Can we store excess sea water underground?

17 May 2016

Question

Why can't we replace the space from which we have extracted crude oil with seawater in an attempt to solve the rising sea level crisis? With the amount of oil we extract surely it could make a difference seeing as the immediate threat is posed by greenland melting and causing sea levels to rise 6-7m? although since water moves in to replace the oil we take out the process would probably have to be done immediately and be extremely complex.

Answer

We asked Dan Jones to if this theory had legs...

Dan - I like this question. I did a really simple, back of the envelope type calculation before the show so everyone please, feel free to go do you own and check this. So, we produce about 90 million barrels of oil per day and with the volume of that we could fill the O2 stadium 1,300 times per year, so fill it up and drain it about 1,300 times with the amount of oil that we produce. But looking at sea level rise, although the report of sea level rise is just a rate of 3.2mm per year, at the moment there's a lot of ocean out there. There's a huge surface area so if you look at just that 3.2mm over the entire volume of the earth, that is the entire volume surface area of the ocean, it's about 1,000 times more than the amount of oil that we produce. So it looks like no, there's not nearly enough room by about a factor of 1,000 unfortunately, and I don't even know if you could do this. If you could put the seawater in those places would it even stay there? The rock might be a bit more...

Chris - When we extract oil from the ground these rocks are porous rocks. They're like a sponge with oil in them and the way the oil is removed is by displacing it out, for the most part, with water already isn't it? So, one could argue that many of these oil wells are already saturated with water by the time you've recovered the oil so, it's a bit of a non-starter by the look of things. But thank you for those fantastic numbers.

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