Spar construction method

• US 6,471,444 B1
• Filed: 09/25/2000
• Issued: 10/29/2002
• Est. Priority Date: 03/25/1998
• Status: Expired due to Fees

• Current Assignee: Offshore Energy Development Corp. (Chevron Corp.)
• Original Assignee: Offshore Energy Development Corp. (Chevron Corp.)
• Inventors: Pollack, Jack
• Primary Examiner(s): Will, Thomas B.
• Assistant Examiner(s): Addie, Raymond W
• Application Number:
  US09/646,865
• Time in Patent Office: 764 Days
• Field of Search: 405/195.1, 405/205, 405/202, 405/204, 405/206, 405/203, 405/207, 114/264, 114/256
• US Class Current: 405/203
• CPC Class Codes: B63B 77/00 Transporting or installing offshore structures on site using buoyancy forces, e.g. using semi-submersible barges, ballasting the structure or transporting of oil-and-gas platforms

Abstract

A method of constructing SPAR buoys comprising an elongate floating body (1) and a deck structure (2). The elongate body (1) is transported to the mooring site in its horizontal position. During erecting of the floating body (1) by ballasting it with water and alignment with the deck structure (2), the deck structure (2) remains attached to its buoyancy member (7). Hereby the use of large derricks can be avoided which provides a substantial cost reduction. After erecting the floating body, the body (1) may be ballasted to pass below the floating deck structure (2). Alternatively, the deck structure (2) may be deballasted or pulling cables (14) may be used to pull the coupling member (4) of the floating body (1) into contact with the coupling member (12) of the deck construction. Alternatively, the floating body (1) is at its upper ends connected to the deck structure (2) via a pivoting connection (22) such that during coupling the floating body may be hinged against the deck structure (2).

Claims

1. Method of constructing a floating structure comprising an elongate floating body (1) and a deck structure (2) connected to the upper end (3) of the floating body (1) comprising the steps of:

providing the elongate body,

providing the deck structure, wherein the deck structure and the elongate body are each provided with coupling means (4, 12) for connecting the elongate body and the deck structure,

transporting the elongate body to its mooring site,

transporting the deck structure on a buoyancy member to the mooring site,

ballasting the elongate body such that it is in its vertically upright position,

positioning the elongate body below the deck structure, and

raising the elongate body by deballasting it,

wherein the elongate body comprises an elongate buoy for oil production and storage and comprising storage and ballast tanks, and having at its bottom ballast material (6) which is retained upon placing the buoy in its upright position, the deck structure and the elongate body during transport being coupled via control lines (15), the control lines (15) being connected between the deck structure (2) and the floating body (1) for control of the ballasting of the elongate body by supply or removal of water to the ballast tanks during transportation of the elongate body, erection and operation, the control lines (15) remaining attached between the deck and body after erecting of the elongate body, the elongate body being free from external buoyancy members prior to erecting said body.

2. Method according to claim 1, wherein the deck structure (2) is mounted on buoyancy members (7) which are at a mutually spaced apart distance that is larger than the diameter of the coupling means (4) of the elongate body.

3. Method according to claim 1, further comprising:

placing the coupling means (4) of the elongate body at a vertical position that is lower than the vertical position of the coupling means (12) of the deck structure (2),

aligning the coupling means (4, 12) of the floating deck structure (2) and the elongate body (1), and

connecting the aligned deck structure and the elongate body.

4. Method of constructing a floating structure according to claim 1, further comprising:

connecting the elongate body in a horizontal position to the floating deck structure via a pivot construction (22),

placing the elongate body in its upright position while pivoting it with respect to the deck structure around the pivot construction such that the coupling means of the deck structure are brought into contact with the coupling means of the elongate body.

5. Method according to claim 4, wherein the deck structure and the elongate body are transported to the mooring site while connected via the pivot construction.

6. Method according to claim 1, wherein after alignment of the deck structure and the elongate body, the deck structure is ballasted such as to be lowered onto the elongate body.

7. Method according to claim 1, wherein the deck structure and the elongate body are connected by at least one cable (14), wherein during connecting of the elongate body and the deck structure, the cable is shortened by a cable pulling device (24, 25) mounted on the deck structure and/or on the floating body.

8. Method according to claim 1, wherein after connecting the elongate body and the deck structure, the buoyancy member is disconnected from the deck structure whereafter the buoyancy of the buoy is increased and/or the buoyancy member is ballasted to provide clearance between the deck structure and the buoyancy member such that the buoyancy member can be removed.

9. Method according to claim 1, wherein the buoyancy member comprises two or more spaced apart partially submerged floating elements.

10. Method according to claim 1, wherein the elongate body comprises at least two thrusters (23, 23′

).

11. Method according to claim 1, wherein the floating member of the deck structure comprises at least two thrusters.

12. Method according to claim 1, wherein the elongate body (1) is ballasted such as to have a negative buoyancy, while being supported by the upper deck structure (2).