Numerical study of flow restart in the pipeline filled with weakly compressible waxy crude oil in non-isothermal condition

The impact of differential thermal heating on pressure propagation is assessed for pipelines filled with weakly compressible gel. The temperature influence on a strain (shear history) dependent rheological model is established from literature data. In order to consider thermal effects on the pressure propagation and flow restart, temperature of the pipeline wall is assumed to be above the wax appearance temperature. The impact of thermal treatment on pressure propagation is analyzed as heat is conducted axially and radially in the pipeline and degrades the gel rheology. Commensurate with weakly compressible fluid properties, isothermal compressibility and fluid thermal expansion coefficients establish density as a function of pressure and temperature. Comparison of results for non-isothermal and isothermal conditions validates the selected numerical algorithm. Axial conduction is negligible in comparison to radial conduction due to the large pipe aspect ratio. Convective flow penetrates only a small axial distance during the pressure propagation process. It is shown that by providing differential heating of gel, the restart process may be accelerated by several orders of magnitude. Preheating of the gel is thereby shown to be an effective method for increasing the velocity of the pressure wave. Finally, it is also shown that the gel deforms faster in the presence of heating, further facilitating flow commencement.