Advancing CO₂ sequestration integrity: Development and application of the CO₂ storage integrity index in diverse geological and operational settings

This study introduces the CO₂ Storage Integrity Index (CSII), an integrated operational framework developed to evaluate the stability and integrity of CO₂ storage within geological reservoirs over time. The CSII integrates crucial risk factors, such as pressure stability, area of review expansion, caprock integrity, and interlayer pressure interactions, offering a robust framework for assessing risks and ensuring regulatory compliance in CO₂ sequestration projects. While CSII consolidates existing monitoring parameters rather than providing new fundamental insights, it addresses the operational need for real-time integrated risk assessment in commercial CCS projects. Through detailed numerical simulations, the dynamic responses of CO₂ storage to various geological and operational parameters are examined, highlighting the critical influence of factors such as reservoir depth, thickness, geological heterogeneity, and injection rates on storage integrity.

Key findings from the application of the CSII reveal that shallow reservoirs (∼800 m) are more prone to higher CSII values and greater sensitivity to changes, resulting in increased risks due to lower pressures and higher buoyancy forces. In contrast, deeper reservoirs (∼3000 m) show more stable conditions, maintaining CO₂ in a supercritical state, which minimizes risks. Thicker reservoirs (∼300 m) exhibit higher variability and sensitivity in CSII, presenting challenges in managing injection pressures, while higher injection rates further exacerbate these dynamics in shallow to mid-depth reservoirs.

While the current study focuses on core risk factors, the proposed extension of the CSII to include additional factors impacting CO₂ storage risk, such as Joule-Thomson cooling, geomechanical risks, thermo-mechanical risks to caprock, dry-out phenomena, and integrity of wells, is discussed as a potential enhancement for future analyses. These factors will further improve the ability of CSII to comprehensively assess the risks in CO₂ storage projects.

The CO₂ Storage Integrity Index (CSII) provides a valuable tool for developing tailored injection strategies based on reservoir-specific characteristics, ensuring safer and more reliable CO₂ sequestration. This framework significantly contributes to the effective risk management of geological storage, supporting the broader implementation of carbon capture and storage (CCS) as a critical technology for achieving net-zero emissions.