In-situ low-temperature CO2 mineralization and hydrogen tracing using ultramafic rocks from Australia and New Zealand

This study investigates the practical effectiveness of in-situ CO2 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 degrees 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 1.95x10(-5) mol g(-1)s(-1) was observed for a Greenhills dunite milled core sample from New Zealand at low-temperature conditions (<70 degrees 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 mmolkg(olivine)(-1)center dot h(-1) was estimated under these low-temperature conditions over the 5-h test period. These findings highlight the dual benefits of CO2 sequestration and hydrogen generation, with the Greenhills Complex theoretically capable of sequestering a minimum of 5 billion tons of CO2 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.