Methods of laying seabed pipelines

Abstract

The disclosure relates to a method of laying a seabed pipeline from a surface vessel (10, 11) in which the vertically oriented lengths of pipe are assembled to form pipe strings suspended vertically from the vessel extending towards the seabed. An end (30) of a previously laid length of pipeline(29) is supported above the seabed by a tether (28) extending to the surface vessel to locate an upwardly facing end of the pipeline at a predetermined level below the vessel corresponding generally to the length of the pre-assembled pipe strings. A further pipe string (31) is then maneuvered from the vessel until the lower end of the string is aligned with the end of the pipeline, after which the pipe string is lowered to engage its lower end with the upwardly facing end of the pipeline. The pipe string is connected to the pipeline to form a further part of the pipeline, and the tether from said end of the pipeline is then released and re-attached to the upper end of the newly attached length of pipeline to support the pipeline suspended from the vessel. The vessel is then moved in the direction in which the pipeline is to be laid and at the same time the newly attached pipe string is lowered by paying out the tether from the vessel to lay the pipeline on the seabed until the upper end of the pipeline reaches said predetermined level. The vessel is then stopped with the upper end of the pipeline supported by the tether above the seabed and facing upwardly ready to receive the next pipe string.