Optimizing in-situ CO2 mineralisation: geomechanics and scalability in dunite and serpentinite rocks - Examples from Australia and New Zealand

Muhannad Al Kalbani; Mehdi Serati; Harald Hofmann; Tom Ritchie; Thierry Bore

doi:10.1016/j.scitotenv.2024.172277

Optimizing in-situ CO₂ mineralisation: geomechanics and scalability in dunite and serpentinite rocks - Examples from Australia and New Zealand

Sci Total Environ. 2024 Jun 1:927:172277. doi: 10.1016/j.scitotenv.2024.172277. Epub 2024 Apr 10.

Authors

Muhannad Al Kalbani¹, Mehdi Serati², Harald Hofmann³, Tom Ritchie⁴, Thierry Bore²

Affiliations

¹ School of Civil Engineering, The University of Queensland, St. Lucia, 4072, QLD, Australia. Electronic address: m.alkalbani@uq.edu.au.
² School of Civil Engineering, The University of Queensland, St. Lucia, 4072, QLD, Australia.
³ School of the Environment, The University of Queensland, St. Lucia, 4072, QLD, Australia; CSIRO, 41 Boggo Road, Dutton Park, 4102, QLD, Australia.
⁴ Hardie Pacific, 57 Leith Street, Dunedin, 9059, New Zealand.

PMID: 38608887
DOI: 10.1016/j.scitotenv.2024.172277

Abstract

The collective drive towards achieving net-zero greenhouse gas emissions by 2050 has spurred interest in engineering solutions for carbon capture and storage worldwide. One such approach involves the permanent storage of CO₂ in earth-abundant Ca-, Fe-, and Mg-bearing silicate rocks and minerals as carbonates via the process of CO₂ mineralisation. This necessitates a thorough understanding of carbonate conversion under geologically relevant conditions. Nevertheless, research on CO₂ injection for mineralisation via naturally fractured host rocks or induced fractures, with a research emphasis on rock mechanics and stimulated reservoir volumes (SRV) within geoengineering CO₂ storage, is continuously expanding. This research addresses critical challenges related to identifying favourable geographic locations for CO₂ mineralisation. It specifically focuses on the abundant availability of Mg, Ca, and Fe cations for exothermic CO₂ reactions and their impact on fracture conductivity during in-situ mineralisation. A comprehensive analysis of 26 dunite and serpentinite samples from diverse locations in Australia and New Zealand, including 10 from a cored drilled hole, was conducted. Quantification of divalent cation (Mg, Ca, Fe) content and cation release capacity using XRF and XRD revealed higher cation percentages in dunite samples (approximately 30 %) compared to serpentinite samples (approximately 26 %). Additionally, the study estimated the stimulated rock mass-to-CO₂ sequestered ratio, [Formula: see text] , with dunite samples averaging approximately 2.20 [Formula: see text] values and serpentinite samples averaging approximately 2.53. Geomechanical testing enabled the prediction of fracture propagation pressures during aqueous CO₂ injection for in-situ mineralisation and the estimation of fracture geometries, emphasizing the role of rock stiffness in determining fracture width (averaging 6.0 mm). Furthermore, the research estimated the rock volume exposed to CO₂-laden fluid during injection, particularly focusing on the GHQ-3 sample, which theoretically amounted to approximately 600 kg of rock capable of sequestering around 300 kg of CO₂ for a 10 m3 fluid volume with a CO₂ concentration of 1molkg^-1. The study established a relationship between injected volume and CO₂ uptake, suggesting the potential for significant CO₂ sequestration scalability by employing horizontal wells and fracturing additional zones, thereby creating and intersecting multiple transverse fractures along a single target zone.

Keywords: Australia; Basalt; CO(2) mineralisation; Climate change; Enhanced mineralisation; Ex-situ; Fracturing; In-situ mineralisation; Mineralisation; New Zealand; Peridotite; Serpentinite; Ultramafic.