The Influence of Salinity, pH, Temperature and Particles on Produced Water Oil Quantification Precision and Accuracy with Confocal Laser Fluorescence Microscopy

The present study investigates the effects of different produced water parameters, such as salinity, pH, temperature, and presence of colloidal particles, in oil quantification using confocal laser fluorescence microscopy (CLFM). The study simulates different produced water samples, which typically contains a mixture of oil, salts, and different concentrations of particles. The accuracy of the quantification was not affected by the environmental condition for any of the conditions investigated. On the other hand, under extreme environmental conditions, such as high pH (pH 8), salinity (250000 ppm), and temperatures (60 °C), the precision of the CLFM oil quantification was reduced. Changes in the average oil droplet size upon variation of the environmental conditions generally correlated with the change in CLFM measurement precision. Interfacial tension and DLVO interactions were further evaluated to gain a better mechanistic understanding of how the environmental conditions affect the size or colloidal stability of the oil droplets and therefore impact the precision of CLFM measurements. To obtain an overall understanding of the relationship of the different environmental parameters and oil droplet properties with the level of CLFM measurement precision, multiple correspondence analysis (MCA) and multiple regression analysis were employed. The results showed that conditions of lower salinity, temperature, and SiO2 concentration, as well as neutral pH (pH 7), favor smaller oil droplet sizes (close to 4 ?m) in the oil-in-water emulsion and more precise CLFM measurements. The better understanding of the impact of different water chemistries on oil droplet stability will be essential for decision-makers on conditions that could impact the precision of the method. This work presents a new perspective of investigating CLFM as an oil-in-water quantification technology and guidance for engineers operating this novel technology on the optimum environmental conditions to achieve the best performance of the technology.