Hacker News new | past | comments | ask | show | jobs | submit
anigbrowl | on: The engineering behind the US Strategic Petroleum Reserve
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

nostrademons | parent | next
There was a good comment on r/oil by someone who worked on the engineering for the SPR. Unfortunately it's fallen off the front page and I can't find it now, but:

> 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.

It turns out that it's trivially easy to prevent the water from leeching out the salt. They presaturate the water with salt, so that it already contains the maximum amount of salt that can be dissolved for a given temperature. When they pump the brine out, it goes into aboveground brine pools that can easily be seen on satellite imagery. The salinity of this brine can easily be controlled: if you want to expand the cavern, you mix it with freshwater so the brine dissolves more of the edges, if you don't you pump it back in as brine.

Edit: Here, found some satellite imagery of one of the SPR sites:

https://maps.app.goo.gl/B8XJ9TVhQfcdErky5

You can clearly see the brine pond, which is as big as the aboveground portion of the SPR itself.

loading story #49738813
loading story #49736560
jordanb | root | parent | next
Are the round things brine ponds? They look like floating roof tanks
loading story #49738857
Kerbonut | root | parent
They look like above ground pits. Empties are showing the white paint and ones with brine look dark.
loading story #49734684
Morromist | parent | next
It would be cool to see what these look like in a photo but I guess they're never empty of liquid. I wonder what happens to the oily water after we use it? Do we boil it until it evaporates?
loading story #49738901
gruez | parent | next
We can't pump saturated salt solution to prevent more salt from being dissolved?
smallmancontrov | root | parent | next
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."
seb1204 | root | parent
I disagree that there is no cost associated with making another. Externalising environmental and rectification cost should not be the default approach.
loading story #49735488
sokka_h2otribe | root | parent
Hard to find that
mixmastamyk | root | parent
I don't know, the article mentions having to deal with brine. Let it evaporate in a pool and you've got plenty.
FlowingRiver | parent
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.
loading story #49736578
jordanb | root | parent
I think there's a statuary limit at 150 million because there must be an "emergency military reserve" but the caverns start collapsing at 70 million.
loading story #49736640