Mesoscopic mechanism of shear breakdown and static recovery characteristics of waxy crude oil gel structures

The primary method for transporting high-wax crude oil is heated pipeline transmission. During shutdowns, the gelled state and structural strength of the congealed oil directly determine the restart pressure required for pipeline resumption, with wax crystals being the dominant internal factor. This study employs synchronized macro-meso rheological measurements to systematically investigate the continuous evolution of wax crystal morphology during network formation, shear-induced yielding, and static recovery, while analyzing the effects of shear cycles and rate. Results indicate that during the isothermal gelation stage after cooling, continuous precipitation, growth, and aggregation of wax crystals lead to significant changes in mesoscopic characteristic parameters (2.60%–45.17%). In the initial shearing stage, the wax crystal network sequentially undergoes yield deformation, fragmentation, and eventually reaches a dynamic equilibrium state where deformation, fragmentation and reaggregation coexist. With increasing shear cycles, wax crystals experience more thorough fragmentation, developing a denser and more uniform spatial distribution with their shapes tending toward sphericity. During the subsequent static recovery stage, only partial fragmented wax crystals undergo re-adsorption and aggregation, resulting in limited changes in characteristic parameters (0.27%–9.84%). Higher shear rates increase the yield stress and shorten the yielding time, while reducing both the equilibrium stress value and structural parameters, simultaneously exacerbating irreversible damage to the wax crystal network and inhibiting the recovery capability of the gelled structure. This study elucidates the correlation mechanism between mesostructural evolution of wax crystals and macroscopic rheological behavior during shear-recovery processes, providing theoretical foundations for addressing complex engineering challenges in pipeline restart operations.