CO₂ sequestration in sandstone reservoirs: How does reactive flow alter trapping mechanisms?

Numerous studies have attempted to assess the possible changes in the petrophysical parameters of sandstone reservoirs for the geological storage of CO₂. However, the results have been highly variable and hardly conclusive, highlighting mineral alteration, precipitation, dissolution, and fine migration as the main drivers of changes in porosity, permeability, and surface wettability. In this paper, a series of systematic experimental studies were carried out on the Berea sandstone samples to carefully analyse the changes in porosity, relative permeability, capillary pressure, and surface wettability after CO₂ treatment. The results obtained indicated that porosity increased in the samples due to dissolution of minerals (calcite and clay) and there was no sign of pore throat closure due to mineral precipitation. It was found that the surface wettability can be shifted towards a CO₂ wet system, probably because of calcite precipitation and clay dissolution or reduction in the hydrophilicity of quartz, leading to a decrease in capillary entry pressure. It appears that the mineral and capillary trapping in sandstone make it a suitable storage site for CO₂, but that require further research to fully understand the changes posed by mineral dissolution in the long term.