Effect of biodiesel on the rheological behavior of waxy crude oil and its data-driven modeling

Low-temperature wax deposition limits the production and transportation of deepwater waxy crude oil. Although biodiesel can improve the flow behavior of waxy crude oil, its influence on crude-oil rheology involves coupled variations among multiple parameters. In this study, the rheological behavior of sunflower-biodiesel-treated Nigerian waxy crude oil was investigated using a shear-stress-biased autoencoder. To describe the nonlinear and non-injective relationship among temperature (T), biodiesel concentration (C), shear rate (γ̇), and shear stress (τ), the encoder of the autoencoder compresses (T,C,γ̇) into a one-dimensional latent variable L, while the decoder, which can operate as a standalone component after model training is complete, combines L with a prescribed target shear stress τ* to generate multiple feasible (T,C,γ̇) combinations. It reveals that high shear-stress states are mainly located in the low-temperature region, while increasing temperature weakens the wax-crystal network and reduces flow resistance. The low-apparent-viscosity region in the temperature-concentration space is mainly concentrated at high temperatures and high biodiesel concentrations. The treated crude oil maintains shear-thinning behavior over 10–60 °C. In addition, the apparent yield stress at 10 °C decreases nonlinearly with biodiesel concentration.