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Replacement of Drift River pipeline section goes according to plan Cruz Construction had to replace a damaged pipeline section under Drift River before the onset of winter ice in Cook Inlet Alan Bailey PNA Contributing Writer
The recent replacement of a section of the Cook Inlet Pipeline under the Drift River on the west side of Cook Inlet involved some pioneering work in difficult conditions. Cook Inlet Pipeline Co., the regulatory agencies and the drilling contractors all had to operate within a tight timeframe, driven by the need to barge equipment to and from the construction site prior to the arrival of winter ice in the inlet.
The Cook Inlet Pipeline transports crude oil from several oilfields on the west side of the Cook Inlet to the tanker terminal at Drift River.
Built in the 1960s The original pipeline, built in the 1960s, lay only six feet below the riverbed. “In our integrity evaluation of the pipeline system we discovered that the pipeline had moved ... (due to) the icebergs that came down the Drift River from the Mount Redoubt volcano in 1989 or 1990,” Jim Shew, manager of Cook Inlet Pipeline Co., told PNA. “We made a determination that the only resolution was to replace the pipeline section under the river,” he said.
The new pipeline section would lie nearly 60 feet below the riverbed.
The decision this summer to replace the Drift River pipeline section left relatively little time to plan and organize the work before the ideal construction period of October and November: during October and November the water level in the river is low enough to ford and winter ice hasn’t yet formed in the inlet. “The regulatory agencies really kicked in and assisted us in getting the permits in a timely fashion,” Shew said.
Cook Inlet Pipeline Co. selected Cruz Construction Inc., based in Palmer, as general contractor for the project. Cruz Construction subcontracted Mears HDD to do the drilling and Houston Contracting to weld the piping.
The project involved drilling from the south side of the river and then pulling the piping through the drill hole from the north side of the river.
Crossing the river Dave Cruz, general manager of Cruz Construction, explained the difficulties of moving the pipe sections and equipment across to the north side of the river, even when the water level was relatively low. “This type of project had never been done in unfrozen conditions,” he said. “We used some low ground pressure (trailers), what they call Nodwell Trailers, and we pulled them with a low ground pressure ‘dozer ... we had to scout a path out that was safe and not too deep.”
With 1,800 feet of 20 inch pipeline to pull though a 30 inch hole below the river, the project required a directional drilling rig more powerful than anything available in Alaska: Cruz Construction brought from the Lower 48 a rig capable of pulling a 330,000 pound load.
Pilot bore hole Cruz explained that the first stage of laying the pipeline involved using an eight and three-quarters inch drill bit to make a pilot borehole under the river. “(The drill bit) goes in at a slight angle (to the surface), then it flattens out — you run (parallel) to the surface of the ground out at a prescribed depth, and then you turn and come back out of the ground,” Cruz said.
The drillers then widened the pilot hole to the required diameter. “We used a 30 inch fly cutter and pushed it across the river (to cut out) a larger hole from eight and three-quarter inches to 30 inches,” Cruz said. “Then we used what is called a swabbing reamer to pack (the sides of) the hole.”
Assembling the piping Meanwhile, a team on the north side of the river assembled the 1,800-foot length of pipeline. Assembly involved welding lengths of piping together, applying a protective coating and then doing pressure testing.
Finally, the drilling rig pulled the pipeline back through the underground hole. The drill team used drilling mud to lubricate the passage of the piping through the hole.
“This is the largest bore we’ve ever done,” Cruz said. “We’ve done them longer, but we don’t have them to that diameter.”
Despite the challenges, the construction team completed the job in less than 30 days. “We feel that it was successful,” Shew said. “Things went as planned — there were no surprises that weren’t already accounted for ... the contractors executed (the project) very well.”
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