Hacker News

The engineering behind the US Strategic Petroleum Reserve

• 27 Comments
• Salt contains the oil and helps seal small fractures. The rock salt surrounding the SPR’s caverns has extremely low permeability, meaning fluids have very little ability to pass through it. It also doesn’t react with petroleum. Under enormous pressures underground, salt also slowly deforms, which helps close small fractures. The salt itself can therefore contain the oil without a steel-and-concrete tank lining the cavern.
  Oil floats on water, which means pumping water into the bottom of the cavern pushes the oil out. As fresh water is pumped into the bottom of the cavern, the oil gets displaced upwards into a delivery system.
  The more water you pump in, the lower the quality of the oil that's pumped out; we are basically loaning the oil refiners money to buy SPR oil they don't really want. Also, the more water we pump in, the more salt leeches into the water and the more the bottom of the chamber deforms, creating shear forces in the upp walls that lower its overall structural integrity.
  I've posted this before; it's a recent report on the status and maintenance of SPR facilities, which is very clearly written and well worth your time if you want to understand the topic better: https://www.gao.gov/products/gao-26-106918

  By anigbrowl 2 hours ago

• I also think I've also replied this to you before, but +1 for the GAO report! I use the full report as my personal model yardstick on how I document technical decisions/issues for non-technical people. The PDF is attached here:
  https://www.gao.gov/assets/gao-26-106918.pdf

  By nxobject an hour ago

• It is funny seeing how the estimates of the lower end stability vary drastically. Have seen numbers between 70 and 150 million barrels. I have just called it half way between that and think 110 million barrels is probably the lowest they should go.

  By FlowingRiver an hour ago

• We can't pump saturated salt solution to prevent more salt from being dissolved?

  By gruez 41 minutes ago

• Seawater is 10% saturated IIRC, so you'd have to make the saturated solution first, and if the easiest way to do that is to dissolve another cavern then using brine doesn't have much of a cost advantage over "use this one until it collapses, then dissolve the rubble or make another."

  By smallmancontrov 33 minutes ago

• Hard to find that

  By sokka_h2otribe 38 minutes ago

• I don't know, the article mentions having to deal with brine. Let it evaporate in a pool and you've got plenty.

  By mixmastamyk 34 minutes ago

• I’m certain engineers have considered this, but it doesn’t seem answered anywhere: why not just pump the original brine back in to move around the oil? Wouldn’t that at least prevent eroding the storage unit and causing it to fail?
  Unrelated: dang, he wasn’t underselling this being a pretty elegant solution! I never would’ve thought of it, for sure.

  By kulahan an hour ago

• Wouldn't you then need to solve the similar problem of where to store the brine in the meantime?

  By aesthesia 40 minutes ago

• Makes you appreciate the physical infrastructure challenges, not just software. Bet the data logging and monitoring systems are ancient but robust.

  By Ellis_dev 2 hours ago

• Yea man the federal government is on top of protecting civilian groundwater supplies and communicating discoveries of contamination

  By bt1a 2 hours ago

• Well worth your time if you are interested in a more detailed discussion https://www.construction-physics.com/p/how-the-strategic-pet...

  By sklargh an hour ago

• One fun fact I’ve heard is that the strategic oil reserve requires like 100-150 million barrels of oil to maintain operational pressure and even be functional. This means we can’t draw it down to zero; not even close.

  By LPisGood 44 minutes ago

• Very cool, big fan of these bite size explainers. Has there been more cycling recently? Are the sizes of the caverns tracked anywhere?

  By hankbond 2 hours ago

• Funnily enough, I guess the more you cycle them, the bigger they get until they just collapse. So you have a lot of potential storage just before you have none.

  By FlowingRiver an hour ago

• id imagine if you have the location of a site that the largest pipes visible from satellite photography would be consistently scaled in some manner with the tank size. this is guess

  By bt1a 2 hours ago

• What do they do with the brine when they fill it back up with oil?
  And do they use fresh water?

  By metrix an hour ago

• An interesting aside is that the process for making these salt domes is also used for mining salt. Drill a hole, pump water down, and up comes brine. The brine can be used as a chemical feedstock, e.g., for production of things like chlorine, sodium hydroxide (lye), and sodium carbonate for glass.

  By analog31 2 hours ago

• Dumb question but why not pump it back into where it was pulled from.. or just leave it in a a reserve paid for by the gov

  By redwood 12 minutes ago

• How long does the crude last uner these conditions? Refined oil products like gas have pretty limited shelf lives (I think 6-12 months for gas).

  By ivraatiems 2 hours ago

• Under ideal conditions - about 200 million years at least. In the salt, I'm not sure.

  By aqfamnzc an hour ago

• well it's been underground in similar conditions for a couple dozen million years, so I think a while

  By buckle8017 2 hours ago

• Politics, politics, politics... guess dang didn't see this one yet.
  Not what the site is for (apparently):
  > Off-Topic: Most stories about politics, or crime, or sports, or celebrities, unless they're evidence of some interesting new phenomenon. If they'd cover it on TV news, it's probably off-topic. [0]
  [0] https://news.ycombinator.com/newsguidelines.html

  By recursivegirth 44 minutes ago

• This isn't a political article?

  By aesthesia 42 minutes ago

• We are just pretending this is relevant... how?
  Come on, I thought this was a site with semi-intelligible people that are able to connect point A-to-B.
  Nothing against OP or the article, but the only reason the reserve is relevant is due to politics (foreign and domestic). Just because you want to shave the sheep and wear the wool for glasses doesn't mean it's not interconnected.
  Honestly my fight isn't with you, it's with the admins of this site who want to filter, censor, and subjugate on a site that portrays to be a bastion of only tech news.

  By recursivegirth 29 minutes ago

• It’s a fascinating engineering project that most people don’t know much about. That’s what HN is for!

  By gordonhart 22 minutes ago

• You complain about politics on HN in the same breath that you implore moderators to stiffle discussion that offends your politics. Do you see the hypocrisy?

  By jLaForest 12 minutes ago