Abstract
Downhole chokes have been extensively implemented in gas and oil fields to improve well performance and facilitate equipment/chemical cost savings. Existing models have been developed based on wellhead choke data. However, compared with a horizontal pipe, vertical two-phase flow presents different flow behavior and patterns. Therefore, the flow patterns should be considered to evaluate the performance of the models for predicting the downhole choke flow rate. In this study, 40 data points were tested on both vertical and horizontal tubes with 4-mm chokes. Moreover, 350 data points (Appendix) were tested on a vertical tube with four choke sizes (2, 4, 8, and 12 mm). Flow patterns, pressure, and mass flow rates were measured and analyzed. From the results of comparative analysis, significant discrepancies between vertical and horizontal evaluation results were reported. The results demonstrated that the downhole chokes changed the flow pattern downstream of chokes, improved the stability of p_d, and prevented the liquid phase downstream of chokes from falling to the upstream. The slug-churn flow transition boundary was accurately predicted by Taitel correlation, and the churn-annular flow transition boundary moved leftward with an increase in pressure. Under the critical flow condition, the Ashford model (RMSE = 0.005 kg/s and R2 = 0.92), Sachdeva model (RMSE = 0.007 kg/s and R2 = 0.80), and Al-Safran model (RMSE = 0.004 kg/s and R2 = 0.96) achieved the highest prediction accuracies for slug, churn, and annular flow, respectively. Based on 170 subcritical flow data points, the Perkins model (RMSE = 0.007 kg/s and R2 = 0.99), Ashford model (RMSE = 0.009 kg/s and R2 = 0.84), and Sachdeva model (RMSE = 0.009 kg/s and R2 = 0.76) are recommended for slug, churn, and annular flow, respectively.
NSTL