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The Engineering Behind the US Strategic Petroleum Reserve
- hankbond 19d agoVery cool, big fan of these bite size explainers. Has there been more cycling recently? Are the sizes of the caverns tracked anywhere?
- bt1a 19d agoid imagine if you have the location of a site that the largest pipes visible from satellite photography would be consistently scaled in some manner with the tank size. this is guess
- FlowingRiver 19d agoFunnily enough, I guess the more you cycle them, the bigger they get until they just collapse. So you have a lot of potential storage just before you have none.
- robocat 18d agoIf saturated brine is pumped in, then salt is not dissolved from the walls. See better comments further above.
- huurtehoog 18d agoThe design characteristics require the storage caves to support 5 drawdown cycles using "raw water" - actual phrasing in official documentation. Also, the SPR is a complex system made up of several locations where salt massifs have been drilled and hollowed out in the shape of highly specified storage caves. There are requirements for pumping throughput for example, and some of the concerns regarding operational life and the dozens of partial drawdowns these caves have been subjected to, relate to them loosing the ability to quickly discharge oil. In a word: it's complicated. I encourage looking up technical documentation online, super easy to find using 'filetype:pdf'. There are a lot of details involved in building, running, and assurances required from the SPR storage system.
- Ellis_dev 19d agoMakes you appreciate the physical infrastructure challenges, not just software. Bet the data logging and monitoring systems are ancient but robust.
- bt1a 19d agoYea man the federal government is on top of protecting civilian groundwater supplies and communicating discoveries of contamination
- walleeee 19d agoI know you jest, but the US govt funds a lot of water science. Whether that's put to use in the public interest is another question ofc and one we should be asking
- analog31 19d agoAn interesting aside is that the process for making these salt domes is also used for mining salt. Drill a hole, pump water down, and up comes brine. The brine can be used as a chemical feedstock, e.g., for production of things like chlorine, sodium hydroxide (lye), and sodium carbonate for glass.
- anigbrowl 19d agoSalt 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 https://www.gao.gov/products/gao-26-106918
- nxobject 19d agoI also think I've also replied this to you before, but +1 for the GAO report! I use the full report as my personal model yardstick on how I document technical decisions/issues for non-technical people. The PDF is attached here: https://www.gao.gov/assets/gao-26-106918.pdf https://www.gao.gov/assets/gao-26-106918.pdf
- pjc50 18d agoPeople like to be dismissive about civil servants without looking at how much extremely high quality work is actually produced on complex subjects. Personally having interacted with them a couple of times I'm also a fan of the UK Parliamentary briefings: https://commonslibrary.parliament.uk/ https://commonslibrary.parliament.uk/ (unfortunately they can't make people read the briefings ..)
- deleted 18d ago[deleted]
- ivraatiems 19d agoHow long does the crude last uner these conditions? Refined oil products like gas have pretty limited shelf lives (I think 6-12 months for gas).
- buckle8017 19d agowell it's been underground in similar conditions for a couple dozen million years, so I think a while
- aqfamnzc 19d agoUnder ideal conditions - about 200 million years at least. In the salt, I'm not sure.
- nostrademons 19d agoIn the salt it's pretty similar. The salt caverns are basically just like the conditions where the early, easily-exploitable oil deposits ("gushers") were.
- thrawa8387336 19d agoOne time I heard the limited shelf life is by design to avoid consumers hoarding. Diesel OTOH fares better
- jaggederest 19d agoNo, it's because gasoline is not a very thoroughly refined chemical, so it basically has a bunch of aromatic rings, benzene, and all sorts of monomers floating around, that rapidly (~year or two) turn into varnish and other polymerized nastiness when they oxidize and crosslink. I believe gasoline was originally a refinery byproduct that was used because it was so cheap as a fuel. Diesel and other heavier fuels generally are much closer to aliphatic hydrocarbons (straight chains, not aromatic) and so are much more storable, because aliphatic hydrocarbons have much less opportunity for oxidation (they're like saturated fat, i.e. much more stable). You can get polymerization inhibitors to put into gasoline if you want it for long term storage, with the caveat that they produce some nastiness at the bottom of tanks that you'll have to avoid when pumping it out, and I think they can also slightly reduce the octane rating.
- metrix 19d agoWhat do they do with the brine when they fill it back up with oil? And do they use fresh water?
- sklargh 19d agoWell worth your time if you are interested in a more detailed discussion https://www.construction-physics.com/p/how-the-strategic-petroleum-reserve https://www.construction-physics.com/p/how-the-strategic-pet...
- kulahan 19d agoI’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.
- aesthesia 19d agoWouldn't you then need to solve the similar problem of where to store the brine in the meantime?
- kulahan 19d agoYeah, but that’s probably easier to solve than eventually losing the whole dang structure!
- rtkwe 18d agoDepends a lot on how quickly it erodes the salt dome and the costs of using and storing the brine instead of using fresh water. Storing that much brine runs into the same space issues that storing the oil above ground would, slight ameliorated by the brine at least not being flammable.
- rtkwe 17d agoLooking broadly at the costs to use brine instead of fresh water you'd need a combo of stored brine and a method to generate brine from freshwater (for withdrawals) and then desalinate the brine (for deposits). And that would require quite a bit of infrastructure to store and process the salt generated and used by the freshwater <-> brine process in both directions. Depending on how quickly you want to be able to draw down the SPR you'd need to store a significant amount of salt at the location. At a maximum to be able to withdraw the entire reserve you'd need 1.3561 × 10^7 cubic meters of halite (this number uses the density of halite as a solid crystal not the density of a pile of ground up halite they'd actually use) weighing 2.94273 × 10^10 kg or 29.4273 Tg (teragrams, a rare treat to get to break out that unit). [0] That number gets smaller when you allow for receiving shipments of salt during the drawdown since they can't instantly pull out the full reserve so they have time to allow for receiving salt shipments. [0] https://www.wolframalpha.com/input?i=%28714+million+barrels+of+water+weight%29+*+.26+%2F+density+of+halite&assumption=%22UnitClash%22+-%3E+%7B%22barrels%22%2C+%7B%22BarrelsOfOil%22%7D%7D https://www.wolframalpha.com/input?i=%28714+million+barrels+...
- recursivegirth 19d ago[flagged]
- aesthesia 19d agoThis isn't a political article?
- recursivegirth 19d ago[flagged]
- gordonhart 19d agoIt’s a fascinating engineering project that most people don’t know much about. That’s what HN is for!
- schainks 19d agoPolitics and infrastructure are often intertwined, but the world you and I enjoy nonetheless relies on said infrastructure and how it works. I don’t see anything political about the article? What made it political for you?
- jLaForest 19d agoYou complain about politics on HN in the same breath that you implore moderators to stiffle discussion that offends your politics. Do you see the hypocrisy?
- LPisGood 19d agoOne fun fact I’ve heard is that the strategic oil reserve requires like 100-150 million barrels of oil to maintain operational pressure and even be functional. This means we can’t draw it down to zero; not even close.
- WalterGR 19d agoAnd indeed, already: https://www.cnbc.com/2026/08/15/strategic-petroleum-reserve-spr-oil-iran-war-caverns.html https://www.cnbc.com/2026/08/15/strategic-petroleum-reserve-... "Depleted strategic oil reserve nears level that raises concerns about damage to caverns, operations" https://fortune.com/2026/08/17/depleted-us-strategic-oil-reserves-risk-damaging-salt-caverns-iran-war/ https://fortune.com/2026/08/17/depleted-us-strategic-oil-res... “U.S. strategic reserves are getting so low the drawdown threatens to damage the 60 underground salt caverns storing American oil”
- askvictor 18d agoWhy can't they pump more water down there to create pressure?
- huurtehoog 18d agoI encourage you to do some digging using filetype:pdf on a search engine. The amount of documentation available on the SPR is fascinating. From what I found out, turns out the question of SPR design and operational limits is a complex issue to say the least. The SPR is a big system composed of many sub-systems and there are entangled legal, policy, technical issues at play. Interesting stuff!
- redwood 19d agoDumb question but why not pump it back into where it was pulled from.. or just leave it in a a reserve paid for by the gov
- schainks 19d agoBrine is useful to sell to industry. AIUI, salt caverns don’t like to be filled with brine because they become more susceptible to temperature changes of the earth and pressure from surrounding rock. Both can heat the cavern, which is bad for structural integrity.
- Loudergood 19d agoThis way the US Gov can be a buyer of last resort. Backdoor bailouts.
- cyberax 19d agoOne thing about salt domes: they almost by definition are surrounded by very low-permeability dry soils. Because otherwise they would have dissolved long ago! And a related way to use salt domes is for natural gas storage.
- CamperBob2 19d agoAnd even helium, which is famous for its ability to leak out of almost any container you put it in. The US formerly maintained a National Helium Reserve (https://en.wikipedia.org/wiki/National_Helium_Reserve https://en.wikipedia.org/wiki/National_Helium_Reserve), in fact, until we decided that a helium reserve wasn't all that useful or important.
- carefree-bob 19d agoUS has some of the world's largest natural gas deposits, and is a major producer of helium, so it makes less sense to have a strategic helium reserve. Even the SPR was created in the aftermath of the last middle east oil crisis, back when the US was a major net importer of oil, and many people have been saying we should scrap the SPR, as no major oil producer has an SPR. The problem with the SPR is that it is used to manipulate prices, which was why Biden on the one hand cut oil leases and reduced domestic oil production, but then did major SPR drawdowns before the election to hide the realities of these policies. Now Trump is playing the same game, sanctioning oil producers and creating wars in the middle east, but using the SPR to hide the effects of these policies until after the midterm. In both cases, we'd probably be better off without an SPR, so all of these actions against oil production would be immediately felt at the pump before the election and voters could respond quickly. It's just too tempting to have this tool to manipulate oil prices that incumbents can use before elections.
- qlte 18d agoHuh? The oil price shock in 2022 and resulting SPR drawdown had nothing to do with oil leases. Prices almost doubled worldwide in the span of a week after Russia invaded Ukraine. Look at any chart of petroleum products and it's clearly visible as a huge, almost vertical line. The explicit purpose of the SPR is to function as a lever to smooth temporary supply shocks. The US increasing oil output by a few percent in either direction wouldn't have made any difference to global disruption of oil markets from a major exporter to Europe starting a war and then getting sanctioned.
- calmlynarczyk 19d agoThis is a pretty popular topic this past month, huh? https://www.construction-physics.com/p/how-the-strategic-petroleum-reserve https://www.construction-physics.com/p/how-the-strategic-pet...
- saghm 18d agoProbably because the oil itself has been getting pretty popular to, on account of the whole "bombing the people who control access to where we usually get it from" thing: https://www.reuters.com/business/energy/oil-stocks-us-strategic-petroleum-reserve-fall-lowest-level-since-1982-2026-09-14/ https://www.reuters.com/business/energy/oil-stocks-us-strate...
- stephbook 18d agoInteresting that these articles don't mention China's storage capacity, which is bigger and more crucial these days. Maybe China publishes less official knowledge?
- rtkwe 18d agoChina is much more cagey about the exact levels and capacity of it's version of the SPR but there's a lot of evidence they're drawing pretty heavily from it to cut their oil imports which has had a big impact on reducing the impact of the whole illegal war in Iran situation.
- Scoundreller 18d agoChina isn’t a member but IEA requires its 32 members to have 90d stockpile worth of oil imports: https://www.iea.org/data-and-statistics/data-tools/oil-stocks-of-iea-countries https://www.iea.org/data-and-statistics/data-tools/oil-stock...
- hiring_signals 19d ago[flagged]
- zachlatta 19d agoThis is so incredibly interesting and one of the best things I’ve seen on HN recently. Thank you for the awesome post!
- rafaelc 19d agoRelated: https://news.ycombinator.com/item?id=49566946 https://news.ycombinator.com/item?id=49566946
- tmellon2 18d agoHmm...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."
- Retric 18d agoYou can’t tile circular objects at 100% efficiency and you definitely don’t want these tanks to touch. You further need space between them with each other and the edge of your property for a host of other reasons such as being able to inspect and paint each tank. Thus looking at actual facilities is going to give you vastly more resources options than just looking at the footprint of each tank.
- tmellon2 18d agoYou have a point. However, the requirement estimate of 45000 acres is off by 10 times ! I have seen some of these tanks - even accounting for spacing between them; at best one needs maybe a total of 5000 acres. BTW - If everyone followed Elon Musk's projection of 100 x 100 miles of Solar; then the US would not need these fossil fuels. See : https://www.reddit.com/r/Futurology/comments/1vq0uu6/solar_is_now_10_of_global_electricity_and_at_its/ https://www.reddit.com/r/Futurology/comments/1vq0uu6/solar_i...
- Retric 18d agoBeing realistic is the opposite of being off. As the article points out fire is a real concern here, which is one of many reasons making salt caverns so appealing. But it’s also a major driver for distance between each above ground tank, you want to isolate risks so a single failure doesn’t propagate across the facility.
- 18d ago
- treebeard901 18d agoI always thought the smartest thing to do since countries chose to accept fiat currency in exchange for oil was to create as many patroleum reserves as possible and print as much money to buy as much oil to store for later use as they would sell.
- sh34r 18d agoIt was a great plan, but all it took to foil it was one orange man in the Epstein files.
- Aboutplants 18d agoUnderground Natural Gas storage is handled the exact same way interestingly enough https://www.phmsa.dot.gov/technical-resources/pipeline/underground-natural-gas-storage/fact-sheet-underground-natural-gas https://www.phmsa.dot.gov/technical-resources/pipeline/under...
- adolph 18d agoIn the S&P article linked by another comment, there is an interesting note about storing other materials: The [Early Storage Reserve] caverns at the Bryan Mound site were originally used by Dow Chemical to store magnesium. https://www.spglobal.com/energy/en/news-research/blog/crude-oil/061516-a-rare-tour-of-the-strategic-petroleum-reserve https://www.spglobal.com/energy/en/news-research/blog/crude-...
- _joel 18d agoThe salt caves were only designed to be used a few times and to be used for maximum draw down, weren't they?
- pbkompasz 18d ago[flagged]
- Jedd 18d agoPeter Zeihan did a 5m video [1] on this 10 days ago (give or take) - and the history of how they've been used, and why the original design (big draw-downs during major emergencies - perhaps 5 of them, ever) hasn't lent itself well to the way they ended up being used. [1] https://www.youtube.com/watch?v=j5g0Ud8i0C0 https://www.youtube.com/watch?v=j5g0Ud8i0C0
- amelius 18d ago> Keep the oil secure against attacks by our adversaries. This is an especially hard challenge because petroleum has this tendency to light on fire, so a huge concentration of it is especially difficult to keep safe. > Release oil quickly so it can reach the market during a supply disruption. But what if the adversaries destroy the refineries or other downstream equipment which is much simpler to do?
- spacephysics 18d agoI think the world events we’ve seen over the last 4 or so years (especially last 12 months), will mean both new (and existing) data centers and refineries will begin to have counter measures beyond a security guard and some fences. Anti-drone equipment for one. The pipelines themselves are tough to secure given how long some are. Closer and closer to a cyberpunk world with faux (or real) military at these data centers and refineries in areas that may not be in direct active conflict. Imagine building a new refinery, the money and time alone, only for a few thousand dollar drone to be snuck in and launched? Insurance on these facilities going to start requiring far more elaborate physical security measures.
- skizm 18d agoWhere can I find more of these incredibly clever engineering solutions explained so simply? Love reading about this sort of stuff.
- deleted 18d ago[deleted]
- georgefrowny 18d agoI 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/high_res_d/1028903.pdf https://digital.library.unt.edu/ark:/67531/metadc840493/m2/1...
- aqfamnzc 18d agoLove the comic sans. It was a different time. :_)
- ck2 18d agoAnd it's going to costs billions to rebuild it in a few years after they finish destroying it by 2028 So I was wondering the other day how many gallons of crude the Epstein Memorial Ballroom could hold if it was sealed off, maybe "AI" can figure it out....