In 2019, the UK became the first major economy to legally commit to achieving net zero CO₂ emissions by 2050. With new evidence of rapid, anthropogenic-induced climate change emerging, it is likely that many climate forecasts have underestimated the speed and extent of climate change. This means that drastic action is needed to both slow emissions and remove carbon from the atmosphere. In this blog, Professor Cathy Hollis, Professor Kevin Taylor, and Dr Lin Ma outline the challenges and opportunities for the UK in carbon capture and storage (CCS) technologies, including a role for the oil and gas sector.

• Carbon capture will be vital in limiting global warming to less than 1.5⁰C over the next century.
• There are currently at least 19 CCS facilities either operating or in development in the UK.
• Depleted oil and gas reservoirs, such as those in the North Sea, are ideal for long-term storage of CO₂ – but require detailed understanding of potential leakage points.
• Policymakers can support and grow the UK’s CCS industry by ensuring it is integrated into net zero solutions, and making oil and gas exploration data available to researchers.

Carbon Capture, Utilization and Storage (CCUS) is the process of capturing carbon dioxide (CO₂) from industrial processes, or potentially directly from the atmosphere, so that it can be recycled for further use or removed to the subsurface. It is one of several negative emission technologies (NETs) that can help achieve net zero. Geological Carbon Storage (GCS) refers to the injection of captured CO₂ into the subsurface to store it permanently, and is the most technologically mature and commercially viable technique for CO₂ storage. GCS has been actioned for over twenty years with a current storage rate of approximately 3.7–4.2 Mt CO₂ a year. The number of projects, and storage capacity, is expected to increase significantly in coming decades with the potential to store up to 25,000 Gt CO₂ globally; this is more than sufficient to limit warming to less than 1.5°C through to the year 2100.

How does Geological Carbon Storage work?

CCUS involves three steps: carbon capture, transport from the source to utilisation or storage sites, then consumption in the industrial process, or injection and storage in a secure geological formation. Typically, GCS refers to the final step, which involves direct and permanent storage of CO₂ in depleted oil and gas reservoirs, water saturated aquifers, salt caverns, or deep coal seams that have not been mined. There are several key criteria for successful direct storage, the most important being that there is physical space to store CO₂, and an overlying impermeable seal to the geological formation to contain the CO₂. This seal prevents leakage to the surface. The CO₂ is injected directly into the host rock, where it migrates locally via fractures or pore spaces in the rock unit. Understanding the size, connectivity and complexity of this pore or fracture network in the host rock, and the sealing properties of overlying strata, is critical to the success of GCS. High-resolution, and multi-scale imaging at The University of Manchester is allowing this to be conducted on a wide range of geological materials at multiple scales. Furthermore, in some cases, such as limestone formations or volcanic rocks, CO₂ can be reacted with the rock and captured as mineral cements. This process is known to occur naturally in geological systems and is now being used on anthropogenic timescales to permanently store CO₂.

The most promising locations for permanent CO₂ storage are depleted oil and gas reservoirs, and many projects are now underway. These have numerous advantages: there is storage capacity for large volumes of CO₂ within pores that previously stored hydrocarbon, the reservoirs have proven seals and traps (having retained millions of cubic metres of hydrocarbon over millions of years), and the well and pipeline infrastructure for CO₂ injection is in place. The reservoirs typically occur at depths of more than 1.5km beneath the surface, usually away from urban areas and often offshore. One challenge is to ensure that injected CO₂ does not leak through existing boreholes to the surface, and therefore new latex-based ‘smart cements’ are being designed to seal boreholes. At a larger scale, research at The University of Manchester is using historical well and seismic data to map seals and determine potential leakage points in North Sea reservoirs leading to development of a confidence matrix for mapping potential leakage points.

Such detailed geological analysis is critical to the safe and secure storage of CO₂, and requires that legacy data from over 50 years of UK oil and gas exploration and production is retained and made accessible to researchers by the government.

What are the challenges of Geological Carbon Storage work so far?

The high cost and low-economic benefit of CCUS, including GCS, has been a major challenge to industry, and it is clear that government support is critical to integrating CCUS into net zero solutions. In 2021, the UK government announced £200 million funding to support the development of at least two carbon capture and storage hub and cluster projects across the UK by the end of the decade. This commitment is essential to the success of blue hydrogen production, which promises a key fuel for future energy use in the UK, but which generates CO₂ during production. Potential sites for hydrogen production include HyNet North West in NW England and North Wales, which are ideally located for storage of industrially-produced CO₂ offshore in depleted gas reservoirs. The scope of work and roadmap to achieve the Green Industrial Revolution are now being rolled out and details are still to be made public.

What is clear is that future solutions will require close collaboration between subsurface engineers and geoscientists, production engineering and the public. Despite the clear benefits to greenhouse gas reduction, there is still uncertainty in the public arena as to the safety and effectiveness of GCS. In particular, although the need for a reduction in atmospheric CO₂ is well understood, some people are concerned about induced earthquakes, leakage of CO₂ and potential hazards to marine life, whilst others fear that it might delay decarbonisation. Some of these concerns can be addressed through advanced atmospheric monitoring and continued public engagement.

It is critical that the geoscience community and the legacy of subsurface research, such as that conducted at The University of Manchester, remains part of the dialogue with government agencies, industry and the public.

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