Executive summary

This briefing explores the options for geological carbon dioxide (CO₂) storage, with the aim of permanently removing CO₂ from the atmosphere, and an emphasis on injecting CO₂ offshore into either deep saline aquifers or depleted oil and gas fields.

Global greenhouse gas emissions have increased by 12% in the last decade, amounting to the highest increase in decadal average emissions on record. To limit warming to 1.5°C or less, future projections suggest that global greenhouse gas emissions must peak between 2020 – 2025, fall by 45% by 2030 and reach net zero by 2050.

To achieve these reductions and transition to a net zero energy system, there will need to be a significant decrease in overall fossil fuel use. However, there will be some end uses, mainly those from industrial processes, agriculture, and heavy-duty transport, that will struggle to decarbonise by 2050 targets. The deployment of carbon capture and storage (CCS) will be vital to both capture emissions from residual point sources and for CO₂ removal from the atmosphere.

There are examples of successful CO₂ geological storage, including the Sleipner Field in Norway which has stored over 25 MtCO₂ over the past 25 years. Existing large-scale projects have demonstrated the ability to monitor the CO₂ plume using time-lapse seismic techniques and shown that, in high permeability formations, the buoyancy of the CO₂ controls the spreading of the plume. These projects have also identified the challenges of: sand production in pressure relief wells, the complexity of the flow in lower permeability formations and the need to control pipe corrosion.

As the CO₂ storage industry develops, there will continue to be significant new technical challenges associated with different geological systems, including structural integrity, flow assurance and geochemical and mineralogical processes.

There will also be new challenges for monitoring, assurance and optimisation of the storage process.

A typical site selected for subsurface CO₂ storage will have permeable rocks, such as sandstone (predominantly quartz) or carbonate (calcite or dolomite) rock, that lie 1.0 – 2.5 km below the surface and may have a porosity of around 10 – 20% of the volume of the formation. Typically, the target reservoir may be tens to hundreds of metres thick and extend laterally for tens of square kilometres.

There have also been some new approaches to geological CO₂ storage in very different rock formations, including basaltic systems, in which CO₂ reacts directly with the rock surface to form minerals.

Global rates of CCS deployment are significantly below those anticipated to be needed to limit global warming to 1.5°C or 2°C, with the present global storage infrastructure only accommodating 40 MtCO₂ /yr. It has been estimated that there is likely to be a need for 7 – 8 GtCO₂ /yr of storage by 2050, and a cumulative storage of approximately 350 – 1200 GtCO₂ by 2100, to keep temperatures below the 1.5°C rise threshold. With typical CO₂ injection wells having injectivity of about 1 – 2 MtCO₂ /year, this will require the global development of many thousands of CO₂ injection wells by 2050. This would be an enormous undertaking, given the multi-year time scale required to plan, develop and commission such wells and the associated reservoirs and transport infrastructure. The technical building blocks are available to build up this industry, but this will need to be underpinned by fundamental research and development to optimise and improve transport, storage efficiency, monitoring and assurance technologies, the systems that link these elements and to identify high quality, secure storage resource. There is also a need for sustainable business models for carbon capture and storage.