Compliant platform with slide connection docking to auxiliary vessel

• US 5,423,632 A
• Filed: 03/01/1993
• Issued: 06/13/1995
• Est. Priority Date: 03/01/1993
• Status: Expired due to Term

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Denison, Early B., Ekvall, Anders G. C.
• Primary Examiner(s): Taylor, Dennis L.
• Application Number:
  US08/024,583
• Time in Patent Office: 834 Days
• Field of Search: 405/224, 405/195.1, 405/203, 114/250, 114/249
• US Class Current: 405/223.1
• CPC Class Codes: B63B 21/502 by means of tension legs
• CPC Class Codes: E02B 17/00 Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor construction methods for floating platforms B63B75/00; anchoring floating platforms B63B21/00; floating platforms, e.g. anchored, B63B35/44; underwater reservoirs B65D88/78

Abstract

An improved method for conducting offshore well operations is disclosed in which a compliant platform is installed adjacent a selected well site and an auxiliary vessel is temporarily docked to the compliant platform to provide for support for the well operations which will be produced through the compliant platform. In the practice of the improved method, the compliant platform is isolated from vertical loads upon the auxiliary vessel docked thereto during the performance of well operations conducted for the compliant platform by the offshore auxiliary vessel. Another aspect of the present invention is an improved system for restraining an offshore drilling vessel temporarily to a compliant platform which uses a slide-connection for isolating the compliant platform from vertical loads upon the offshore drilling vessel during the well operations.

Claims

1. An improved method for conducting offshore well operations from a tension leg platform moored with at least one tendon, in which the tension leg platform is installed adjacent a selected well site;

and

an auxiliary vessel is temporally docked to the compliant platform with facilities on board for support of well operations;

the improvement comprising;

protecting the tendon of the tension leg platform from excessive vertical loading transmitted through a docking system by isolating the tension leg platform from vertical loads acting upon the auxiliary vessel during well operations conducted for the tension leg platform by the offshore auxiliary vessel.

2. An improved method for conducting well operations in accordance with claim 1, wherein isolating the tension leg platform from vertical loads upon the auxiliary vessel comprises:

docking the auxiliary vessel to the tension leg platform through a vertically sliding connection.

3. A improved method for conducting well operations in accordance with claim 2, further comprising:

providing a plurality of first engaging members on the auxiliary vessel;

providing a plurality of second engaging members on the tension leg platform; and

releasably securing said first and second engaging members in a vertically sliding connection such that the auxiliary vessel is free to move vertically with respect to the tension leg platform.

4. An improved method for conducting well operations in accordance with claim 3 wherein the method conducts well operations from a derrick facility on the auxiliary vessel which is vertically aligned with a well bay of the tension leg platform and a well on an ocean floor.

5. An improved method for conducting well operations in accordance with claim 3 wherein the tension leg platform is brought out of alignment with a well on an ocean floor and the auxiliary vessel restrained with respect to the tension leg platform is brought into substantially vertical alignment therewith.

6. An improved method for conducting offshore well operations from a tension leg platform secured to the ocean floor through a plurality of tendons, in which

a tension leg platform is restrained out of its normal position substantially over a well pattern;

an offshore drilling vessel is positioned over a selected well site of the well pattern at a location at the surface of the water not accessible to the offshore drilling vessel with the tension leg platform in its normal position; and

well operations are conducted through a substantially vertical riser, the improvement comprising;

protecting the tendons of the tension leg platform from excessive vertical loading by isolating the tension leg platform from vertical loads upon the offshore drilling vessel during well operations conducted for the tension leg platform by the offshore drilling vessel.

7. An improved method for conducting well operations in accordance with claim 6, wherein isolating the tension leg platform from vertical loads upon the offshore drilling vessel comprises:

docking the offshore drilling vessel to the tension leg platform through a vertically sliding connection.

8. A improved method for conducting well operations in accordance with claim 7, further comprising:

providing a plurality of first engaging members on the offshore drilling vessel;

providing a plurality of second engaging members on the tension leg platform; and

releasable securing said first and second engaging members in a vertically sliding connection such that the offshore drilling vessel is free to move vertically with respect to the tension leg platform.

9. A improved method for conducting well operations in accordance with claim 8, wherein releasable securing said first and second engaging members further comprises:

adjusting the ballast of the offshore drilling vessel to bring a key presented by one of the first engaging members into alignment with a track entry to a vertical track providing one of the second engaging members;

moving the key into the track entry; and

adjusting the ballast of the offshore drilling vessel to secure the key within the track by taking the key out of alignment with the track entry.

10. An improved method for conducting well operations in accordance with claim 9, wherein additional first and second engaging members are provided with additional keys and corresponding track entries at relative positions such that ballast levels aligning the additional keys and track entries will maintain the engagement of the first key within its corresponding track, said method further comprising:

further adjusting the ballast of the offshore drilling vessel and swinging the offshore drilling vessel with respect to the tension leg platform to align the additional keys and track entries;

moving the additional keys into the corresponding track entries while maintaining the engagement of the first key within its track; and

adjusting the ballast of the offshore drilling vessel to secure the additional keys into additional vertically extending tracks.

11. In an improved system for restraining an offshore drilling vessel temporarily to a tension leg platform, which is moored with a plurality of tendons, to provide well operations in support of the tension leg platform, the improvement comprising:

a slide-connection for isolating the tension leg platform from vertical loads upon the offshore drilling vessel during the well operations, whereby the tendons of the tension leg platform are protected from excessive transfer of components of vertical load from the offshore drilling vessel to the tension leg platform.

12. An improved system for restraining an offshore drilling vessel in accordance with claim 11, wherein said slide-connection further comprises:

a strut connected to the offshore drilling vessel and extending outwardly therefrom;

a key presented on the outboard end of the strut; and

a vertically extending track configured to receive the key in a vertically slidable engagement.

13. An improved system for restraining an offshore drilling vessel in accordance with claim 12 further comprising a plurality of corresponding keys and tracks presented by the offshore drilling vessel and tension leg platform, respectively.

14. An improved system for restraining an offshore drilling vessel in accordance with claim 13, wherein said tension leg platform is a tension leg well jacket.

15. A system for restraining an offshore drilling vessel temporarily to a tension leg platform, which is moored with a plurality of tendons, to provide well operations in support of the tension leg platform, comprising:

an elongated swinging strut connected to the offshore drilling vessel in a horizontally pivoting connection and projecting outboardly;

a first key presented on the outboard end of the swinging strut;

a rigid frame strut connected to the offshore drilling vessel and projecting outwardly therefrom;

a second key presented on the outboard end of the frame strut;

first and second tracks presented on the tension leg platform and disposed to receive the fast and second keys, respectively, in a vertically extended sliding reception; and

track entries into the first and second tracks to accept entry of the first and second keys, respectively;

whereby the offshore drilling vessel may be docked to the tension leg platform without subjecting the tendons of the tension leg platform with vertical loads transmitted across the system.