Effect of Monovalent–Divalent Ions on Fines-Migration Initiation in Sandstone: DLVO Analysis and Experimental Validation

Fines migration is a major formation-damage mechanism in sandstone reservoirs, and is strongly influenced by brine salinity and ionic composition. Changes in injected-water chemistry can destabilize fines, leading to pore-throat blockage, permeability reduction, and injectivity decline. This study investigates the influence of monovalent and divalent ions on the critical salt concentration (CSC) for fines-migration initiation in Berea sandstone. The proposed framework combines zeta-potential measurements, machine-learning predictions, DLVO modeling, and coreflooding experiments. Zeta potentials were experimentally measured for NaCl/KCl, NaCl/KCl/CaCl2, and Caspian Sea brines, while values for pure KCl were predicted using the TabM model. These data were incorporated into DLVO calculations to estimate CSC under different brine compositions. For pure KCl, the model predicted a CSC of 0.03 M, which is in agreement with the experimentally determined range of 0.03–0.04 M obtained through coreflooding, pressure-drop monitoring, and UV–Vis effluent analysis. For NaCl/KCl mixtures, the predicted CSC decreased from 0.05 M at an 80/20 ratio to 0.04 M at a 20/80 ratio. For ternary NaCl/KCl/CaCl2 mixtures, the predicted CSC decreased from 0.045 M to 0.005 M as the CaCl2 fraction increased to 50%. The analysis was further extended to multicomponent Caspian Sea brine to evaluate fines stability under more complex ionic conditions. The results highlight the importance of accounting for ion identity, valence, and brine composition when predicting CSC and provide a framework for preliminary injection-water compatibility assessment and formation-damage prevention.