Salt precipitation and associated pressure buildup during CO₂ storage in heterogeneous anisotropy aquifers

CO₂ can be injected into deep saline aquifers for storage, thereby reducing the concentration of CO₂ in the atmosphere. When CO₂ is injected into the aquifer, salt precipitation may occur, which may impair the injectivity and affect storage safety. In this study, numerical simulation was used to study salt precipitation in heterogeneous anisotropic sandstone aquifers, the feedback effect of salt precipitation on the flow was considered, and the additional pressure increase caused by salt precipitation was evaluated. The results showed that the maximum decrease in formation permeability and the maximum additional pressure buildup caused by salt precipitation reached 88% and 4.91 MPa, respectively. The salinity of the formation water and the maximum additional pressure buildup is approximately proportional when the salinity is low. Once the salinity exceeds a certain value (approximately 20% in this study), the maximum additional pressure buildup increases sharply. As the permeability increases, the additional pressure buildup decreases. When permeability reaches a certain threshold (approximately 5×10^-14 m² in this study), the maximum additional pressure buildup decreases rapidly and changes only slightly as permeability increases. The CO₂ injection rate is basically proportional to the maximum additional pressure buildup. When the vertical permeability increases, the additional pressure buildup due to salt precipitation shows a downward trend. The low-permeability interbeds above the CO₂ injection well will cause more local salt precipitation near it, which will further cause a greater and wider pressure buildup. The heterogeneity of the formation will greatly enhance salt precipitation, thereby promoting the formation pressure buildup. The formation heterogeneity must be considered in the study of the salt precipitation and its effect on CO₂ injection, especially when the formation permeability is low, the CO₂ injection rate is high, and the salinity of the formation water is high.