posted on 2025-01-09, 04:43authored byYaguang Zhu, Lolya McWest, Carl I. Steefel, Ying Wang, Qingyun Li, Zhenwei Gao, Jiumei Yang, Young-Shin Jun
Supercritical (sc) CO2 in geologic carbon
sequestration
(GCS) can chemically and mechanically deteriorate wellbore cement,
raising concerns for long-term operations. In contrast to the conventional
view of “sulfate attack” on cement, we found that adding
0.15 M sulfate to the acidic brine can significantly reduce the impact
of scCO2 attack on Portland cement, resulting in stronger
cement than that found in a sulfate-free system. Scanning electron
microscopy revealed a decreased total attack depth in reacted cement
in the presence of sulfate. With a newly defined minimum porosity
term in reactive transport modeling, our model suggests that sulfate
caused CaCO3 to fill more nanopore spaces in the cement.
Small angle X-ray scattering experiments also showed that sulfate
can decrease the pore sizes of the carbonate layer. The results suggest
that the interactions between sulfate and cement can generate a less
porous CaCO3 layer, which better resists acidic brine.
Using this mechanism as a proof-of-concept, we tested the incorporation
of sodium sulfate into Portland cement and synthesized new cement
composites that show stronger resistance against scCO2 attacks.
These newly discovered interfacial interactions between CaCO3 and sulfate provide new insights into engineering mechanically strong
and green materials for safer GCS.