Wax crystal dynamics and viscosity abnormal reduction in asphaltene-containing waxy oil at low temperatures

A micro-rheological integration experiment was conducted on model oils without asphaltene and with 0.05 wt% asphaltene. The study examined the viscosity-temperature characteristics of both model oils under different cooling rates and shear rates. Significant changes were observed in the viscosity-temperature curve of the asphaltene-containing model oil. At low shear rates, a distinct wavelet peak was identified in the temperature range of 37-30 degrees C, where viscosity initially increased, then decreased, and subsequently increased again. This wavelet peak diminished with the increasing shear rate, eventually forming a "buffer platform". The underlying mechanism was attributed to asphaltene altering the wax crystal behavior from "uniform precipitation network structure formation" to "formation of unstable large aggregates - dissociation into multiple small stable aggregates - growth into larger stable aggregates." In addition, the wax precipitation rate remained constant in the model oil without asphaltene, while in the asphaltene-containing model oil, the rate significantly accelerated between 34.5 degrees C and 32.5 degrees C. And the asphaltenes promoted the formation of small wax crystal particles but inhibited the growth of wax crystal particles. [GRAPHICS ]