Tuesday, January 11, 2011

The Alaskan Pipeline stoppage

Some years ago I drove up the Dawson Highway from Fairbanks to the Yukon River, and as the highway paralleled the Trans-Alaska Pipeline, we stopped at one of the pumping stations to take a look. I think we were there about a minute before a security vehicle came whipping up alongside to tell us a) that we were not permitted to stop there and b) that we couldn’t take photos. Which is why I am not illustrating the post today about the leak at one of the pumping stations, with my own photo of one. However I am quite happy to borrow one from the Pipeline Website.

Pump Station 1 (Alyeska Pipeline )

The pipeline was shut down on January 8th when the leak, which is in a section of pipe feeding into the first of the pump sets along the line, occurred. Because the leak was within the plant the leak was caught early, only 10 barrels of oil spilled into the basement before the system was shut down. While the initial options were to either repair the leak, which is in a length of the pipe that is encased in concrete, or bypass it, the current plan is to install a bypass length of about 157-ft which will effectively replace the damaged section and bring the system back on line. This is expected to happen before the end of the week. As long as this holds true then the impact of this short-term 650 kbd of oil will be minimal, since the oil feeds into storage tanks that remain, at the present, comfortably full. Unfortunately the company did not have spare parts on hand, and these have bad to be made in Fairbanks, and transported to the site at Prudhoe Bay.

UPDATE: Because of fears of the problems caused by the falling temperatures in the pipeline, the flow has been restarted at a low level, without the bypass installed. I have added a paragraph of explanation at the end of the story. And in a further UPDATE, the problem pig is stuck about half-way down the pipeline.FURTHER UPDATE (THURS) The pipeline is now flowing at around 400 kbd but the pig is still moving to the transfer point, and remains in the line, but with no problems encountered, except that the leak is worse, but that should be be fixed this weekend.

Last November, for example, one the runs of the instrumented pigs down the pipeline indicated that there might be significant corrosion in the pipeline at Isabel Pass.
Isabel Pass, is a gap in the eastern mountains of the Alaska Range. Located approximately 11 miles north of Paxson at Pipeline Milepost 592.50, the Top of the World is geographically known as a funnel valley, a land feature that compresses the wind flowing north or south of the Alaska Range through this narrow passage. Work at the site was, in fact, halted for two days due to extremely high winds in mid-November.

The second challenge with this site also involves geography: the confluence – the meeting point – of Phelan Creek and the Delta River. The pipeline runs directly under this northern waterway. Aufeis – groundwater that swells up through layers of ice – is also a common feature at this location, adding to the water challenge of this project.
Interestingly back in 2006, when flows along the pipeline were reduced to 650 kbd, the lower flow caused some vibrations along the pipeline just south of Isabel Pass. At that time the pipeline was still producing 800 kdb, from a peak supply of over 2 mbd. It has now fallen pumping some 642 kbd in December, against an annual average of 620 kbd. That drop in flow rate has also increased the time it takes the oil to reach Valdez. (Since the pipeline remains full, at lower flow volumes, the oil moves more slowly than it did at peak). Thus a transit time of 4 days at peak production, now takes 13 days to arrive. Because of the longer residence times in the pipe, the oil, which enters the pipe at 110 def F cools more than it did before, and below 70 deg F wax begins to precipitate out on the walls. This has to be removed, and that means that the pigs used to clean the pipe are sent down more frequently now. (Every 4-7 days instead once every few weeks).

The next concern long-term problem may come as flow continues to drop may come if/when the flow drops below 500 kbd, since at that point the temperature may fall below 32 degrees, and ice may start to form in the pipeline. (H/t Luke H). ) However, in the short-term, this is the longest the pipeline has been shut down in winter and if the delay continues much longer, Alyeska President Kevin Hostler has explained the problem to Congress thus:
Our current studies and plan indicate that if the pipeline is shutdown during continuous minus 40 F temperatures, we will need to restart within 14 days to avoid significant problems. If BP reduces throughput this winter to 500,000 barrels or less, we may only have 9 days to restart after a cold temperature shut down.

There are four issues about cold restart that concern us: the crude oil develops a gel strength that is too strong to allow pipeline start-up; water drops out of the crude oil, collects in low spots, and freezes; ice in the pipeline upon restart could plug the mainline pump suction piping and custody transfer flow meter strainers, causing restart to fail; and the pipe steel temperature cools to minus 40 F or minus 50 F, making pipe welds susceptible to fracture.
The pipeline was designed for quite sever loads, Luke H, put up some pictures after my pipeline post, showing how it coped with an earthquake that moved the earth along the pipeline route.


And after the earthquake

(Photos from Luke H ).

Overall it looks as though this stoppage may not, in itself, cause any problems, but as with so many events in the oil business, these days, it is a warning of problems in the years ahead.

UPDATE: Well about the time I was writing this story, Alyeska began pumping oil down the pipeline again. They had found a way to temporarily route oil around the leak, so that enough flow could be achieved to stop the pipe from reaching the freezing point. The problem is made worse in this case because there is a pig in the line, and a continued drop in temperature would cause ice and wax to settle in the pipe. Then, when the pig moved, it would sweep this material before it, and if there was enough of it, this could then cause a pipe blockage, or get into and damage the pumps. By starting the pipeline before the temperature falls that low, the pig can be moved to a place where it can be taken out of the line. At the same time the line temperature can be brought back up to the level where some of the solids will re-melt and move back into circulation. It is still going to take about four days to get the parts needed for the bypass finished, and this would have taken the pipeline into the critical time period for a cold restart. The leak is continuing to flow small amounts of oil, and a total of 1,200 barrels has now been captured. The company are accepting the consequences of the leak continuing.
The restart would cause a small amount of oil to leak from the broken pipe that was discovered last weekend, but industry officials said that leaking a little more oil was better than leaving liquid idle in the pipes in freezing temperatures. Without warm oil moving through the system, water in the pipes could freeze and expand, possibly causing cracks in the pipeline or around the North Slope oil wells. . . . . . . .Industry officials in Alaska said that if it took more than a week or two to repair the leaky pipe, many wells could also suffer damage from freezing water.

A freeze in the system “is a nightmare, a worst-case scenario” that could shut production for several weeks, said one Alaska oil executive, who asked for anonymity because he was not authorized by his company to discuss the situation.

7 comments:

  1. I posted about this a bit myself, some of the info may be of interest. The "What is TAPS" site is very nice. peakoil.com member Bratticus provided some handy Google Earth + Maps links, if you want to eyeball PS 1.

    I was curious about how long things shut down in 2006, and wondered if this being winter might exacerbate problems, and to what degree. Looks like they're going to fire 'er up, at least for a day: Oil Pipeline in Alaska Has Plan to Restart (NYT).

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  2. Rule of thumb for pipelines is that they can be turned down to 10% of design capacity -- which would suggest a limit of around 200,000 BOPD for TAPS. Because of the extreme conditions, it seems that TAPS will run into problems at rates well above that.

    This highlights an interesting challenge relating to infrastructure -- one that is a serious emerging issue in the North Sea as well on the North Slope. When major trunk lines are shut down, any remaining oil in the fields which fed the pipeline becomes stranded. Further exploration and development becomes futile; there is no way to get the production from modest discoveries to market.

    As a practical example, production from ANWR on the North Slope would also yield more oil from Prudhoe Bay and other North Slope fields, by allowing the TAPS line to stay above its operating limit for a longer period of time.

    Continued exploration is thus a key contributor to maximizing efficiency.

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