Carbon capture and utilization (CCU) is one of the key technologies that may help to reduce industrial emissions. However, the deployment of CCU is hampered by various barriers, including high levels of technical, policy and market uncertainty. The real options theory (ROT) provides a method to account for these uncertainties and introduce flexibility in the investment decision by allowing decisions to be changed in response to the evolution of uncertainties. ROT is already being applied frequently in the evaluation of renewable energy or carbon capture and storage (CCS) projects, e.g., addressing the uncertainty in the price of CO₂. However, ROT has only found a few applications in the CCU literature to date. Therefore, this paper investigates the specific types of uncertainty that arise with the utilization of CO₂, identifies the types of real options present in CCU projects and discusses the applied valuation techniques. Research gaps are identified in the CCU literature and recommendations are made to fill these gaps. The investment decision sequence for CCU projects is shown, together with the uncertainties and flexibility options in the CCU projects. This review can support the real options-based evaluations of the investment decisions in CCU projects to allow for flexibility and uncertainty.

Carbon Capture and Utilization (CCU) involves the capture and use of CO₂ as a resource to create valuable products. The economic viability of CCU technologies is crucial for its implementation in real life. The competitiveness of various CCU technologies has been investigated frequently resulting in a variety of economic feasibility studies and economic indicators. This study performs a tutorial review, in which practical guidance is given on the implementation of TEAs for chemical CCU technologies. The tutorial review will critically examine the economic feasibility studies that have been performed in this field and will advise how these studies can be improved in the future. A thorough review of the literature set is performed, in which we evaluate the quality of the economic feasibility studies in the literature set by comparing these studies to the guidelines from Zimmermann et al. (2020). The five phases of an exhaustive TEA are (I) goal and scope, (II) data inventory, (III) calculation of indicators, (IV) interpretation, and (V) writing the report. We evaluate the implementation of these five phases in the economic feasibility studies in the literature set. The tutorial review shows that economic feasibility studies for chemical CCU technologies can and should be improved in various manners. Phase I and II are often skipped or incomplete. Phase III, the calculation of assessment indicators, shows diversity in the indicator base which hampers comparability across CCU technologies of the technical and economic criteria that are key for the feasibility. Phase IV, the interpretation of results, is often missing in the literature set or lacks thorough uncertainty and sensitivity analyses. These findings suggest that future economic feasibility studies should be made in a more standardized way to improve both the quality and comparability of economic feasibility studies. This tutorial review has raised important questions about the management of uncertainty and flexibility in economic feasibility studies. The integration of Real Options Analysis (ROA) within the TEA is proposed to analyse the investment decision in CCU technologies in a dynamic setting.

The subsurface is increasingly being recognized as a multifunctional resource supporting key activities in the transition towards a sustainable society (e.g. geothermal energy, CO ₂ storage and groundwater extraction). In existing literature, there remains a lack of integrative, cross-disciplinary research addressing the interactions and trade-offs between these activities. Addressing this gap is essential for sustainably managing the subsurface. This paper introduces the DIAMONDS Elevator, a conceptual framework designed to support such collaboration by organizing subsurface decision making across interconnected levels and facilitating knowledge exchange between disciplines. The framework is developed within the DIAMONDS research initiative and is applied to a case study on the multifunctional use of the subsurface in Flanders, focusing on interactions between aquifer thermal energy storage and groundwater extraction. Through this case study, we demonstrate how the DIAMONDS Elevator can be used to structure interdisciplinary analyses and decision-making processes, illustrated in detail from the perspective of an economics researcher. In addition, we position integrative methods and tools, including principles, criteria and indicators, within the Elevator framework. This paper shows how structured interdisciplinary approaches can enhance transparency, support scenario development and inform more sustainable subsurface governance. The DIAMONDS Elevator, as a visual guideline, intends to support interdisciplinary collaboration for sustainable subsurface management.