Fracture Topology in Mafic Formations: Implications for Geological Carbon Storage

Abstract

[Abstract]: Carbon mineralization pilot projects have demonstrated effective CO2 sequestration, yet uncertainties persist for large-scale deployment, particularly regarding the role of fracture networks and evolving fracture-matrix interactions. In this study, we integrate field data, numerical simulations and gravimetric-volumetric analyses to investigate the fracture characteristics of basalt formations and their implications for CO2 storage. Fracture aperture is shown to be proportional to block size, governed by thermal contraction during lava cooling, with the aperture-to-block size ratio β ranging from ∼0.7·10–2 to 6·10–2 depending on mineralogy. Network modeling reveals that initial aperture variability is amplified by dissolution near the injection zone (high Peclet and low Damköhler numbers); however, the hexagonal fracture topology enhances mixing and delays hydrochemical feedback and flow localization. Chemo-gravimetric analysis indicates that mineralization can sequester 0.2–0.3 g CO2 per gram of rock, significantly exceeding pore-space storage via supercritical or dissolved CO2. However, volume-positive mineralization eventually reduces fracture transmissivity. Aperture shut-off depends on the aperture-to-block size ratio β and the mineralization expansion factor ε. The reacted volume fraction at shutoff can range from 7 to 24%. Mineralogy emerges as a primary control on fracture topology, chemical reactivity and storage capacity. Results underscore the need for careful reassessment of CO2 storage capacity in mafic rocks.