Cellular SPAR apparatus and method

Abstract

According to various aspects of the invention, a buoyancy apparatus, a buoyancy system and a buoyancy method are provided. In one example embodiment of the present invention, a buoyancy apparatus for drilling and production caisson is provided for use in deep water offshore well operations. The buoyancy apparatus comprises a central cell, and a plurality of secondary cells essentially surrounding the central cell and secured to the central cell; wherein the perimeter surface of the buoyancy apparatus is essentially continuous along the length of at least the secondary cells. In one example embodiment, rigidly connecting the central cell and the secondary cells creates void chambers. The tops, bottoms, and sides, of the void chambers are sealed for buoyancy or production fluid storage. In another example embodiment, the void chambers have open bottoms. Another example embodiment comprises a mixture of sealed and open bottomed void chambers. In yet another example embodiment of the buoyancy apparatus comprises non-traditional curved shapes, rigidly connected. In alternate embodiments, any combination of the central cell, secondary cell, and the void chambers provide fixed ballast, variable ballast, buoyancy, or production storage as will occur to those of ordinary skill in the art.

Description

BACKGROUND OF THE INVENTION

[0001] This invention is generally related to structures used offshore in drilling and production of hydrocarbons and more particularly to floating vessels such as ships, semi-submersibles (e.g. SPARs), and tension leg platforms.

[0002] The SPAR platforms used in the offshore industry are deep draft floating platforms that support heavy decks generally weighing from 5,000 tons to 50,000 tons.

[0003] The SPARs typically range in length from 500 feet to 750 feet and in diameter from 70 feet to 150 feet. Methods of constructing SPARs are similar to ships with the axis of the cylinder being horizontal. Normally SPARs are constructed on land in a building berth which comprises a graving dock which can be flooded so the vessel can be floated out, or a dry-dock which can be submerged on slip-ways which allows the vessel to slide down into the water, or on skid-ways which allow the vessel to be skidded onto a launch barge. These methods and related equipment have been used for building ships for a long time.

[0004] Current practice has been to fabricate short segments of the cylinder and set these in a building berth where they are joined together with a previous block until the structure reaches its full length. In a descriptive sense, it is like putting checkers together on a flat table to form an elongated cylinder. The structure is then skidded out onto a barge or a heavy lift vessel where it is transported to the installation site. This construction method has a number of problems. Some of these problems include the large diameter cylindrical segments require very close tolerances to insure good welds at the joints where the segments are joined together; a substantial number of the welded segments are out of position; a significant portion of the assembly must be performed high above the ground; the building dock must support the fall weight of the structure; and the finished structure must be skidded onto the transit vessel.

[0005] Attempts to solve these problems include U.S. Pat. No. 6,213,045 B1; U.S. Pat. No. 4,702,321; U.S. Pat. No. 4,740,109; U.S. Pat. No. 5,197,826; U.S. Pat. No. 5,443,330; U.S. Pat. No. 3,510,892; U.S. Pat. No. 3,360,810; U.S. Pat. No. 4,234,270; U.S. Pat. No. 4,630,968, and France 2,553,371. All of the previously-mentioned patents are incorporated herein by reference.

[0006] The '045 patent describes floatation tubes arranged in a variety of configurations. The '321 patent describes an oil-storage caisson with a plurality of water-ballast compartments. The '109 patent describes a multi-tendon, buoyant tower. The '826 patent describes a buoyant tower for flaring natural gas. The '330 patent describes a deep-water platform with a single, buoyant flexible pile. The '892 patent describes a floating platform on a hollow cylinder with a flat disc to improve stability in swells. The '810 patent describes a single, buoyant tank for buoyancy and storage of petroleum. The '270 patent describes an elastic, pre-stressed column with buoyancy tanks. The '968 patent teaches a method of constructing a buoyancy apparatus with a plurality of cylinders. The '968 patent is the U.S. foreign-counterpart application for the '371 French patent. There is a long felt need for an improvement to the classic SPAR design with many compartments, fixed and variable ballast, possible production fluid storage, buoyancy chambers, and an improved method of constructing a buoyancy apparatus.

SUMMARY OF THE INVENTION

[0007] According to various aspects of the invention, a buoyancy apparatus, a buoyancy system, and a buoyancy method are provided. In one example embodiment, a buoyancy apparatus for drilling and production caisson is provided for use in deep water offshore well operations. The buoyancy apparatus comprises a central cell, and a plurality of secondary cells essentially surrounding the central cell and secured to the central cell; wherein the perimeter surface of the buoyancy apparatus is essentially continuous along the length of at least one secondary cell. Rigidly connecting the central cell and the secondary cells creates void chambers. The tops, bottoms, and sides, of the void chambers are sealed for buoyancy or production fluid storage. In another example embodiment, the void chambers have open bottoms. Still a further example comprises a mixture of sealed and open bottomed void chambers. In yet another embodiment, the buoyancy apparatus comprises non-traditional curved shapes, rigidly connected. Any combination of the central cell, secondary cell, and the void chambers provide fixed ballast, variable ballast, buoyancy, or production storage as will occur to those of ordinary skill in the art.

[0008] In a further aspect of the present invention, a method of constructing a buoyancy apparatus is provided, the method comprises: attaching a central cell to a first secondary cell with a first elongated member; attaching a second secondary cell to the first secondary cell and the central cell with a second elongated member and a third elongated member, thereby creating a void chamber between the central cell, the first secondary cell, and the second secondary cell; and continuing to attach a plurality of secondary cells to the central cell with a plurality of elongated members, until a loop of secondary cells and a plurality of void chambers are formed.

[0009] In a further aspect, a buoyancy apparatus for a drilling and production caisson for use in deep water offshore well operations is provided. The buoyancy apparatus comprises a central elongated cell, defining a center well, an elongated member connected to the central cell on one end and connected at the other end on a secondary cell or on a secondary elongated member. The secondary cell or secondary elongated member is directly connected to the central cell or is connected to the central cell through a succession of complimentary elongated members and/or complimentary cells, wherein said cells and/or elongated members unaccompanied or in combination with each other define an elongated chamber. The cells and/or elongated chambers are used for buoyancy or variable ballast, or a combination of thereof.

[0010] Further objects and advantages of the invention will be readily apparent from the various examples below. Variations of these examples are within the scope and spirit of the invention.

BRIEF DESCRIPTION OF THE FIGURES

[0011] FIG. 1 shows an example embodiment of the present invention having a platform configuration with seven cells connected using void chambers between the cells for buoyancy.

[0012] FIG. 2 shows a cross-sectional view of the platform configuration with seven cells connected using void chambers between the cells for buoyancy.

[0013] FIG. 3 shows a plan view of an example embodiment having a platform configuration with nineteen cells connected using void chambers between the cells for buoyancy.

[0014] FIG. 4 shows a side view of an example embodiment of wet dock construction of a buoyancy apparatus using a support beam.

[0015] FIG. 5 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes.

[0016] FIG. 6 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with one secondary cell.

[0017] FIG. 7 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with two secondary cells.

[0018] FIG. 8 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with three secondary cells.

[0019] FIG. 9 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with five secondary cells.

[0020] FIG. 10 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with six secondary cells.

[0021] FIG. 11 shows a side view of an example embodiment of a wet dock construction of a buoyancy apparatus using dockside cranes with one central cell and seven secondary cells.

[0022] FIG. 12 shows a cross-sectional view of an example embodiment comprising a central cell, eight secondary cells, void chambers, elongated members and shaped members.

[0023] FIG. 13 shows a cross-sectional view of an example embodiment with variable curvature.

[0024] FIG. 14 shows a cross-sectional view of an example embodiment with constant curvature.

[0025] FIG. 15 shows an example embodiment using a &pgr;-core construction.

[0026] FIG. 16 shows further aspects of an example embodiment of the present invention having interstitial chamber compartments.

[0027] FIG. 17 shows a further example embodiment having egg-shaped secondary cells.

DETAILED DESCRIPTION EXAMPLE EMBODIMENTS OF THE INVENTION

[0028] In one example embodiment of the present invention, a buoyancy apparatus for drilling and production caisson is provided for use in deep water offshore well operations. As illustrated in FIG. 1, the buoyancy apparatus comprises a central cell 120, and a plurality of secondary cells 130 essentially surrounding the central cell 120 and secured to the central cell.

[0029] In a further embodiment, the perimeter surface 190 of the buoyancy apparatus is essentially continuous along the length 170 of at least the secondary cells 130. As those of ordinary skill in the art will recognize the perimeter is essentially continuous because holes are found in various embodiments to allow the flow of water in and out of the cells and chambers. In a further embodiment, the buoyancy apparatus 100 further comprises at least one elongated member 140 connecting the central cell 120 and at least one secondary cell 130. Those of ordinary skill in the art will recognize that while the perimeter surface 190 may comprise the connection and combination of many different cells 120 , 130 or elongated members 150, because the cells 120 , 130 or elongated members 150 are connected along the length 170 of at least one of the secondary cells 130, an essentially continuous surface 190 is formed.

[0030] In a further embodiment, the central cell 120, the secondary cells 130 and the elongated members 140 create void chambers 150 between the outside of the central cell 120, the outside of at least one secondary cell 130, and the elongated member 140.

[0031] In a further embodiment, illustrated in FIGS. 1 and 2, the central cell 120 and the secondary cells 130 further comprise an elongated tubular cell. In a further embodiment, the elongated members 140 comprise metal surfaces rigidly connecting the central cell 120 and at least one secondary cell 130. Of course in alternate embodiments, the central cell 120, the secondary cell 130, the void chambers 150, and the elongated members 140 comprise various shapes and sizes as will occur to those of ordinary skill in the art.

[0032] In alternate embodiments, any combination of the central cell 120, secondary cell 130, and void chambers 150 provide buoyancy, production fluid storage, variable ballasts, or fixed ballasts or any other function that will occur to those of ordinary skill in the art. In alternate embodiments, the central cell 120, secondary cells 130, or the void chambers 150 further comprises pumps, valves, or any other device that will occur to those of ordinary skill in the art to control the ballast or to control and adjust the buoyancy of the apparatus 100 while in use.

[0033] In the illustrated example, the central cell 120 and the secondary cell 130 comprise substantially the same diameter cells. Example storage capacity of the buoyancy apparatus 100 with uniform size cell diameters for the central cell 120 and the secondary cell 130 and cell lengths of 550 feet are seen in the Table 1, below: 1 Oil Storage Capacity Cell Diamter (feet) Weight (tons) (Barrels) 50 18,000 1,100,000 45 16,000 900,000 40 13,500 704,000 35 12,000 539,000 30 10,000 400,000 25 8,000 275,000

[0034] In one example embodiment, the buoyancy apparatus 100 will float an estimated fifty-feet above the water surface 110. The bottom of the buoyancy apparatus 100 will be submerged about five hundred feet below the water surface 110.

[0035] An example embodiment illustrated in FIG. 2 shows a cross-section of the buoyancy apparatus 100 shown in FIG. 1 with seven substantially equal diameter cells 120, 130. FIG. 2 shows an embodiment of the buoyancy apparatus 100 with the central cell 120 centrally located, surrounded by six secondary cells 130 with the central cell 120 and the secondary cells 130 rigidly connected with the plurality of elongated members 140. The elongated members 140 provide a seal along a substantial portion of the entire length of the central cell 120 and the secondary cells 130.

[0036] In some embodiments, the central cell 120, the secondary cells 130, and the elongated members 140, comprise metal, while, in other embodiments, the central cell 120, the secondary cells 130 and the elongated members 140 comprise non-metal.

[0037] The central cell 120, the secondary cells 130, and the elongated members 140 are rigidly connected in some embodiments, by attaching means (for example, ties and other connectors).

[0038] In another example embodiment, the buoyancy apparatus 100 comprises cells having unequal diameters. For example, the cells 120 and 130 comprise different diameters.

[0039] Referring to FIG. 3, in a further example embodiment, nineteen substantially equal diameter cells form a buoyancy apparatus 100 in a hexagon shape. A central cell 120 connects to six secondary cells 130 with a plurality of elongated members 140, forming a plurality of void chambers 150. The six secondary cells 130 connect to twelve additional secondary cells 130 with additional elongated members 140 to create additional void chambers 150.

[0040] In various embodiments, the void chambers 150 function in a manner similar to the cells 120, 130 with pumps and valves to control the buoyancy of the void chamber 150, in order to affect the buoyancy of the buoyancy apparatus 100. The weight of the buoyancy apparatus 100 will change as production fluid is produced and stored in the void chambers 150, the central cell 120 and the secondary cells 130. The buoyancy is adjustable, to accommodate the weight of the production fluid. The configuration of FIG. 3 comprises a high degree of compartmentalization. Compartmentalization diversifies risks of failure of the system as a whole because other chambers compensate for one failed chamber. As a result, the failure of one chamber will have minimal change on the overall draft or stability of the buoyancy apparatus 100 compared to non-compartmentalized vessels.

[0041] As will occur to those of ordinary skill in the art, the nineteen-cell embodiment enables the use of smaller cells than needed for the seven-cell embodiment with the same amount of buoyancy. Smaller cells require smaller cranes to construct the buoyancy apparatus 100.

[0042] As illustrated in FIG. 12, in a further embodiment, the buoyancy apparatus 100 further comprises at least one shaped member 1260. In a further embodiment, at least one end of the shaped member 1260 is secured to a secondary cell 130. In alternate embodiments, the shaped members 1260 are curved, straight or any other shape that will occur to those of ordinary skill in the art. As will occur to those of ordinary skill in the art, in alternate embodiments, the combination of the central cell 120, the secondary cells 130, the shaped members 1260 and the elongated members 150 create void chambers 150 of varying shapes and sizes between the outside of the central cell 120, the outside of the secondary cell 130, the shaped members 1260 and the elongated members 150.

[0043] In a further embodiment, illustrated in FIG. 16, the buoyancy apparatus 100 further comprises interstitial chambers 1680 between the central cell 120 and the secondary cells 130. In a further embodiment, the buoyancy apparatus 100 further comprises water openings 1690 in the interstitial chambers 1680. In still a further embodiment, the central cell 120, secondary cell 130 and interstitial chambers 1680 are divided into compartments 1685, 1645. In some embodiments, the cylindrical compartments 1645 (central cell 120 and secondary cell 130) are for buoyancy only and are assembled at atmospheric pressure. In an even further embodiment, the interstitial chamber compartments 1685 are open at each of their respective bottoms 1690 to the hydrostatic pressure from the ocean 110. Of course, in alternate embodiments, any cell is open to the sea at its respective bottom. Furthermore, in further embodiments, a plurality of horizontal bulkheads in any of the secondary cells, elongated chambers, or interstitial chambers are provided. In most embodiments, the central cell comprises a center well and is open. In further embodiments, to control the water level inside the compartments 1685, air is pumped in and out of the top of the compartment with an air pump 1695. This accomplishes three things: (1) the pressure gradient is minimized between the inside of each interstitial chamber 1680 and the hydrostatic pressure of the sea 110, (2) a means for variable ballast is provided, (3) and pressure gradient between the interstitial chamber compartment 1685 and the central cell 120 and secondary cells 130 is minimized on a global scale. In further embodiments, each cylindrical compartment 1645 (central cell 120 and secondary cell 130) is designed for a specific pressure gradient depending on the nominal water depth at which it is located. It is less expensive to design a cylindrical shape for pressure than a non-cylindrical shape (e.g. the interstitial spaces), which is why in some embodiments, the interstitial chamber compartments 1685 are pressurized with air to reduce the pressure gradient. In further alternate embodiments, any combination of the central cell 120, the secondary cell 130, the void chambers 150, and the interstitial chamber compartments 1685, and cylindrical compartments 1645 comprise production fluid storage, buoyancy, fixed ballast, variable ballast or any other function that will occur to those of ordinary skill in the art.

[0044] In a further embodiment, a “&pgr;-core” construction of a buoyancy apparatus 100 is provided. As illustrated in FIG. 15, a further embodiment comprises a plurality of the secondary cells 130 essentially surround the central cell 120. In a further embodiment, the secondary cells 130 comprise an outer or curved longitudinal surface 1535, and at least one radial surface 1525. In a further embodiment, the plurality of secondary cells 130 essentially surround the central cell 120. In a further embodiment, the radial surface 1525 and the longitudinal surface 1535 are essentially perpendicular.

[0045] In a further embodiment, the at least one radial surface 1525 is connected to the central cell 120 without an inner surface 1515. In alternate embodiments, various shapes of the “&pgr;-core” construction are used such as gamma-shaped outer surfaces, tau-shaped outer surfaces or any other shape that will occur to those of ordinary skill in the art. For example, in a gamma-shaped (&Ggr;) embodiment, a radially extending member and a longitudinally extending member are provided. The radially extending member and the longitudinally extending member are essentially perpendicular. In alternate embodiments, the radially extending member and the longitudinally extending member are straight, curved, or any other shape that will occur to those of ordinary skill in the art. In still a further embodiment, a tau shaped (T) embodiment is provided. A tau-shaped embodiment comprises a radially extending member and one or two members essentially perpendicular to said radial member. The radial member and the essentially perpendicular members are, in alternate embodiments straight, curved, or any other shape that will occur to those of ordinary skill in the art.

[0046] In a further embodiment, illustrated in FIGS. 13 and 14, a buoyancy apparatus 100 further comprises a plurality of secondary cells 130. In a further embodiment, the secondary cells 130 essentially surround the central cell 120. In a further embodiment, at least one end 1365 of the secondary cell 130 is secured to the central cell 120 and at least one other end 1375 is secured to another secondary cell 130. In a further embodiment, the connection of the secondary cells 130 creates an essentially continuous perimeter surface 190. In a further embodiment, the secondary cell 130 comprises an inner surface 1385 and an outer surface 1395. In a further embodiment, the sum of the inner surfaces 1385 essentially create the central cell 120. In still a further embodiment, the sum of the outer surfaces 1395 comprise an essentially continuous perimeter surface 190. In a further embodiment, the secondary cells 130 comprise an outer surface 1395 and a radial surface 1345 with no inner surface 1385. In a further embodiment, the radial surface 1345 is directly connected to the central cell 120 and the outer surface 1395 is connect to another secondary cell 130.

[0047] In a further embodiment, illustrated in FIG. 14, the secondary cell 130 comprises a single curved surface 1400, wherein one end 1365 of the curved surface 1415 is directly connected to the central cell 120 and the other end 1375 is connected to another secondary cell 130. In a further embodiment, the sum of inner surfaces 1415 essentially create the central cell 120. In a further embodiment, the connection of the secondary cells 130 creates a continuous perimeter surface 190.

[0048] In another example embodiment, as illustrated in FIG. 17, the cells comprise elliptical or egg shape cross sections. Of course, in alternate embodiments the cells are various shapes as will occur to those of ordinary skill in the art. In a further embodiment, the buoyancy apparatus further comprises a cylinder 1710 surrounding the central cell 120 and the at least one secondary cell 130.

[0049] According to a further aspect of the invention, a method of constructing a buoyancy apparatus is provided. The method comprises attaching a central cell 120 to a first secondary cell 130 with a first elongated member 140, attaching a second secondary cell 130 to the first secondary cell 130 and the central cell 120 with a second elongated member 140 and a third elongated member 140, thereby creating a void chamber 150 between the central cell 120, the first secondary cell 130, and the second secondary cell 130, and continuing to attach a plurality of secondary cells 130 to the central cell 120 with a plurality of elongated members 140, until a loop of secondary cells 130 and a plurality of void chambers 150 are formed. According to a further aspect of the invention, assembly of various examples seen above is provided, in one example, as seen in FIG. 4. A central cell 120 is held by a plurality of supports 410 on a support beam 420 that supports the central cell 120. In addition, the water partially supports the central cell 120. The support beam 420 moves with a pulley system comprising a winch cable 450, a dock pulley 460, a beam pulley 470 and a winch 480. The beam pulley 470 connects to the support beam 420. The dock pulley 460 connects to a dock wall 430. The winch 480 mounts on a dock surface 465. The dock surface 465 connects to the dock wall 430, which connects to a dock bottom 440. The winch cable 450 runs through the dock pulley 460, the beam pulley 470 to the winch 480, whereby the winch 480 moves the support beam 420 vertically. Although not shown, the plurality of pulley systems are used, one at each end of the support beam 420.

[0050] In another example embodiment, a plurality of support beams 420 are spaced at selected distances to prevent the central cell 120 from being over stressed by a single beam 420. The elevation of the plurality of support beams 420 is adjusted as needed to keep the central cell 120 from being over-stressed as the assembly continues. The support 410 and the weight of the central cell 120 is set to prevent the central cell 120 from moving as a result of wave, wind, and tidal forces.

[0051] In still another example embodiment, adding or removing ballast water from the cells 120, 130 controls the buoyancy of the buoyancy apparatus 100. The combination of ballast water and the elevation of the support beam 420 give the wet dock a great deal of flexibility for constructing, assembling, and repairing certain types of the buoyancy apparatuses 100 at relatively low cost.

[0052] FIG. 5 shows an example embodiment of wet dock construction using cranes. The central cell 120 supports the secondary cell 130 attached to the central cell 120 with the elongated members 140. Water in the wet dock supports the central cell 120. A first crane-cable-connection 500 and a second crane-cable-connection 505 stabilize the central cell 120. The first crane-cable-connection 500 connects a first crane cable 510 to the central cell 120. On the other side of the central cell 120, the second crane-cable-connection 505 connects a second crane cable 515 to the central cell 120. The first crane cable 510 connects to a first crane 520. The first crane 520 controls the first crane cable 510 with a first crane boom 530. In addition, the first crane 520 controls the length of the first crane cable 510. The second crane cable 515 connects to a second crane 525, with a second crane boom 535 to control the second crane cable 515. The second crane 525 also controls the length of the second crane cable 515. The first crane 520 and the second crane 525 are on the dock surface 465. Although not shown, in reality, more than two cranes hold the buoyancy apparatus 100.

[0053] In another example embodiment, the central cell 120 rests against the dock wall 430 to stabilize the central cell 120. In another example embodiment, ballast water aids the buoyancy of the buoyancy apparatus 100.

[0054] However the buoyancy apparatus 100 is supported, the example of FIG. 6 shows an example of a method of wet dock construction provided according to the present invention. The buoyancy apparatus 100 is rotated with the first crane cable 510 connected to a third cable connection 600 and the second crane cable 515 connected to a fourth cable connection 610 making room for another secondary cell 130 to be connected on the buoyancy apparatus 100. In FIG. 7, another secondary cell 130 is transported by another crane (not shown) on top of the buoyancy apparatus 100 to be joined to the buoyancy apparatus 100. The second crane cable 515 connects to the fourth cable connection 610 and the first crane cable 510 connects to a fifth cable connection 700. Turning now to FIGS. 8-11, the buoyancy apparatus 100 is again rotated with the cables making room for another secondary cell 130 to be connected on the buoyancy apparatus 100 one at a time until the central cell 120 is essentially surrounded by secondary cells 130. In another example embodiment, a second ring of secondary cells 130 encircle the first ring of secondary cells 130 attached to the central cell 120 as shown in FIG. 3.

[0055] Various cable connections allow cranes to transport the secondary cells 130 to the buoyancy apparatus 100 for construction. The various transport cable connections are used to control the buoyancy apparatus 100 after the secondary cell 130 is rigidly connected to the buoyancy apparatus 100. Other embodiments use various numbers of cranes in the construction method.

[0056] The benefits of the construction methods comprise: minimizing out of position welding, reducing foundation loads, lift-load requirements, launching problems, and that in some example embodiments, the construction is not completed at relatively high elevations as is the case with classic SPAR construction methods. In even further alternate embodiments, for example, multiple cranes 520, 525 crane-cable-connection 500, 505 and crane booms 530 or any other equipment that will occur to those of ordinary skill in the art are used to secure, rotate and attach the cells 120, 130, and elongated members 140. In alternate embodiments, the cells 120, 130, and elongated members 140 are attached by welding, gluing or any other method that will occur to those of ordinary skill in the art.

[0057] Those of ordinary skill in the art will appreciate that in alternate embodiments, each embodiment of the buoyancy apparatus 100 is constructed using any combination of the construction methods described above or any other construction method that will occur to those of ordinary skill in the art.

[0058] Turning to a method aspect of the invention, a method is disclosed for a method of providing buoyancy for a hydrocarbon well platform. The method comprises isolating a first curved volume from the pressure, isolating a second curved volume from the pressure, isolating a third curved volume from the pressure with the first and the second volumes, and isolating a fourth curved volume from the pressure, where each of the curved volumes is continuous.

[0059] In some embodiments, isolating the curved volume comprises rigidly connecting a plurality of cell plates together, whereby creating a void chamber between the cell plates. The means for isolating a curved volume comprises rigidly connecting a plurality of cell plates with a central volume. The cell plates comprise in various embodiments, variable curvature cell plates (FIG. 13) and constant curvature cell plates (FIG. 14). Such means are described above with reference to FIGS. 4-11 and further include welds, glue, clamps, ties, and other connectors, as will occur to those of skill in the art.

[0060] Yet another aspect of the invention comprises a method of constructing a SPAR platform. The method comprises a plurality of buoyancy cells together with a plurality of elongated members, thereby creating a plurality of void chambers between the buoyancy cells.

[0061] According to another example embodiment, a method of providing buoyancy for a hydrocarbon well platform is provided. The method comprises isolating a plurality of curved volumes from the pressure. The curved volumes form a continuous structure. In a further embodiment, the method comprises isolating a plurality of cylindrical volumes from the pressure.

[0062] In a further embodiment, a method of providing buoyancy for a hydrocarbon well platform is provided. The method comprises isolating a first curved volume from external pressure, wherein the isolating a first curved volume provides at least a partial support capacity for a well platform, isolating a second curved volume from external pressure wherein the isolating a second curved volume provides at least a partial support capacity for a well platform, isolating a third curved volume from external pressure, wherein the isolating a third curved volume provides at least a partial support capacity for a well platform, and isolating a fourth curved volume, with the first, second, and third volumes, from pressure.

[0063] In a further embodiment, the isolating a fourth curved volume comprises surrounding a central volume with the first, second, and third volumes. In a further embodiment, the curved volumes comprise variable curvature shaped curved volumes. In still a further embodiment, the curved volumes comprise substantially uniform shape curved volumes. In a further embodiment, the curved volumes comprise constant curvature shape curved volumes.

[0064] In a further embodiment, a system of providing buoyancy for a hydrocarbon well platform is provided. The system comprises a means for isolating a first curved volume from the pressure, a means for isolating a second curved volume from the pressure, a means for isolating a third curved volume from the pressure with the first and the second volumes, and a means for isolating a fourth curved volume from the pressure, where each of the curved volumes is continuous. In a further embodiment, the curved volumes comprise constant curvature curved volumes. In a further embodiment, the curved volumes comprise substantially uniform size volumes. In a further embodiment, the curved volumes comprise variable curvature curved volumes. In a further embodiment, the curved volumes comprise substantially uniform size volumes. In a further embodiment, the system further comprises a means for isolating a central cylindrical volume. In a further embodiment, the curved volumes comprise constant curvature curved volumes. In a further embodiment, the means for isolating comprises welding. In a further embodiment, the curved volumes comprise variable curvature curved volumes. In a further embodiment, the means for isolating a first curved volume comprises a cell. In a further embodiment, the means for isolating a second curved volume comprises a cylinder. In a further embodiment, the means for isolating a third curved volume comprises a cylinder.

[0065] In a further embodiment, a buoyancy apparatus is provided for offshore petroleum well platforms. The apparatus comprises a central elongated buoyancy cell, a first secondary elongated buoyancy cell connected with a first elongated member to the central elongated buoyancy cell, a second secondary elongated buoyancy cell connected to the first secondary elongated buoyancy cell and the central elongated buoyancy cell with a second elongated member and a third elongated member, wherein a void chamber is defined between the center, the first, and the second elongated buoyancy cells.

[0066] Although the description above contains many example embodiments, these merely provide illustrations and should not be construed as exhaustive the scope of the invention. Further objects and advantages of the invention will be readily apparent from the various example embodiments.

Claims

1. A buoyancy apparatus for a drilling and production caisson for use in deep water offshore well operations, comprising:

a) a central elongated cell defining a center well;

b) an elongated member connected to the central cell on one end and connected at the other end on a secondary cell or on a secondary elongated member;

c) said secondary cell or secondary elongated member being directly connected to the central cell or being connected to the central cell through a succession of complimentary elongated members and/or complimentary cells, wherein said cells and/or elongated members unaccompanied or in combination with each other define an elongated chamber;

d) wherein said cells and/or elongated chambers are used for buoyancy or variable ballast, or a combination of thereof.

2. The buoyancy apparatus of claim 1, wherein a perimeter surface of the buoyancy apparatus is essentially continuous along the length of at least one elongated chamber.

3. The buoyancy apparatus of claim 1, wherein the perimeter comprises openings for water flow.

4. The buoyancy apparatus of claim 1, wherein said elongated chambers further comprise void chambers.

5. The buoyancy apparatus of claim 1, wherein said secondary cell further comprises a circular cross-section.

6. The buoyancy apparatus of claim 1, wherein said secondary cell further comprises a non-circular cross-section.

7. The buoyancy apparatus of claim 6,wherein said secondary cell further comprises an egg-shaped cross-section.

8. The buoyancy apparatus of claim 1, wherein the elongated members comprise metal surfaces.

9. The buoyancy apparatus of claim 1, further comprising a plurality of elongated members comprising curved shapes essentially surrounding the central cell;

wherein one end of each elongated member is secured to the central cell and the other end of each elongated member is secured to a secondary elongated member.

10. The buoyancy apparatus of claim 1, wherein the elongated member further comprises a radial elongated member and the secondary elongated member further comprises a longitudinal elongated member; wherein said radial elongated member is essentially perpendicular to said longitudinal elongated member.

11. The buoyancy apparatus of claim 10, further comprising &pgr;-shaped cells essentially surrounding the central cell.

12. The buoyancy apparatus of claim 1, further comprising an interstitial chamber.

13. The buoyancy apparatus of claim 12, further comprising a bulkhead within said interstitial cell.

14. The buoyancy apparatus of claim 12, further comprising a water opening in the interstitial chamber.

15. The buoyancy apparatus of claim 14, further comprising an air pump.

16. The buoyancy apparatus of claim 1, further comprising a bulkhead within said secondary cell.

17. The buoyancy apparatus of claim 1, further comprising a water opening at essentially the bottom of the secondary cell.

18. The buoyancy apparatus of claim 1, further comprising a bulkhead within said elongated chamber.

19. The buoyancy apparatus of claim 1, further comprising a water opening at essentially the bottom of the elongated chamber.

20. A method of constructing a buoyancy apparatus, the method comprising:

attaching a central cell to a first secondary cell with a first elongated member,

attaching a second secondary cell to the first secondary cell and the central cell with a second elongated member and a third elongated member, thereby creating a void chamber between the central cell, the first secondary cell, and the second secondary cell, and

continuing to attach a plurality of secondary cells to the central cell with a plurality of elongated members, until a loop of secondary cells and a plurality of void chambers are formed.

21. The method of claim 20 wherein:

the central cell and the secondary cells comprise substantially elongated cells,

the central cell is supported lengthwise in water, and

the central cell is rotated between the attaching the central cell to the first secondary cell and the attaching the second secondary cell to the first secondary cell.

22. The method of claim 21, wherein the secondary cell buoyancy cells comprise metal.

23. The method of claim 21, wherein the attaching comprises welding.

24. The method of claim 21, wherein the secondary cells comprise composites.

25. The method of claim 21, wherein the attaching comprises gluing.