In 1977, one of the engineering marvels of the modern world made its debut: the trans-Alaska pipeline, 48 inches of steel traversing 800 miles, three mountain ranges and more than 800 rivers and streams.
   In its heyday in the 1980s, the pipeline carried as much as 2.1 million barrels of oil a day from America's largest oil field at Prudhoe Bay to the port of Valdez. Alaska was transformed into a petro state with an oil savings account worth $33.3 billion.
   Today, however, the pipeline is carrying only about 660,000 barrels of oil a day, and production from the North Slope's aging fields is set to steadily decline over the next decade.
   What this means for the continued delivery of oil to the rest of the U.S. from Alaska is significant. Engineers have warned that the pipeline — the only means of delivery of North Slope oil — will develop potentially dangerous problems with corrosion and ice if flows drop below 500,000 barrels a day, as they are expected to within the next five to 10 years.
   At 350,000 barrels a day, which pipeline operators say could happen by 2022, frost heaves could cause the underground portions of the pipeline to dangerously wrinkle and kink.
   Already, oil that once took 4½ days to surge from Prudhoe Bay to Valdez now crawls through in 14 days, with flow rates slowed to 2 mph.
   Upgrading the pipeline to handle lower flows is possible but will cost "hundreds of millions of dollars," according to officials from the Alyeska Pipeline Service Co., which manages the facility for the three major oil companies that own most of it.
   Since closing down the pipeline means shutting off all North Slope oil — 14% of the nation's domestic production — Alyeska has been working to reengineer the structure and says it hopes to keep it operating through 2030. The company has already replaced single-speed jet turbine pumps with variable-volume electric pumps, decommissioned six pump stations no longer needed and reconfigured others.

A study to be completed in December will determine just how low the oil flow can go before the pipeline is no longer viable. Options include heaters or chemical additives to keep ice from forming, lowering the water content of the oil before pumping or redesigning the "pigs" that course through the pipeline and clean it of wax buildup. Another is to just give up and build a smaller-diameter pipe.    "We can't tell you what the end date of the pipeline is. We believe we can operate down to 300,000 barrels a day, maybe less than that. But it's going to take some significant investment," said Mike Joynor, senior vice president of Alyeska's operations division.    Alaska officials say the best way out of the pipeline dilemma is to generate new production. Yet prospects for major new oil production on the North Slope have seldom looked so grim.    The BP oil blowout in the Gulf of Mexico has prompted the Obama administration to freeze new offshore oil exploration off the North Slope; the U.S. Army Corps of Engineers has rejected a key permit to allow access across the Colville River to expanded drilling in the National Petroleum Reserve-Alaska; the U.S. Fish and Wildlife Service is reviewing calls for permanent wilderness protections for the Arctic National Wildlife Refuge, which holds up to 15 billion barrels of oil; and oil companies are balking at spending the estimated $40 billion needed to coax new oil out of existing fields, partly in protest of Alaska's oil production taxes, raised significantly under the administration of former Gov. Sarah Palin.

   "We need more oil for that pipeline. But ANWR [the Arctic refuge] is locked up to the east, offshore is now locked up in federal waters, and to the west, in the NPR-A, they declined a permit to ConocoPhillips to move forward," Gov. Sean Parnell said in an interview.
   "We are now blocked on three sides, with the remaining state land in the middle," he said.
   Conservationists who have urged a slowdown in the march of oil development into the vulnerable regions of the Arctic coastal plain and outer continental shelf, home to threatened polar bears and bowhead whales, concede the problem with pipeline flows but say the oil companies, including BP, ConocoPhillips and ExxonMobil, are using the threat of a pipeline shutdown to get access to more oil without paying for the scientific studies needed to do it safely.
   "These are the richest corporations in the world, and they're being crybabies. Yes, putting oil in a pipeline in the Arctic is very, very hard. I admire their science and engineering, and by God they ought to do more of it and quit crying about it," said Jim Ayers, a Juneau-based conservation consultant and former chief of staff to ex-Gov. Tony Knowles.
   Kevin Banks, director of the state Division of Oil and Gas, conceded that new flows or major new investments were needed to keep the pipeline operational. But he said the slowdown in exploration on the North Slope was partly due to the recession, and production could ramp up slightly, if temporarily, by 2013.
   State officials estimate that about 5.16 billion barrels of recoverable oil remain on the North Slope. The old workhorses on the North Slope, Prudhoe Bay and Kuparuk, largely operated by BP, are petering out.
   But BP is set to begin pumping oil at its new, near-shore Liberty prospect as early as late 2011, eventually reaching production of 40,000 barrels a day. And ConocoPhillips' new satellite fields in the national petroleum reserve, west of Prudhoe Bay, could generate 12,000 to 18,000 new barrels a day of production.
   The real bonanza is offshore, in the Beaufort and Chukchi seas, which hold an estimated 27 billion barrels of recoverable oil.
   Shell Alaska, which paid the federal government $2.1 billion for its Chukchi leases and spent nearly an additional $1 billion on seismic evaluations and scientific studies, has said its offshore oil production could generate enough oil to extend the life of the pipeline by 15 to 20 years.
   The company had been delayed by a series of environmental lawsuits but planned to finally launch exploratory drilling this summer, until the Gulf of Mexico blowout prompted the Obama administration to order a freeze on new drilling in the Arctic.
   Now, it's unclear when exploration drilling can commence.
   Pete Slaiby, vice president of Shell Alaska, said the company was willing to wait and see if the Obama administration moved expeditiously to lift the Arctic drilling freeze, imposed because of the nightmarish potential damage posed by an oil spill in icy, highly remote Arctic waters.
   "What we need to do is really gauge the support we have through the administration, and through the Department of Interior," Slaiby said. "We're never going to be free and clear of litigation. But what we really need are continued clear signals, and we've had some from the administration and Interior."
   Oil analysts say there are also large potential reserves of heavy oil — perhaps up to 35 billion barrels — above existing light oil deposits on the North Slope that until now has been too thick to recover. Sucking the oil out of the ground would require billions of dollars in new technology, an expenditure big North Slope companies say is not likely under the state's current tax regime.
   BP, which operates the giant Prudhoe Bay and Kuparuk oil fields, has reduced its investment in "bread-and-butter" oil-field development work by 30% since 2007, company spokesman Steve Rinehart said.
   North Slope companies have estimated that $40 billion in new investments in existing fields over the next 10 years will be needed just to keep them at a rate of decline of 6% a year, which is significantly higher than the state's estimate of 2.8%.
   Though a group of Republican lawmakers earlier this year called for a rollback of production taxes, the Legislature focused mainly on a proposed new gas pipeline that would run near the existing trans-Alaska pipeline, opening the door for the first production of the North Slope's abundant gas reserves.
   There were few tears shed for the oil companies' financial plight.
   "If you look at what happened in the years when there was virtually no tax, they were not exploring for new oil. They were basically in harvest mode," said state Rep. David Guttenberg, a Democratic lawmaker from Fairbanks.
   "They probably knew they were going to get to this point in the life of the pipeline and have to do something. But their concept was just to pump it out as fast as they can, and we'll see what happens."
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kim.murphy@latimes.com