Fluid connectivity and evolution of pore water in continental margin basalt reservoirs for carbon storage

Permanent storage of gigatons of carbon in basalt requires thick, uncompartmentalized sequences that allow lateral dissipation of CO₂ away from injection sites. Here we assess the presence of flow barriers by evaluating the variations in ⁸⁷Sr/⁸⁶Sr patterns in pore water, a method used extensively in sedimentary successions. Present-day pore water ⁸⁷Sr/⁸⁶Sr was measured from residual salts in core samples, while past water compositions were reconstructed from carbonate cements of different ages. We reveal smooth and uninterrupted trends in strontium isotopes through a 100 m thick basalt section indicating a common fluid reservoir unaffected by low-permeability massive lava flow interiors. The data further indicate that unconsolidated overburden sediments act as a good seal preventing seawater to mix with in situ pore water, and buoyant supercritical CO₂ to leak. Finally, basaltic sequences form viable targets for CO₂ storage and suggests that fractures may bypass low-permeability units to create a well-connected reservoir system.