Methods of laying subsea pipeline (1300) on a seafloor comprising: providing a pipe laying vessel (1100), placing a spooling structure assembly (1200) on the seafloor, and laying the subsea pipeline (1300) in a loop around the spooling structure assembly and associated systems.

A wax control element for subsea processing of well fluids in a wellstream comprises a bundle of flowlines within an elongate tensile structure. That structure defines inlet and outlet ends and has cooling and heating provisions that act on the flowlines, in use, to promote deposition of wax in the flowlines and subsequent entrainment of wax in the wellstream.

A method of converting a subsea laying system of a surface vessel from a laying mode to an abandonment or recovery mode includes clamping at least one tubular sleeve in at least one clamp of the laying system. A winch wire can then run longitudinally through the or each clamped sleeve when suspending an elongate subsea element such as a pipe string during abandonment or recovery operations. The sleeve protects gripping pads of the clamp from damage due to clashing with the wire and so makes it unnecessary to remove the pads in preparation for abandonment or recovery

A subsea pipeline coated with a thermally insulating coating has a radially outer surface shaped to define external hold-back formations. In a J-lay operation, the weight load of a pipeline catenary is held back using a complementary bushing or clamp of an installation vessel engaged with the hold-back formations. The weight load is transferred from the catenary to the bushing or clamp by shear forces acting through the coating. The coating extends continuously along the pipe and is interposed between the hold-back formations and the underlying pipe. The hold-back formations may be integral with the coating.

A subsea pipeline coated with a thermally insulating coating has a radially outer surface shaped to define external hold-back formations. In a J-lay operation, the weight load of a pipeline catenary is held back using a complementary bushing or clamp of an installation vessel engaged with the hold-back formations. The weight load is transferred from the catenary to the bushing or clamp by shear forces acting through the coating. The coating extends continuously along the pipe and is interposed between the hold-back formations and the underlying pipe. The hold-back formations may be integral with the coating.

Systems, methods, and apparatuses for adjusting and repositioning a coiled tubing tensioning device while deployed. The system comprises a tubing guide for receiving a coiled tubing, a tensioning device for maintaining the coiled tubing in tension, and a tower frame having a moveable platform supporting the weight of the tensioning device. The moveable platform is adjustable vertically to raise and lower the tensioning device with respect to the tower frame, and the tower frame permits the tensioning device to move horizontally with respect to a fixed ground point.

Systems, methods, and apparatuses for adjusting and repositioning a coiled tubing tensioning device while deployed. The system comprises a tubing guide for receiving a coiled tubing, a tensioning device for maintaining the coiled tubing in tension, and a tower frame having a moveable platform supporting the weight of the tensioning device. The moveable platform is adjustable vertically to raise and lower the tensioning device with respect to the tower frame, and the tower frame permits the tensioning device to move horizontally with respect to a fixed ground point.

A method includes calculating a frequency and a phase of a vibration of a floating vessel, generating a control signal based on the vibration frequency and the vibration phase, operating a motion compensation system of the floating vessel during an i.sup.th control cycle using the control signal to mitigate the vibration of the floating vessel, calculating a first vibration amplitude based on the control signal, updating one or more parameters including a magnitude of the control signal, a decay rate of the vibration, the vibration phase, and the vibration frequency using the first vibration amplitude, updating the control signal based on the one or more updated parameters, and operating the motion compensation system based on the updated control signal during an (i+1).sup.th control cycle.

An improved system and method for laying on the seabed a pipeline and/or installing a subsea riser including one or more accessories are disclosed. In the system, a trolley rail for an auxiliary trolley is provided which includes a retractable trolley rail part supported by the tower via an associated mobile rail support assembly. Displacement of the retractable trolley rail part together with the auxiliary trolley when arranged on said retractable trolley rail part with respect to the tower is allowed, between an active position, wherein the auxiliary trolley is positioned to engage on an accessory in the firing line, and a retracted and non-operable position wherein a clear envelope about the firing line is created.

An improved system and method for laying on the seabed a pipeline and/or installing a subsea riser including one or more accessories are disclosed. In the system, a trolley rail for an auxiliary trolley is provided which includes a retractable trolley rail part supported by the tower via an associated mobile rail support assembly. Displacement of the retractable trolley rail part together with the auxiliary trolley when arranged on said retractable trolley rail part with respect to the tower is allowed, between an active position, wherein the auxiliary trolley is positioned to engage on an accessory in the firing line, and a retracted and non-operable position wherein a clear envelope about the firing line is created.