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Enstar installs longest horizontal directional drilled pipe in Alaska Work done last winter on west side of Cook Inlet to replace portion of 20-inch transmission line in danger of being washed out Kristen Nelson Petroleum News Editor-in-Chief
In 1991, Enstar Natural Gas Co. did the first horizontal directional drilling in Alaska when it replaced a section of its Beluga pipeline under the middle channel of the Susitna River on the west side of Cook Inlet. Enstar, a subsidiary of Semco Energy, is the natural gas transmission company for Southcentral Alaska. Its Beluga line brings gas from the west side of Cook Inlet to Anchorage, primarily from the Beluga gas field but also from the Steelhead platform and smaller fields along the way.
Last winter, Enstar did the longest horizontal directional drill in the state to date when — after the river shifted again — the company relocated the crossing 2,000 feet to the north, with a 4,305-foot horizontal directional drill under the middle channel.
Horizontal directional drilling was also done when ARCO Alaska (now ConocoPhillips Alaska) installed the Alpine pipeline under the Colville River on the North Slope, a distance of 4,279 feet, and more recently as part of the Kenai Kachemak Pipeline installation on the Kenai Peninsula. It requires a special drilling rig that sits at an angle to the ground, allowing it to drill shallow horizontal holes.
John Lau, Enstar’s director of transmission operations, told Petroleum News the company had to wait for a real winter in the Cook Inlet area of Southcentral Alaska. It didn’t get cold enough in the winter of 2002-03 to build the ice road necessary to reach the work site. But, he said, as soon as weather projections for 2003-04 indicated cold weather, pipe was ordered and preparations begun.
That included bringing in 10,000 feet of coated 20-inch pipe and the horizontal directional drilling rig needed for the job. Hole drilled, expanded, pipe pulled through The horizontal directional drilling was done to get the pipe, which carries about two-thirds of the natural gas coming into Anchorage, 60 feet under the middle channel of the Big Su — far enough beneath the bed of the river that it wouldn’t be washed out as the channel changes.
Lau said in the worst case this crossing should last 50 years: “But the best case is, it’ll last forever,” depending on what the river does.
The pictures illustrate part of the procedure: The horizontal directional drill was used to create an initial hole from one side of the channel to the other; then the hole was reamed out to 30 inches so that the 20-inch transmission pipe could be pulled through; the 20-inch pipe was welded together and pulled through; that pipe was then welded to conventionally laid pipe and the whole new section of pipe welded into the existing line. Ice road, ice bridges required The work had to be done in the winter because the site is in the Susitna Flats State Game Refuge, and could only be done when the ground is frozen, Enstar engineer Steve Cooper, the project manager, told Petroleum News.
Cooper said the work started the second week of January with the ice road construction. Fifteen miles of ice road had to be built from the end of the road system off of Knik Goose Bay Road, as well as five ice bridges across the Little Susitna River, Fish Creek, a tributary of Fish Creek and the east and middle channels of the Susitna River.
By the end of January, Cooper said, the ice on the river channels was five feet thick, adequate for the heaviest equipment.
They started stringing pipe at the end of February, beginning of March.
The horizontal directional drilling portion of the project began Feb. 21 and pulling the 20-inch pipe through was completed March 26. Before the 4,300-foot section was pulled it was welded, x-rayed and hydro-tested. Twelve-hour window to connect When the new section of pipe was connected, Enstar had to shut down approximately 40 miles of pipeline between two block valves. And the window to accomplish that work was 12 hours.
“In that 12-hour window,” Cooper said, “the gas supplies from the Beluga field had to be shut down. The pipeline was shut in and blown down between the block valves, we had to do the cutover, pig the line and pressure it back up.” In that 12-hour window, supply for Anchorage came in on Enstar’s two 12-inch lines from the Kenai Peninsula. “It took cooperation between all the producers to get gas swapped over,” he said.
The tie-in was completed on April 4, and equipment was moved out of the site by April 7, just as the weather was warming up and the ice road was melting. Project cost right at $5 million In addition to having to wait for a winter cold enough for ice roads, the $5 million project also faced sea challenges: 54 joints of pipe were washed overboard in the Gulf of Alaska on the way to Whittier and 46 additional joints were damaged, so Enstar had to find about 5,400 feet of replacement pipe and get that coated and barged to Alaska.
Lau said an advantage of the standard pipe Enstar uses is that it was able to replace the lost and damaged pipe in time to meet project schedules.
And as for the weather, Lau said “it never froze up out there winter before last.” This winter, however, there were “some long cold snaps and a warmer week here and there — but it didn’t stop us.”
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