Modular arctic structures system

• US 4,486,125 A
• Filed: 12/30/1982
• Issued: 12/04/1984
• Est. Priority Date: 12/30/1982
• Status: Expired due to Term

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Reusswig, Gerhard H.
• Primary Examiner(s): Taylor, Dennis L.
• Application Number:
  US06/454,827
• Time in Patent Office: 705 Days
• Field of Search: 405/195, 405/217, 405/203-208, 405/61
• US Class Current: 405/217
• CPC Class Codes: E02B 17/0021 against ice-loads

Abstract

A modular and floatable offshore exploration and production platform system for use in shallow arctic waters is disclosed. A concrete base member is floated to the exploration or production site, and ballated into a predredged cavity. The cavity and base are sized to provide a stable horizontal base 30 feet below the mean water/ice plane. An exploration or production platform having a massive steel base is floated to the site and ballasted into position on the base. Together, the platform, base and ballast provide a massive gravity structure that is capable of resisting large ice and wave forces that impinge on the structure. The steel platform has a sloping hourglass profile to deflect horizontal ice loads vertically, and convert the horizontal load to a vertical tensile stress, which assists in breaking the ice as it advances toward the structure.

Claims

1. A floatable and reusable modular offshore oil and gas production or exploration platform system, said system being particularly adapted for arctic environments, said system comprising in combination:

(a) a floatable base member towable to an exploration or production site, said base member including;

i. ballasting means for lowering the base member below the water plane to an offshore ocean floor;

ii. said floatable base member defining a first massive base that extends upwardly to a predetermined distance below the main water plane for supporting said offshore exploration or production platform, said first massive base providing lateral load resistance therefor by gravity engagement with the ocean floor; and

iii. an upwardly extending annular rim;

(b) a plurality of temporary buoyancy caissons which are attached to said first base member before ballasting;

(c) means for filling the annular space defined by said rim with sea water to provide an interior lake on the top surface of said base, said interior lake and said buoyancy caissons balancing said base member as it is ballasted below the water plane;

(d) an offshore exploration or production platform, said platform member towable to said exploration or production site, said platform member comprising;

i. ballasting means for lowering the platform onto said first base member;

ii. a steel gravity structure having a conical sloping surface at the mean water plane defined by the height of said first base member and said platform, said sloping surface forming an ice shield upon use in an arctic environment; and

(e) said base member and said platform including at least one vertically extending aperture for oil and gas exploration or production,

whereby the platform and the first base member are separately deballastable at the end of the exploration or production service and refloatable to a new exploration or production site.

2. A modular offshore oil or gas exploration and production platform system as claimed in claim 1, comprises a high-shear gripping means between said platform and said first base member, said gripping means being confined by said annular rim.

3. A modular offshore oil and gas exploration or production platform system as claimed in claim 1, wherein said high shear gripping means comprises a sandbed formed within said rim.

4. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said first massive base member is ballasted to a predredged ocean floor, said base member extending upwardly to a predetermined distance below the main water plane.

5. A modular offshore oil and gas exploration and production platform system as claimed in claim 4, wherein said predredged ocean floor is layered with sand before said base member is ballasted into position.

6. A modular offshore oil and gas exploration and production platform system as claimed in claim 4, wherein said first base member includes means for pumping a sand slurry into a plurality of annular cavities formed between the ocean bottom and said base member.

7. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said first base member has an annular configuration with an external sloping side.

8. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said first base member is formed of modular components and assembled on site before ballasting.

9. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said first base member defines a plurality of compartments for receiving sand, water, or a mixture thereof as ballast generate lateral load stability.

10. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said base member is formed of prestressed reinforced concrete.

11. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said platform has an hourglass profile with a massive gravity base, said massive gravity base cooperating with said first base member to impart lateral load stability to the system.

12. A modular offshore oil and gas exploration and production platform system as claimed in claim 1, wherein said platform comprises heat exchanger means adjacent the outer walls of said conical portions of said platform to prevent freezing of the ballast tanks and adfreezing of ocean water to said platform.

13. A modular offshore oil and gas exploration and production platform system as claimed in claim 12, wherein said heat exchanger means is connected to a scavenger system utilizing heat generated by at least one work engine mounted within said platform.

14. A method of installing a floatable and reusable offshore oil and gas exploration or production platform, said method comprising:

(a) dredging a cavity in the ocean floor, said cavity being dredged to a predetermined level below the mean water plane of the ocean;

(b) floating a massive base member to said cavity and ballasting said base member into said cavity, said base member extending upwardly to a predetermined level below the mean water plane;

(c) attaching a plurality of buoyancy caissons to the upper surface of said base member;

(d) pumping sea water into an annular cavity defined by the upper surface of said base member to form an interior lake on the upper surface thereof;

(e) filling a plurality of internal buoyancy chambers defined within said base member with water, sand, or a mixture thereof to ballast the base member below the water plane into said cavity; and

(f) floating said oil and gas exploration or production platform over said base member, and ballasting said platform into gravity engagement with said base member, whereby the platform and the base member are separately reballastable at the end of the exploration or production service period and refloatable to a new exploration or production site.

15. A method as claimed in claim 14, which includes the step of backfilling said ocean floor cavity with sand before said base member is ballasted into position.

16. A method as claimed in claim 14, which includes the step of pumping a sand slurry into a plurality of cavities formed between the base and the ocean floor.

17. A method as claimed in claim 14, which includes the step of forming a sandbed on the upper surface of said base member before said platform is ballasted into position.

18. A method as claimed in claim 14, which includes the step of assembling said first base member from a plurality of modular components.