Riser buoyancy system

#The present invention relates to buoyancy “cans” used to provide uplift force to toptensional risers.

#Vast oil reservoirs have recently been discovered in very deep waters around the world, principally in the Gulf of Mexico, Brazil and West Africa. Water depths for these discoveries range from 1500 to nearly 10,000 ft. Conventional offshore oil production methods using a fixed, truss-type platform are not suitable for these water depths, where these platforms become dynamically active (flexible). Stiffening them to avoid excessive and damaging dynamic responses to wave forces is prohibitively expensive.

#Deep water oil and gas production has thus turned to new technologies based on floating production systems. These systems come in several forms, but all of them rely on buoyancy for support and some form of a mooring system for lateral restraint against the environmental forces of wind, waves and current.

#FIG. 1 shows a side view of an embodiment of the invention.

#FIG. 2 shows a sectional view of an embodiment of the invention.

#FIG. 3 shows a perspective view of an embodiment of the invention.

#Referring now to FIG. 2, according to one aspect of the present inventions, a frame 30 is provided. In some embodiments, frame 30 comprises a stem pipe 31; although, in alternative embodiments, the frame is connected to the riser 18, itself. The particular example shown of frame 30 comprises a support 33 which extends radially and longitudinally from the stem pipe 31. Flange 35 is attached to support 33. Frame 30 comprises the structure around which a buoyancy system, according to an example embodiment, is constructed.

#FIG. 3 shows a perspective view of a frame 30 in which like components are illustrated with like numbers. Horizontal bulkhead 37 and horizontal bulkhead 39 are attached to support 33 and flange 35.

#In various further embodiments of the invention, flange 35 comprises a solid strip of steel, coated with anti-wear material (for example, bronze, ultra-high molecular weight polyethylene, and/or Teflon®). Alternatively, flange 35 includes an integrally formed outer surface of anti-wear material; while, in still another embodiment, the wear material WS (FIG. 2) is welded to the flange. Support 33 comprises metal plate, in various embodiments. In the example seen in FIG. 3, voids are formed in support 33, making it a web for reduction of overall weight of the resulting buoyancy can. The framework formed by the support 33 and flanges 35 forms a stiff backbone structure capable of resisting hydrodynamic and inertial loads that are imposed on the buoyancy system. The transverse bulkheads 37 and 39 stabilize the T-beam members formed by supports 33 and flanges 35, preventing lateral buckling of supports 33. The wear material on the surface of the T-beam endures abrasion loads caused by the relative motions between the buoyancy cans and the vessel. Further, the T-beams transfer the side-loads caused by vessel motion through the T-beam, into the center pipe 31, and throughout the frame structure 30, rather than having the load transferred directly through a wall. Further still, the T-beams react to bending forces caused by lateral side-loads and hydrodynamic forces acting on the structure.