PSL Energy Services is carrying out excavation work for Norsk Hydro’s Ormen Lange project. The contract, worth some Nkr50 million, was awarded to the company’s Norwegian subsidiary in February, its first major excavation assignment.
One of the foremost challenges faced by the Ormen Lange development is the installation of pipelines from field to shore on an extremely rugged and irregular seabed, particularly in the area of the prehistoric Storegga slide where the seafloor shelves sharply from a water depth of about 250 m to 1,000 m over a distance of 20 km. PSL will literally smooth the path for the two 30-in. export pipelines, MEG lines, and umbilicals by blasting 5-m wide corridors through protruding features.
PSL is using its patented Jet Prop system to excavate pipeline routes for the Ormen Lange project.
The company’s scope of work calls for a total of some 10,000 cu m of seabed soil to be removed from 121 different locations, according to general manager Ole Grimsmo. Mobilization for the first phase, at near-shore locations, took place in early March. The bulk of the work will be performed in a second phase starting in early May.
PSL is using its patented Jet Prop system, combined with a clay cutter manifold, to fragment the seabed soils and disperse them beyond the edge of the planned corridor. The excavation set-up consists of a manifold delivering water to a number of nozzles positioned against the seabed. The material is blasted free of the seabed and dispersed by the Jet Prop fan arrangement.
Operations will be performed from Island Offshore’s newbuild subsea intervention vesselIsland Frontier, making use of its integrated module handling tower, DP3 dynamic positioning capability, and active heave compensation system.
High-pressure pumping
The seabed equipment will be deployed on 6 5/8-in. drill pipe hung from the tower. A comprehensive pumping spread installed on the deck will suck in seawater through a standpipe and pump it down the drill pipe at a rate of 50 bbl/min and pressure of 3,000 psi, Grimsmo says. Ten thousand horsepower motors power the pumping system.
PSL will also equip the vessel with a full survey capability to enable the corridors to be surveyed and the results recorded on 3D seabed charts, which will be accurate to within a few centimeters.
