In-situ low-temperature CO2 mineralization and hydrogen tracing using ultramafic rocks from Australia and New Zealand
Muhannad Al Kalbani, Mehdi Serati, Harald Hofmann, Thierry Boré, Hamid Roshan
Abstract
This study investigates the practical effectiveness of in-situ CO 2 mineralization in ultramafic rocks under realistic conditions, focusing on early-stage reactions. Samples from a pilot well intersecting an ultramafic body in New Zealand, along with other ultramafic samples from New Zealand and Australia, were used. The tests involved serpentinite and dunite samples subjected to low bottom-hole static temperatures (25–70 °C) in a batch reactor designed to replicate in-situ conditions. Results indicated early mineralization yields of up to 4% within 5 h. The highest reaction rate of 1 . 95 × 1 0 − 5 mol g − 1 s − 1 was observed for a Greenhills dunite milled core sample from New Zealand at low-temperature conditions ( < 70 ∘ C ). Additionally, hydrogen was collected during the reaction of another dunite sample from the Greenhills cored well, suggesting significant potential for geological hydrogen production. A generation rate of 0 . 5 mmol kg olivine − 1 ⋅ h − 1 was estimated under these low-temperature conditions over the 5-h test period. These findings highlight the dual benefits of CO 2 sequestration and hydrogen generation, with the Greenhills Complex theoretically capable of sequestering a minimum of 5 billion tons of CO 2 due to its area of 14 km 2 and dunite thickness exceeding 600 m. The region’s proximity to major emission sources enhances the feasibility of large-scale sequestration and highlights the valuable insights this work offers for sustainable carbon management. • Examines CO 2 mineralization at depth using data from a pilot well in ultramafic rock. • Early mineralization rates are lower in in-situ conditions than ex-situ scenarios. • Up to 4% mineralization yield achieved at 25–70 °C within 5 h. • Hydrogen detected in low-temperature tests suggests geological hydrogen production. • CO 2 mineralization in ultramafic rocks could contribute to sustainable carbon management.