Numerical investigation on oil–water flow characteristics and construction optimization for novel wellbore lubrication fitting

Water-lubricated oil–water flow is an effective low-energy consumption method for pipeline transportation. This study proposes a novel wellbore lubrication fitting (WLF) for developing a core-swirling flow to reduce flow resistance and enhance lubrication efficiency. The pressure drop across the lubricating fitting, the maximum oil volume fraction at the overflow outlet and the drag reduction percentage of core-swirling flow were taken as the indicators, and the fluid calculation software Ansys Fluent was applied to optimize the structural parameters of the WLF with orthogonal and single-factor methods. The experimental study was carried out with mineral oil and tap water. The results indicate that the swirl generator can develop a stable and low-viscosity liquid annulus to isolate the oil from the pipe wall and reduce the flow resistance of viscous oil. The optimized WLF demonstrates the clear core-swirling flow with input velocity between 0.48 and 0.62 m/s. The experimental pressure drops deviate from the simulated data within ±25%. The drag reduction percentage of the core-swirling flow is above 90% with the input velocity above 0.51 m/s. The results of this study have important engineering value for efficient application of WLFs.