|
BP spending three-quarters of a million dollars a day at Northstar Offshore pipeline trenching under way; gravel at island construction above level of ice; onshore portion of pipeline in place Kristen Nelson PNA News Editor
BP Exploration (Alaska) Inc. and its contractors are well into this winter’s work at Northstar, a project estimated to be costing about three-quarters of a million dollars a day. By the end of the second week in March, enough gravel had been hauled out over the sea ice road to bring the island site above sea level — in this case, frozen sea, which first had to be cut out and hauled away from the site to an ice dump north of the island. Some of the pilings had also been set for the dock on the southern side of the island.
There is no margin for error when wind chill brings the temperature down to the equivalent of -75 degrees F, BP Exploration Northstar project manager Dirk Smit said March 10 at the island construction site. That was why, said Peter Gadd, an engineering consultant on the project, that pile driving for the dock was on temporary hold.
“They started the dock structure … but had to suspend their operations of construction here for the last several days because of the high wind. Their (metal) sheets are about 40 to 60 feet long and in the wind they started sailing around and it was very dangerous to try and construct.”
Gravel hauling, pipeline welding and pipeline trenching were proceeding.
North Slope work BP officials said at a North Slope briefing that production from Northstar is scheduled to begin in late 2001 at 65,000 barrels a day. Expected field life is 15 years, although Greg Mattson, BP Exploration (Alaska) business unit leader for new developments, said that possibilities exist in the area for satellite development which could extend the life of the project. BP Exploration (Alaska) is 98 percent owner at Northstar; Murphy Oil Co. owns the other 2 percent.
Project manager Smit said some 250 pieces of equipment and 500 workers were hauling gravel, building the island and trenching and laying the offshore pipeline, with construction expected to peak within the month at around 700 workers on the North Slope. Work is also proceeding in both Anchorage and Fairbanks, with a sealift scheduled out of Anchorage this summer for the first modules. Drilling will start next winter with an injection well the first to be drilled.
Gravel construction At a gravel pit onshore south of the project 12 B70s were hauling gravel — about 50 yards a load — from a mine in the Kuparuk River. A total of 700,000 cubic yards will be placed at the island. The gravel pit will be reclaimed by the river in the spring, and will provide an over wintering location for fish. A crew was placing explosives to contour the sides of the pit into benches for fish habitat.
Blasting for gravel removal was complete and gravel was being loaded into both sides of the B70s which took the gravel out on the sea ice road to a dump where the ice was still bottom-fast. There it was loaded onto smaller trucks in 25-30 yard loads for the trip out over floating ice to Northstar island.
The $5-$5.5 million ice road system is complete and is just being maintained, said Gadd, with seawater pumped onto the surface of the sea ice roads and crews daily blowing out and filling with freshwater the cracks caused by tidal effects and the expansion-contraction of the ice sheet.
A second contingency ice road parallels the road used for gravel haul, Gadd said, because the road is subject to a lot of wear and tear with the heavy trucks.
As gravel continued to be delivered, the island would be built up, Gadd said, to about 20 feet above sea level to allow for compacting once the weather warmed. Pile driving, including the dock and the metal perimeter wall, was believed to be the largest pile-driving project ever done in Alaska, Gadd said. Cement shore protection will be fastened to the metal perimeter wall to protect the island from erosion. Inside the sheet metal wall, the working surface area of the island will be about 5 acres, he said, although the total area above the water is closer to 10 acres.
Offshore pipeline trenching Along the offshore pipeline route, ditch witches cut slots in the ice like huge chain saws, said Intec pipeline engineer Peter Bryce. Trenching was started in deeper water because it takes longer there, he said, and in an estimated three to four weeks trenching from shore will meet up with deeper water work.
A pair of long-reach backhoes were working not far from Northstar island on March 10, the first removing blocks of ice from the trench and the second trenching the sea floor. There are eight of these backhoes in the world, four working at Northstar and one on standby in case one of the four fails. They rest on pontoons — about the height of a man — to spread the weight over the ice. As long as there’s seawater, Bryce said, the trench can’t completely refreeze and a skin of 12 to 18 inches is easy to remove. Ice removed from the trench — and from the surface at the island — was being hauled to an ice dump area out beyond the island to keep the weight off the working surface.
Along the pipeline construction route, 200 feet wide and with the ice thickened to eight feet, the mechanical pipeline contractor occupies the east side of the trench and the civil contractor who’s doing the digging occupies the west side. The separation, Bryce said, makes for a more efficient and a much safer construction site.
Pipeline being welded Closer to shore was the “firing line”: a line of shacks which are moved down the pipeline by cranes as welding proceeds on the pipeline.
The pipe is unloaded onto skids to keep it a couple of feet off the ground so the welders can weld all the way around. Then a crew makes sure the ends of the pipe are clean. At the firing line, the pipes are brought together, the joint is preheated to weld temperature and in the “bead shack” the first two passes of weld are made. As welders finish, shacks are moved down the line to unwelded sections. A second group of welders does a third pass.
The process, Bryce said, “is one of putting molten metal into the gap between the two pipes so that the whole thing becomes fused together and the weld metal and the pipe metal all become one.”
Behind the welders come the weld testers. The first test is an X-ray through the steel which puts a picture on film that’s wrapped around the other side of the weld. The second test is an automatic ultrasonic testing device which sends sounds waves into the metal which bounce back and “depending on the pattern that they make when the sound waves bounce back we can tell if there are any ... flows in the weld.”
Flawed welds are not fixed — they are cut out and the welding process begins again from scratch.
Onshore pipeline on VSMs The onshore portion of the pipeline is already in place on vertical support members. The design here is different than older pipelines, Bryce said, because the North Slope Borough specified there had to be five feet of clearance under the onshore pipeline — nothing could hang under the pipeline into the five-foot clearance.
On older pipelines vibration dampeners — which prevent pipeline motion during high wind conditions — are hung under the pipeline. On the Northstar line, and also on Badami, vibration dampeners are mounted on top of the pipeline rather than hanging below.
Alaska-based contractors working on Northstar include: Alaska International Construction for island construction and pipeline trenching; Alaska Petroleum Contractors for structural steel fabrication, pipe spool fabrication, pipe rack erection, pipeline tie-in skid fabrication, steel/pipe movement; Houston Contracting Co. for pipeline construction; VECO Construction for module fabrication, North Slope installation, pipe and construction bulks procurement; and VECO Engineering for infrastructure design, pipeline tie-in skid design, construction support; major equipment procurement.
| 