Long-term
storage of CO2 in geological reservoirs can
be achieved by mineral trapping through the formation of carbonate
minerals. Hence, investigating the precipitation and dissolution processes
of carbonate minerals and their effects on the storage space of the
target reservoir are of great significance. In this study, a suite
of shale samples collected from the southern Sichuan Basin were selected
for supercritical carbon dioxide (scCO2)–H2O–shale experiments. Mineralogical composition, surface morphology,
and gas adsorption feature variations before and after scCO2–H2O–shale reaction were studied. The results
reveal that the carbonate, clay, and feldspar mineral contents in
the samples decrease, while the concentrations of Ca2+,
Mg2+, and K+ cations in the reacted filtrate
increase, indicating the dissolution process. The elevated concentrations
of K+ and Na+ cations in the flushed filtrate
are ascribed to the redissolution of the precipitated carbonates.
The precipitation process has a tendency to decrease the mesopore
volume. However, this influence on micropores merely occurs in samples
with lower calcite content. After flushing, mesopore volume exhibits
an increasing trend, because of the redissolution of soluble precipitates.
Precipitation and redissolution also affect pore geometrical characteristics,
characterized by increased hysteresis coefficient, initiating blocked
pore structure and greater pore heterogeneity. This mainly develops
in ink bottle pores, uneven capillary pores, and parallel plate pores.
In summary, mineral dissolution, precipitation, and redissolution
during scCO2–H2O-shale experiments can
significantly alter the storage space of reservoirs. Understanding
these dynamic variations and their underlying mineralization mechanism
during CO2 storage is a matter of considerable concern
for “Carbon Neutrality”.
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