Speaker
Description
Basaltic formations represent promising geological reservoirs for permanent CO2 storage through mineralization, yet their unique pore architecture and reactive transport dynamics differ fundamentally from conventional sandstone systems. This study integrates experimental flow-through investigations with multiscale characterization and pore-network analysis to elucidate the coupled mechanisms controlling carbonate precipitation and permeability evolution in vesicular basalts under CO2-acidified seawater injection conditions. Our findings reveal that carbonate mineralization under flow conditions is nucleation-controlled and stochastic rather than growth-controlled and deterministic, challenging conventional reactive transport paradigms that rely on thermodynamic supersaturation predictions. Despite continuous supersaturation throughout experimental columns, isolated carbonate precipitate pockets formed randomly along flow paths, demonstrating that bulk thermodynamic calculations cannot forecast actual nucleation locations or timing. Residence time emerged as a major control mechanism, with an order-of-magnitude reduction in flow rate (from 0.05 to 0.005 mL/min) required to achieve visible carbonate formation. This flow rate dependence creates spatial partitioning between high-flux, low-mineralization flow highways and low-flux, high-mineralization matrix blocks. Multiscale characterization using micro-CT imaging and pore-network extraction reveals that vesicular basalts exhibit coordination numbers with a modal value of 2, approximately threefold lower than typical sandstones with a modal coordination of 5. This low-coordination topology creates a serial rather than parallel flow architecture, where individual pore throats act as critical bottlenecks rather than redundant pathways. Connected porosity fractions ranging from 1.3% to 32.2% differ notably from total porosity values of 18-42%, demonstrating that network topology rather than porosity magnitude controls permeability. Percolation theory analysis indicates that basalts are exceptionally vulnerable to catastrophic permeability loss from modest mineral precipitation. Pore-scale reactive transport simulations reveal a counterintuitive finding: numerous small, distributed precipitates cause more severe permeability degradation than fewer large, isolated accumulations, as distributed precipitation systematically eliminates the limited redundancy in low-coordination networks. Secondary mineral assemblages comprise calcite-dominated carbonates and smectite clays, with magnesium carbonates notably absent despite thermodynamic favorability, reflecting kinetic limitations below 100°C characteristic of seawater systems. Mg/Ca ratio and sulfate concentration introduce competing reactions that reduce carbon mineralization efficiency compared to freshwater systems. Smectite clay formation can sequester divalent cations, passivates reactive basalt surfaces, and occludes pore throats, simultaneously reducing mineralization rates. These findings indicate that successful basaltic CO2 storage requires probabilistic rather than deterministic reactive transport models, the explicit incorporation of realistic pore network topologies for reservoir layers, and the incorporation of competing reactions. The low-coordination topology of vesicular basalts creates both opportunities through high initial permeability and vulnerabilities through catastrophic permeability loss from modest precipitation, necessitating fundamentally different reservoir management approaches than those employed in conventional sandstone CO2 storage operations.
| Country | Norway |
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