Challenging the Water Depth Limitation on a Conventional TLP Tendon Design

摘要

Tension Leg Platforms (TLPs) have been recognized by their favourable response especially in the heave, roll and pitch degrees of freedom and therefore are ideal platforms to support Top Tensioned Risers (TTRs) in harsh environments. TLPs are also the most suitable platforms to support Steel Catenary Risers (SCRs) in relatively shallow water (600 to 1,200 m). They offer large ventilated deck area and can be fully integrated at quayside. However, the industry has always been under the assumption that the TLP feasibility beyond 1,600~1,800 m cannot be established due to the challenges associated with the tendon design in these deep water depths. In this paper, this key assumption is challenged as TLP’s limit is not just a function of water depth, but also a function of displacement (hence payload) and environmental conditions. Several case studies are prepared where TLPs supporting incremental increase in payloads and located at deep and ultra-deep waters in different areas of the world are considered. Topside payloads in the range of 10,000 mt to 60,000 mt are considered. TLPs located in the Gulf of Mexico (GoM) and offshore West of Africa are studied. Designs in water depths from 1,000 to 3,000 m are investigated. Feasibility envelopes as a function of payload, water- depth and location are then established accordingly and presented in this paper. Feasibility of alternative tendon designs to enable the TLP outside of the conventional tendon defined feasibility envelopes is also discussed.