (5) are all arranged to fit into a depression in the sliding sleeve ( 7). Sealing device according to any one of the preceding claims, wherein the valve opening (12) is oval shaped in the longitudinal direction of the bottom tube (11). A sealing device according to claim 10, wherein the valve openings (12) are shaped as enclosures having a cone angle of 20 °.