Pressure Drop Predicting Model for Gas and Oil-Based Drilling Fluid Two Phase Flow in Vertical Annulus

Blowout is among catastrophic accidents in oil and gas drilling, and it is caused by abnormal pressure resulted from gas kick from reservoir which cannot be prevented due to limits of drilling technology. Accurate prediction of wellbore pressure is an effective method to prevent blowout. Based on electrical capacitance volume tomography (ECVT), the experiments of gas and white oil two-phase flow with viscosity of 16 mPa·s, 23 mPa·s, 26 mPa·s and 39 mPa·s in vertical annulus are carried, and the pressure drop in vertical annulus is tested. Considering the influence of viscosity, modification of the friction loss coefficient and prediction of the pressure gradient in bubble flow, slug flow and churn flow are studied. The prediction accuracy of the modified model is compared with the pressure gradient model established in the Caetano’s experiment (air-kerosene, ID 42.2 mm and OD 76.2 mm). The results show that under the Caetano’s experimental conditions and the experimental conditions of this experiment, the maximum error and the prediction mean absolute error of the pressure gradient model with the corrected friction loss coefficient are lower than those of Caetano’s model.