Evaluation of Water Content and Average Droplet Size in Water-in-Crude Oil Emulsions by Means of Near Infrared Spectroscopy(ABSTRACT)

摘要

The demulsification operation constitutes a key-process for removing water from the crude oil in the production platforms and in the refinery. In particular, demulsification stages are required at the desalting plants generally found in the refineries in order to remove water-soluble salts from the crude oil. The stability of water-in-crude oil emulsions has been considered as one of the greatest challenge problem in the separation of crude oils. Indeed, the break-up of these emulsions is a difficult task and generally requires physical, thermal and chemical treatments. In most processes, information on demulsification evolution is found essentially through off-line measurements of droplet size distribution and water content of samples taken from the vessels. Very little is usually known about the emulsion resolution until the demulsification run is finished or the lab provides a result, with delays that may reach some hours. Therefore, developing techniques for evaluating water content and droplet size distribution is of practical importance.Successful applications of near infrared (NTR) spectroscopy have been reported in literature. Through a brief review of some of them, it can be well seen that this kind of spectroscopy can be used for a suitable estimation not only of chemical compositions but also for size determination of particulate materials. Besides, some applications show even the possibility of using NIR spectroscopy as a powerful tool for in-line estimation of key properties of petroleum systems.The main objective of this work is evaluating the influence of water content and average droplet size upon the NIR spectra collected during water-in-crude oil emulsions synthesis and observing whether NIR spectroscopy may be used for predicting these properties simultaneously. It is shown that NIR spectra are sensitive to changes of the average droplet size, and that standard empirical models (PLS-partial least squares) may be built to correlate average droplet size and light absorbance at certain wavelengths fairly well. Finally, it is shown that these models allow the in-line evaluation of average droplet size in water-in-crude oil emulsions with NTR spectroscopy, even when very low water contents (<5% v/v) are employed.