Investigation of salt precipitation under CO2-brine displacement in micromodels
Abstract
Salt precipitation during CO2 injection into saline reservoirs poses a major challenge to maintaining injectivity and long-term storage security. Yet its pore-scale dynamics remains poorly understood. In this study, we combine a high-resolution microscope imaging system (MIS) and a full-field imaging system (FFIS) to investigate how multiphase flow conditions govern salt formation in a microfluidic glass model. Two distinct salt morphologies were observed using MIS: compact, transparent crystals that preferentially form near brine-CO₂ interfaces in liquid-rich zones; and dark, porous clusters that develop in gas-dominated regions. Quantitative analysis using a region-specific salt precipitation index shows that the porous clusters grow at a rate approximately six times higher than the crystals. FFIS captured the spatiotemporal evolution of multiphase flow and salt formation under varying injection rates. The total amount and spatial distribution of precipitated salt were closely linked to the volume and distribution of residual brine after carbon dioxide breakthrough. At low injection rate, CO2 advanced with a stable displacement front in the beginning, leading to localized brine trapping near the outlet. At higher injection rates, the displacement became increasingly unstable and finger-like, causing earlier breakthrough and more dispersed brine retention. Replication of high injection rate experiments further confirmed the stochastic nature of the displacement process. These findings highlight the critical role of residual brine distribution in governing salt growth and offer mechanistic guidance for injection strategies that minimize pore-scale clogging in CO₂ storage reservoirs.