Reactivation of Serpentine Fracture Networks in Ultramafic Reservoirs

Abstract Fluid–rock interactions are pivotal to lithospheric evolution and have widespread implications for subsurface energy technologies in mafic-ultramafic reservoirs, including critical mineral recovery, in situ mineralization, and stimulated geologic hydrogen. Although serpentinization-driven fracture propagation through volumetric expansion has been observed in laboratory and natural settings, sustained permeability enhancement under CO2-bearing fluids remains unclear. Using controlled laboratory experiments, we present observations consistent with pre-existing serpentine veins acting as reactive templates for fracture evolution in peridotite exposed to wet supercritical CO2 (scCO2) and aqueous-dissolved CO2 (CO2(aq)). In both environments, the CO2-bearing fluids appear to drive coupled dissolution–precipitation reactions that increase porosity and reactivate fracture pathways that are often associated with serpentine networks. In wet scCO2 we observe carbonate precipitation at fracture openings, often containing porosity within the carbonate itself. In CO2(aq) we observe dissolution along pre-existing serpentine veins with carbonate precipitation within these reactivated fractures. Together, these observations suggest that pathway evolution may reflect coupled dissolution–precipitation processes whose relative expression varies with fluid composition. These results highlight the importance of pre-existing structure and fluid composition in controlling permeability evolution during fluid injection in ultramafic rocks.