How to Store CO2 Underground: Insights from early-mover CCS Projects

Reduction in global greenhouse gas emissions is a key issue for modern human civilization. Part of the solution to this challenge is long-term storage of CO₂ in deep geological rock formations. Other key solutions to achieving reductions in greenhouse gas emissions are to greatly expand the use of renewable sources of energy and to use energy much more efficiently. To explain why we need engineered geological storage of CO₂ we first review the history of use of fossil fuels and then look at the history of the discovery of the greenhouse gas effect. This provides the basis for the urgent need to achieve the low-carbon energy transition. CO₂ Capture and Storage (CCS) is vital because it: (a) provides a mechanism for decarbonising power supply and industry, (b) allows the energy transition to be achieved faster and at a cheaper cost than by using only renewable energy sources, and (c) it allows negative net-CO₂ emissions projects to be deployed. Finally, we explain the components of CCS - a set of technical solutions to remove CO₂ from industrial processes and to inject it into the subsurface in order to isolate the CO₂ from the atmosphere. 

In this chapter we will review the main processes involved in the geological storage of CO₂ and then consider the overall feasibility of storing large volumes of the CO₂ in the deep subsurface. This leads us into an evaluation of the CO₂ storage capacity and the various theoretical and practical constraints for CO₂ storage projects, globally. The essential questions for any CO₂ storage project are: (a) where can we store the CO₂? (b) how much CO₂ can we inject? (c) can we store it safely? and (d) can we store it cost-effectively? We address these questions by reviewing what is known about containment and trapping mechanisms, and then discuss methods for calculating storage capacity, flow dynamics, injectivity and the geo-mechanical response. Insights from early-mover projects are pulled in at each stage to illustrate the how underlying theory can be applied in practice.

Designing CO₂ injection projects and maturing them from the concept stage to the execution stage is a major undertaking, but at the same time based on established practice. Using historical practices developed in the oil and gas industry, we can adapt engineering design concepts to the CO₂ storage task. Here we look at injection well design and CO₂ transport systems, drawing on real project experience. We then develop a framework for managing CO₂ storage sites and look at approaches for forecasting CO₂ flow behavior in the subsurface. Handling well integrity issues forms an important part of project design, while monitoring methods allow us to manage the site during injection operations and in the post-closure period. Operational experience demonstrates that CO₂ storage projects can be executed safely and that there are tools and methods in place to handle and mitigate technical risks. The real challenges, at present, are the lack of societal and market drivers needed to accelerate the technology.

Engineered geological storage of CO₂ is an active and established technology. We have demonstrated this, using examples from the long-running offshore projects at Sleipner and Snøhvit in Norway and the onshore industrial-scale projects at In Salah in Algeria, Quest in Canada and Decatur in the USA. Useful insights from smaller pilot projects were also drawn. However, CCS as a climate-mitigation action is progressing much slower than needed. To accelerate the deployment rate, four key drivers are needed: (a) emphasizing the climate-mitigation value of CCS, (b) stimulating carbon prices (c) leveraging the benefits of CCS-hub infrastructures, and (d) pulling in negative emissions technologies. If these factors begin to gain traction, then we might indeed see the acceleration in CCS project deployment that is required to meet global climate-mitigation objectives.