Permafrost

Permafrost thaw is now disrupting Interior Alaska boreal forest near Fairbanks

North Slope oil operators face a long-term, existential threat to infrastructure for which there is no easy solution — thawing permafrost.

Scientists at the University of Alaska Fairbanks have been taking deep temperature measurements in permafrost soils underlying the producing oilfields on the slope and along the Trans-Alaska Pipeline System. Since 1978, when measurements began, temperatures at the 65-foot depth have shown steady warming with the steepest increase at 6 degrees F in the oil fields at the northern end of TAPS.

In 1978 the permafrost at 65 feet near the Prudhoe Bay was about minus-16 degrees F. By 2018 it had warmed to 22.5 degrees F.

In a new report recently published by the university’s Geophysical Institute the warming has been projected forward for the first time. With the rate of warming at rates of half a degree to one degree C every ten years. The melt point, 0 degrees C (32 degrees F) would be reached in 2100 at 65 feet, the modeling suggests.

The rate of change correlates with the rising atmospheric temperatures in the Arctic, which is related to climate change. The warmer air gradually raises soil temperatures, said Santosh Panda, a scientist at UAF’s Geophysical Institute. The 65-foot depth was selected for measurement because this is deep enough to be unaffected by seasonal freeze-thaw cycles.

What’s important is that the thaw point will be reached much earlier at shallower depths. By 2050, three decades from now, many ice-rich silty soils underlying the North Slope will be at 32 degrees Fahrenheit, essentially turning into a silt slurry. That’s because water absorbs heat more efficiently and acts as an accelerator in melting, Panda said.

“It’s going to be a big mess at the top. I can’t even imagine what the landscape will look like,” he said.

Most of the North Slope is underlain by ice-rich silt that extends to bedrock. The depth of bedrock varies but it’s deep in many places, said Doug Goering, dean of UAF’s College of Engineering and Mines.

“The mostly-organic material in the silt tends to collect water. There is a lot of ice in the first 20 to 30 feet of material that is particularly vulnerable to thaw,” he said.

If the thaw extends down 15 feet to 30 feet the soils below surface infrastructure like roads and airports become unstable. “We’ll see road surfaces sink,” Goering said.

There are also massive pure ice wedges, some as deep as 90 feet, and when these melt soil subsidence can happen quickly. Instances of five and six feet of sinking in one year have been observed.

Even two feet of subsidence can cause a lot of problems and this could occur faster than people think. “There could be a lot of changes occurring in the active layer in the next 20 years that will lead to increased thaw depth,” Goering said.

The solution at present is to just keep piling on gravel,” to insulate and keep the soil frozen and stable, he said. “But at some point we’ll get to a regime where this doesn’t work anymore.”

Subsidence from permafrost thaw hasn’t yet appeared in the oilfield areas but state highway engineers are now on the front line of this battle on the Dalton Highway, the gravel road connecting the oil fields to Interior Alaska and which is a vital supply link.

Sinkholes created

Permafrost thaw is creating sinkholes and subsidence at one point 50 miles south of Prudhoe Bay. “It’s a maintenance nightmare,” said Jeff Currey, materials engineer for the state Department of Transportation and Public Facilities.

Keeping the roadbed stable for trucks carrying oil field supplies is requiring constant laydown of new gravel. “It’s been about 20 to 30 truckloads so far this year, and that’s a lot for a small area,” of several hundred yards, Currey said.

“This is a short-term fix but it’s the best we can do for now.”

A thick ice wedge that appears to extend diagonally across the road bed is causing the problem and highway engineers have no idea how thick the ice is yet, and whether it is a horizontal slab or vertical. “It could be 10 feet to 90 feet deep,” Currey said.

As the ice wedge thaws the roadbed will keep sinking. “We can’t stop the settling. We really don’t have a long-range plan to deal with this,” he said. Rerouting the road would cost several million dollars and may cause the problem to be repeated at a new location because it is the road that is causing the thaw. Thaw subsidence is appearing at other points along the highway, too.

The Trans Alaska Pipeline System is near the Dalton Highway and its operator, Alyeska Pipeline Service Co., hasn’t reported problems yet with Vertical Support Members, or VSMs, for the pipeline, which is built above-ground in the area because permafrost.

However, a small fuel gas line that supports TAPS operations became exposed a few years ago because of ice subsidence and erosion, according to reports. Alyeska placed rock to solve the immediate problem but the filled area is now covered in water due to melting.

Natalie Lowman, spokesperson for ConocoPhillips, says her company has yet to see evidence of permafrost thaw that can be attributed to climate change. However, the company is sponsoring research at the University of Alaska Anchorage that includes permafrost.

In Interior Alaska the permafrost warming and thaw is more pronounced. Alyeska installed refrigeration systems at vertical supports in permafrost areas south of the Brooks Range when the pipeline was built in 1977. Those appear to be working well to keep soil stable in a radius around each VSM.

Goering thinks industry will find solutions to the problem, although what they might be is unknown.

Producers’ trickiest problem isn’t so much the field well pads, or the gravel pads that support producing wells. Those can always be elevated on thicker gravel, and the technology of clustering wells on the pads and drilling extended horizontal wells in different directions underground is already well established.

The challenge will be in protecting the high-value field processing plants and the Trans Alaska Pipeline System itself.

In the long term North Slope fields may be developed, or redeveloped, more like offshore fields.

Harold Heinze, former ARCO Alaska President and also a former state natural resources commissioner, is more upbeat and feels doomsday predictions may be unwarranted.

Large process plants have been installed on piling and thick gravel pads with future permafrost impacts in mind, Heinze said. Many incorporate refrigeration systems to keep soils stable. However, roads and airfields may be at risk, he acknowleged.

Heinz believes industry has shown itself capable of dealing with permafrost over five decades and can rise to new challenges. “Facility and pipeline design on the North Slope, including a gas line someday, all incorporate possible future permafrost situations,” he said.

“Current facilities have had minimal problems over the last fifty years because the assumptions of conditions have resulted in very robust designs that have neutralized potential problems,” Heinze said.

“People know how to build in specific permafrost situations and anticipating the condition 50 or 100 years from now is already on the table,” he said.

“It’s not a threat. It’s just another factor in going forward, and it’s why you hire good engineers.”

A costly problem

But reengineering and even reconstructing the North Slope oilfields to deal with sinking ground surface and unstable soil will cost a lot of money. The economics of this will be a key factor.

If there’s enough oil to be recovered from existing oilfields rebuilding might be worth it. If not, the fields may have to be abandoned prematurely with oil still left in the underground reservoirs.

It’s an existential question for the state of Alaska, too. Alaska still depends heavily on oil production revenues to help support its budget, although earnings from the Permanent Fund are now also tapped.

If the North Slope land surface becomes a quagmire, the ability of oil to offer substantial support becomes more questionable.

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