Method of installing a buoy and apparatus for tensioning a buoy to an anchoring location
A method of installing a production buoy at a subsea anchoring location is disclosed. The method includes floating a production buoy over a subsea anchoring location. Then, hanging at least a tether off the production buoy such that the or each tether extends from the production buoy towards the subsea anchoring location occurs. The method includes submerging the production buoy to a depth which allows connection of the or each tether to the subsea anchoring location. An apparatus suitable for use with this method is also provided.
1. A method of installing a production buoy to subsea anchoring foundations, the method comprising, in order, the steps of:
floating a production buoy over the subsea anchoring foundations;
hanging at least one tether off the production buoy such that the or each tether extends from the production buoy towards the subsea anchoring foundations;
submerging the production buoy to a connection depth which allows connection of the or each tether to the subsea anchoring foundations; and
connecting the or each tether to the subsea anchoring foundation beneath the buoy.
2. The method as claimed in claim 1 , further comprising the step of submerging the production buoy to a first predetermined depth prior to hanging the or each tether off the production buoy.
3. The method as claimed in claim 1 , wherein the step of submerging the production buoy comprises suspending a chain with clump weights from a pair of vessels attached to either side of the production buoy.
4. The method as claimed in claim 1 , wherein the production buoy comprises a square or rectangular shape and four tethers are hung off the production buoy, one at each corner of the production buoy.
5. The method as claimed in claim 1 , wherein the production buoy comprises a triangular shape and three tethers are hung off the production buoy, one at each corner of the production buoy.
6. The method as claimed in claim 1 , wherein the step of securing the or each tether to the subsea anchoring foundations comprises tilting the production buoy to one side in order to secure a pair of tethers at the one side of the production buoy to corresponding subsea anchoring foundations at the one side of the production buoy, and then tilting the production buoy to an other side in order to secure a pair of tethers at the other side of the production buoy to corresponding subsea anchoring foundations at the other side of the production buoy.
7. The method as claimed in claim 6 , wherein the step of tilting the production buoy is performed by lowering a chain and clump weights from a vessel attached to one side of the production buoy and then by lowering a chain and clump weights from another vessel attached to the other side of the production buoy.
8. The method as claimed in claim 6 , wherein the step of tilting the buoy is performed by selective flooding of ballast compartments within the buoy.
9. The method as claimed in claim 1 , wherein the method further comprises attaching the production buoy to the subsea anchoring foundations with at least a further tether.
10. The method as claimed in claim 9 , wherein the method comprises attaching the production buoy to the subsea anchoring foundations with a further four tethers for a square or rectangular buoy or with a further three tethers for a triangular buoy.
11. The method as claimed in claim 9 , wherein the step of attaching the production buoy to the subsea anchoring foundations with at least a further tether comprises lowering the or each further tether until the lower end of the or each further tether is adjacent the subsea anchoring foundations, and an attachment portion, toward the upper end of the or each further tether is adjacent the production buoy, and then attaching the lower end to the subsea anchoring foundations and the attachment portion to the production buoy.
12. The method as claimed in claim 11 , wherein the step of lowering includes lowering the or each further tether from a crane provided on a support vessel.
13. The method as claimed in claim 3 , wherein the production buoy comprises a triangular shape and three tethers are hung off the production buoy, one at each corner of the production buoy.
14. The method as claimed in claim 10 , wherein the step of attaching the production buoy to the subsea anchoring foundations with at least a further tether comprises lowering the or each further tether until the lower end of the or each further tether is adjacent the subsea anchoring foundations, and an attachment portion, toward the upper end of the or each further tether is adjacent the production buoy, and then attaching the lower end to the subsea anchoring foundations and the attachment portion to the production buoy.