A study on high-viscosity oil-water two-phase flow in horizontal pipes

摘要

A study on high-viscosity oil-water flow in horizontal pipes has been conductedapplying experimental, mechanism analysis and empirical modelling, and CFDsimulation approaches.A horizontal 1 inch flow loop was modified by adding a designed samplingsection to achieve water holdup measurement. Experiments on high-viscosityoil-water flow were conducted. Apart from the data obtained in the presentexperiments, raw data from previous experiments conducted in the sameresearch group was collated. From the experimental investigation, it is foundthat that the relationship between the water holdup of water-lubricated flow andinput water volume fraction is closely related to the oil core concentricity and oilfouling on the pipe wall. The water holdup is higher than the input water volumefraction only when the oil core is about concentric. The pressure gradient ofwater-lubricated flow can be one to two orders of magnitude higher than that ofsingle water flow. This increased frictional loss is closely related to oil fouling onthe pipe wall.Mechanism analysis and empirical modelling of oil-water flow were conducted.The ratio of the gravitational force to viscous force was proposed tocharacterise liquid-liquid flows in horizontal pipes into gravitational forcedominant, viscous force dominant and gravitational force and viscous forcecomparable flow featured with different basic flow regimes. For viscous forcedominant flow, an empirical criterion on the formation of stable water-lubricatedflow was proposed. Existing empirical and mechanistic models for the predictionof water holdup and/or pressure gradient were evaluated with the experimentaldata; the applicability of different models is demonstrated.Three-dimensional CFD modelling of oil-water flow was performed using thecommercial CFD code Fluent. The phase configurations calculated from theCFD model show a fair agreement with those from experiments and mechanismanalysis. The velocity distribution of core annular flow is characterised withnearly constant velocity across the oil core when the oil viscosity is significantly higher than the water viscosity, indicating that the high-viscosity oil core flowsinside the water as a solid body. The velocity profile becomes similar to that ofsingle phase flow as the oil viscosity becomes close to the water viscosity.