Cold flowability improvement of waxy crude oil doped with graphene nanoparticles and its mechanism

Waxy crude oil exhibits poor cold flowability and complex rheological behavior at ambient temperature, posing a series of flow assurance challenges for its production and transportation. In this paper, the effects of graphene nanoparticles (GNPs) at various dosages and doping temperatures on the cold flow behaviors, such as yield stress and moduli as well as apparent viscosity, of a waxy crude oil were systematically investigated. The results indicate that the cold flowability of the waxy crude oil could be improved with an increasing GNPs dosage from 0 to 200 ppm. However, the GNPs' efficacy cannot be further improved beyond the dosage of 200 and up to 500 ppm. Doping temperature is another primary factor influencing the GNPs' efficacy. The apparent viscosity gradually decreases with the doping temperature increase from the wax appearance temperature (WAT) to the wax dissolved temperature (WDT). However, further improvement of efficacy is not observed by the continued increase of doping temperature above the WDT. Microscopy, impedance, and X-ray diffraction results indicate that GNPs could accumulate on wax particle surfaces, acting as the nano-templating effect, and thus weaken the attraction among the wax particles, which may contribute to the cold flowability improvement of waxy crude oil.