Dissolution potential of SO2 Co-injected with CO2 in geologic sequestration

Area of Science:

• Geochemistry
• Environmental Science
• Chemical Engineering

Background:

• Geologic sequestration of carbon dioxide (CO2) is a key climate change mitigation strategy.
• Sulfur dioxide (SO2) is being considered as a co-injectant with CO2.
• SO2 dissolution in formation brines could lead to acidification, impacting sequestration viability.

Purpose of the Study:

• To determine the solubility of SO2 in CO2 under geologic sequestration conditions.
• To model the diffusion-controlled dissolution of SO2 from a CO2 plume.
• To assess the impact of SO2 co-injection on brine pH and CO2 phase properties.

Main Methods:

• Calculated pressure-, temperature-, and salinity-adjusted Henry's Law constants and fugacity coefficients for SO2.
• Developed a non-steady-state diffusion model for SO2 dissolution in supercritical CO2.
• Simulated SO2 dissolution over 1000 years at depths of 0.8-2.4 km.

Main Results:

• Adjusted SO2 solubility is predicted to be 0.04 times lower than previously estimated due to depth-dependent factors.
• Simulations show 65-75% of SO2 remains in the CO2 phase after 1000 years.
• SO2 increases CO2 phase density by up to 12% (for 5% SO2) and has a negligible effect on the critical point.

Conclusions:

• Slow SO2 dissolution largely mitigates potential brine acidification during co-injection.
• The transport limitations of SO2 significantly reduce its impact on formation brines.
• Co-injection of SO2 with CO2 is a potentially viable sequestration strategy with manageable environmental risks.