Two Tier Well Riser Top Tensioning System

Abstract

The paper presents the results from a feasibility study carried out by Kvaerner for a top tensioned riser system adapted for its deep-water Deep Draft Floater production unit, which often is referred to as a multileg SPAR. The study addressed allimportant aspects of a multi-riser system (array), including effective drilling/ work-over arrangements for a GOM deepwater application. The presented paper demonstrates the proposed two tier well and work-over riser top tensioning system has several attractive features and advances the capabilities of the mechanically tensioned systems considerably. Hydralift USA has been the co-operating partner on the hardware side. The introductory part of the paper addresses the present art systems (as used in the SPARs) as opposed to the principles of the proposed "two-tier well riser tensioning system". The nature of riser strokes is discussed on a general level along with a proposed approach to develop the basis for functional requirements for the two-tier system, being a mechanical top tensioning system. Two case studies, based on 1500 and 5000 feet water depth respectively, are used to illustrate the stroke demand. The paper puts the main emphasis on the justification of the new philosophy of splitting the tensioning system duties into two parts, based on certain observations made in the frequency domain. In short the split duty philosophy involves separation of the low frequency and steady stroke motions from the wave induced stroke frequency (high frequency). It is believed that this philosophy is a step forward for the mechanically tensioned systems. The configuration of the proposed system has inspired the use of the term "two tier tensioning system", as the proposed system is analogue to hydraulic cylinders working in series. It is concluded that the proposed system can be designed and developed from present state of the art mechanical tensioning equipment components. The two-tier system is especially attractive when used in conjunction with dry tree solutions.

Floating Offshore Platform Design

“…Figures 7.11 and 7.12 show two Figure 7.11 Hydraulic tensioner system for dry tree semi (from Wanvik and Koos, 2000) Figure 7.12 Passive spring riser tensioner for Prince TLP (from Koon, et al 2002) methods used to transmit riser tension to a floater. Figures 7.11 and 7.12 show two Figure 7.11 Hydraulic tensioner system for dry tree semi (from Wanvik and Koos, 2000) Figure 7.12 Passive spring riser tensioner for Prince TLP (from Koon, et al 2002) methods used to transmit riser tension to a floater.…”

A Project Oriented and Technology Robust Dry Tree Semi Concept

“…However, this also impacts or may even jeopardize the topside and hull integration method. Some other design approaches, for example, discussed in References [6] and [7], were also pursued for development of a dry tree semi-submersible. Changing the hull shape may have some effect on the platform vertical motion, but at the same time it may introduce additional complexity and cost of the of hull structures for both in the construction phase and the lifelong maintenance of the unit.…”