Locked away: geological carbon storage

To keep global warming temperatures below 1.5°C, many thousands of CO₂ storage wells will be required by 2050 to lock away millions of tonnes of CO₂ underground for thousands of years. This report outlines the latest evidence on the practicalities and challenges associated with storing CO₂.

What is Geological Carbon Storage? 

Once CO₂ has been captured from point sources, such as industrial plants, or directly from the air, it can be compressed and injected into rocks at depths of 1 – 2.5km below the surface of the Earth, safely trapping it for thousands of years. These storage reservoirs are typically made up of a sandwich of permeable rock, with overlying and underlying layers of impermeable rock which prevent the CO₂ from escaping. 

What are the challenges of Geological Carbon Storage?

The geology of each potential storage site is unique and thus it is required to characterise each site to determine:

• How much and how fast CO₂ can be injected.
• How the CO₂ migrates within the rock. 
• The presence of potential leak paths.

As the site develops, different challenges related to monitoring, assurance and storage optimisation will arise and need to be overcome to maximise the efficiency of a site. 

Is Carbon Capture and Storage (CCS) safe?

The chance of CO₂ escaping the reservoir is low, and well-regulated wells are estimated to retain 98% of their CO₂ over 10,000 years. Measures to ensure CO₂ is injected safely include:

• Using an injection rate suitable for the site-specific geology to avoid fracturing seal rocks.
• Using pressure relief wells to reduce sub-surface pressure. 
• Continuous monitoring to detect and rectify leaks.

What is the future for Geological Carbon Storage?

CCS is a required practise to achieve Net Zero. As the CO₂ storage industry develops, there will be continued advances in improving predictions of CO₂ migration, technologies for monitoring reservoirs, and enhancing the capacity of storage systems. All of these advances will increase the efficiency of CO₂ storage and speed of setting up new CCS sites. 

In addition, novel storage techniques are also emerging, including harnessing reactions between CO₂ and minerals to store carbon, which could dramatically increase the number of places where CCS is geologically possible. 

It is predicted that up to 400 new wells are required each year up to 2050 to achieve global climate ambitions. This will need to be underpinned by fundamental and continual research, and the emergence of an appropriate policy and regulatory environment to make CCS a safe and effective practise for a low-carbon future.