Gel Based Materials for High Insulation and Long Cool Down Time in Deep Water
Authors: Bonnissel Marc , Ozoux Valérie , Couprie Stéphane , Chomard Angèle 
Published: October 2008

Flow assurance requirements, commonly given as arrival temperature, cool down time and warm up / reheating time, are key drivers in the definition of Risers and Flowlines systems. The choice of the insulation material is of major importance in overall design and operation philosophy. After successful execution of Girassol deepwater project, SAIPEM has developed with its partners, and a strong operators involvement, non compressible insulation material that have been qualified for water depth down to 3000 m.

The "Gel insulation material" and "ILS insulation material" have been studied and tested since 1998. Qualification program was completed at the end of 2002. Gels are low cost insulation that facilitate onshore integration and increases local content.

Introduction

One of the most critical problem for deep water field developments is flow assurance, for both steady state production and transient conditions (shutdown / restart).

The first deep sea flowlines characteristic is their need to be efficiently thermally insulated, in order to avoid solid deposits on the pipe wall. Actually deep offshore fields which exploitation is forecast to be profitable are often spread on very large areas, that implies long flowline layout on the sea bottom into low sea water temperature. The main parameter of the steady state production is the Overall Heat Transfer Coefficient (OHTC) or U value.

The cool down time to reach the hydrate formation temperature in shutdown condition is a major requirement of deep sea flowlines; it must be long enough to allow the completion of flowlines crude oil displacement or to start dedicated heating feature. The cool down time of an insulated pipeline is linked to the U value but also to the thermal inertia of the pipeline and its insulation. Generally speaking, the thermal inertia is related to the density and heat capacity of the material (high value leads to high thermal inertia). An elegant solution for increasing the thermal inertia is to use a Phase change material (PCM) which adds to the mass thermal inertia, the latent heat of crystallisation.

In the first part of this article, gel insulating material and phase change material are described in terms of properties, qualification and applications. In the second part, the benefits of use of these materials providing very long cool down time are discussed in terms of future subsea developments like satellite fields.

Gel material

The driving idea of the gel based insulating materials is that a liquid, with a low thermal conductivity, is a perfect pressure resistant insulation material, with a gelling process allowing to prevent any potential convection.

In the following paper we will name Gel the gel without phase change and ILS the gel with phase change ability. The plural Gels is used to describe properties or applications for both (with an without phase change).

Gel insulating material

Gel development has followed the objective of first selecting the best solvent (hydrocarbon based), with low cost and good thermal properties and second finding the right association with a very robust network in order to reach a safe, permanent and stable insulation material. In addition to its in-place stability and performances, developments were focussed on allowing a simple and robust manufacturing process, dedicated to onshore integration in fabrication yard.