Buoyancy module with pressure gradient walls

A buoyancy module configured to be coupled to a deep water riser, comprising:

• a) an elongate vessel having a vessel wall formed of a composite material, and upper and lower ends, and configured to be attached to the riser, vertically oriented, and submerged under a surface of water such that the upper end is disposed at a lower water pressure, and the lower end at a higher water pressure;
• and
• b) the vessel wall having a thickness that varies from a thinner wall thickness at the lower end to a thicker wall thickness at the upper end;
• and
• c) the vessel being configured to be internally pressurized with air such that an internal air pressure of the vessel substantially equals the higher water pressure at the lower end of the vessel resulting in a lower pressure differential at the lower end with the thinner wall thickness and a higher pressure differential at the top end with the thicker wall thickness.

A modular buoyancy system configured to be coupled to a deep water riser, comprising:

• an upper elongate vessel, configured to be submerged beneath a surface of water, vertically oriented, and coupled to the riser, and having an upper wall with a thickness, and upper and lower ends;
• a lower elongate vessel, configured to be submerged beneath a surface of water and vertically oriented, and having an upper end directly attached to the lower end of the first elongate vessel, and further having a lower wall with a thickness thinner than the thickness of the upper wall;
• and
• the vessels being configured to be internally pressurized with air such that an internal air pressure of the vessels substantially equals the higher water pressure at the lower end of the lower vessel resulting in a lower pressure differential at the lower end with the thinner wall thickness and a higher pressure differential at the top end with the thicker wall thickness.