DRY-TREE SEMI-SUBMERSIBLE PRODUCTION AND DRILLING UNIT

• US 20130032076A1
• Filed: 04/25/2011
• Published: 02/07/2013
• Est. Priority Date: 04/26/2010
• Status: Active Grant

• Current Assignee: AKER Solutions As (AKER Solutions ASA)
• Original Assignee: Aker Subsea Incorporated (Akastor ASA)
• Inventors: Zeng, Yijian, Wanvik, Leiv Gunnar, Wang, Tao, Rasmussen, Stein, Lu, Renjian
• Granted Patent: US 8,807,874 B2
• Time in Patent Office: Days
• US Class Current: 114/265
• CPC Class Codes: B63B 1/107 Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
• CPC Class Codes: B63B 2001/128 comprising underwater connectors between the hulls
• CPC Class Codes: B63B 2039/067 effecting motion dampening by means of fixed or movable resistance bodies, e.g. by bilge keels
• CPC Class Codes: B63B 21/50 Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers

Abstract

A deep draft semi-submersible production and drilling platform unit with dry trees is described. The platform unit preferably comprises four columns, a ring pontoon, a two-axis symmetrical hull with draft in the range of 100 to 155 feet, top-tensioned risers with push or pull tensioners of preferred combined vertical stiffness of 10% to 30% of the platform water plane stiffness, a well-bay with a well spacing in the range of 12 to 18 feet, a riser guiding system supported by the pontoons or at an elevated level, topside facilities supported by a box type of deck structure, mooring lines, and catenary risers.

Claims

1. A dry-tree semi-submersible production and drilling platform unit, comprising:

a semi-submersible hull portion, the hull portion including a ring pontoon and at least four columns connected to the ring pontoon;

a mooring portion anchored to a sea floor and mechanically coupled to each of the at least four columns;

a topside portion supported by the hull, the topside portion including a deck box with at least one of a plated bottom and a grated bottom;

a wellbay portion positioned in a central location of the deck box and configured to support a drilling substructure, a production substructure and a plurality of top-tensioned risers, the wellbay portion including a plurality of well slots arranged in a grid pattern, the drilling substructure configured to provide vertical access to each well slot in the grid pattern;

a top-tensioned riser portion including the plurality of top-tensioned risers and at least one of dry-trees and direct vertical access to each of the plurality of well slots;

a catenary riser portion including a plurality of steel catenary or flexible risers, each of the steel catenary or flexible risers being hung from the ring pontoon; and

a riser tensioning subsystem having a plurality of riser tensioners configured to provide vertical motion compensation for each of the plurality of top-tensioned risers,

wherein the riser tensioning subsystem is characterized by a tension level parameter, a stroke length parameter, and a stiffness parameter, and wherein a set of values for the tension level parameter, the stroke length parameter, and the stiffness parameter is determined based on a field water depth, a number of wells in the wellbay portion, a predetermined top-tensioned riser configuration, and a predetermined topside capacity.

2. The semi-submersible production and drilling platform unit of claim 1, further comprising a riser guide frame configured to constrain a rotation-induced moment on at least one of the plurality of riser tensioners.

3. The semi-submersible production and drilling platform unit of claim 1, wherein the tension level parameter, the stroke length parameter, the stiffness parameter, and a number of top-tensioned risers are determined such that an effective total stiffness of the riser tensioning subsystem is maintained within a range of between 10% and 30% of a platform water plane stiffness at in-place operating conditions.

4. The semi-submersible production and drilling platform unit of claim 1, wherein the hull portion has a draft configured between about 100 feet and 155 feet.

5. The semi-submersible production and drilling platform unit of claim 1, wherein the hull portion is configured to suppress platform heave motions to enhance riser performance while maintaining a predetermined hull portion maximum height for quayside integration of the topside portion with the hull portion.

6. The semi-submersible production and drilling platform unit of claim 1, wherein the platform unit is configured such that a pontoon to platform displacement ratio is maintained in a range of between 0.3 and 0.5.

7. The semi-submersible production and drilling platform unit of claim 1, wherein the platform unit is configured such that a heave natural period of the platform unit is maintained within a range of between 5 seconds and 8 seconds longer than a peak period of a predetermined governing design storm with all risers installed.

8. The semi-submersible production and drilling platform unit of claim 1, wherein the plurality of well slots is arranged in a grid pattern having a well spacing in a range of between 12 feet and 18 feet, wherein the grid pattern is one of a rectangular grid pattern and a square grid pattern.

9. The semi-submersible production and drilling platform unit of claim 1, wherein a configuration of the mooring portion is based on a nominal stroke position of each of the plurality of riser tensioners, the respective nominal stroke positions being determined in accordance with a predetermined maximum up stroke and a predetermined maximum down stroke relating to each of a normal operational mode, an extreme storm mode, and a survival mode.

10. The semi-submersible production and drilling platform unit of claim 1, wherein the drilling substructure uses an X-Y skidding system to provide the vertical access to each well slot in the grid pattern.

11. The semi-submersible production and drilling platform unit of claim 1, wherein the hull portion includes six columns and a truss deck, wherein the truss deck is integrated with the topside portion, and wherein the mooring portion is mechanically coupled to four of the six columns.

12. The semi-submersible production and drilling platform unit of claim 1, wherein the topside portion further includes an integrated truss deck.