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

Flow assurance challenges associated with waxy crudeoil precipitationat low ambient conditions are significant concerns for oil industriesduring production, transportation, and storage. Numerous methods havebeen employed to mitigate wax deposition and gelation issues. Sincewax precipitation is temperature-sensitive, heating has emerged asa promising method to enhance oil flowability. The present work intendsto examine the degelation behavior of waxy oil using rheometry, differentialscanning calorimetry, and microscopy techniques. In addition, a non-isothermalflow restart simulation is performed using an in-house numerical simulatorconsisting of a rheological model of sol-gel transition developedin the current work. A numerical simulation of a preheated gelledpipeline demonstrates the significance of the degelation temperature.The effects of the wax concentration, initial gel temperature, andaging period on the degelation temperature are examined. The observeddegelation temperature is higher than the gelation temperature, leadingto thermal hysteresis. The extent of thermal hysteresis reduces witha decrease in the heating rate. The numerical simulation uses thefinite volume method with variables placed on a staggered grid. Thegel heated above and below the degelation temperature shows a significantvariation in axial velocity profiles. However, further heating doesnot affect the velocity profiles. A shear banding type of effect isobserved in the axial velocity profile above the degelation temperature.Heating the gelled oil to the degelation temperature instead of thewax disappearance temperature saves excessive heating energy duringstorage and transport operations.

Automated summary

Flow assurance challenges associated with waxy crude oil precipitation at low ambient conditions are significant concerns for oil industries during production, transportation, and storage. This study aims to investigate the degelation behavior of waxy oil and simulate the flow restart process using numerical simulations. The results show that the degelation temperature is higher than the gelation temperature, leading to thermal hysteresis. Heating the gelled oil to the degelation temperature instead of the wax disappearance temperature can save excessive heating energy during storage and transport operations.