Sequestering CO2 Underground
While the significance of tackling climate change by reducing the amount of carbon dioxide we’re releasing into the atmosphere in the first place is paramount, capturing the gas and storing it somewhere where it is not heightening the severity of global warming can be an important part of the solution.
You’ll often hear about companies boasting about how many trees they’ve planted to offset their carbon footprint, but another way to remove carbon dioxide from the atmosphere is by storing it deep underground. This week, The Royal Society published a policy briefing on this very field: offshore carbon storage wells. The report, titled Locked Away - Geological Carbon Storage, details the viability of processes to permanently store carbon dioxide into deep saline aquifers or depleted offshore oil and gas reserves. Here to give us the lowdown is Andy Woods from the Department of Earth Sciences at the University of Cambridge, who chaired the report’s working group.
Andy - There are parts of the energy system where it's very hard to decarbonize, particularly in industry. So in cement manufacture, in fertiliser manufacture, and in iron and steel manufacture, there's a lot of carbon emissions as part of the process of making those products. And so one solution is to capture the carbon as you produce those products. And then that carbon can be compressed and pumped and then stored in deep saline aquifers offshore. There's a couple of projects being developed at the moment. In the UK there's the net zero Teesside project, which is planning to capture a whole series of carbon sources and pump them offshore and store them in a reservoir one and a half, two kilometres below the sea floor in the North Sea.
James - Can you go into a bit more detail on that? What does geological carbon storage look like? How does it work?
Andy - These streams of carbon dioxide, they're compressed and it becomes a very dense, high pressure liquid with a density close to, but a bit smaller than the density of water. And that's injected into these sandstone layers about one to two kilometres below the sea bed. Typically, the geologic strata isn't exactly horizontal, but it'll have highs and low points. And if you can find a region where there can be some trapping, if you put the carbon dioxide into that, it'll float on top of the water in this sandstone layer. And you'd be looking for one where there's shale or some other very low permeability, low conductivity rock above, and that'll trap the carbon dioxide in that store. That gives you what's called structural trapping. And then, over time, the carbon dioxide is soluble in the water in this saline aquifer and so it'll gradually dissolve into the water and that'll increase the integrity of that storage.
James - You mentioned before a couple of the projects already underway. What's the aim then with publishing this report? Is the UK going to be able to perhaps position itself as a real player in geological carbon storage?
Andy - So what we wanted to do is actually focus on the storage side of 'carbon capture and storage' and just look at the technical and engineering challenges and the sciences needed to drive this technology forward, but also to identify how big a part of the energy transition this will be. So the IPCC have projected that we'll need to store between about 300 and 1000 gigatons of carbon by the end of the century. And just to put that in scale for reference, if you look at a net zero energy system, the International Energy Agency have a model about what a net zero energy system looks like in 2050. And that will include carbon storage storing about seven or eight gigatons a year. And that's about 20% of the total emissions that we produce today. So it's a very large fraction of the total carbon emissions.
Andy - And that requires a scale up of our carbon storage potential from what we have today, which is about 40 megatons a year up to this seven or eight giga tons a year. So that's scaling it by a factor of 200. And so the purpose of this report was really to highlight, to policy makers, the great potential of this carbon storage as a very important part of the energy transition, but also to alert them to the need really to scale up investment and regulation, and the policy framework to actually accelerate our implementation of carbon storage. And for the UK this could be a major source of growth and a major new industry that we could develop with huge potential to export the technology and the technical solutions, as well as storing lots of our own carbon emissions.