Abstract: A riser tensioning system with an individual riser unit on an oil or gas platform. The platform has a traveling trolley structure with at least one trolley bearing and a centralizer. The trolley bearing is coupled to at least one guide rail configured to allow vertical movement of said traveling trolley structure. The traveling trolley structure is coupled to a riser collar configured to support a top of the riser. The riser tensioning system has at least one cylinder coupled to the traveling trolley structure on one end and secured on an opposite end such that the cylinder is adapted to push or pull the traveling trolley structure vertically.

Abstract: In a substructure (10) for a floating oil or gas production platform, an arrangement to tension a plurality of risers (16) extending from the sea bed up to the substructure, the arrangement comprising: a conventional hydraulic tensioner/heave compensator (17) for each riser, in which there is a soft spring formed by a piston cylinder combination acting against an accumulator, the heave compensators for the risers being disposed to compensate for vertical oscillations of relatively short period (e.g.

Abstract: A surface vessel is anchored almost geostationarily by a turret rotatable relative to the vessel about a vertical axis and having mooring cables extending to the seabed. A well is drilled from a drilling section in the vessel at a distance from the axis of rotation of the turret. The drilling is performed using a drill string through a riser extending from the seabed to the drilling section, which riser can be broken and shut off between the seabed and the vessel. By manipulating (hauling in and slackening) the mooring cables, the vessel is held in position so that the derrick is kept almost geostationary relative to the well during drilling operations. The system includes a surface vessel, a turret rotatable relative to the vessel about a vertical axis and which can be anchored to the seabed by a plurality of mooring cables, and a riser extending from the seabed to the vessel through which the well can be drilled with a drill string from a derrick in a drilling section on board the vessel.