With oilfields entering the high water-cut development stage, unheated gathering and transportation technology has been widely applied. However, the oil-gas-water three-phase flow in gathering pipelines is complex, and the problem of crude oil wall adhesion is prominent with unclear mechanisms. Taking the gathering pipeline in the near-wellhead area as the research object, a field experimental device was developed to achieve visual observation and analysis of multiphase flow patterns and crude oil adhesion behaviors during mechanical oil recovery. A composite constitutive equation incorporating Newtonian fluid, power-law fluid, and Herschel-Bulkley fluid models was established to characterize the sol-gel transition process of crude oil. A mathematical model for multiphase flow in gathering pipelines was constructed using the VOF(volume of fluid) method, systematically analyzing phase distribution, velocity fields, crude oil morphological evolution, and adhesion behaviors under variable pumping unit stroke conditions.It was revealed that periodic stroke variations of pumping units dominated flow characteristics in gathering pipelines, inducing synchronous but phase-lagged periodic flows. Subjected to staged excitation from variable pumping unit strokes, the multiphase flow exhibited unsteady evolutionary features with dynamic adjustments in flow structures and phase distributions, manifested through gradual gas-oil ratio increases and time-varying water content elevation. The oil phase undergoes morphological transitions from continuous layers→segmented layers→elongated clusters→discrete clusters→micro clusters, while forming strip-shaped, lumpy, spotted, and dispersed filmy adhesion patterns on pipe walls. A competitive relationship existed between oil adhesion and flow shear forces. At high oil content (20%~34%) with stable flow velocity (0.72~1.61 m/s), adhesion dominates, reaching maximum wall gelled oil accumulation of 6.08%. Conversely, under low oil content (4%~15%) with turbulent flow conditions, shear effects intensify significantly, removing 1.1% of wall-adhered gelled oil. Flow direction alterations exacerbate oil adhesion through localized velocity reduction. In vertical pipe sections, gravity-driven acceleration enhances multiphase mixing effects, effectively stripping wall-adhered gelled oil.