As the second most widely used artificial lift method in petroleum industry,ESPs help maintain or increaseflow rates by converting kinetic energy to hydraulic pressure.During the entire life of an oilfield,water isinvariably produced with crude oil.As the field ages,the water cut in production increases.Due to highshear force inside rotating ESPs,the oil-water emulsions may form,which can be stabilized by naturalsurfactants or fine solids existing in the crude oil.The formation of emulsions during oil production createhigh viscous mixture,resulting in costly problems and flow assurance issues,such as pressure drop increaseand production rate lost.This paper,for the first time,proposes a new mechanistic model for predictingoil-water emulsion rheology and its effect on the boosting pressure in ESPs.The model is validated withexperimental measurements with an acceptable accuracy.The new mechanistic model starts from Euler equations for centrifugal pump,and introduces a conceptualbest-match flowrate QBM,at which the outlet flow direction of ESP impeller matches the designed flowdirection.The mismatch of velocity directions,resulted from varying liquid flow rates,is used to deriverecirculation losses.Other losses due to flow direction change,friction,and leakage flow etc.are alsoincorporated in the new model.QBM is obtained by matching the predicted performance curve with thecatalog curve for water.With the best match flow rate determined,the ESP hydraulic head under viscousfluid flow can be calculated.For oil-water emulsions,a new rheology model based on Brinkman(1952)correlation is developed,which accounts for ESP rotational speed,stage number,and interfacial propertiesetc.By incorporating the rheology prediction model into mechanistic model,the ESP boosting pressureunder oil-water emulsion can be obtained.The mechanistic model-predicted ESP water performance curves are found to match the catalog curvesperfectly.With high-viscosity fluid flow,the model predictions of ESP boosting pressure agree well with theexperimental data.For most calculation results within medium to high flow rates,the prediction error is lessthan 15%.With oil-water two-phase flow,the proposed rheology model predicts the effective viscosities ofemulsions match testing results with 10% prediction error.The inversion points,at which the continuousphase changes from oil to water as water cut increases,are also predicted.The predictions of ESP boosting pressure under oil-water emulsion flow by coupling the mechanistic model and emulsion rheology modelare comparable with experimental results.
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