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.
    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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