(29d) Gelation and Rheological Behavior of Wax-Oil Systems

Gelation and Rheological Behavior of Wax-Oil Systems

Yansong Zhao^*, Lalit Kumar, Kristofer Paso,  Johan Sjöblom

Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Trondheim 7491, Norway

^*Corresponding author. E-mail address: yansong.zhao@ntnu.no  (Yansong Zhao)

Tel: +47-73550339

Abstract

    Crude oil is a complex mixture of hydrocarbons, containing paraffins, aromatics, naphthenes, asphaltenes, and resins.¹ Gelation and rheological behavior is significant in waxy crude oil transportation strategies. Shut-in and restart of transport pipelines often result in reducing the temperature of crude oil fluid below the pour point temperature (PPT). Subsequently, paraffin wax gelation at the low temperature conditions leads to the strong solid-liquid gels formation.²The mechanisms of waxy crude oil gelation and formed gel breakage are important for waxy crude oil transportation.

  Therefore, gelation and rheological behavior of wax-oil systems (model wax-oils and waxy crude oils) is investigated in this work. Differential scanning calorimetry, rheometry, microscopy and X-ray diffraction are the common methods used for wax-oil systems gelation and rheology investigation. Subsequently, 1 w/w% to 20 w/w% macro-crystalline wax in dodecane, 1 w/w% to 20 w/w% micro-crystalline wax in dodecane, 1 w/w% to 30 w/w% xylene in model wax-oil, 0.01 w/w% to 0.08 w/w% asphaltene in model wax-oil and 5 w/w% macro-crystalline wax in Primol 352 are prepared. Furthermore, effect of shear history, thermal history, wax content, wax type, xylene, asphaltene and additives on model wax-oil gelation and gel breakage process is investigated. It is shown that the gel strength decreases when shear stress is applied to the sample during the gel formation process. Larger crystals can be formed at relative lower cooling rates, which lead to stronger gels. Yield stress decreases with increasing asphaltene content ranging from 0.01 w/w% to 0.08 w/w% in model wax-oil used in this work. XRD results show that crystal lattice still forms even with the addition of a high-efficiency wax inhibitor.²Novel gelation and gel breakage models are established based on model wax-oil experiments and previous modeling results. Moreover, waxy crude oils have been used to check the novel gelation and gel breakage models. It is shown that the novel models are applicable for the waxy crude oils, which is useful for the shut-in and restart process of waxy crude oil transportation prediction.

(1) Venkatesan, R.; Östlund, J. A.; Chawla, H.; Wattana, P.; Nydén, M.; Fogler, H. S. Energy Fuels 2003, 17(6), 1630-1640.

(2) Zhao, Y. S.; Kumar, L.; Paso, K.; Ali, H.; Safieva, J.; Sjöblom, J. Ind. Eng. Chem. Res. (Revised)