Paper Number
GG23 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
Precipitated wax content and yield stress of model wax-oil mixtures determined by arrest of flow during cooling at fixed stress

Presentation Date and Time
October 11, 2022 (Tuesday) 11:30

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

1. Harris, Conor G. (University of Michigan, Chemical Engineering)
2. Rice, Christina E. (University of Michigan, Mechanical Engineering)
3. Shetty, Abhishek (Anton Paar USA Inc., Rheology Department, Advanced Technical Center)
4. Mahir, Luqman (TotalEnergies, E&P)
5. Larson, Ronald (University of Michigan-Ann Arbor, Chemical Engineering Department)

Author and Affiliation Lines (in printed abstract book)
Conor G. Harris¹, Christina E. Rice², Abhishek Shetty³, Luqman Mahir⁴ and Ronald Larson^1
1Chemical Engineering, University of Michigan, Ann Arbor, MI 48105; ²Mechanical Engineering, University of Michigan, Ann Arbor, MI 48105; ³Rheology Department, Advanced Technical Center, Anton Paar USA Inc., Ashland, VA 23005; ⁴E&P, TotalEnergies, Houston, TX 77002

Speaker / Presenter 
Rice, Christina E.

Keywords
experimental methods; gels; rheometry techniques

Text of Abstract
Currently, wax deposition models for oil pipeline flows do not quantitatively predict actual deposition thickness measurements, in large part because models of fluid-to-solid transitions for waxy oils have been based on experiments at a single composition, temperature history, or stress history, since collecting experimental data for all these variables would overwhelm the experimenter. We therefore propose a temperature-arrest measurement that approximates pipeline transport conditions in subsea oil pipelines by maintaining constant shear stress during cooling, thereby avoiding the need to develop a general but complex constitutive equation that captures the effects of the histories of both temperature and shear rate or stress.

In our method, model wax-oil mixtures are cooled under constant shear stress until a temperature is reached at which flow is arrested by gelation due to wax crystal formation, allowing estimation of yield stress and other rheological properties of model waxy oils relevant to the modeling of wax deposition in pipelines with cold walls or model “cold-finger” experiments. Combining these data with measurements of the temperature dependence of precipitated wax concentration by differential scanning calorimetry (DSC), the apparent yield stress at which flow arrests is then related to the concentration of precipitated wax under various conditions. Using a single experiment for each condition, we explore the impact of wax concentration, applied stress, and cooling rate in two independent wax-oil mixtures: a commercial Clarus wax and a six-alkane mixture. To validate our findings, DSC results are compared with the Coutinho model, and the rheological results are fit to the Hershel-Bulkey constitutive equation.