Prediction of Critical pH for Fines Migration Pre-and Post-Nanofluid Treatment in Sandstone Reservoirs using the DLVO Modelling

Injection water pH affects the release of fines in sandstones. The force equilibrium between fines and sand governs the attachment or release of fines in the system. At a pH higher than a critical value, fines are released and block the pores, causing formation damage. The fines release can be avoided by adjusting the pH and using nanofluids. This paper introduces the concept of DLVO modelling to estimate the critical pH before and after the application of nanofluids without extensive experimentation. Scanning electron microscopy determines the average size of in-situ fines collected from sandstone core. Injection brine of 11700ppm and 0.1wt% nanofluid are prepared, zeta potentials of dispersed sand are measured with varying pH from 2 to 12, and the resulting attractive and repulsive surface forces between fines and sand grains are quantified. The DLVO models are developed to predict the mobilization of fines and a critical pH before and after the application of silica nanofluids. The zeta potentials are measured by a Zetasizer and are in the range of-5 mV (less repulsion) to-31 mV (more repulsion). Furthermore, the application of nanofluids increases the zeta potential to a range of-3 mV to-24.9 mV, indicating a compression in electric double layers. Measured zeta potentials, ionic strength, and fine size are used as inputs to compute surface forces, and DLVO models are developed. The critical pH, at which total DLVO interactions shift from negative to positive, as predicted by the model, is about 8. The DLVO model also predicted an improved critical pH of 11 following the use of nanofluids, demonstrating a reduction in repulsion forces. DLVO modelling approach helps estimate a critical pH before and after applying nanofluids, and nanotechnology validates nanoparticles' ability to control fines migration and improve critical pH for waterflooding and alkaline flooding operations.