GB2102044A - Riser bend restrictor for subsea wells - Google Patents

Abstract

A subsea well installation has a christmas tree apparatus 20 landed at the subsea well head with a riser conduit 14 run from an over head location which may be a drilling or production platform or floating vessel wherein riser conduit bend restrictor means 30 are provided adjacent the subsea well head associated apparatus 20 for restricting lateral bending movement of lower portions of the riser conduit 14, the restrictor means including an outer brace means 31 run one guide frame 26 from the over head platform or vessel to the subsea well installation and an inner brace means 32 supported by the outer brace means 31 and adapted to engage and confine the lower portions of the riser conduit 14 situated therein to a predetermined amount and configuration of lateral bending during production or drilling operations. <IMAGE>

Description

SPECIFICATION Riser bend restrictor for subsea wells The present invention relates in general to subsea well installation wherein a riser conduit for production or drilling operations is run from an above sea location, such as a platform or floating vessel, to a subsea well head located on the ocean floor, More specifically, the present invention relates to a means for restricting bending movement of the riser conduit.

Subsea well drilling and production operations are normally conducted through a riser, which is a string of connected conduits, run from the over head platform or floating vessel to the subsea well head associated apparatus. As the need for oil encourages deeper sea drilling and production operations, longer and longer riser connections are being experienced between the over head platform or vessel and the subsea well installation.

During rough sea conditions, or strong ocean currents, the lony riser tends to bend a considerable amount placing high stress loads on the connections between the riser and the over head platform or vessel as well as at the subsea well head connection. It is known heretofore to use ball joint or flex joint connections between the riser and the over head platform or vessel as well as between the riser and the subsea well head apparatus. In production operations, it is common to use a somewhat smaller diameter riser conduit than in drilling operations and the riser is less able to withstand the high stress loads encountered under severe bending conditions.It is also expensive and time consuming to have to make up ball joint or flex joint connections in a riser installation and it has been recognized that it would be desirable to be able to avoid the need for such flexible connections, particularly between the lower end of the riser and the subsea well head apparatus.

It is therefore the primary object of the present invention to disclose and provide a means for effecting a subsea well head to over head platform or a floating vessel riser connection without the need for a flexible joint or ball joint connection between the riser and subsea well head apparatus.

It is another object of the present invention to disclose and provide a mechanical means of a static nature to limit the curvature of a riser, including tubes or conduits connected toyether in a vertical string, run from an over head location to a subsea well head, and to specifically limit the curvature of the riser at its attachment on the ocean floor to reduce stresses otherwise induced into the riser due to bending under normal sea conditions encountered during production or drilling operations.

It is a further object of the present invention to disclose a mechanical means as in the foregoing object which would be susceptible of having a riser confining means of predetermined configuration which could use a computer developed riser bending curve for a given riser installation to provide an optimum minimum of stresses for the riser connection to the subsea well apparatus.

Generally stated, the present invention in a subsea well installation having a riser conduit run from an above sea location to a subsea well associated apparatus comprises the provision of bend restrictor means adjacent the subsea well head associated apparatus for restricting lateral bending movement of lower portions of the riser conduit to a predetermined amount and configuration. Means are provided by the within invention for mounting the bend restrictor means on the subsea well head associated apparatus to which the riser conduit is connected with lower portions of the riser passing through the restrictor means.

It is contemplated within the present invention to provide means for mounting and running the restrictor means to the subsea well head associated apparatus, such means in an exemplary embodiment including a guide frame on which the restrictor means is mounted with the guide frame being run to the subsea well by otherwise conventional guide posts mounted at the well head and guide cables run from the over head platform or vessel to the guide post.

More specifically, the present invention includes the provision of an inner brace means for engaging a longitudinal extent of the riser at a lower end of the riser where it extends upwardly from the well head apparatus to which it is connected without the provision of a flexible joint or ball joint connection. In exemplary embodiments, the inner brace means may be an upwardly flaring conduit, a series of enlarging internal diameter annular ring members or an upwardly expanding interior tube of other than round configuration, such as rectangular. Outer brace means are secured on the aforementioned guide frame and are provided with interconnecting horizontal brace members for securing the inner brace means to the guide frame in a location spaced upwardly and clear of the well head apparatus and the connection of the riser lower end therewith.

A more complete understanding of the present invention, as well as a recognition of additional advantages and objects of the present invention, will be afforded to those skilled in the art from a consideration of the following detailed description of a preferred and two alternative exemplary embodiments of riser bend restrictor means for subsea wells in accordance with the present invention. Reference will be made to the appended sheets of drawings which will first be described briefly.

Fig. 1 is a side elevation, partially in section, of an exemplary embodiment in subsea well installation including a riser conduit run from an overhead sea location to a subsea well head with a preferred exemplary embodiment of riser bend restrictor means in accordance with the present invention; Fig. 2 is a detail view of the bend restrictor means of Fig. 1; Fig. 3 is a cross-section view of a portion of the bend restrictor means of Fig. 2 taken therein along the plane Ill Ill; Fig. 4 is an alternative exemplary embodiment of bend restrictor means in accordance with the present invention shown in association with an exemplary subsea well installation including a riser conduit run an over head floating platform to a subsea well head;; Fig. 5 is a detail view, partially in section, of a portion of the alternative exemplary embodiment of bend restrictor means of Fig. 4; and Fig. 6 is a cross-section view of a portion of the bend restrictor of Fig. 5 taken therein along the plane VI--VI.

Referring now to Figs. 1 through 3, a preferred exemplary embodiment of riser bend restrictor means is illustrated generally at 30 in the environment of a subsea well apparatus indicated generally at 10. The exemplary subsea well apparatus, indicated generally at 10, includes a conventional drilling template 11 sitting over the well casing 12 on the ocean floor 1 3. A conventional riser conduit 14 is shown run from an over head stationary platform, floating vessel or like above sea location from which drilling and production operations are conducted to the subsea well apparatus.

Guide frame means 1 5 are provided in conventional manner for landing on intermediate conduit portion 1 6 extending downwardly from the guide frame to land in the template and support the downwardly extending well casing 1 2.

Guide frame 15 is also provided with a plurality, preferably four, upwardly extending guide posts 1 7 which are connected by cables 1 8 to the over head platform or vessel. Riser flange 1 9 is connected to the well head apparatus as seen in Fig. 1 and as discussed hereinafter, without the need for a ball joint or flex joint at this riser connection.

A conventional christmas tree apparatus is indicated generally at 20 and is landed on the well head by its associated guide frame 21 which is provided with conical guides 22 which fit about posts 1 7. Associated hydraulic controls may be operated by hydraulic fluid flow lines connected from the over head platform or vessel by conduit such as hydraulic line 23.

A hydraulically operated coupling member 25 is landed by its guide frame 26, the latter having conical guides 27, on the upper portions of the christmas tree apparatus indicated generally at 20. The lower end of the tool 25 may be joined directly to lower end of riser conduit 1 4 by the riser flange 19.

It has been found theretofore, particularly during production operations wherein a fairly small diameter riser conduit is used, that the riser conduit tends to have severe lateral bending action between the subsea well apparatus and the over head platform or vessel, particularly where heavy seas or strong sea currents are experienced. Flex joints and ball joint connections have been made heretofore in the riser conduit string between the over head platform and the well apparatus to relieve stresses which can occur at the riser end connections due to this bending. As is particularly contemplated within the present invention, riser bend restrictor means, indicated generally at 30, are provided in accordance with the present invention to restrict bending movement of the riser at its connection with the subsea well apparatus.

The exemplary embodiment of riser restrictor means, indicated generally at 30, includes an outer brace means 31 which is mounted on and run with the associated guide frame 26. The outer brace means may comprise a large diameter, thick walled conduit which is welded or otherwise securely supported to guide frame 26. The exemplary restrictor means further includes inner brace means 32 which is supported from the outer brace 31 and is configured to engage and limit lateral bending of the lower portions of the riser 14 in a predetermined manner. Inner brace 32 may be made of a thick walled conduit of slightly larger internal diameter then riser 14 in its lower portions with, as seen in Fig. 1, in approximate upper one-fourth thereof having an outward flare.

Inner brace member 32 may be mounted by a welded or integral flange 33 welded or otherwise secured to outer brace 31 at a location spaced upwardly from the bottom end of brace 31 to provide clearance for the riser connection to the well head apparatus and the associated well apparatus as seen in Fig. 1. A top annular flange 34 may be formed integrally of the inner brace 32 or be welded to it and to outer brace 31.

It is presently contemplated that the bending configuration of the riser 1 4 should be restricted to a very narrow amount of bending in lower portions near the well head apparatus connection with a progressively greater amount of bending allowed in the vertically ascending direction.

Towards this end, it is believed that the lower three quarters of the inner brace member 32 may be provided with a generally linearly enlarging internal diameter portion 35 with an approximately one-quarter upper portion 36 having a geometrically enlarging, or flaring, internal diameter as seen in Fig. 2. An exact configuration for the internal diameter of member 32 from its lower end to its upper extremities can be provided which will reduce the bending stresses to an optimum minimum by the use of current computer technologies for any specific size of riser 14 and its expected bending loads.

The exemplary riser bend restriction means may be run down to the well along with landing of the riser on the christmas tree apparatus. As can be seen from the foregoing disclosure, the hydraulic connector 25 is secured directly to the lower end of the riser 14 with guide frame 26 mounted about and to the connector 25. The bend restrictor means, indicated generally at 30 is supported on frame 26. Then the assembly of restrictor means, guide frame 26 and connector 25 may be run together with riser 14 to the well with the guide frame guiding the connector into latching relation with the christmas tree apparatus indicated generally at 20.

Referring now to Figs. 4 through 6, an alternative exemplary embodiment of riser bend restrictor means is illustrated generally at 130 in association with the aforedescribed subsea well bead apparatus indicated generally at 10 and riser conduit 14, reference numerals in this embodiment referring to the same elements of the well head apparatus and riser conduit as like reference numerals refer in the prior embodiment described hereinbefore.

In the present exemplary embodiment, the exemplary riser bend restrictor means indicated generally at 130 includes an outer brace means having a plurality of vertical brace posts 1 31 extending vertically upwardly from the associated guMe frame 26. Posts 131 may be welded or secured by end flanges to guide frame 26 and are spaced from each a distance sufficient to accornmodate the inner brace means therebetween. In this exemplary embodiment, the inner brace means comprises a plurality of annular members of ring like configuration as seen in Figs.

4 through 6. A lower array of annular members 132 is seen in Fig. 4 which may have the same internal diameter, or a slightly enlarging relative diameter from the lower most member 132 to the upper most member 132 over more than one-half of the vertical extent of the restrictor means.

However, the upper annular members preferably have a geometrically enlarging or flared relative relationship for the internal diameters thereof. As seen in Fig. 5, annular member 133, 134 and 135 have internal diameters which are enlarged at a greater relative amount between adjacent annular members then in the lower portion of the restrictor means in order to provide a flared like resultant confining action for the bending riser conduit 1 4.

Each of the annular members may be supported by appropriate cross brace bars 1 36 from the outer brace means. It is contemplated that a more precise interrelationship between the internal diameters of the vertical array of inner brace means annular members can be determined for a specific proposed installation through the use of stress analysis and computer technology in designing a minimum bending stress condition for a given riser conduit installation.

Having thus described a preferred and two alternative exemplary embodiments of riser conduit bend restrictor means in accordance with the present invention, it is believed that those skilled in the art will appreciate that the restrictor means of the present invention achieves the objects and has the advantages therefore stated hereinbefore and that various modifications, adaptations and equivalent constructions can be made in view thereof which come within the scope of the present invention which is defined by the following claims.

Claims (14)

1. In a subsea well installation including a riser conduit run from an above sea location to a subsea well head associated apparatus, the improvement comprising the provision of: bend restrictor means for restricting lateral bending movement of portions of said riser conduit adjacent said subsea well head associated apparatus.

2. The improvement in subsea well installation of claim 1 comprising the additional provision of: means for mounting said bend restrictor means on said subsea well head associated apparatus to which said riser conduit is connected with portions of said bend restrictor means extending upwardly relative said apparatus about said portions of said riser conduit.

3. A subsea well head apparatus for use with a riser conduit run from a floating platform to a subsea well head, said apparatus comprising: restrictor means for restricting the amount of bending allowed for a bendable conduit run therethrough; and means for mounting said restrictor means on said subsea well head in a position to receive said riser conduit therethrough and to restrict lateral bending of a lower portion of said riser conduit lying within said restrictor means.

4. The subsea well apparatus of claim 3 wherein said means for mounting said restrictor means comprises: guide post means associated with said well head and a guide frame underlying said restrictor means and having associated guide means for locating said frame relative to said posts whereby said guide frame is guided by said guide means and guide post into a predetermined landed relation on said well head.

5. The apparatus of claim 3 wherein said restrictor means comprises: inner brace means for engaging a longitudinal extent of said riser at a lower end of said riser where it extends upwardly from said well head; and outer brace means for bracing said inner brace means under engagement of said riser with said inner brace means.

6. The subsea well apparatus of claim 5 wherein: said inner brace means provides a progressively enlarging bore in an upward direction with said riser conduit lying in said bore.

7. A subsea well apparatus as in claim 6 wherein: a lower portion of said inner brace means which is greater than one-half of its vertical extent has a substantially linearly increasing bore internal diameter per unit of length of vertical rise and an upward portion of less than one-half of the length of said inner brace means has a substantially geometrically increasing bore internal diameter per unit of length of vertical rise.

8. A subsea well apparatus as in claim. 5, 6 or 7 wherein said inner brace means comprises: a plurality of annular members in vertical spaced array with a succession of two or more of said members having bores of relatively increasing internal diameter in a vertical direction.

9. A subsea well head apparatus for use with a riser conduit run from a floating platform to a subsea well head, said apparatus comprising: restrictor means for restricting amount of bending allowed for a bendable conduit run therethrough; means four mounting said restrictor means on said subsea well head in a position to receive said riser conduit therethrough and to restrict lateral bending of a lower portion of said riser conduit lying within said restrictor means; and wherein said restrictor means comprises inner brace means including a plurality of annular members in vertical spaced array for engaging a longitudinal extent of said riser at a lower end of said riser where it extends upwardly from said well head; and outer brace means including a plurality of brace bars mounted to each of said annular members and to said outer brace means for bracing said inner brace means under engagement of said riser with said inner brace means.

10. A method of maintaining engagement of a riser conduit run from a floating vessel to a subsea well head apparatus comprising the steps of: running bend restrictor means on a guide frame guided on cables run from said vessel to said well head; confining lower portions only of said riser which lie within said bend restrictor means to a limited lateral bending movement of a predetermined extent and in a predetermined configuration.

11. The method of claim 10 including the further step of: confining the lower most portions of the riser to the smallest lateral movement and allowing progressively larger amounts of lateral bending of the riser in a vertical direction extending upwardly from the lowest portion.

12. The method of claim 10 including the further step of running said guide frame and said bend restrictor means down to said well head apparatus on the lower end of said riser as said riser is run to said well head.

13. In a subsea well installation including a riser conduit run from an above sea location to a subsea well head associated apparatus, the improvement comprising the provision of: riser restrictor means for restricting lateral bending movement of portions of said riser conduit adjacent said subsea well head associated apparatus; and means for mounting said restrictor means on said subsea well head associated apparatus to which said riser conduit is connected with portions of said restrictor means extending upwardly relative said apparatus about said portions of said riser conduit, said mounting means including inner brace means for engaging a longitudinal extent of said riser at a lower end of said riser where it extends upwardly from said well head and outer brace means for bracing said inner brace means under engagement of said riser with said inner brace means.

14. The subsea well apparatus of claim 13 wherein: said inner brace means provides a progressively enlarging bore in an upward direction with said riser conduit lying in said enlarging bore.

1 5. A subsea well apparatus as in claim 14 wherein said inner brace means comprises: a plurality of annular members in vertical spaced array with a succession of two or more of said members having bores of relatively increasing internal diameter in a vertical direction.