Experimental Study On Two-phase Flow Pattern Of Horizontal Gas Wellbore In Western Sichuan

West Sichuan gas field belongs to the category of low-permeability tight gas reservoir. It is mainly developed by the horizontal well technology. At present, the horizontal gas wells generally produce a certain amount of water, which lead to the wellbore flow complex and the flow pattern of each section confused. Most flow pattern predicting methods were presented for a single vertical, inclined or horizontal pipe, which were only suitable for a small range of angle. And most methods were originally developed for oil wells with low gas-liquid ratio, which is distinctly different from the high gas-liquid ratio condition of the horizontal gas wells. What's more, the current researches ignored the affects of the three-section structure of the vertical, inclined, horizontal pipe on the flow patterns, which makes it difficult to correctly predict the gas-liquid flow patterns of horizontal gas wells. To solve above problem, the technical route of combining the experimtal study, the theoretical study and the engineering application was adopted in this paper. The gas-liquid upward flow of the horizontal gas well was deeply studied. And new flow pattern predicting methods were then presented. Specific work is as follows:(1) The data of production, well structure, and pressure measurement from 36 horizontal gas wells were collected. The fluid parameter range of the densities, the viscosities, the surface tensions and the flow velocities were obtained, based on the computation methods of the physical parameters and the flow parameters. The dimensionless velocity numbers defined by Duns & Ros were optimized as the similarity parameter, which were then used to determine the range of the experimental parameters.(2) An visual experimental loop for simulating two phase flow in horizontal gas well was established with variable inclination angle of 0-90°. The experimental pipe is made of plexiglass tube with the inner diameter of 50 mm. It consists of a 5-m-long horizontal section, a 4-m-long inclined section (variable inclination angle) and a 4-m-long vertical section. The experimental equipments and the measurement system were also included in the experiment. The experimental loop was ready for the wellbore flow experimental study of horizontal gas well under different inclination angle and gas/liquid rate.(3) Using air and water as the experimental fluid, a total of 508 two phase flow pattern experiments under different gas/liquid velocity and 8 inclination angles were carried out. The flow pattern recognition method that combined with high speed camera and the pressure differential analysis was adopted. According to the distribution morphology of interface and the flow characteristic of each phase,5 types of flow patterns were summarized. Respectively substituting the gas and liquid velocity number into the horizontal and vertical coordinates, a total of 82-D flow pattern maps were drawn and 19 flow pattern transition curves were obtained. The affects of the inclination angle, gas/liquid velocities on the flow patterns were then analyzed.(4) Based on the 8 two-dimensional flow pattern maps, considering the 0-90° continuous changes of the angle in the horizontal well, with the gas/liquid velocities and inclination angle as the coordinate parameters. a new three-dimensional flow pattern map for the horizontal gas wells in West Sichuan was established. In order to further solve the non-smooth problem of the flow pattern transition surfaces and the fitting difficulty of the transition equations, a new BP neural network model for predicting the flow patterns was established, adopting the gas/liquid velocity numbers and the inclination angle as input layer, the 5 flow patterns as output layer, the experimental data as training sample.(5) The BP neural network model was validated by the 20 pressure test data of horizontal gas wells in West Sichuan Gas Field. The accuracy of the model was up to 90%. The new method was then used to predict the wellbore flow patterns at different production stages of the 23-5H horizontal well. Some useful conclusions were finally achieved.The results provide important technical supports for the wellbore condition diagnosis, the production anomaly judgement and the deliquification treatment for the horizontal gas wells in West Sichuan Gas Field. They also have certain significance for the development of the similar gas field.