Systems and Methods for Bracing Subsea Wellheads to Enhance the Fatigue Resistance of Subsea Wellheads and Primary Conductors

Abstract

A device for bracing a subsea wellhead includes a wellhead coupling configured to be mounted to the subsea wellhead. In addition, the device includes a plurality of circumferentially-spaced anchor couplings disposed about the wellhead coupling. Each anchor coupling is radially spaced from the wellhead coupling and is configured to be mounted to a subsea anchor. Further, the device includes a plurality of circumferentially-spaced rigid wellhead support members. Each wellhead support member has a radially inner end coupled to the wellhead coupling and a radially outer end coupled to one of the anchor sleeves. The wellhead support members are configured to transfer lateral loads from the wellhead coupling to the anchor coupling.

What is claimed is: 
     
         1 . A device for bracing a subsea wellhead, the device comprising:
 a wellhead coupling configured to be mounted to the subsea wellhead;   a plurality of circumferentially-spaced anchor couplings disposed about the wellhead coupling, wherein each anchor coupling is radially spaced from the wellhead coupling and is configured to be mounted to a subsea anchor;   a plurality of circumferentially-spaced rigid wellhead support members, wherein each wellhead support member has a radially inner end coupled to the wellhead coupling and a radially outer end coupled to one of the anchor sleeves, and wherein the wellhead support members are configured to transfer lateral loads from the wellhead coupling to the anchor coupling.   
     
     
         2 . The device of  claim 1 , further comprising a plurality of rigid anchor coupling support members, wherein one anchor coupling support member extends between each pair of circumferentially adjacent anchor coupling and is configured to transfer loads therebetween. 
     
     
         3 . The device of  claim 1 , wherein the anchor couplings are uniformly circumferentially-spaced about the wellhead coupling. 
     
     
         4 . The device of  claim 1 , wherein each anchor coupling is disposed at a radial distance R1 from the wellhead coupling, and wherein each radial distance R1 is the same. 
     
     
         5 . The device of  claim 4 , wherein each radial distance R1 is between 4.0 and 6.0 m. 
     
     
         6 . The device of  claim 1 , wherein a lower end of each anchor coupling is vertically aligned with a lower end of the wellhead coupling. 
     
     
         7 . The device of  claim 1 , wherein the wellhead coupling is a wellhead sleeve configured to be disposed about the wellhead and each anchor coupling is an anchor sleeve configured to be disposed about one subsea anchor. 
     
     
         8 . The device of  claim 7 , wherein the lower end of the wellhead sleeve and the lower end of each anchor sleeve comprises a funnel. 
     
     
         9 . The device of  claim 1 , further comprising a plurality of circumferentially spaced locking devices mounted to the wellhead coupling, wherein each locking device is configured to engage and lock onto the subsea wellhead. 
     
     
         10 . The device of  claim 1 , wherein the plurality of anchor couplings comprises at least three uniformly circumferentially-spaced anchor couplings. 
     
     
         11 . An offshore system for drilling or producing a subsea well, the system comprising:
 a subsea wellhead extending from the well proximal the sea floor;   a plurality of circumferentially-spaced anchors disposed about the well and secured to the sea floor, wherein each anchor has an upper end positioned above the sea floor;   a support frame mounted to the wellhead and the anchors, wherein the support frame comprises:
 a wellhead sleeve disposed about the wellhead, wherein the wellhead sleeve has a central axis; 
 a plurality of circumferentially-spaced anchor sleeves disposed about the wellhead sleeve, wherein each anchor sleeve is radially spaced from the wellhead sleeve and is disposed about one of the anchors; 
 a plurality of circumferentially-spaced rigid wellhead support members, wherein each wellhead support member extends from the wellhead sleeve to one of the anchor sleeves and is configured to transfer lateral loads therebetween. 
   
     
     
         12 . The system of  claim 11 , wherein each anchor is a driven pile or a suction pile having a lower end disposed below the sea floor. 
     
     
         13 . The system of  claim 11 , wherein each anchor sleeve is axially and radially fixed to the upper end of the corresponding anchor. 
     
     
         14 . The system of  claim 13 , wherein the wellhead sleeve is radially fixed to the wellhead. 
     
     
         15 . The system of  claim 11 , wherein an annulus is radially positioned between the wellhead and the wellhead sleeve; and
 wherein the annulus is at least partially filled with cement.   
     
     
         16 . The system of  claim 11 , wherein an annulus is radially positioned between the wellhead and the wellhead sleeve;
 wherein the support frame further comprises a plurality of circumferentially spaced locking devices mounted to the wellhead sleeve, wherein each locking device extends radially inward from the wellhead sleeve through the annulus and into engagement with the wellhead;   wherein each locking device is configured to prevent the wellhead from moving radially relative to the wellhead sleeve and allow the wellhead to move axially relative to the wellhead sleeve.   
     
     
         17 . The system of  claim 11 , wherein the anchors are uniformly circumferentially-spaced about the wellhead. 
     
     
         18 . The system of  claim 17 , wherein each anchor is disposed at a radial distance R1 from the wellhead, and wherein each radial distance R1 is the same. 
     
     
         19 . The system of  claim 18 , wherein each radial distance R1 is between 4.0 and 6.0 m. 
     
     
         20 . The system of  claim 11 , wherein the wellhead sleeve and each anchor sleeve are positioned above the sea floor. 
     
     
         21 . The system of  claim 11 , wherein the plurality of anchors comprises at least three uniformly circumferentially-spaced anchors; and
 wherein the plurality of anchor sleeves comprises at least three uniformly circumferentially-spaced anchor sleeves, each anchor sleeve being secured to one of the anchors.   
     
     
         22 . A method for enhancing the fatigue resistance of a subsea wellhead, the method comprising
 (a) deploying a bracing device subsea, wherein the bracing device comprises:
 a wellhead coupling; 
 a plurality of circumferentially-spaced anchor couplings disposed about the wellhead coupling, wherein each anchor coupling is radially spaced from the wellhead coupling; 
 a plurality of circumferentially-spaced rigid wellhead support members, wherein each wellhead support member extends from the wellhead coupling to one of the anchor couplings; 
   (b) mounting the wellhead coupling to the wellhead;   (c) mounting each anchor coupling to an anchor;   (d) securing each anchor to the sea floor;   (e) transferring lateral loads and bending moments applied to the wellhead to the anchors with the bracing device after (b), (c), and (d).   
     
     
         23 . The method of  claim 22 , wherein the wellhead coupling is a wellhead sleeve; and
 wherein (b) comprises aligning the wellhead sleeve with the wellhead and lowering the bracing device to receive the wellhead into the wellhead sleeve.   
     
     
         24 . The method of  claim 23 , wherein each anchor coupling is an anchor sleeve; and
 wherein (d) comprises advancing one anchor through each of the anchor sleeves and into the sea floor.   
     
     
         25 . The method of  claim 22 , further comprising:
 (f) radially fixing each anchor coupling relative to the corresponding anchor to prevent relative radial movements therebetween;   (g) radially fixing the wellhead coupling relative to the wellhead to prevent relative radial movement therebetween.   
     
     
         26 . The method of  claim 25 , further comprising:
 supporting the bracing device with the sea floor during (d); and   raising the bracing device off the sea floor after (c) and (d), and before (f) and (g).   
     
     
         27 . The method of  claim 25 , wherein (g) comprises actuating a locking assembly to extend an extension member radially inward from the wellhead coupling into engagement with the wellhead. 
     
     
         28 . The method of  claim 22 , wherein each anchor coupling is disposed at a radial distance R1 from the wellhead, and wherein each radial distance R1 is the same. 
     
     
         29 . The method of  claim 28 , wherein each radial distance R1 is between 4.0 and 6.0 m.