A NEW METHOD FOR PREDICTING CRITICAL GAS VELOCITIES OF LIQUID LOADING IN GAS WELLS

When a gas well suffers liquid loading, the gas velocity is not sufficient to fully lift liquid to the surface, which may kill the gas well. The accurate prediction of the critical gas velocity can remind operators to take measures in time to prevent the occurrence of liquid loading. Upon the minimum gas-liquid interface shear stress of annular flow and the velocity profile of uniform liquid film near the pipe wall, a new critical gas-velocity prediction model is proposed. By combining equations of liquid-phase flow rate and gas-phase momentum of annular flow, the expression of gas-liquid interface shear stress is obtained, and making its derivative with respect to film thickness equate to zero comes into the critical gas velocity, which simplifies the calculation. The effects of well deviation, tubing diameter, pressure, and droplet entrainment in gas core on the critical gas velocity are included in the new model. The laboratory and field data are collected to evaluate the accuracies of the new model and other typical models. The model verification shows that the new model outperforms other models. For experiments of vertical and inclined pipes with diameters of 1 in, 2 in, 3 in, 4 in and 6 in, the average relative error of the new model is 1%. For the vertical wells with diameters of 2.441 in~4.28 in and the wells with diameters of 1.75 in~6.18 in and the deviation angles of 13°~64°, the average relative error is less than 23%.