ON THE USE OF MODULATED TEMPERATURE DIFFERENTIAL SCANNING CALORIMETRY TO ASSESS WAX CRYSTALLIZATION IN CRUDE OILS. PART II: COMBINING RHEOMETRY, MICROSCOPY AND MODULATED TEMPERATURE DIFFERENTIAL SCANNING CALORIMETRY

It has long been known that wax crystallization during crude oil production and transportation can cause flow assurance issues that give rise to nonproductive times and increase in costs. In this second part of the present work we show how experimental parameters of a type of Modulated Temperature Differential Scanning Calorimetry (SSDSC) can be adjusted to make the cooling protocol reproducible by rheometry and microscopy. It was found that the different values used for the SSDSC cooling parameters do not impact the oil's rheological behavior significantly at the applied shear rate, although a greater viscosity increase during isothermal time segments is favored by higher temperature steps in the cooling procedure. As shown by Microscopy calculations, this likely results from a greater degree of wax crystal nucleation, which is associated in turn with medium supersaturation. Furthermore, there is a good agreement between the onset of the peak detected on the RC portion of SSDSC thermograms and a significant increase in wax crystal number during the cooling procedure, which occurs at a temperature much lower than the actual start of wax crystallization (WPT). Therefore, the peak on RC arises from an increase in crystallization rate and it is then only after this increase that the gelation temperature is detected for these oil samples. This supports the need for a saturated medium of precipitating, interacting crystals for identification of the gelation temperature of waxy crude oils and clearly distinguishes it from measurements of the WPT