Subsea wellhead assembly

Abstract

A method of installing or removing a subsea wellhead assembly is provided. The method comprising providing a suction anchor that in use acts as a subsea well foundation, wherein the suction anchor comprises an outer suction skirt; and an inner member, wherein the inner member comprises a high pressure wellhead housing; and installing or removing the suction anchor together with the high pressure wellhead housing on or from a seabed.

Claims

1. A suction anchor for forming, or having previously formed, a subsea well assembly at an upper end of a subsea well and with the well extending through the suction anchor, the suction anchor comprising: an outer suction skirt; and an inner member integral with the outer suction skirt, wherein the inner member comprises a conductor housing and a high pressure wellhead housing but does not comprise a low pressure conductor pipe, and the conductor housing holds and supports the high pressure wellhead housing, and wherein the outer suction skirt and the inner member are positioned relative to each other so that any casing strings or pipes hung from the high pressure wellhead housing extend through the volume surrounded by the outer suction skirt.

2. The suction anchor according to claim 1, wherein the inner member does not comprise a central suction anchor tube.

3. The suction anchor according to claim 1, wherein the inner member of the suction anchor comprises a wellhead housing extension pipe.

4. The suction anchor according to claim 1, wherein the conductor housing is received within a conductor housing receptacle and is mechanically fixed to the suction anchor within the conductor housing receptacle.

5. A subsea wellhead installation and/or removal apparatus, the wellhead installation apparatus comprising a suction anchor according to claim 1 and a device connected to the high pressure wellhead housing for permitting the suction anchor to be lowered and/or lifted subsea, wherein the device is a well control device, a subsea tree or a capping stack.

6. The subsea wellhead installation and/or removal apparatus according to claim 5, wherein the device further comprises at least one of a device for adjusting the pressure inside the suction anchor, or a verticality measuring and controlling device.

7. A method of installing or uninstalling a subsea wellhead assembly, the method comprising: providing a suction anchor according to claim 1 that in use acts as a subsea well foundation located at an upper end of a subsea well and with the well extending through the suction anchor; and installing or uninstalling the suction anchor together with the high pressure wellhead housing on or from a seabed.

8. The method according to claim 7, wherein the method comprises connecting a device to the high pressure wellhead housing such that the suction anchor is held by the device connected to the high pressure wellhead housing during installation or uninstallation, and wherein the device is a well control device, a subsea tree or a capping stack.

9. The method according to claim 8, wherein the device connected to the high pressure wellhead housing is further comprises at least one of a device for adjusting the pressure inside the suction anchor, or a device for measuring and controlling the verticality of the device connected to the high pressure wellhead housing.

10. The suction anchor according to claim 1, wherein the suction anchor further comprises a top structure, wherein the top structure comprises a plurality of radiating fins that are fixed to the top of the suction anchor, and the fins are in the form of I-beams.

11. A subsea wellhead assembly located at an upper end of a subsea well, the subsea well head assembly comprising: a conductor housing; a suction anchor comprising an outer suction skirt and an inner pipe connected to the outer suction skirt, wherein the conductor housing does not support a conductor pipe, wherein the assembly does not comprise a conductor pipe, wherein the conductor housing is supported by the suction anchor such that loads can be transferred from the conductor housing to the suction anchor, and wherein the conductor housing is located above the inner pipe.

12. The subsea wellhead assembly according to claim 11, wherein the assembly comprises a high pressure wellhead housing and wherein the high pressure wellhead housing is located within and supported by the conductor housing, and wherein the high pressure wellhead housing is attached to and supports a wellhead extension pipe.

13. The subsea wellhead assembly according to claim 11, wherein the conductor housing is connected near or at its top end and near or at its bottom end to the suction anchor.

14. The subsea wellhead assembly according to claim 11, wherein the conductor housing is received in a conductor housing receptacle and mechanically fixed to the suction anchor.

15. The subsea wellhead assembly according to claim 11, wherein a bottom of the conductor housing is received on and supported by a mount attached to the suction anchor, and wherein the conductor housing is locked in position relative to the suction anchor via a clamp, and wherein the clamp and mount each provide a path for loads to be transmitted from the conductor housing to the suction anchor.

16. The subsea wellhead assembly according to claim 11, wherein a high pressure wellhead housing is landed in the conductor housing, and wherein the high pressure wellhead housing does not support a wellhead housing extension pipe.

17. A subsea wellhead assembly located at an upper end of a subsea well comprising: a high pressure wellhead housing; and a suction anchor comprising an outer suction skirt and an inner pipe connected to the outer suction skirt, wherein the high pressure wellhead housing does not support a wellhead housing extension pipe, wherein a casing hanger that supports a casing is landed in the high pressure wellhead housing, and wherein the inner pipe of the suction anchor is immediately around the casing.

18. The subsea wellhead assembly according to claim 17, wherein the high pressure wellhead housing is located within and supported by a conductor housing, and wherein the conductor housing does not support a conductor pipe.

Description

(1) Certain preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic of a suction anchor;

(3) FIG. 2 is a schematic of another suction anchor;

(4) FIGS. 3 to 6 show various stages of an installation and/or removal method;

(5) FIG. 7 shows part of a subsea well assembly;

(6) FIG. 8 shows another subsea well assembly; and

(7) FIG. 9 shows a schematic of yet another subsea well assembly

(8) FIG. 1 shows a suction anchor 1 with an outer suction skirt 2 and an inner member 4. The inner member 4 is made up of a central tube 6 and a high pressure wellhead housing 8 that may support a wellhead housing extension pipe 8′. The central tube 6 may be a tube of the suction anchor 1 into which the high pressure wellhead housing 8 is located and fixed or it may be a conventional low pressure conductor, made up of a conductor housing and a conductor pipe which is connected to the outer suction skirt 2. The central tube 6 could also comprise both a central tube of the suction anchor 1 and a conventional low pressure conductor pipe (although this is not shown in these figures). The inner member 4 is connected to the outer suction skirt 2 by means of a connection portion 10 which may be in the form of an annular plate.

(9) The high pressure wellhead housing may be connected or fixed to the central tube 6 such that it is integral therewith. The high pressure wellhead housing 8 may be connected to the central tube 6 via a conductor housing 30 as shown for example in FIG. 8. The conductor housing 30 however may not be attached to and/or may not support a conductor pipe.

(10) The suction anchor 1 is arranged so that the high pressure wellhead housing 8 can be installed and/or removed with the rest of the suction anchor 1 into or from a seabed.

(11) The outer suction skirt 2, central tube 6 and connection portion 10 may together form an annular volume in which the pressure can be adjusted relative to the environment outside the suction anchor 1. This permits the suction anchor 1 to be forced into or out of the seabed during installation or removal.

(12) Additionally or alternatively, the volume inside the high pressure wellhead housing 8 may be able to be adjusted during installation or removal of the suction anchor 1.

(13) FIG. 2 shows an alternative suction anchor 100. This suction anchor 100 is the same as the suction anchor 1 shown in FIG. 1 except that it does not comprise central tube 6.

(14) In this suction anchor 100 the high pressure wellhead housing 8 is directly connected (although again this may be via a conductor housing) to the outer suction skirt 2 and directly with the suction skirt 2 forms the volume in which pressure can be adjusted relative to the external environment. Aside from this, the above description of the suction 1 is equally applicable to the suction anchor 100 shown in FIG. 2.

(15) The suction anchor 100 does not comprise a low pressure conductor pipe. However, despite not comprising a conductor pipe it may comprise a conductor housing. In use, the outer suction skirt 2 may achieve the structural support functions usually provided by a lower pressure conductor pipe.

(16) FIGS. 3 to 6 show various stages of an installation and/or removal method of a subsea wellhead assembly. Whilst the suction anchor 1 shown in these figures is the suction anchor 1 as shown in FIG. 1, it could equally be the suction anchor shown in FIG. 2, 8 or 9. Thus, the following description of the installation and/or removal method is equally applicable irrespective of whether the suction anchor 1 or 100 is as shown in FIG. 1, FIG. 2, FIG. 8 or FIG. 9.

(17) The method of installation and/or removal involves installing or removing the high pressure wellhead housing 8 and the suction anchor 1 together in one step. The high pressure wellhead housing 8 is integral (e.g. fixed or connected to the outer suction skirt 2, directly or indirectly) with the suction anchor 1 to permit the components to be installed and/or removed together.

(18) As shown in FIG. 3, the suction anchor 1 with the integral high pressure wellhead housing 8 may be arranged so that the suction anchor 1 can be lifted or lowered by a device 12 (e.g. a well control device (such as a blow out preventer (BOP)), a Christmas tree (which may also be referred to as a subsea tree), a capping stack etc.) that is connected to the high pressure wellhead housing 8.

(19) The device 12 and suction anchor 1 with high pressure wellhead housing 8 may together form what is regarded as a subsea wellhead installation and/or removal assembly 20.

(20) The device 12 may be used to hold/support the suction anchor 1. The suction anchor 1 may optionally also be supported by other means such as wires or chains but these are not shown in the figures.

(21) During installation the assembly 20 may be lowered under the action of gravity. Due to the weight of the assembly 20 the suction anchor and the inner member 4 may penetrate the seabed 14 and thus form a closed volume within the suction anchor suction skirt 2 and/or within the high pressure wellhead housing 8 (as shown for example in FIG. 4). The pressure may then be reduced inside the volume so as to force the suction anchor 1 into the seabed 14 as shown in FIG. 5. Alternatively, the assembly 20 may penetrate sufficiently under its own weight and the weight of the device 12 such that suction to pull the suction anchor into the sea bed is not necessary.

(22) The device 12 connected to the high pressure wellhead housing 8 (e.g. a BOP) may be in contact with rig utilities, e.g. via a riser 16.

(23) The device 12 may be used to establish a differential pressure inside the suction anchor 1 that results in it being forced into (or in the case of removal, forced out of) the seabed as shown for example in FIG. 5.

(24) Thus a fluid connection 18 may be formed between the device 12 connected to the high pressure wellhead housing 8 and the inner volume(s) of the suction anchor 1. This fluid connection 18 may be a line, such as a suction line.

(25) After the suction anchor 1 is installed, the device 12 may either be left attached to the high pressure wellhead housing 8 and used during operation of the well, or it may be detached and removed as shown in FIG. 6.

(26) The removal method may effectively be the opposite of the installation method.

(27) The removal method may comprise attaching a device 12 to a high pressure wellhead housing 8 (in the case that the device 12 is not already connected to the high pressure wellhead housing 8). The method may comprise increasing the pressure inside the suction anchor outer suction skirt 2 and/or the high pressure wellhead housing 8 so as to force the suction anchor 1 out of the seabed 14. As with the installation method, this pressure adjustment may be achieved by the device 12 such as by a line 18.

(28) Once the suction anchor 1 has been forced (at least partially or entirely) out of the seabed 14, the device 12 may be used to lift the suction anchor 1 and high pressure wellhead housing 8 together to the surface.

(29) FIG. 7 shows part of a subsea well assembly 200. This assembly 200 may or may not be installed according to the above described method. The subsea well assembly 200 comprises a conductor housing 30, but no conductor pipe.

(30) The assembly 200 comprises a suction anchor comprising an outer suction skirt 2 connected to a central tube 6 via a connection portion 10 so as to form a sealed annular volume between the central tube 6 and the outer suction skirt 2. The connection portion 10 may comprise an inner pipe support ring 102.

(31) This inner pipe support ring 102 may attach to and support central tube 6 of the suction anchor. The central tube 6 may hang from the inner pipe support ring 102.

(32) Supported on the inner pipe support ring 102 may be a mount ring 104. The mount ring 104 may provide a landing surface for conductor housing 30.

(33) The conductor housing 30 is received in a conductor housing receptacle 31. The conductor housing receptacle 31 is a tubular part in which the conductor housing 31 is received and mechanically fixed within.

(34) The conductor housing 30 may be clamped in position on the mount ring 104 by means of a clamp ring 106 that fixes to a top structure 108 of the suction anchor, the top structure 108 comprising a plurality of radially extending fins that are fixed to the top of the suction anchor can via connection portion 10. The radially extending fins of the top structure 108 connect to the conductor housing receptacle 31 such that forces can be transmitted from the receptacle into the top structure 108.

(35) The conductor housing 30 is not attached to and does not support a conductor pipe. However, the conductor housing may have the external and/or internal profile of known and/or standard conductor housings such as GE Vetco 30″ conductor housing.

(36) The conductor housing 30 may hold, support and directly connect to high pressure wellhead housing 8 as shown for example in FIG. 8.

(37) The high pressure wellhead housing 8 may be attached to and support a wellhead extension pipe such as high pressure wellhead casing 110.

(38) Thus the wellhead assembly may comprise a central tube 6 of a suction anchor which is immediately around (i.e. without any other intermediate components) a high pressure wellhead head casing 110.

(39) The clamp ring 106 and mount ring 104 may each provide a path for loads to be transmitted from the conductor housing 30 to the suction anchor (e.g. top structure 108 and/or conductor housing receptacle 31) from where they can be distributed into the seabed.

(40) FIG. 9 shows schematically part of a subsea well assembly 300. This assembly 300 may or may not be installed according to the above described method.

(41) The assembly 300 comprises a suction anchor comprising an outer suction skirt 2 connected to a central tube 6 via a connection portion 10 so as to form a sealed annular volume between the central tube 6 and the outer suction skirt 2.

(42) The connection portion 10 is integrally formed with a conductor housing 301. This housing 301 may not have the usual outer profile of a conductor housing (as it is integral with the top structure 108) but it may have an inner profile of a conductor housing such that the high pressure wellhead housing 8 can be landed within it. Supported on the integral conductor housing 301 may be a conductor pipe 302. This integral conductor pipe 302 may form the inner member 6 around which the annular volume of the suction anchor is formed.

(43) The wellhead housing 8 may be landed in the conductor housing 302 and this may be done before the assembly 300 is deployed subsea.

(44) Once deployed subsea a bore may be drilled through the centre pipe 6 of the assembly and cased with a casing 304. The casing 304 may be supported by a casing hanger 306 that is landed in the high pressure wellhead housing 8. This casing may be a 13⅜″ casing and may be regarded as the first “regular” casing that is run by the rig after drilling.

(45) The wellhead housing 8 may not support a wellhead housing extension pipe. Thus, the conductor pipe 302 may immediately surround (i.e. with no other intermediate components) the casing 304.