Science Questions

Can we store excess sea water underground?

Mon, 16th May 2016

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Question

Kaelan asked:

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 theFloods in Yourkshire 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 thereís a lot of ocean out there. Thereís 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, itís about 1,000 times more than the amount of oil that we produce. So it looks like no, thereís not nearly enough room by about a factor of 1,000 unfortunately, and I donít 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. Theyíre 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 isnít it? So, one could argue that many of these oil wells are already saturated with water by the time youíve recovered the oil so, itís a bit of a non-starter by the look of things. But thank you for those fantastic numbers.

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I see a problem with energy balance.
In the early days of oil exploration, it took 1 barrel of oil to extract 100 barrels of oil. Fairly efficient, you might say.

If we are going to pump sea-water underground, that will take energy - probably much of it from fossil fuels.

But the "easy" and "accessible" sources of oil have now been largely consumed. Recently, the US & Canadian governments were seriously considering using tar sands to provide oil to the USA. This source is thought to consume about 30 barrels of oil to deliver 100 barrels of oil. That is really inefficient, and will result in more CO2 being emitted.

If we look at the cause of sea level rise, it is not the pulse of increased energy output that humans have produced from their beeswax candles, wood stoves, or oil, coal and nuclear power stations. That is a mere drop in the bucket compared to the solar radiation which arrives on Earth every day (and leaves every night), or even the geothermal energy which comes out of the Earth every day.

It is the fact that we have put extra CO2 into the atmosphere, while chopping down (and often, burning) the trees that would have absorbed some of it.

The melting is caused because the small increase in CO2, from 350 ppm to (now) slightly over 400 ppm holds in a tiny fraction of the Sun's heat which escapes overnight. For every Joule that humans generate from fossil fuels, the Sun injects more Joules into the atmosphere and even more into the oceans and ice sheets.

So the solution is not to use fossil fuels to refill the old oil reservoirs, but for people to vote with their roof and install solar panels etc, which will at least slow down the rate of heat retention and sea-level rise.
evan_au, Wed, 20th Jan 2016

The total oil we have ever used is less than 100 km≥ ( I have assumed a density of 1, yes I know it's wrong but...).

That would be less than a third of a milimeter of sea level rise if you put that much back down into the ground.

The world's oceans are really big!!! I mean really really big! Tim the Plumber, Fri, 26th Feb 2016

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