Trans-Alaska pipeline engineers say they are confident they can keep the pipeline on which Alaska depends flowing despite declining throughput.
What they don't know yet is what they'll have to do to keep the oil moving, as the slower flow of oil brings with it a host of technical challenges.
"The pipeline is larger than we really need right now," said Pat McDevitt, senior project manager for low flow studies for Alyeska Pipeline Service Co., the operator of the pipeline.
The flow, which once peaked at more than 2 million barrels of oil a day, is now less than 700,000 barrels per day as Prudhoe Bay and other North Slope oil fields age.
If a pipeline were built today to carry that amount of oil, it would probably be built at 30 inches in diameter or less, compared to the 48-inch behemoth that snakes across central Alaska.
McDevitt spoke to the Legislature's House Resources committee at an informational session.
Among the challenges in connection with that slowing flow is a declining temperature of the oil.
Oil that enters the pipeline at its northern terminus at Deadhorse has a temperature of 110 degrees. By the time it reaches the Valdez tanker terminal 13 days later, the oil temperature is down to 40 degrees. Somewhere below 32 degrees, water in the oil begins to form ice, and at 25-28 degrees may begin to drop out of the oil.
That's a consequence of the declining volume; when the oil flowed faster, it took only four days to reach Valdez.
Now, temperature becomes a concern, McDevitt said.
"It's like your refrigerator; the longer time something is in there, the closer it gets to the temperature of the refrigerator," he said.
In the case of TAPS, the refrigerator can be the frigid Arctic winter. That's a problem both during regular operations, when water or ice can drop out and collect at low points, promoting corrosion.
And in emergency shutdowns, standing water could freeze and might even prevent restart, McDevitt said.
Other concerns with a colder pipeline might include frost heaves where thawed soil refreezes and stresses the pipe.
"TAPS was designed as a warm oil pipeline," he said.
In the 660-mile pipeline, only about nine miles are at risk of frost heaves, however, McDevitt said.
Crude oil flowing through TAPS is relatively dry, averaging 0.35 percent water content, he said. Still, given the volumes involved, that means the oil is carrying thousands of gallons of water with it.
An additional problem with a colder, more slowly flowing pipeline is wax drop-out and build-up along the inside of the pipe.
The wax also can work in conjunction with the water to threaten the pipeline. It can trap water next to the steel pipe, where it can promote corrosion, he said.
Alyeska is building models with which to test pipeline operations under various conditions, trying to determine how they may need to modify their operations as flows decrease.
The good news, said Mike Joyner, Alyeska's vice president for pipeline operations, is that they started the studies years ago.
"We believe we are ahead of the curve," he said.
Also good news for Alaska: The 30-year-old pipeline is holding up remarkably well, he said.
"The line is in exceptional shape for its age," Joyner said.
In places where the pipe can be viewed, such as near valves, it appears like new, he said.
Another TAPS advantage is the actual strength of the pipeline, Joyner said.
Among the ways McDevitt and his team are considering adapting to the low flows is heating the oil, adding chemicals to it, and increasing use of PIGS, the maintenance scrapers and sensors that clean and monitor the inside of the pipeline.
Joyner warned that the volume of chemicals could be prohibitive, and said even heating oil would be "pretty pricey."
The best option would be to add additional oil to the pipeline, which could come from new finds, with top prospects including the outer continental shelf, Arctic National Wildlife Refuge, National Petroleum Reserve-Alaska or elsewhere.
Resources Co-chair Craig Johnson, R-Anchorage, pushed the Alyeska representatives at the meeting for hints to the "magic number," at which TAPS could no longer operate.
That's been a key piece of information in the oil tax battles in the Legislature, as tax cut advocates have said the pipeline will have to close within 10 years unless the decline is stemmed. They urge tax cuts as an incentive for the oil companies to boost the flow above a claimed 300,000 barrel per day minimum.
State officials say they expect the pipeline to remain in service for decades more, with a minimum flow of between 100,000 and 200,000 barrels per day.
TAPS is owned by Alaska's big three oil producers, BP, ConocoPhillips Co. and ExxonMobil Corps, and a few others owning tiny ownership percentages.