Installation and connection of long riser to offshore seabed pipeline, connects riser to surface installation and guides lower end, controlling tension

摘要

A first end (26) is connected to a surface offshore installation (14). A subsea section (22) is hung in a catenary between the surface installation and the sea bed installation (16). The other end (28) is guided towards the sea bed installation. This extends the subsea pipeline, creating retractive tension on the second end. The second end is caused to approach the seabed installation, slackening as necessary to permit positioning and suspension, whilst transferring the tension to the seabed installation and making the connection. The sea bed installation is the free end of a seabed pipeline. The second end of the riser has a mobile connector (32) and the subsea installation has a second connector (36). These are engaged before slackening the second end in suspension. The second end is surface-guided, using a cable joining it to a surface ship. The ship extends the subsea riser (22), whilst orientating its lower section parallel to the seabed pipeline, taking it to a point opposite the seabed installation. The second end and seabed installation are held suspended together, once they are connected. An independent claim is included for the corresponding equipment.