Modeling Salt Precipitation Dynamics During CO2 Injection into Saline Aquifers

Abstract Salt precipitation, induced by the dry-out effect in the CO2 injection process, reduces the reservoir porosity and impairs the permeability in the vicinity of the wellbore, further impacting the CO2 injectivity. Accurately predicting and understanding the distribution and growth of salt precipitation in porous media near the wellbore is essential for optimizing CO2 injectivity in saline aquifers. In this work, a comprehensive model is established to simulate the dynamics of salt precipitation, incorporating the coupled effects of fluid flow, salt transport, and evaporation-induced salt concentration changes. The impacts of local heterogeneity and surface wettability on salt distribution are explored within various porous media. In addition, the effects of capillary-driven backflow are considered, which have the potential to alter salt transport and accumulation. By simulating these interactions under varying reservoir conditions, the model accurately captures the spatial and temporal dynamics of salt precipitation, enabling an in-depth understanding of the factors that contribute to injectivity impairment. The simulation results show that altering the direction of CO2 injection has minimal influence on salt distribution within homogeneous porous media. However, localized decreases in porosity and permeability arise from the nucleation and aggregation of salt, altering capillary forces and instigating the movement of water from regions of higher to lower water saturation. This heterogeneity leads to uneven salt deposition, with more pronounced salt accumulation in regions where lower permeability zones impede fluid movement, further exacerbating the local changes in porosity and permeability. Strongly water-wet porous media exhibits a higher rate of salt precipitation compared to the intermediate-wet conditions due to a faster rate of water evaporation, resulting in more substantial permeability reductions. Capillary-driven backflow enhances the migration of saline fluids into less saturated zones, causing non-uniform salt accumulation and localized permeability declines. This work predicts variations in salt distribution under different conditions. The consideration of localized fluid dynamics offers significant advancements in understanding and managing the impact of salt precipitation on reservoir permeability and injectivity, addressing one of critical challenges in CO2 sequestration.