Patent ID: 7500439

Claim:
A method of controlling the buoyancy of a repositionable structure with a buoyant fluid, the buoyant fluid comprising a liquid and a plurality of rigid containers, the rigid containers each having a sealed void containing a gas, the method comprising: (a) injecting the buoyant fluid in a first direction into a first container, wherein the first container is connected to or integral with the repositionable structure to manipulate an overall buoyancy of the repositionable structure; (b) immersing the first container in an immersion fluid, wherein the buoyant fluid has a lower density than the immersion fluid; (c) maintaining the buoyant fluid within the first container as a fluid; (d) removing at least a portion of the buoyant fluid from the first container in a second direction, the second direction opposite the first direction, to decrease the overall buoyancy and therefore lower the repositionable structure when the repositionable structure is at least partially immersed in the immersion fluid; wherein acts (a) and (b) may be performed in either order or simultaneously.