L51598 Tow Methods Design Guide for the Installation of Offshore Pipelines

In an effort to progress the development of hydrocarbon fields found in water depths beyond 1000 feet, the oil and gas industry is considering cost effective methods of subsea pipeline installation. As an established and reliable oil and gas transportation system, the pipeline will be an important factor in deepwater development. Surface installation methods are expected to become costly in deepwater due to the necessary equipment modifications and vessel requirements which are synonymous with increased tension capability and deepwater station keeping ability. This estimated increase in installation costs has spurred interests in alternative pipeline installation methods that possess the potential for economic competitiveness. Limiting parameters for single as well as bundled pipeline configurations are evaluated for surface, near-surface, mid-depth, off-bottom and bottom tow methods of pipeline installation. The evaluation shows that the viable towing methods for construction of offshore pipelines include the mid-depth and bottom tow methods. Buckle collapse criteria should be utilized in the design of deepwater pipelines to achieve low submerged weights with minimum buoyancy requirements. Low submerged weight provides the maximum pipe tow string length, reducing the number of mid-line connections. A cost estimating program in LOTUS 1-2-3 format is included with this study. The costing program generates cost for each tow method based on user specified pipeline parameters. The cost program also includes J-lay estimating capabilities for single pipelines.