Pore-Scale Experimental Investigation of the Effect of Supercritical CO₂ Injection Rate and Surface Wettability on...

Injectivity is one of the most important factors to evaluate the feasibility of CO₂ geological storage. Salt precipitation due to the mass of dry CO₂ injected into a saline reservoir may cause a significant decrease in injectivity. However, the coupling effect of injection parameters and reservoir conditions on salt precipitation is not clear. Here, we conducted pore-scale visualization experiments to study the morphology and distribution of salt precipitation in porous structures and their effects on permeability reduction. The experimental results are achieved by controlling the supercritical CO₂ injection rate and the surface wettability at the reservoir temperature and pressure. It is found that for hydrophilic and neutral porous surfaces, ex situ precipitation occurs and blocks the entirety of pore throats and bodies, which results in a significant reduction in permeability. Increasing the CO₂ injection rate can suppress the capillary reflow and prevent the permeability reduction. For a hydrophobic porous surface, in situ precipitation occurs and occupies much smaller pore volume, which has a slight effect on permeability reduction compared to the hydrophilic samples at the same injection rate. Increasing the CO₂ injection rate and dewetting the injection well and formation nearby reduce the possibility of salt accumulation, which has less effect on CO₂ injectivity.