Probabilistic CO₂ storage capacity appraisal of the Greensand Project in the depleted Nini oil field, offshore Denmark

The Greensand Geological Carbon Storage (GCS) project aims to repurpose multiple depleted oil fields in the North Sea Basin for carbon sequestration, storing up to 8 megatonnes (Mt) of CO₂ per year by 2030. It is anticipated that 0.45 mtpa will be stored in the Nini West oil field, offshore Denmark, between 2026 and 2040. This study provides an independent probabilistic appraisal of the storage capacity feasibility of Project Greensand, utilizing publicly available data and following the SPE Storage Resources Management System (SRMS) framework. Arps Decline Curve Analysis (DCA) demonstrated an excellent fit to the historical production rates, with a cumulative error of 0.41 %, confirming its effectiveness. History matching using the Gaussian Pressure Transient (GPT) equation, supported by Sequential Quadratic Programming (SQP) optimization and sensitivity analysis of reservoir parameters, resulted in a highly accurate fit with an error of just 0.0068 %. Having thus constrained reservoir parameters, the Estimated Ultimate Storage (EUS) capacity appears to surpass the 10-year storage target of 4.5, with a deterministic EUS of 8.38 (average 2,296 t/day). The EUS, using SRMS terminology, accounts for just ∼4.71 % of the Total Storage Resource (TSR), indicating vast additional potential for future storage. Subsequent probabilistic analysis reveals that the deterministic estimate closely aligns with the P50 estimate of 7.73 Mt, whereas the P90 estimate of 3.25 is slightly lower than the planned target of 4.5 Mt. Flow scaling ratio investigation shows that lateral flow will dominate during the early injection stages and in wellbore proximity, whereas buoyancy will become increasingly prevalent after three years of injection. Given that public funding supports Project Greensand, full transparency in the reporting of storage capacity and sharing of relevant data are advocated here.