Effect of Data Errors on Multiphase Flow Correlations

Abstract

In absence of downhole permanent gauges, multiphase flow correlations are widely used to predict well flowing pressures and production under variety of conditions. They also have wide applications in nodal analysis and artificial lift optimization. In our previous work (SPE-175805), we collected a large database of more than 3000 multiphase pressure points and tests. We used this large database to develop guidelines to select the most accurate correlations for different pipe and flow conditions. Typically, there are close to 20 input parameters used in the calculations of multiphase flow correlations. In this study, we used sensitivity analysis techniques with our large database to determine which input parameters affect the multiphase flow correlations results for different pipe and flow conditions. Among these important input parameters are producing gas-oil ratio (GOR), API, gas specific gravity and tubing roughness. For each of the important input parameters, we change the value of the input parameter within the measurement accuracy in the field and find out their effect on the calculated pressure in comparison with the measured pressure. We categorized the large database into clusters representing different pipe and flow conditions, then used a commercial pipe flow software to model these wells. We then performed hundreds of sensitivity studies on almost all input parameters for oil wells. It was observed during the study that several parameters have significant effect on multiphase correlations results. These effects were different for low and high production rate wells and low and high GOR wells. For example, accuracy of API was found to have low effect on results. However, GOR had significant effect on results. Pipe roughness was found to be much less important in oil wells especially at low production rates and at low GOR. Based on the results of the sensitivity studies for the large database, we developed guidelines for which parameters are important for which wells and under what conditions. The guidelines will help engineers working on developing multiphase flow models for wells focus on obtaining good values for the most important input parameters.