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.
    nine_k · 1789613184 · focus · HN ↗
    > as well store the oil in those tanks
    Salt does not burn, unlike oil. It would be sufficient to store dry salt, and prepare the brine during the pumping. Still a lot of hassle, of course.
    chabska · 1789622535 · focus · HN ↗
    Please, literally every other country in the world store their petroleum reserve in surface tanks. We have fifty years of experience in designing the safety systems around oil tanks, and the only recent major incidents are from drone strikes in Russia and Saudi Arabia. Just because the US luck out in having the specific geological formation to store oil cheaply doesn't mean the alternative is untenable.
    > It would be sufficient to store dry salt
    Absolutely impractical. Storing and moving around solids in the megatons is very difficult compared to liquids that can be pumped. For comparison, the absolute largest solids moving operation in the world is a copper mine in Chile, it moves 300,000 metric tonne of mineral per day. The east-west pipeline in Saudi Arabia can move three times that in liquid, 1,000,000 metric tonne per day.
    dd8601fn · 1789630971 · focus · HN ↗
    This method appears to be, in nearly every way, far better suited for purpose.
    lelandbatey · 1789614433 · focus · HN ↗
    You don't need tanks to store the brine, just a huge pit/pool. If you look at satellite imagery, that giant pit with brine in it is exactly what they have next to the storage facilities.
    wildzzz · 1789615247 · focus · HN ↗
    Yes but the risks associated with storing brine are far less than oil. Brine leaks out? It might kill the flora nearby but rain will eventually wash it away. Someone blows up the brine tank? Divert some freshwater until you can rebuild.
    But in reality, storing all of that brine would be a massive undertaking on its own. The largest salt cavern is 37M barrels which equates to a circular pond that's 600m across and 20m deep. That's huge. And of course you don't want the brine seeping into the ground water so it needs a good liner. But I suppose you really don't need a pond that big, how often are we completely draining the cavern anyway? We're at half capacity right now and that's the lowest it's been in 50 years. Normally it's been much much higher. So you really don't need all that brine, just enough for the normal ebb and flow of the reserves, maybe like 10%. In the event the reserves get drained, divert some freshwater to compensate.
    tedd4u · 1789621148 · focus · HN ↗
    Do they really have brine storage tanks for enough brine to pump out all the oil? If true, they would have just exectly the right volume of above-ground tanks to just store the oil in the first place and not mess with all these caverns and brine and whatnot.
    Kerbonut · 1789625984 · focus · HN ↗
    They most likely truck in the brine from a mixing facility to reclaim the oil and truck out the brine to disposal when refilling the oil stock.
    NonHyloMorph · 1789672028 · focus · HN ↗
    You could store the salt. You go up far beyond saturation. Salt sediments on the floor (which also might seal it). When you need brine you pump in seawater into a tunnelsystem in the sediment. The saturated brine should be lighter and further up. Overflow to second basin, where it's pumped into the cavern. Thus size comes down to whatever size is needed to store enough salt and or, be big enough to guarantee a certain rate of volume of fully saturated water per time; so basically dimensions that guarantee a phase separation and high enough diffusion rate. And some bad ass pumps (or have the basin be below sealevel and a dam with gates; probably the pumps for reasons of security>efficency in that case)
    fourthark · 1789630565 · focus · HN ↗
    That doesn't solve the someone-might-blow-it-up design problem cited in TFA.

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