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.

Experimental and Numerical Investigation of the Degelation Behavior and Non-Isothermal Flow Restart of a Waxy Oil Pipeline

“…The time t = t̂ ( L χ θ P W s ) is scaled in terms of gel compressibility and pressure to capture pressure propagation in gelled oil. The details of the scaling and numerical simulation scheme in a preheated gelled pipeline are discussed in the work of Kumar et al and Sanyal et al In addition, the sol–gel transition-based rheological model is combined with the shear-strain-based gel degradation model utilized in the literature. , μ ( γ ) = μ normals [ 1 + f · true{ 1 − exp ( − m γ ) γ true} ] …”

“…Combining the sol–gel transition-based rheological model in eq with the shear-strain-based gel degradation model in eq utilized in the literature, , we get μ = μ normals [ 1 + f · exp true( ln ( μ gel ) − ln ( μ eql ) 1 + exp [ θ − θ o φ ] true) true{ 1 − exp ( − m γ ) γ true} ] …”

“…The details of the scaling and numerical simulation scheme in a preheated gelled pipeline are discussed in the work of Kumar et al 13 and Sanyal et al 41 In addition, the sol–gel transition-based rheological model is combined with the shear-strain-based gel degradation model utilized in the literature. 13 , 41 …”

“…Recently, a few researchers have numerically examined the effect of preheating on the flow restart of a gelled pipeline. ,− The preheating process results in faster gel degradation and an effective reduction in viscosity, facilitating improvement in the flow restart operation. The heating of the waxy gel pipeline results in the de-crystallization of existing wax crystals in the vicinity of the pipeline wall.…”

Chemical Additives as Flow Improvers for Waxy Crude Oil and Model Oil: A Critical Review Analyzing Structure–Efficacy Relationships

“…The flow in the gelled pipeline is not possible using normal operating pressure. It requires a much higher pressure than the normal operating pressure to start the flow in the gelled pipeline, − which comes with an extra cost of pumping due to high capacity pump installation and higher pumping power consumption …”