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The engineering behind the US Strategic Petroleum Reserve (https://johnjwang.com)

279 points by johnjwang 5 days ago | 115 comments | View on ycombinator

anigbrowl 3 days ago |

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

kulahan 3 days 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.

Ellis_dev 3 days ago |

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

cyberax 3 days ago |

One thing about salt domes: they almost by definition are surrounded by very low-permeability dry soils. Because otherwise they would have dissolved long ago!

And a related way to use salt domes is for natural gas storage.

tmellon2 3 days ago |

Hmm...The Math does not hold up. 300 feet diameter circular area is 1.62 acres. So at max you would need about 1130 x 2 = 2260 acres and not 45000 acres as projected !

From the post :

"300 feet in diameter..."

"To hold 714 million barrels of oil (the full capacity of the Strategic Petroleum Reserve), you’d need about 1,130 of these tanks. If you use the standard capacity of the largest commercial petroleum farms (e.g., in Cushing, Oklahoma), you need about 45,000 acres to store these tanks."

Aboutplants 3 days ago |

Underground Natural Gas storage is handled the exact same way interestingly enough

https://www.phmsa.dot.gov/technical-resources/pipeline/under...

zachlatta 3 days ago |

This is so incredibly interesting and one of the best things I’ve seen on HN recently. Thank you for the awesome post!

skizm 3 days ago |

Where can I find more of these incredibly clever engineering solutions explained so simply? Love reading about this sort of stuff.

LPisGood 3 days 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.

georgefrowny 3 days ago |

I wondered to what extent they know the size and shape of the cavern at any given time and what they use to monitor it. The answer is apparently sonar, and there are some pretty pictures here:

https://digital.library.unt.edu/ark:/67531/metadc840493/m2/1...

amelius 3 days ago |

> Keep the oil secure against attacks by our adversaries. This is an especially hard challenge because petroleum has this tendency to light on fire, so a huge concentration of it is especially difficult to keep safe.

> Release oil quickly so it can reach the market during a supply disruption.

But what if the adversaries destroy the refineries or other downstream equipment which is much simpler to do?

ivraatiems 3 days 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).

hankbond 3 days ago |

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

analog31 3 days 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.

sklargh 3 days ago |

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

Jedd 3 days ago |

Peter Zeihan did a 5m video [1] on this 10 days ago (give or take) - and the history of how they've been used, and why the original design (big draw-downs during major emergencies - perhaps 5 of them, ever) hasn't lent itself well to the way they ended up being used.

[1] https://www.youtube.com/watch?v=j5g0Ud8i0C0

rafaelc 3 days ago |

metrix 3 days ago |

What do they do with the brine when they fill it back up with oil?

And do they use fresh water?

_joel 3 days ago |

The salt caves were only designed to be used a few times and to be used for maximum draw down, weren't they?

redwood 3 days 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

undefined 3 days ago |

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ck2 3 days ago |

And it's going to costs billions to rebuild it in a few years after they finish destroying it by 2028

So I was wondering the other day how many gallons of crude the Epstein Memorial Ballroom could hold if it was sealed off, maybe "AI" can figure it out....

treebeard901 3 days ago |

I always thought the smartest thing to do since countries chose to accept fiat currency in exchange for oil was to create as many patroleum reserves as possible and print as much money to buy as much oil to store for later use as they would sell.

calmlynarczyk 3 days ago |

This is a pretty popular topic this past month, huh?

https://www.construction-physics.com/p/how-the-strategic-pet...

hiring_signals 3 days ago |

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pbkompasz 3 days ago |

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recursivegirth 3 days ago |

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