Project Overview
The Greensand Project is a landmark carbon capture and storage (CCS) initiative designed to permanently store captured CO₂ in depleted sandstone reservoirs within the Nini Field, approximately 1,800 metres below the seabed in the Danish North Sea.
At full development, the project has the potential to store 0.45–1.45 million tonnes of CO₂ per year by 2025–2026, rising to up to 8 million tonnes annually by 2030 – equivalent to more than 13% of Denmark’s current annual emissions.
As CCS projects scale globally, the technical challenge of repurposing legacy oil and gas infrastructure safely and efficiently has become increasingly important. These projects require a combination of deep hydrocarbon wells expertise and emerging low-carbon engineering capability.
Since 2022, Elemental Energies has supported INEOS and its project partners by updating the DNV-certified proof of concept for Phase 2, focused on the conversion of existing wells in the Nini West and Nini Main fields for CO₂ injection.
In March 2023, the project reached a major milestone when CO₂ captured in Belgium was successfully injected and stored beneath the Danish North Sea — marking the first cross-border offshore CO₂ storage project in the world.
Scope of Work
Elemental Energies led the conceptual well engineering assessment to evaluate the conversion and repurposing of legacy oil and gas wells for CO₂ injection as part of the Greensand CCS development.
The team updated the original DNV-certified proof of concept, incorporating technical advances, updated CCS industry guidance, and evolving project requirements ahead of a final investment decision for commercial deployment.
Scope included:
- Updating the original DNV-certified proof of concept for Phase 2 CCS development
- Conceptual design for the conversion of Nini West and Nini Main wells to CO₂ injection service
- Detailed engineering review of legacy well integrity and barrier systems
- Evaluation of pressure limits and operational constraints for CO₂ injection in wells originally designed for hydrocarbons
- Assessment of potential conversion of legacy wells into CO₂ monitoring wells
- Engineering support for decommissioning of redundant platform wells
- Field-wide evaluation of well integrity and lifecycle management requirements for long-term storage operation
“Projects like Greensand demonstrate how existing offshore infrastructure can be safely repurposed to support large-scale CO₂ storage. Our rolefocused on ensuring the legacy wells could meet the integrity requirements of long-term injection and storage.”
Julie Copland, Head of Wells
Elemental Energies
Key Highlights
The Greensand Project required a multidisciplinary approach combining wells engineering, well integrity assessment, and CCS-specific technical expertise.
Key challenges addressed included:
Legacy well design for CCS
Many wells in the Nini fields were drilled decades ago, before CCS was considered. The team recalculated safe operating pressure limits, verified existing well barriers, and identified where additional barriers may be required to minimise leakage risks.
Batch vs continuous CO₂ injection
Unlike pipeline-fed CCS projects, Greensand may involve CO₂ transported by ship and injected in batches. This introduces multiple start-up and shut-down cycles, requiring careful evaluation of their impact on well integrity.
CO₂ behaviour and materials compatibility
The team assessed the phase behaviour of CO₂, corrosion risks, and potential interactions with water within the reservoir and well system, ensuring safe long-term storage conditions.
Lifecycle well integrity
The study evaluated operational integrity across the full lifecycle of the project, including monitoring, potential well interventions during the injection phase, and eventual abandonment.
Alignment with CCS industry guidance
The work aligned the project with emerging industry best practices, including OEUK well decommissioning guidance for CO₂ storage projects.
Conclusion
The Greensand CCS development represents a major step forward in the commercial deployment of carbon storage in Europe.
While the safe delivery of CCS projects depends heavily on well engineering expertise, the complexities of repurposing legacy oil and gas infrastructure demand multidisciplinary teams capable of combining traditional hydrocarbon experience with emerging low-carbon engineering knowledge.
Elemental Energies’ work on the Greensand Project helped provide the technical foundation required to de-risk well conversion and support the project’s progression toward full-scale commercial deployment.
