1. Nonlinear viscoelastic characteristic investigations of waxy crude oils under stress-controlled large amplitude oscillatory shear (LAOStress).
- Author
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Liu, Hongfei, Li, Hongying, Zhao, Yang, Wang, Xuefeng, Li, Huiyuan, and Zhang, Jinjun
- Subjects
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PETROLEUM , *LISSAJOUS' curves , *YIELD stress , *ENERGY dissipation , *FOURIER transforms , *SEPARATION of variables , *VISCOELASTICITY - Abstract
Gelled waxy crude oils can be considered as an elasto-viscoplastic material, exhibiting the transition from linear to nonlinear viscoelasticity. The LAOStress measurements have rarely been applied in the crude oil rheology literature to investigate the nonlinear viscoelasticity. In this study, we present results of the nonlinear viscoelastic characteristics under LAOStress by a series of analytical methods of Fourier transform rheology, Chebyshev strain decomposition, Lissajous curves analysis, energy dissipation calculation, viscoelastic measures quantification, and Pipkin diagram interpretation. Both the elastic and viscous nonlinearities were found to be first strengthened before yielding and subsequently weakened after yielding with the increase in imposed stress amplitude σ0, and a more striking nonlinear response can be captured when using a lower angular frequency ω. However, the defined viscoelastic measures and energy dissipation characteristics continue to keep getting more significant with increasing σ0, even after structural fracture. The results of Lissajous curves analysis reflect that a lower applied ω is more favorable for the structural nonlinear destruction and thus flowability enhancement of interlocking waxy network. The Pipkin diagrams were finally plotted to represent the nonlinear rheological signatures to an oscillatory input, showing a higher measured yield stress under a higher imposed ω. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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