Restart behavior of gelled waxy crude oil pipeline based on an elasto-viscoplastic thixotropic model: A numerical study

Restart of gelled waxy crude oil pipeline is one of the major flow assurance concern in petroleum production. Reliable representation of rheological behavior of gelled waxy crude oil serves as the basis for pipeline restart analysis and modeling. In this work, the Dullaert-Mewis elasto-viscoplastic thixotropic model was modified and applied to improve the representation of the rheology of gelled waxy. Numerical analyses were conducted to evaluate the effects of compressibility, Reynolds number, yield stress number and structural breakdown rate of gelled waxy crude oil on pipeline restart. Combined with rheological experiment data, the effect of viscoelasticity of gelled waxy crude oil on pipeline restart was analyzed. The results suggest that with increasing compressibility of gelled waxy crude oil, the speed of propagation of yield front during restart decreases, the total restart time and steady-state velocity increase and the minimum required pressure difference for successful restart decreases. Low Reynolds number, high yield stress number and low structural breakdown rate lead to high minimum required pressure difference for successful restart and prolonged total restart time. It was also observed that the modified Dullaert-Mewis elasto-viscoplastic thixotropic model provides more optimistic restart assessments, characterized by lower minimum required pressure difference, higher steady-state velocity and shorter total restart time, compared with assessments with a viscoplastic thixotropic model.