Chocking system protects against wave damage

Edited by the Engineeringtalk editorial team Jan 3, 2008

PVC-proofed nylon SmartShim slips are filled with a polyurethane resin, with sufficient elasticity to absorb the wave effects while holding the riser or caisson firmly in place within the guides.

SmartShim technology has been installed in a major subsea installation project on StatoilHydro's Oseberg Sor platform in the North Sea, to protect against conductor damage as part of an underwater repair programme.

The technology from Furmanite is designed to prevent costly damage to conductors or caissons created when the lateral force of wave movement causes them to impact against the conductor guides, resulting in fatigue or fracturing.

The SmartShim chocking system was originally developed following modelling using SESAM (a DNV-developed finite element analysis structural model) to simulate the effects of wave loading on conductors and flowlines, demonstrating how the loading manifests itself as a stress issue with corresponding wellhead displacement.

Analysis identified the beneficial effects of chocking as a solution, showing dramatic reductions in stress, resulting in the development of the Smart Shim chocking system.

By mathematically representing the dampening effect of varying shore hardnesses for the SmartShim resin, the optimum dampening characteristic was obtained.

PVC-proofed nylon SmartShim slips are filled with a polyurethane resin, which is engineered with sufficient elasticity to absorb the wave effects while holding the riser or caisson firmly in place within the guides.

Because they are cast in-situ, the SmartShims will form to fit the gap between conductor and guides precisely, whatever the dimensions.

Applying SmartShim subsea requires additional factors to be considered, including external water pressure and increased distance over which the resin has to be pumped from the deck of the diving vessel.

A specialist resin for subsea applications has been developed, as well as purpose-designed equipment such as support frames to help keep the SmartShim slips in place while being filled with resin.

On the Oseberg Sor platform, StatoilHydro experienced problems on the conductors due to wave induced displacements inside the guides.

The subsea installation of SmartShims will protect the conductors from sustaining any further damage.

27 slots were SmartShimmed, at 15m depth, involving a total of some 4km of hoses, nine tonnes of resin and 30 tonnes of equipment.

This was deployed from the diving support vessel by Acergy to undertake the installation with Furmanite technicians on board the vessel to ensure correct pumping of the resin and providing direction to the divers.

Furmanite International Head of Sales Mike Tucker said: "Subsea SmartShim installation involves some considerable added challenges, but this was successfully achieved and the installation will now extend the conductor fatigue life by minimising the movement caused by wave loading.

The effect of wave loading on the conductors is amplified the higher up you go, so it's advantageous to be able to install as low as possible, as was done here, helping to minimise movement topside.

StatoilHydro's Oseberg field has been producing for two decades and is characterised by safe operation, high regularity and cost-effective operations.

StatoilHydro's objective is a recovery rate of 72%.

The company aims to ensure Oseberg field life beyond 2030.