One of our main takeaways from the CO₂ storage efficiency conference in London on 14-15 September was the shared concern about industry credibility. Here’s one of the reasons why: Communication.

More specifically: Within the technical subsurface world, our scientists have a standard way of communicating potential and confidence. These numbers represent a theoretical potential of how much CO₂ that can be stored safely underground. Yes, the important keyword here is theoretical. And the situation right now, in many parts of the world, is that policy makers and business developers have taken the theoretical numbers for face value. It is quite possible that the technical subsurface experts haven’t been too successful in communicating the underlying assumptions and resulting uncertainty, and that’s really the reason for this.

Seeing these estimates as a reality would be like a business developer juxtaposing market potential and short-term earnings. Put differently: It’s a best-case scenario for which there is no guarantee.

Many evaluations stop at the definition of pore space in the trap alone

We assess the project lifetime injectable capacity. Read further to see how this is done.

Considering CO₂ storage potential is generally about three steps:

STEP 1 (static domain): CO₂ atlases

The country-based CO₂ atlases are presenting a very large hypothetical estimate. The potential is based on very rough assumptions and does not necessarily consider real traps where the CO₂ can be stored.

The numbers are large: UK has estimated a CO₂ storage potential of 75 gigatonnes (Gt), Denmark has estimated 22 Gt, while Norway has estimated 70 Gt. It is also worth noting that the estimates are without time constraints, which means that a poor reservoir can still be relevant if you have 10 000 years to inject a certain amount of CO₂.

STEP 2 (static domain): Identifying traps and storage complexes

It is up to each company to identify traps and CO₂ storage complexes consisting of the following: sealing rock, reservoir rock and aquifer with enough porosity and permeability that the resulting pressure pulse from the CO₂ injection can move far.

OPEN AQUIFER VS. CLOSED TRAP: A SIMPLIFIED ILLUSTRATION

The advantage of an open aquifer is greater storage capacity. However, the injected CO₂ can migrate long distances over time. In a closed trap, you have full control.
Please note that the simplified illustration is for informational purposes only.

STEP 3 (dynamic domain): Reservoir modelling

In the last step of the maturation phase, a reservoir simulation model is built to model how fluids will flow and pressure will build up in the reservoir. This is done to ensure that the sealing rock will not break. Within the constraints of the seal, the reservoir and aquifer, it is possible to calculate how much CO₂ can be injected into a potential storage site within a given time period, which is often set at 25 years.

The data availability, data quality and hence confidence is considered in connection with relevant business aspects, such as distance to infrastructure and preferences of strategic business alliances.

A full-scale reservoir simulation model, where the number of injection wells are optimised, is often both expensive and time consuming. Because of this, only the most promising CO₂ storage sites are modelled in the dynamic domain within the standard 25 years’ time frame for a business case.

Realistic storage potential: A Norwegian example

Let us explain this further with an example from a project we did for a client of ours. To be clear: We have Intellectual Property rights to the data, which is why we can share this information.

STEP 1: Hypothetical estimate

The Norwegian CO₂ storage atlas presents the estimated potential in this area to be 4.4 Gt (4.400 million tonnes).

STEP 2: Evaluating well and seismic data

An independent evaluation of the well data and seismic data available was carried out, integrating all aspects into a comprehensive understanding of the geology underground that forms the elements of a CO₂ storage complex:

the sealing shales and how much pressure they can hold before they break,
the reservoir, its quality and how much CO₂ it potentially can store with an endless time frame.
the aquifer, its quality, connectivity and how large it potentially can be.

The estimate is now 470 million tonnes, about 11 percent of the estimate in Step 1.

STEP 3: Simulation model

With all elements forming the static part of the CO₂ storage complex defined, we computed the storage capacity of the best prospects based on injectivity. This let us predict how the CO₂ will flow in the reservoir and how it will push the existing brine water already present underground out into the aquifer.

When we used our simulation model to predict the full CO₂ injection capacity over 25 years in the dynamic domain, we ended up with a final estimate of 200 million tonnes distributed over several closed traps. This is about 5 percent of the estimate in Step 1.

Senior Geoscientists Gustavo Lopez and Sveinung Hatløy, ExploCrowd.

Is it all a guessing game?

Absolutely not!

Even though the more realistic potential is merely a fraction of the theoretical storage capacity communicated in national CO₂ atlases, the storage potential of both UK, Norway and Denmark is still considerable. When the storage capacity estimates at the different levels of maturity are fully understood by more people, it is likely that some business cases will be calibrated. But still, hundreds of millions of tons of CO₂ emitted and captured in Europe can be stored:

For instance, if only 5 percent of the estimated storage i UK, Norway and Denmark turned out to be realistic, then we would be talking about 8 Gt (8.000 million tonnes) CO₂ storage capacity.

Our core message is this: Finding quality storage sites require detailed insights at a local scale and in a regional context for the subsurface. This will make you able to rank the possibilities and select the best business opportunity. There are companies with experts already ready to target the best and commercially most attractive CO₂ storage sites. And as we all now: Time is of the essence to secure the best acreage.

Are you a participant in the shadow race of getting hold of the best acreage? When competing for aquifer, you want to be the first mover, ensuring that you are the first to inject the CO₂ into the storage site. If you don’t know why, feel free to contact us, and we will share more of our knowledge.

CO₂ storage potential: Getting the numbers right