Permanent CO₂ Trapping through Localized and Chemical Gradient-Driven Basalt Carbonation

Area of Science:

• Geochemistry
• Environmental Science
• Reservoir Engineering

Background:

• Basalt formations are recognized as secure geological repositories for anthropogenic CO2 emissions through carbon mineralization.
• Understanding the factors influencing CO2 mineralization in basaltic reservoirs is crucial for effective carbon sequestration.

Purpose of the Study:

• To investigate the impact of transport limitations, reservoir temperature, and brine chemistry on CO2 carbonation reactions in fractured basalts.
• To assess how these parameters affect CO2 sequestration capacity and flow paths.

Main Methods:

• High-temperature, high-pressure core flooding experiments using CO2-rich aqueous fluids injected into fractured basalts.
• Geochemical analysis to identify precipitate localization and reaction fronts.
• Comparison of experimental results with 2D reactive transport model predictions.

Main Results:

• At 100 °C and 6.3 mM NaHCO3, carbonate precipitates were localized on reactive mineral grains.
• Increased NaHCO3 (640 mM) enhanced carbonation in diffusion-limited zones but increased clay precipitation, potentially obstructing flow.
• Elevated temperature (150 °C) further enhanced carbonate and clay precipitation, reducing fracture volume and increasing fracture bridging.

Conclusions:

• CO2 mineralization in basaltic reservoirs is favored in buffered, diffusion-limited zones adjacent to flow paths.
• Alkaline reservoirs with geothermal gradients enhance the extent of carbon trapping.
• Transport limitations and mineral precipitation kinetics are critical factors controlling CO2 sequestration efficiency in fractured basalts.