Research on nonlinear rheological properties of waxy crude oil based on large amplitude oscillatory shearing

The rheological properties of waxy crude oil are important for its economical and safe pipeline transportation. In actual pipeline transportation, waxy crude oil often exhibits nonlinear rheological characteristics, among which viscoelastic-thixotropic characteristics are the main ones, while there are currently few related studies. This article carried out a study of large amplitude oscillatory shearing (LAOS) for typical Daqing waxy crude oil, and conducted analysis of the nonlinear rheological characteristics of the low temperature waxy crude oil based on the periodic strain loading mode. Using the Fourier transform rheology, Lissajous curve, and stress decomposition method, the effects of strain amplitude and frequency on the nonlinear rheological characteristics under LAOS conditions are analyzed. Results show that when the Fourier transform method analyzes the non-linear rheological characteristics area, the relative intensities of frequency triple and frequency quintuple increase with the increase of strain amplitude and frequency, and it cannot accurately reflect the non-linear rheological properties of waxy crude oil under high-frequency conditions. The Lissajous curve method is more suitable for the study of the nonlinear rheological characteristics of waxy crude oil under low frequency conditions and establishing a prediction formula of dissipated energy density. In addition, the nonlinear viscoelastic parameters obtained by the stress decomposition method can accurately characterize the nonlinear viscoelasticity of waxy crude oil. This research deeply explores the nonlinear rheological properties of waxy crude oil, which can provide theoretical guidance for practice.