Predicting the critical salt concentrations of monovalent and divalent brines to initiate fines migration using DLVO modeling

Abstract

Fine particles are released from sandstone reservoirs at a salinity known as the critical salt concentration (CSC), which is strongly dependent on monovalent and divalent ions in the permeating liquid. Formation water is an ionic liquid, and when the salinity of the sand-fine-brine (SFB) system goes below the CSC, repulsive surface forces increase, and fine particles are dislodged from the sand surface plugging the pore throat as a result of fines migration. In this study, the effect of monovalent and divalent ions is modeled using the DLVO theory, and CSCs are predicted for monovalent and divalent salts individually and in different combinations. Using the average fine particle size and zeta potential of the SFB system, DLVO models are developed considering attractive and repulsive surface forces for various concentrations of monovalent and divalent salts to predict CSC. Zeta potentials were measured or collected from previous studies. The DLVO models predict the CSCs of 0.11 M, 0.04 M, 0.0001 M, and 0.0001 M for NaCl, KCl, CaCl2, and MgCl2, respectively, and all the results are found to be in close agreement with the experimental CSCs. Furthermore, several mixtures of NaCl and CaCl2 are utilized, and CSCs are predicted. This study showed that divalent ions significantly reduce the CSC, and their presence in the formation water and injection water is beneficial to control fines migration even at low salinity of the injection water. The application of our developed method to predict CSC yields reliable and accurate results without requiring extensive experimentation.