Offshore platform construction and installation rely heavily on techniques developed for civil engineering.
Construction of a second bridge across U.K.'s River Sevem estuary by Laing GTM shows technology transfer the other way.
A fleet of small jack up rigs is installing 36 caissons on which the bridge will rest. Crane rigs place hollow steel-reinforced concrete caissons on the riverbed. Then rigs that are little more than concrete mixers on stilts fill the caissons.
Rig moves are carried out by Sar 111, a specially designed tug barge. It can operate in very shallow water to maximize daily operating limits imposed by the river's 14 m tidal range.
Martin Valender, master of the Sar 111, has experience in North Sea drilling rr moves. He believes characteristics of the barge could be applied to coastal pipelaying and other oil and gas projects.
MICRO PIGS
"When I first saw the rigs they wanted me to move, I just laughed," said Valender. "You can't call those jack ups, I said."
Sar Ill's hull is much smaller than North Sea pipelay barges on which Valender worked. Sar III, 100 m long, by 33 m wide, is designed to carry 2,500 metric tons of equipment on its flat deck, besides moving rigs.
The vessel's draft is 1.5 m unladen and 2.:-; m fully loaded. It has four 2,000 hp engines, which are retractable so the barge can navigate shallow channels at the beginning and end of its twice daily tidal working windows.
The bare locks onto the rigs very quickly by means of two specially designed mating devices. Securing the rig to the barge, raising the rig's legs enough to maneuver, then moving the rigs often takes less than 1 hr.
"We use lots of unusual bits and pieces of equipment here," Valender said. "These were designed partly from experience in offshore operations and partly by cobbling together things specifically for this job.
FRANTIC PACE
The twice daily working tidal window means the work has a parallel with the North Sea's annual weather window, but the pace is comparatively frantic.
"In all the years I worked in the North Sea and Egypt," Valender said, "I was involved in 40 or 50 rig moves. This year alone we're approaching 200 tightly coordinated moves.
" Typically we carry out 15-20 rig moves a month. Moving rigs takes up about half of our working time. The rest of the time we fetch and carry all sorts of equipment and supplies to the rigs, as well as delivering the bridge's caissons."
Valender said when the barge was built 2 Years ago the plan was to scrap it once the bridge was complete in 1996. Now it appears likely the barge will be used on other bridges.
Such has been the success of the barge that Valender is helping CMC Ltd., Aberdeen, promote the concept for purpose built vessels. The companies are starting to look for oil industry projects in shallow water. Most promising regions are seen as Southeast Asia and the former Soviet Union.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
