Pressure Drop Prediction Model for Vertically Upward Annular Flow in Annular Space of Oil Tube and Casing

In view of insufficient experimental research on annular multiphase flow tests with high gas-liquid ratios and low prediction accuracy of pressure drop, water and air were selected as the experimental media, and the two different combinations of oil tube and casing (The outer diameter of the oil tube and the inner diameter of the casing were 38.5 mm × 62.0 mm and 38.5 mm × 76.0 mm, respectively) were selected. Moreover, experimental studies were carried out in an 11.5 m long test tube. The experimental results show that the total pressure drop increases with the increase as the apparent gas-liquid flow rate increases for vertically upward annular flow. The increase in the total pressure drop accelerates as the gas flow rate rises. At the same apparent gas-liquid flow rate, the friction pressure drop of the tube with a smaller cross-sectional area is larger. Based on the pressure drop calculation method for annular flow in the annular space established in the literature [1], the flow rate difference between liquid films of annular flow in the annular space inside and outside the tube is considered in calculating the friction coefficient between liquid film and tube wall and between liquid film and gas core. According to the momentum balance condition between the liquid film and the gas core, the thickness ratio equation for liquid films inside and outside the tube given by literature [4] is employed. The new pressure drop prediction model for annular flow in the annular space is developed and compared with the existing model for verification based on the experimental data. The results show that the calculation error of the new model is less than 10%, and the prediction results are reliable, which can provide a theoretical basis for the prediction of annular pressure in oil tubes and casing, gas lift design, and the analysis of oil well production conditions.