Abstract

The present paper describes the extension of well proven TLP technology to applications in ultra deep waters. It is concluded that the careful optimisation of the TLP hull and topside as well as the use of composite risers and tethers lead to economical and technically feasible TLP solutions at water depths as large as 3000 m.

The paper addresses the following subjects:

  • TLP technology and hydrodynamic optimization

  • Composite risers and tethers impact on overall TLP design

  • Composite riser and tether design and fabrication

  • Status on the composite tether and riser development program which is ongoing through the Conoco/Kvaerner Composite AllianceM

  • Installation of composite tethers

  • A case study including cost estimates

Introduction

The TLP concept has proven to be suitable in both harsh and benign climate conditions during the last two decades. TLPs have been chosen at water depths down to approximately 1300 m. However, for water depths larger than this, the weight of conventional tether and riser systems becomes large and begins to dominate the entire global configuration of the TLP. This may result in a solution which is not feasible either from an economical or a technical point of view.

Alternative floating dry completion units have recently been introduced for large water depths. In particular the Spar buoy concept has been successful in the Gulf of Mexico. The alternative solutions are, however, technically challenging, typically involving large relative motion between the dry wellheads and the floater as well as significant offshore work prior to installation.

In 1995, Kvaerner and Conoco established a Composite Alliance with the aim of exploring the business potential of composite solutions in the offshore and shipbuilding industries. It was concluded in a holistic study that the largest potential lies in the development of composite risers and tethers. As a result, two large development programmes were initiated, namely the CompRiser programme initiated in 1996, and the CompTether programme initiated in 1998. The main objective of the two programmes is to qualify the technology by prototype testing and offshore demonstration.

The application of composite tethers and risers go a long way in resolving the main concerns of employing TLPs for deep water applications. This fact, together with the excellent track record of the TLP and the prospects for new deep water field developments, led to the initiation of a development project within Kvaerner Oil & Gas (KOGAS) in 1999. The main objective was to improve the economy of TLP solutions and to extend the water depth range for economical and technically feasible TLP solutions down to 3000 m both for harsh and benign environments.

This goal was achieved by bringing in new ideas for the overall configuration, construction and installation of the TLP, and by using composite materials for the fabrication of tethers and risers. The present paper summarises the main conclusions from this development project and the composite development projects.

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