Abstract: A tower structure for offshore oil and gas fields is formed from various vertically spaced and interconnected tower sections. At least one of the tower sections is rotated about a vertical axis relative to another section so as to define a twisted portion. The number and orientation of the tower sections are varied depending on the particular environment and, particularly the water depth where the tower structure is located.

Abstract: A tension leg platform for supporting an oil rig above a seabed includes a deck, a buoyant hull and a single tubular tether. The tether has a lower end penetrating into the seabed and an upper end that is secured to the hull to hold the hull down against its own buoyancy. The deck is secured to the hull and adapted to support an oil rig. Multiple casing strings extend through the tether from the deck to the seabed. Supplemental buoyancy, tanks can be provided between the hull and the tether or within the tether itself.

Abstract: The invention provides an improved structure for standing offshore, particularly in arctic environments, and a method for installing this structure. The structure comprises a shield portion which rests on a seabed and primarily resists environmental loads, such as from ice, and a separate support portion which comprises a plurality of piles driven into the seabed to support a deck payload. The method for installing the structure comprises moving a shield portion of the structure to its intended location with piles pre-installed therein, setting the structure on the seabed, driving the piles into the seabed, and then severing any connection between the piles and the shield portion.

Abstract: An offshore base-supported column structure for installation in the water on an offshore floor having an elongate column vertically supported entirely from a column foundation on the offshore floor and releasably engaged to the foundation with the top of the column extending above the offshore water level. A column support base is supported from the offshore floor and engages and provides lateral support for the column with a slidable connection. A support structure is connected to the top of the column above the water level.