Salt-Responsive Phenol Formaldehyde Resin: Changes of Interface Energy on the Aggregation Process

Phenol formaldehyde resins (PFRs) as a colloidal oil displacement agent were commonly used to plug pores in crude oil reservoirs for enhanced oil recovery (EOR). The aggregation–dispersion and charging behavior of PFR may affect the rheology and plugging performance of the suspension. To understand the aggregation–dispersion and charge of PFR, turbidity, dynamic light scattering, and electrophoretic light scattering experiments were carried out at pH = 10 with different concentrations of salt solutions (NaCl, MgCl2, CaCl2, NaCl/MgCl2, and NaCl/CaCl2). The aggregation rate and ζ-potential were measured, and the critical coagulation concentration (CCC) and critical coagulation ionic strength (CCIS) were further obtained. Based on the triple-layer surface complexation (TL) model, the adsorption ability of cations and the surface characteristics of the PFR particles were studied, and these differences were explained by interface energy. Thus, Derjaguin–Landau and Verwey–Overbeek (DLVO) theory modified by interface energy was applied to explain the aggregation behavior of PFR particles in different types of ion systems. We concluded that, in the presence of multiple ions, DLVO theory modified by interface energy has good applicability to the aggregation–dispersion of PFR particles.