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Gasline trial trenching under way near Deadhorse for Arctic conditions Study team costs hit $120 million; if gas pipeline gets green light producers will order several made-to-order trenchers for the Arctic, Fairbanks next Kay Cashman PNA Publisher
Trenching trials are under way near Deadhorse by the North Slope producers’ gas study group — one of the final duties of the Alaska Gas Producers Pipeline Team before it’s completely disbanded, Dave MacDowell told PNA March 11. MacDowell is the former external affairs manager for the team. He’s currently BP Exploration (Alaska) Inc.’s external affairs manager for gas.
The price tag on the producers’ gas study has risen from $100 million to $120 million — the $5.2 million price tag for trenching is part of that figure, MacDowell said.
Trenching is a “hugely important” part of the construction of a gas pipeline from Prudhoe Bay to Lower 48 markets, he said.
“This pipeline is going to be buried its entire length — 3,500 miles. If you can improve the trenching efficiency, increase the distance you can go in a day, you can save dramatically on the money you spend.” Savings could be substantial It’s too early to say if the trenching trials will result in a cost savings but Dave Calvin, the Alaska to Alberta pipeline project manager for the gas team, told PNA March 12 that the savings could potentially be in the “tens of millions of dollars.”
The purpose behind the trenching trials is two-fold, Calvin said. Most important is to verify that the cost estimate the team has already presented to the producers — BP, ExxonMobil Corp. and Phillips Alaska Inc. — is accurate.
“It’s the first time a chain trencher of this size has been used in the Arctic,” Calvin said.
“The rates we assumed in the cost model are reasonable rates; there is good science behind them. We have taken what we know are reasonable rates in more moderate climates and taken what we know of the Arctic and … come up with an estimate. These trials will tell us if we were correct in our assumptions,” he said.
“At a minimum we hope to validate that our rates in the cost model can be achieved. … The stretch, the upside, is if we can try some new ideas, experiment with new techniques, and possibly get better rates and save even more money,” Calvin said.
The trials have been going well, Calvin said, despite the fact he had hoped for colder weather.
“The weather has been pretty moderate — minus 15 (Fahrenheit) to minus 25. We were hoping for … minus 40 or so.” A fancy “Ditch Witch” Two trenchers are being used in the trials. The largest weighs in at 300,000 pounds and digs a trench five feet wide and 10 feet deep; the smaller trencher digs 16 inches deep by 10 feet wide.
Four sites are being used to conduct tests — two locations near the Deadhorse Airport and two sites at the Put-23 gravel mine (Put River) off the Elliott Highway outside of the coastal zone about 20 miles north of Fairbanks.
The machines, which Calvin referred to as “fancy Ditch Witches,” will do a series of parallel trenches — seven to 10 miles total.
Thirteen trenches are being dug at each site with a minimum space of 35 feet between the trenches, using multiple different trenching techniques.
Each trench is five feet wide, 10 feet deep and approximately 1,500 feet long. Purpose built to operate in Arctic The trenchers that will be designed for the actual gas pipeline will dig holes six feet wide and eight to 12 feet deep, Calvin said. But no six-foot trenchers were available for these tests.
“If the pipeline goes, we’ll be sitting down and specifying design changes to the trenching manufacturers. … We’ll come up with a machine that is purpose built to operate in the Arctic. … It will most assuredly be larger than the ones we’re using now. We’ll be buying several of them,” Calvin said.
The soil conditions being tested for chain trenching include poorly drained tundra with deep organic ice-rich silts and sands; shallow overburden over frozen gravel; deep organic ice-rich silts; and bedrock overlain with residual weathered soils.
“We’re trying a number of different techniques with each soil type,” Calvin said. “One technique won’t work for all soil types.”
When the trenching is finished in April, Calvin and his people will sit down and analyze the results of the trenching and come up with techniques they think will work best, he said. A smaller footprint “One of the benefits of using chain trenchers is that they will likely save money but also, in the Arctic in particular, you “have a smaller footprint with these types of machines because you dig exactly the trench that you need, and no more,” Calvin said, He explained that conventional trenchers dig holes that are wider at the top than at the bottom, whereas chain trenchers dig “straight, vertical walls and flat bottoms.”
Areas disturbed by the trenching tests and related activities will be restored following breakup in spring 2002.
Calvin, who was born in Fairbanks, sees the trenching trial as a positive sign that BP is serious about the gas pipeline project.
“These trials aren’t just meetings,” he said. “They’re real work; something that could impact actual construction.”
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