Colloidal stability of nanosuspensions based on highly mineralized solutions

Abstract

The potential use of nanosuspensions in enhanced oil recovery is currently under vigorous investigation. A large body of evidence supports the viability of this research direction. However, considerable challenges still remain in this area. One such challenge is the high degree of mineralization observed in formation water in many oil fields. In such conditions, nanosuspensions may exhibit low aggregation and sedimentation stability. This study represents a systematic investigation into the potential for improving the sedimentation stability of SiO₂ (18 nm) nanosuspensions prepared using highly mineralized water (up to 300 g/l) of varying composition. This is the first time such an investigation has been carried out. To stabilize SiO₂ nanosuspensions in mineralized water, the effect of various additives (ethylene diamine tetraacetate acid dynatrium salt solution, synthanol, starch, sodium citrate, ammonium tartrate, and malonic acid) was investigated at the concentrations up to 3 wt%. The impact of salt type and concentration, as well as stabilizer type and concentration on the colloidal stability of nanosuspensions was examined. The results demonstrate that nanosuspensions exhibit a loss of colloidal stability at salt concentrations above 100 g/l. Furthermore, their sedimentation stability in formation water is approximately two times lower than that in a NaCl-based solution with the same degree of mineralization. The results of the conducted studies indicate that the optimal stabilizing properties for nanosuspensions in highly mineralized waters are possessed by additives of malonic acid and sodium citrate at a concentration of 1 wt%.