A New Concept of TLP With Gravity-Type Template
Authors: Kobayashi H. , lida Y. , Mori N. , Kawanishi T. , Hirakawa S. 
Published: October 2008

A new concept of TLP (Tension Leg Platform) with gravity-type template which allows slide to ultimate earthquake load is verified to be reasonable and practical by means of analyses and laboratory experiments.

The TLP is applicable for the water depth equal to or more than 500m and the seabed, fairly flat with certain bearing capacity. Installation work of the TLP is planned to be performed without divers so that the platform has small cost sensitivity vs. water depth.

INTRODUCTION

Deep sea is one of new frontiers for oil production. Traditional jacket type platform is no more a special type of structure for deep sea. Various types of production systems have been proposed requesting R&D of marine structures applicable with reduction of increasing cost of platform in deep-water oil fields.

TLP has been applied practically at Hutton Field in North Sea in 1984 and at Green Canyon in the Gulf of Mexico in 1989 2. TLP is considered to be a promising structure to conquer the new frontier of deep sea.

Japan Ocean Industries Association has organized a committee for R&D of a new concept of TLP which can be installed in the oil field of earthquake districts. The committee has worked on the discussion of a new concept of TLP which is economical and safe for deep sea in earthquake districts and performed R&D of techniques sustaining the concept.

This paper deals with the outline of the TLP explaining design, construction method, activity of R&D conducted for the sustaining techniques and especially, analyses and experiments on a 1I200-scale model for verifying its behavior and force induced by earthquake load simulated in a water tank with shaking table at its floor.

Features of the structure have been developed during the study fulfilling the requirements imposed on the structure and shown in the following.

The layout of the prototype structure is shown in Figure 1, where a steel hull IS moored with four sets of tendons stretched vertically downward to a template of hybrid structure. A deck is placed on top of the hull. CD The TLP has its application to oil production at deep sea with water depth equal to or more than 500m and seabed, fairly flat with certain bearing capacity.

®Range of seabed conditions applicable for the TLP is determined by those corresponding to possible slide of template due to horizontal acceleration exceeding 2m/s2 of design earthquake as the upper limit and those corresponding to possible slide of template due to wave as well as bearing capacity of seabed as the lower limit.

®The slide of the gravity-type template by ultimate earthquake load IS analyzed to be only a few centimeters, which is owing to disconnection of transmission of earthquake load between seabed and template.

®The horizontal movement of the hull is also small enough below the allowance required by operations of oil drilling and production as well as living on board.

Template is made in a single body of shell structure, which facilitates exact installation of tendons and assures stability of the TLP during operation.