Shims are smart answer to absorb wave motion

Edited by the Engineeringtalk editorial team Jan 25, 2007

The first ever subsea installation of SmartShim was successfully completed last autumn on Shell's Nelson platform.

The first ever subsea installation of SmartShim - the patented cast in-situ chocking system from technical services company Furmanite - was successfully completed last autumn on Shell's Nelson platform, marking a new breakthrough in the application of this award-winning innovative technology.

The SmartShim technology 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 even fracturing.

The PVC-proofed nylon SmartShim slips are filled with a specialist Furmanite-developed polyurethane resin which, crucially, is engineered with sufficient elasticity to absorb the wave energy 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.

Now that the technology has been successfully applied subsea, SmartShim can be applied at lower levels on the caissons, helping to reduce movement topside.

"The effect of the wave loading on the caissons is amplified the higher up the caisson you go, so it's advantageous to be able to install the lower SmartShims as low as possible - and that can now be below sea level", Furmanite technical support engineer Nick Collingbourne explains.

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 SmartShim chocking system.

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

Applying SmartShim subsea has involved further research and analysis to cater for additional criteria such as external water pressure and increased distance over which the resin has to be pumped (from the deck of the diving support vessel).

A specialist resin for subsea application has also been developed.

The first subsea application undertaken on the Nelson platform was at 15 metres below sea level.

"Extensive trials were undertaken in advance of this ground-breaking application to ensure that the correct pressures had been identified (both to enable the resin to travel the distance through the 125 metre high pressure hoses, and to counter the effects of the external water pressure), that a proper fill was achieved, and the conductor would be satisfactorily stabilised", Collingbourne explains.

Onshore installation trials were also undertaken with divers, testing the purpose-designed equipment such as the support frames developed to help keep the SmartShim slips in place subsea while being filled with resin.

These were designed to be in a cartridge to be diver-friendly, and so that with minor modifications they could be made ROV-deployable.

Two Furmanite technicians were present on the diving support vessel during the installation, ensuring correct pumping of the resin and providing direction to the divers.

The installation was successfully completed last autumn, increasing conductor fatigue life, with further SmartShim chocking also to be undertaken at higher levels.

Furmanite international offshore business manager Graham McKay adds: "This is an exciting new development".

"The ability to install SmartShims subsea is a valuable next step forward for this technology, to minimise movement caused by wave loading at as low a level as possible, offering improved benefits to our customers in the oil and gas industry".