Sulfate Promotes Compact CaCO₃ Formation and Protects Portland Cement from Supercritical CO₂ Attack

Area of Science:

• Geochemistry
• Materials Science
• Environmental Engineering

Background:

• Supercritical CO2 in geologic carbon sequestration (GCS) poses risks to wellbore cement integrity.
• Conventional understanding suggests sulfate attacks cement, but this study explores a counterintuitive benefit.

Purpose of the Study:

• To investigate the effect of sulfate on Portland cement's resistance to supercritical CO2 attack.
• To understand the microstructural mechanisms behind sulfate's protective role.

Main Methods:

• Experimental analysis using scanning electron microscopy and small-angle X-ray scattering.
• Reactive transport modeling incorporating a minimum porosity term.
• Synthesis and testing of novel cement composites.

Main Results:

• Sulfate addition significantly reduced the chemical and mechanical deterioration of cement by supercritical CO2.
• Sulfate promoted CaCO3 precipitation in nanopores, creating a less porous and more protective layer.
• Synthesized cement composites demonstrated enhanced resistance to supercritical CO2.

Conclusions:

• Sulfate can act as a beneficial additive, improving cement's durability in GCS environments.
• The interaction between sulfate and cement creates a robust CaCO3 layer, enhancing resistance to acidic brine.
• This research provides a new strategy for engineering durable and safe materials for GCS.