How the US hides 714 million barrels of oil in salt caverns
The engineering behind the US Strategic Petroleum Reserve
Storing hundreds of millions of barrels of crude oil securely for decades is a tough engineering problem. Aboveground tanks are vulnerable to attack, and underground steel tanks like Red Hill proved costly and leak-prone. The US Strategic Petroleum Reserve solved it by dissolving caverns in Gulf Coast salt domes. Salt's low permeability seals the oil, and since oil floats on water, fresh water pumped in pushes it out. At about $3.50 per barrel, it's far cheaper than aboveground storage.
The actual solution, like many great engineering solutions, is incredibly elegant and simple.
- anigbrowl
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
- georgefrowny
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...
- kulahan
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.
- pbkompasz
The Wikipedia page needs an update, this map[1] still shows Gulf of Mexico.
Thank you for your attention to this matter!
[1] https://en.wikipedia.org/wiki/Strategic_Petroleum_Reserve_%2...
- skizm
Where can I find more of these incredibly clever engineering solutions explained so simply? Love reading about this sort of stuff.
- Aboutplants
Underground Natural Gas storage is handled the exact same way interestingly enough
https://www.phmsa.dot.gov/technical-resources/pipeline/under...
- tmellon2
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."
- Ellis_dev
Makes you appreciate the physical infrastructure challenges, not just software. Bet the data logging and monitoring systems are ancient but robust.