The foamability analysis of foam drainage in liquid-producing gas wells

The foamability is a key factor for the foam drainage in liquid-producing gas wells; however, its evaluation relies on experimental means, lacking support from theoretical models. At present, there is still no foaming model for annular flow and churn flow. Based on the energy conservation law, considering the effect of surface tension on gas entrainment, it is assumed the turbulent kinetic energy of liquid film jet used for inducing gas entrainment is equal to the increase rate of surface energy of the entrained bubbles, so as to establish the forming model, and this model is verified by experimental data. On the basis of the established foaming model, the prediction formula is proposed for the interface tension required by the foaming of annular flow and churn flow, and the foamability of different flow patterns is also analyzed. The results show that with the decreasing of interface tension in annular flow and churn flow, gas is entrained if Weber number is larger than the critical value. The large gas mass flow rate ensures sufficient gas entrained into liquid film, presenting strong foamability. The gas entrainment rate increases with the decreasing of interface tension in slug flow. However, limited by the small gas mass flow rate, the foamability is weak. In bubble flow, bubbles are accumulated at the top interface of bubble flow with the decreasing of interface tension. However, the bubble accumulation rate is limited by the small gas flow rate, which results in weak foamability. The strong foamability exists in annular flow and churn flow, applicable to foam drainage. The interface tension required by foaming can be calculated by the prediction formula proposed in this paper. © 2019, Editorial Office of ACTA PETROLEI SINICA. All right reserved.