Experimental study and model modification of downhole throttling pressure drop laws in the gas wells with foam drainage gas recovery process

Downhole throttling in gas wells is one key technology for the low-cost development of gas fields, and under suitable conditions, “downhole throttling + foam drainage gas recovery” process can improve the liquid carrying capacity of gas well. When the traditional gas-liquid two-phase choke flow pressure drop model is used for the size design of the downhole throttling choke in the gas well with foam drainage gas recovery process, the requireed production proration of the gas well cannot be satisified. Testing the throttling pressure drop laws and establishing or improving the mathematical model is conducive to improve the design level of downhole throttling in the gas wells with foam drainage gas recovery process. Physical simulation experimental equipment was designed and established for the downhole throttling in the gas wells with foam drainage gas recovery process. Then, the throttling pressure drop laws at different mass fractions of foam drainage agent were tested by using the foam drainage agent UT-11. In addition, four common mechanism models of gas-liquid two-phase choke flow (Sachdeva model, Perkins model, Ashford model and slippage numerical model) were evaluated from the aspects of choke flow regime transition predicting capacity and mass velocity and pre-choke pressure predicting capacity by using the experimetnal data. Finally, a formula for calculating the slippage factor of foam flow was constructed based on the experimental data. In this way, the accuracy of the slippage numerical model is improved, the absolute percentage error of mass velocity is decreased from 13.7% to 7.69% and that of pre-choke pressure is decreased from 16.5% to 8.01%. In conclusion, the research results provide an important theoretical base for the size design and pre-choke pressure prediction of downhole choke in the gas wells with foam drainage gas recovery process.