ABSTRACT

A new compliant pile concept for use in the design of guyed and unguyed towers is described. Tower design concepts are described for application in severe environments to support very heavy topsides. Kodel test results for a 3501 tower, with and without guylines, are presented. Comparisons with other deepwater structures are included.

INTRODUCTION

The continuing development of oil and gas fields in deeper Maters his leant that engineers have had to search for lore efficient and cost effective ways of supporting the facilities required. The compliant tower concept offers one possible avenue to achieve this goal. Recent development of a new compliant pile has enabled the compliant tower concept to be designed to carry heavy payloads in severe environment It is now possible, for example, to design compliant, bottom founded guyed tower platforms for the North Sea which can support in excess of 35,000 tonnes without the need for additional buoyancy. In addition, compliant towers without guylines have been designed, using the compliant pile, to accommodate medium payloads in less severe environment such as the Gulf of Mexico (GOM).

DEFINITION OF COMPLIANT TOWER PLATFORM IN THE CONTEXT OF THIS PAPER

There are many types of compliant platform. This paper is concerned primary with the application of a new compliant pile design to piled compliant towers which are either guyed or unguyed. The unguyed version is often referred to as the 'Compliant Piled Tower' (CPT) and the guyed version as simply the 'Guyed Tower',

In order to perform, satisfactorily, these types of compliant platform should have surge periods in excess of about 30 seconds 50 that the cyclic effects of wave load are considerably reduced. In addition, they must have enough overturning capacity to resist the other loads present such as current, wind and self weight offset from the centre line (P-delta effect, Compliant towers resist these loads by several means:

  • moment resisting foundations

  • buoyancy {both self and additional

  • guylines

The CPT lay have either the first, or the first two leans of resistance, whereas the guyed tower lay have all three, only two or even just the third means

THE NEW COMPLIANT PILE

All piles lily be claimed to have sale compliance. The first production guyed tower, LENA (ref. II has piles clustered around the vertical axis of the tower, These extend in guides to the top of the tower where they are attached and welded off. Hence, the tower is able to sway through a relatively large angle without axial overstressing the piles because they extend (or compress) only very skill amount. The overturning 10lent of resistance due to the piles is low because of the small moment are; the tower relies for overturning resistance on the guylines and to a lesser extent on the moment of resistance provided by the in-built additional buoyancy tanks.

This content is only available via PDF.
You can access this article if you purchase or spend a download.