Shortage of deck space no barrier to deepwater pile installation.
The driven-pile anchors for Murphy Oil’s Kikeh spar, stationed 120km off the coast of eastern Malaysia, were installed by Technip using an underwater hammer provided by Acteon company MENCK. Technip’s choice of equipment was actually straightforward, as MENCK is currently the only company supplying hammer systems capable of being used routinely at depths like those found in the Kikeh field – in excess of 1300m.
As far as the pile installation is concerned, depth was not actually the biggest issue on Kikeh – the current depth record for driven pile installation is held by Kerr McGee’s Constitution spar at 1564m. What made this project different was that, for the first time, the whole operation was performed from a relatively simple, DP Class 2 monohull vessel, the Rockwater II, rather than from a more normal Class 3 semisubmersible crane barge or similar large – and expensive – vessel.
The main challenge was shortage of space. The deck area of, for example, Saipem’s S7000 is around 9000m² , while the deck on the Rockwater II is 1150m². In fact, the MENCK team succeeded in getting the hammer and its underwater power pack, plus all the supporting equipment, into an area no greater than 400m².
The available lifting equipment on the boat was a 150t crane with a 13m radius of operation and 475m of wire. This was perfectly adequate for handling the MHU 500T hammer, which weighs 107t in air and has specially designed trunnions to make upending the unit very easy. To overcome the shortage of wire on the crane, the hammer was lowered to working depth using extension pennants and subsequently kept there for the 10 days required to complete the project.
Using the MENCK hammer, the ten 84in diameter mooring piles for the spar and four piles for a tender-assisted drilling unit were installed, in four clusters roughly 3km apart, in a total net driving time of just over 21h.
The project, which was free of any safety or environmental incidents, proved the MENCK hammer could be deployed from a less costly vessel with generally better availability than the large crane barges commonly used for this kind of work.