Thread

The engineering behind the US Strategic Petroleum Reserve

281 points · 115 comments · johnjwang

anigbrowl · 1789601755 · focus · HN ↗
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: <a href="https://www.gao.gov/products/gao-26-106918" rel="nofollow">https://www.gao.gov/products/gao-26-106918
1. gruez · 1789605389 · focus · HN ↗
  We can't pump saturated salt solution to prevent more salt from being dissolved?
  1. chabska · 1789609814 · focus · HN ↗
    If you're gonna build a bunch of tanks on the surface to store that saturated salt solutions, you might as well store the oil in those tanks. The point of this salt cavern system is how little infrastructure it needs to store the huge volume of liquid.
    justinator · 1789611381 · focus · HN ↗
    Just spitballing here, can't you just store the salt alone and make the hyper-saturated salt water on the fly? That seems reasonable.
    wildzzz · 1789614257 · focus · HN ↗
    How do you get the salt to make the brine? You'd need to evaporate the water from the brine which means you either need very large evaporation pools or lots of energy to boil the water (and money to maintain the immense amount of scale you create).
    dylan604 · 1789615083 · focus · HN ↗
    Build a water desalination plant next door. Make it a twofer
    seb1204 · 1789615979 · focus · HN ↗
    Agreed, considering that sor.say future wars will be around (drinking) water it seems reasonable to at least link some cost to the brine or the water required.
    rightnutwingjob · 1789618799 · focus · HN ↗
    Salt mines.
    Here’s one in the USA:
    <a href="https://youtube.com/shorts/zXzvUKXhMBo" rel="nofollow">https://youtube.com/shorts/zXzvUKXhMBo
    Here’s a list of salt mines in the USA:
    <a href="https://en.wikipedia.org/wiki/Category:Salt_mines_in_the_United_States" rel="nofollow">https://en.wikipedia.org/wiki/Category:Salt_mines_in_the_Uni...
    nostrademons · 1789660791 · focus · HN ↗
    They used an even easier method than what's described in the other comments: the salt comes from the initial construction of the SPR caverns.
    When they first built the SPR, they filled it with water to wash away any easily-dissolvable salt features as well as any impurities inside the cavern. The result of filling the cavern and letting it sit for a while is saturated brine: eventually all the salt that can be dissolved is dissolved. Then they pumped that brine to aboveground brine ponds.
    Those brine ponds contain exactly the amount of salt water needed to completely fill the cavern with saturated brine. So future drawdowns just use the same water that has already been saturated. Some of the water will evaporate on the surface, leaving behind salt crystals at the edges of the brine pond, but the crucial thing to remember is the quantity of salt in the newly created brine pond is equal to the amount of salt needed to generate enough saturated brine to completely fill the cavern. Because that's where it came from in the first place. So if you need to replenish it with more water, you just pump in fresh water, it dissolves the extra salt in the brine pond, filter out any surface guck, and then pump it back into the cabin.
    Periodically you might want to add a little extra salt if say the cavern expands or wind erosion carries salt away from the dry brine pond bed. But this quantity is much less, it's the delta in cavern size, not the full initial size of the cavern.
    justinator · 1789668123 · focus · HN ↗
    Amazing -- appreciate the explanation.

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