Arrangement for Supporting a Wellhead

Abstract

A device is for reducing the load on a wellhead casing from a bending moment generated by a horizontal load component from a well element arranged over a wellhead. A supporting frame is connected to an upper portion of the wellhead casing and projects outwards from the center axis of the wellhead casing and is provided with an abutment which rests supportingly against a base at a radial distance from the wellhead casing. The supporting frame is arranged to absorb a portion of said bending moment.

Claims

1. A device for reducing the load on a wellhead casing from a bending moment generated by a horizontal load component from a well element arranged over a wellhead wherein a supporting frame is connected to an upper portion of the wellhead casing and projects outwards from the center axis of the wellhead casing and is provided with abutments which rest supportingly against a base at a radial distance from the wellhead casing, the supporting frame being arranged to absorb a portion of said bending moment.

2. The device according to claim 1, wherein the supporting frame comprises a well-casing extension adapted for connection to the wellhead casing.

3. The device according to claim 1, wherein the ratio of the maximum bending moment absorbed in the supporting frame to the bending moment applied to the wellhead casing is at least 1:2.

4. The device according to claim 1, wherein the ratio of the maximum bending moment absorbed by the supporting frame to the bending moment applied to the wellhead casing is at least 3:4.

5. The device according to claim 1, wherein the ratio of the maximum bending moment absorbed in the supporting frame to the bending moment applied to the wellhead casing is at least 9:10.

6. The device according to claim 1, wherein the connection between the supporting frame and the wellhead casing, possibly between the supporting frame and the well-casing extension is formed as a zero-clearance connection.

7. The device according to claim 6, wherein the supporting frame comprises a coupling formed as a sleeve which encloses a portion of the wellhead casing with a press fit.

8. The device according to claim 6, wherein the supporting frame comprises a coupling formed as a sleeve which encloses a portion of the well-casing extension with a press fit.

9. The device according to claim 6, wherein the supporting frame comprises a coupling formed as a sleeve which has been shrunk around a portion of the wellhead casing.

10. The device according to claim 6, wherein the supporting frame comprises a coupling formed as a sleeve which has been shrunk around a portion of the well-casing extension.

11. The device according to claim 1, wherein the base is a seabed or a wellhead foundation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In what follows, an example of preferred embodiments is described, which is visualized in the accompanying drawings, in which:

[0022] FIG. 1 shows a principle drawing of a wellhead provided with a supporting frame directly connected to an upper portion of a wellhead casing;

[0023] FIG. 2 shows, in a highly simplified manner, the elements that absorb load when a wellhead is subjected to a bending moment from a horizontal load component; and

[0024] FIG. 3 shows a principle drawing of a wellhead provided with a supporting frame connected to an upper portion of a wellhead casing via a well-casing extension integrated in the supporting frame.

DETAILED DESCRIPTION OF THE DRAWINGS

[0025] Reference is first made to FIG. 1. A subsea well 1 extends downwards in an underground 4 under a water mass 5. A wellhead 11 is arranged immediately above a seabed 41, an upper portion 12a of a wellhead casing 12 projecting up from the seabed and forming the wellhead 11 in which one or more wellhead elements 2 are arranged, at least a Christmas tree including a blowout preventer (also referred to as a BOP), a wellhead connector 21 connecting the wellhead elements 2 to the wellhead casing 12. From the wellhead element 2, at least a marine riser 3 extends up through the water mass 5 to a surface installation (not shown). The riser 3 is shown as being deflected in order to indicate a situation in which the wellhead 11 is subjected to a horizontal load component L.sub.h which subjects the wellhead casing 12 to a bending moment M. The deflection of the riser 3 may be due to currents in the water mass 5 or the position of the surface installation not shown. Currents in the water mass 5 may also subject the wellhead element 2 to a horizontal load component L.sub.h, and skewed distribution of the mass of the wellhead element 2 will also subject the wellhead 11 to a horizontal load component L.sub.h.

[0026] The wellhead casing 12 is shown here as a casing 122 extending up through a so-called conductor casing 121 which bounds the well 1 in a manner known per se towards the unconsolidated masses in the upper part of the base 4. An upper portion 12a of the wellhead casing 12 is rising from an upper portion 121a of the conductor casing 121.

[0027] Connected to the upper portion 12a of the wellhead casing 12, there is a supporting frame 6 which projects radially outwards from the wellhead casing 12 and is provided with several abutments 61 resting in a supporting manner on a base 13 shown schematically here as an element which is partially embedded in the seabed 41. The base 13 may be any wellhead foundation, for example a suction foundation or a well frame which provides a sufficiently large degree of stability and ability to absorb a load L.sub.v which is transmitted through the supporting frame 6.

[0028] The wellhead casing 12 and the supporting frame 6 are connected to each other in a way that makes it possible for the supporting frame 6 to absorb a bending moment M.sub.f as a reaction to the horizontal load component L.sub.h from the wellhead element 2 subjecting the wellhead casing 12 to said bending moment M.sub.w. A coupling 62 may be arranged in such a way that the wellhead casing 12 is allowed a certain deflection before hitting the supporting frame 6 and the further load being substantially absorbed by the supporting frame 6. The design of the coupling 62 and the dimensioning of the supporting frame 6 can thereby be used to control how great a load the wellhead casing 12 may be subjected to. Calculations carried out by the applicant and other instances have shown that the supporting frame 6 may absorb 75 to 95% of the strain caused by said horizontal load component L.sub.h.

[0029] To ensure a greatest possible relief of the wellhead casing 12, the coupling 62 is advantageously formed as a sleeve 621 surrounding a portion of the wellhead casing 12 without radial clearance. This is advantageously achieved by shrinking the sleeve 621.

[0030] The supporting frame 6 according to FIG. 1 is suitable for permanent installation on the wellhead 11 . Reference is now made to FIG. 3, in which the supporting frame 6 is provided with a well-casing extension 63 which is adapted for insertion between the wellhead casing 12 and the wellhead element 2. Thereby the supporting frame 6 can be installed without any intervention into the wellhead casing 12. This embodiment is well suited for temporary installation, for example while drilling is in progress, indicated here by a drill string 7 extending from a surface installation not shown and through the wellhead 11. The well-casing extension 63 also works as a protection of the wellhead 11 during the temporary installation of wellhead elements 2 or the insertion or withdrawal of drilling equipment.

[0031] FIG. 2 shows the statics of the supporting frame 6 in principle. Solid, oblique connecting lines between horizontal and vertical lines indicate that the connection is rigid. Broken, oblique connecting lines indicate that the connection can allow a restricted relative movement, as is described for the coupling 62 above.

[0032] When the supporting frame 6 is mounted on the wellhead 11 and the wellhead 11 is subjected to a bending moment M.sub.w generated by a horizontal load component L.sub.n from above-lying elements 2, 3, the supporting frame 6 is subjected to a vertical load L.sub.v which is transmitted to the seabed 41 at a distance from the center axis of the wellhead casing 12 through the abutment of the supporting frame 6 against the base. Depending on the amount of play the coupling 62 between the supporting frame 6 and the wellhead casing 12 allows and how great a bending stiffness the wellhead casing 12 and the supporting frame 6 exhibit, the portion of the applied bending moment M.sub.w absorbed by the supporting frame, that is to say M.sub.f/M.sub.w, M.sub.f being the bending moment absorbed by the supporting frame 6, will vary. Calculations show that it is quite possible to dimension the supporting frame 6 to enable absorption of at least 9/10 of the bending moment M.sub.w applied.

[0033] It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative embodiments without departing from the scope of the dependent claims. In the claims, reference numbers in brackets should not be regarded as restrictive. The use of the verb “to comprise” and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article “a” or “an” before an element does not exclude the presence of several such elements.

[0034] The fact that some features are stated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.