A method of laying an off-shore pipeline (1) comprises: installing on the seabed (3) a fixed receiving structure (4) having a redirecting device (5), paying-out from a laying vessel (7) a pipeline (1) with the pipeline end termination device (9) vertically towards the seabed (3), extending a damping cable (6) from the pipeline end termination device (9) through the redirecting device (5) to an underwater damping buoy (14), connecting an underwater suspension buoy (15) to the pipeline end termination device (9), inclining the pipeline (1) from a vertical orientation towards the horizontal orientation, using: the suspension buoy (14) to counterbalance at least part of the weight of the pipeline end termination device (9), the damping buoy (14) for damping the pipeline (1).

A method of assembling a pipeline at a seabed location comprises landing a connection tool on the seabed over a free end portion of a first pipeline section already placed on the seabed. The connection tool is locked to the free end portion of the first pipeline section, a lower end of a second pipeline section is connected to the connection tool via an initiation line. While applying tension to the initiation line against reaction force of the connection tool, at least a lower end portion of the second pipeline section is landed on the seabed with the lower end facing a free end of the first pipeline section. The lower end of the second pipeline section is then pulled into mechanical engagement with the free end of the first pipeline section.

A towable pipeline bundle for installation underwater at a subsea oil or gas production site has two or more bundled elongate elements, at least one of which is a flowline for carrying production fluid along the bundle. A rigid buoyancy pipe of polymer-composite material extends along and supports the bundled elongate elements. The buoyancy pipe has an internal buoyancy chamber and at least one port for introducing fluid into the buoyancy chamber. The buoyancy pipe is arranged to have positive buoyancy in seawater when its buoyancy chamber contains a fluid less dense than seawater. In this way, the buoyancy pipe confers substantially neutral buoyancy on a towable unit comprising the bundle. The unit can then be towed in mid-water to the production site and lowered there onto the seabed.

A towable pipeline bundle for installation underwater at a subsea oil or gas production site has two or more bundled elongate elements, at least one of which is a flowline for carrying production fluid along the bundle. A rigid buoyancy pipe of polymer-composite material extends along and supports the bundled elongate elements. The buoyancy pipe has an internal buoyancy chamber and at least one port for introducing fluid into the buoyancy chamber. The buoyancy pipe is arranged to have positive buoyancy in seawater when its buoyancy chamber contains a fluid less dense than seawater. In this way, the buoyancy pipe confers substantially neutral buoyancy on a towable unit comprising the bundle. The unit can then be towed in mid-water to the production site and lowered there onto the seabed.

A towable unit for subsea processing of well fluids comprises a pipeline bundle extending between, and capable of acting in tension between, a first towhead at an upstream end of the bundle and a second towhead at a downstream end of the bundle. At least one of the towheads has an on-board processing facility for processing the well fluids, which facility effects at least separation of water phases that are present in the well fluids.

Disclosed is an underwater laying device for offshore oil and gas pipelines. By using a steel cuboid as the main body, a first mud-ploughing rake, a first mud-ploughing hoe, a second mud-ploughing rake, a second mud-ploughing hoe, and a mud delivery plate are disposed on the lower surface of the cuboid main body. Further, by cooperation of a mud collection hood and an elongated pipeline-delivery cylinder, and according to structural characteristics of traditional farming tools, submarine trenching, pipeline laying, and pipeline burying can be successively performed and all implemented by the device of the present invention. Further disclosed is a pipeline laying method of the device of the present invention. The device of the present invention has a simple structure, and overcomes the structural complexity of the conventional underwater robot on the premise of achieving the function requirements, thus greatly reducing the manufacturing cost and being mass-producible.

Disclosed is an underwater laying device for offshore oil and gas pipelines. By using a steel cuboid as the main body, a first mud-plowing rake, a first mud-plowing hoe, a second mud-plowing rake, a second mud-plowing hoe, and a mud delivery plate are disposed on the lower surface of the cuboid main body. Further, by cooperation of a mud collection hood and an elongated pipeline-delivery cylinder, and according to structural characteristics of traditional farming tools, submarine trenching, pipeline laying, and pipeline burying can be successively performed and all implemented by the device of the present invention. Further disclosed is a pipeline laying method of the device of the present invention. The device of the present invention has a simple structure, and overcomes the structural complexity of the conventional underwater robot on the premise of achieving the function requirements, thus greatly reducing the manufacturing cost and being mass-producible.

The present invention provides a cable planning method based a fast marching method applied with simulated annealing (FMM/SA) algorithm. In the FMM/SA algorithm-based cable planning method, the FMM used to obtain the optimal submarine cable path with the lowest life-cycle cost, and the SA algorithm is used to continuously adjust the weight of each design consideration with the aim to achieve an optimal cable path that is as close as possible to a real-life cable path which has a history of cost-effectiveness and resilience. The set of weights contributed to the optimal cable path is then used as an optimal set of weights of design considerations for cable path planning. The FMM/SA algorithm-based cable planning method can provide a computationally effective approach which has lower computation costs and better performance in generating cable paths with optimal life-cycle cost and reliability.