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.

Due to the high content of heavy components such as wax, resin and asphaltene, leading to the poor fluidity of heavy oil, it is very easy for heavy components to deposit and block the pipeline during pipeline transportation, which brings serious safety challenges. Dilution with light oil is one of the methods to improve the fluidity of heavy oil, but the current research pays less attention to the deposition from blended crude oil. Therefore, the present work aims to systematically investigate the effects of light oil type, blending ratio, deposition time, etc. on the deposition from dilute heavy oil with a small deposition experiment device. The results show that with the increase of deposition time, the sedimentation from the blended crude oil increases gradually. The stirring contributes to the decrease of sedimentation of the blended crude oil. The greater the stirring rate, the smaller the sedimentation. Increasing the ratio of light oil blending, both the wax appearance temperature and the sedimentation of the blended system decrease. It is revealed that the wax, resin and asphaltenes should be responsible for the increase of the sediment. It is proposed that the wax appearance temperature should be taken into consideration as an important index parameter during dilute heavy oil transportation. This conclusion provides theoretical guidance for the determination of main incoming line indicators and pigging cycle of heavy oil diluted with light oil for transportation.