| 摘要 |
<p>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. from 1 second to about 5 minutes) between the risers and a vertically adjustable Xmas tree deck (18); and a vertical position adjustment system (21/22) capable of intermittent operation to adjust the vertical position of the Xmas tree deck (18) relative to the floating substructure (10) to compensate for longer term changes which would otherwise cause the individual riser's tension or stroke position to depart from its target value/range; the Xmas tree deck vertical position adjustment system being normally located in one particular position within its range of movement to compensate for the longer term changes.</p> |
