The effects of partial preheating on pressure propagation and Flow-Restart phenomena in a clogged pipeline with a weakly compressible gel

Abstract

The present article aims to decipher the effect of preheating a segment of the pipe on the pressure propagation mechanisms and flow restart operation in a gelled pipeline. During the restart operation, shear-thinning thixotropic rheology governs the gel properties, where the viscosity is a function of shear strain and thermal history. A finite volume method is employed to solve the governing equations for a weakly compressible gel. Rheology of the initial gel incorporates the effect of temperature distribution from the preheating stage. Flow restart in the thixotropic gel involves three different timescales: namely, the compressive diffusion timescale (acoustic wave propagation timescale), the viscous timescale, and the gel degradation timescale. In an isothermal case, the flow restart occurs at the gel degradation timescale, whereas flow restart in the preheated gel takes place at the viscous timescale. Time evolution of nonlinear axial pressure profile and residual viscosity provides a theoretical understanding of the gel degradation process in the thermal diffusion-controlled and advection-controlled flow regimes, defined in terms of Peclet number (Pe). The results indicate that the gel degradation process is affected by thermal-induced melting in addition to shear melting. Partial preheating tends to dislodge the gel into plugs, and this is more significant at low Pe and high pristine gel strength. The local Nusselt number (Nu) at the heated portion of the wall during flow restart suggests that the wall-heat transfer is prominent when the pressure wavefront has not reached the outlet.