Wax deposition characteristics under oil-water two-phase stratified flow in pipeline

Wax deposition in subsea pipelines transporting waxy crude oil under oil-water stratified flow remains a critical flow assurance challenge. This study systematically investigates wax deposition characteristics using an experimental flow loop that simulates deep-sea conditions. Experiments were conducted with waxy simulated oil and deionized water under varying superficial velocities of both phases. Results show a crescent-shaped deposition layer exclusively on the upper oil-wetted wall, with no deposition on the water-contacted lower wall. Notably, the deposit near the oil-water interface exhibits higher wax content and enriched heavy components compared to the top wall, indicating localized aging behavior. A key finding is that increasing oil or water superficial velocity reduces deposition thickness but enhances wax content and promotes aging. The deposit mass per unit area correlates negatively with oil-phase actual velocity, while wax content and heavy component concentration show strong positive correlations. This work provides novel insights into the circumferential heterogeneity and phase-specific aging of wax deposition in stratified oil-water flow, offering a foundation for improved predictive models.