Flow pattern and pressure gradient of the gas-liquid two-phase flow in the vertical wellbore with rotary inner boundary

The existence of sucker rod in the wellbore can interfere with the gas-liquid two-phase flow in the wellbore and then influence its flow pattern and pressure gradient, while the calculation of the pressure gradient in the wellbore is an important part of oil/gas well production optimization. Gas-liquid two-phase flow experiments were carried out at different rotation speeds by using the partially transparent plexi glass tubular with progressive cavity pump (ID Ø88.9 mm, length 7 m). And accordingly, the transition interface from the bubble flow to the plug flow during the rotation of progressive cavity pump was obtained. Then, it was compared with the flow pattern transition model without sucker rod, and the flow pattern transition model modified at the rotation speed of 0 r/min, 30 r/min, 60 r/min and 90 r/min was obtained. Finally, the pressure gradient formula at different rotation speeds was set up after the pressure gradient at different rotation speeds in the wellbore with sucker rod was corrected according to the experimental data. It is indicated that the transition from the bubble flow to the plug flow occurs earlier in the wellbore without sucker rod when the liquid-phase apparent velocity is the same. With the increase of the rotation speed, the flow friction resistance increases and its increasing amplitude is smaller. With the increase of the gas-phase apparent velocity, the total pressure gradient and the decreasing rate of pressure gradient decline gradually.