First, the paper gives a classification of the calculation models commonly used for the calculation of multiphase vertical pressure drops in oil wells. The main parameters of the experimental data used to develop the different empirical correlations are presented indicating the ranges where the correlations are expected to perform best. Next, an analysis and classification of the many possible causes of calculation error is given. Deviation of calculated and measured pressure drops is shown to stem from different sources that can have different importance from case to case.

The author collected and summarizes in the paper the findings of the many previously published investigations on the accuracy of the different pressure drop calculation models. A table including all available data on calculation accuracies is also presented. Statistical parameters of these investigations are shown to be widely scattered and to be of limited use to engineers seeking the most accurate model. Differences and contradictions in the results are evaluated and explained.

Finally, the author describes the petroleum engineer's proper attitude towards vertical pressure drop correlations. Practical implications of the proposed philosophy are also detailed. In conclusion, the paper provides the required insight and proper attitude to petroleum engineers facing the problem of predicting multiphase pressure drops in oil wells.

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