DLVO Modeling to Predict Critical Salt Concentration to Initiate Fines Migration Pre- and Post-Nanofluid Treatment in Sandstones

Abstract

Summary The critical salt concentration (CSC) of injected water used for various water-based oil recovery operations is the salt concentration below which fine particles are released and their migration starts within sandstone reservoirs containing clays. This phenomenon could be one of the potential causes of formation damage and associated injectivity and productivity declines. This paper proposes a novel method of quantifying surface forces between fines and sand grains and using DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) modeling to predict a CSC pre- and post-nanofluid treatment. Furthermore, the effectiveness of varying concentrations of silica nanoparticles (SNPs) in controlling fines migration and reducing CSC was modeled by the DLVO approach and experimentally validated. The experimental CSC was determined by performing corefloods and analyzing effluent turbidity and absorbance under various salinities of the injected brine to validate the developed models. The zeta potentials of sand-fine-brine (SFB) systems were measured and ranged from −35.2 to 29.5 mV. The average size of fine particles was 800 to 900 nm based on scanning electron microscopy (SEM) results. Using DLVO modeling before the application of nanoparticles (NPs), the CSC was predicted to be 0.11 M (6,400 ppm) NaCl brine, at which the total DLVO interaction energy shifted from attraction to repulsion. Moreover, another DLVO model was developed considering the effect of SNPs. Models predicted 0.085 M (4,900 ppm) and 0.075 (4,400 ppm) NaCl CSC values after the application of 0.05 and 0.1 wt% SNPs, respectively. Afterward, corefloods were performed that showed that the experimental results of CSC with and without SNPs treatment were in close agreement with the DLVO models. Fines migration was observed at 0.08 M (4,700 ppm) and 0.07 M (4,100 ppm) salinity after nanofluid treatments. Many oil recovery processes, including but not limited to low-salinity waterflooding and alkaline flooding, require the estimation of the CSC to avoid formation damage. The proposed DLVO model is instrumental to predict the CSC for monovalent NaCl brine pre- and post-nanofluid application without requiring extensive experimental work. Moreover, the use of nanofluid showed promising results in terms of fines migration control and reduction in CSC.