In-Situ CO2 Mineralization Case Study: Optimizing Well Design and Injection Strategy in the Greenhills Ultramafic Deposits, New Zealand

Summary In this paper, we present a detailed case study of in-situ carbon dioxide (CO2) mineralization in the Greenhills dunite deposit in New Zealand, highlighting a comprehensive approach to well design, hydraulic fracturing, and injection modeling using carbonated water. Leveraging experimentally derived geomechanical and reaction kinetics data, an integrated hydraulic fracturing and reservoir simulator was used to evaluate various well trajectories and injection parameters under strike-slip stress conditions. Results show that optimized multistage horizontal wells, particularly those aligned in the Shmin direction, can generate fracture networks with surface areas sufficient to store up to 90 kt of CO2 per well, with annual injection rates exceeding 50 kt/yr. While mineralization kinetics were studied in a previous publication, this case study provides a technically grounded framework for deploying ultramafic formations as long-term carbon sinks. The study also outlines strategies for well completion and monitoring and emphasizes the importance of future economic assessments and regulatory readiness to advance field deployment of in-situ mineralization technologies.