Confocal microscopy as a new real-time quantification method for oil content in produced water

Abstract

This research proposes confocal laser fluorescence microscopy (CLFM) as an enabling technology to quantify oil prior to produced water disposal. This method takes advantage of the self-fluorescing properties of oil to visualize and quantify in 3D oil droplets in water in real-time. This investigation initially involves the identification and optimization of parameters affecting CLFM oil measurements in synthetically prepared produced water, followed by validation of the optimum CLFM parameters for oil quantification in real produced water. This study demonstrated that the optimized excitation wavelength, z-step size, image analysis threshold value, and minimum sampling size parameters for the CLFM method are suitable for different types of oil. The optimum amount of time for analysis, however, changed for oils with different densities due to different oil upward movement velocities. The detection range of the CLFM was determined to be between 1 and 250 ppm. The quantification of oil content in three different produced water samples were also investigated with the CLFM method and results were compared with the standard EPA 1664 method. The results for both methods correlated well, which suggests that the CLFM has potential to be used as an initial real-time screening of the oil quantities of treated produced water prior to environmental releases in water streams. This technique has several advantages over other methods, such as does not require hazardous solvents for oil extraction, is less labor intensive, and can be automated for real-time online applications, such as subsea systems.