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Optical techniques for determining wax appearance temperature of waxy crude oil

Accurate determination of wax appearance temperature (WAT) is of great significance for the safe running of crude oil pipelines. At present, a variety of WAT measuring methods have been developed, among which optical techniques have attracted great attentions due to their advantages in convenient operation and non-contact measurement, etc. Here, we summarize optical methods for WAT measurement according to different light effects, including absorption, scattering, and birefringence, during light transmission in crude oil. We introduce the principles of light transmission method, near-infrared absorption spectroscopy, polarization microscopy, optical speckle method, and fluorescence imaging method, and discuss their advantages and disadvantages. Among them, the laser-scanning confocal fluorescence microscopy can be used to study factors such as cooling rates to nucleation and its subsequent wax growth morphology, which helps to enrich our understanding of paraffin nucleation mechanism. Finally, we also discuss other related methods for WAT measurement.