“Oh no! I’d better call the Porthos office to stop construction (of our CO2 injection project)! Apparently, we are injecting in unviable depths!”, wrote Joop de Kok from EBN in the Netherlands as a comment to a LinkedIn post from Rachael Moore (CarbStrat) the other day.
In her post, Rachael criticises the decisions made by the authors of a newly published Nature paper in which the authors present a reassessment of the total global CO2 storage capacity. The authors conclude that the current total CO2 storage capacity is about an order of magnitude less than what was previously assumed – from around 11,800 to 1,460 Gt CO2 .
News outlets picked up on this. For instance, the Financial Times came up with the following title: “Carbon capture set to be less useful in tackling climate change, scientists warn”. Rachael suggested a new title though: “Sufficient carbon storage resources to meet next 100-200 years of CCS needs”.
As the reaction from Joop de Kok already alludes to, it is the deviation from otherwise widely accepted depth criteria for successful CO2 storage projects that has not only surprised Rachael Moore, but also the Global CCS Institute. In an official release, they state: “For example, their depth limits of 2,500 meters for subsurface storage ignore successful projects like Northern Lights operating at 2,600 meters, while their 300m ocean depth restriction overlooks Brazil’s decade-long experience with CO2 injection at 2,000m water depths.”
And it is not only the maximum depth limit the authors are restrictive about, it is also the minimum depth. Rather than using the conventional and widely accepted 800m mark, the team of researchers applied a 1,000 m minimum depth. By using a more restricted depth window, it is no surprise that the estimated storage capacity is smaller than what was previously thought.
The authors also applied a very conservative spatial buffer of 25 km between densely populated areas and new injection projects. The Global CCS Institute adds: “The study’s 25km buffer zone around populated areas also appears conservative when compared to operational experience and discordant with the typical approach to permitting. CarbFix operates at 8km from populated areas and Shell Quest at 15km. Existing projects demonstrate through rigorous permitting and risk assessments that high safety standards can be met in practice.”
What is very important to stress is that despite this “downgrade”, and whatever you think of its assumptions, there is still plenty of storage space available. Rachael writes in her post, “We need 3-12 Gt/yr of CO2 storage by 2050, depending on how long we continue to use fossil emissions.” We have plenty of space to fill.
I’d say, geological storage space is a rather uninteresting factor in the whole debate of getting CO2 injection projects over the line. The limiting issue at the moment is not related to subsurface factors, but rather the financial side of it. That’s where the challenges lies.
