A semi-submersible, multicolumn, deep draft, floating offshore oil and gas drilling
and production platform comprises a floating hull having an adjustably buoyant
base, a plurality of columns vertically upstanding from the base, and an equipment
deck that is supported atop the columns when the platform is operationally deployed.
Each of the columns comprises a cellular structure that includes a plurality of
elongated tubes having a variety of cross-sectional shapes extending from the base
to the top of the column. Each of the tubes defines one or more closed compartments.
At least one of the compartments has a buoyancy that is fixed, and at least another
one of the compartments has a buoyancy that is adjustable. The buoyancy of the
compartments and the base can be controllably adjusted with pressurized air to
provide a safer and less costly method for deploying the platform for offshore operations.