Investigation on working principle of pipe string for liquid retention and refoaming in the wellbore of natural gas well with foam drainage gas recovery

Abstract

ABSTRACT The use of foam drainage gas production in natural gas wells can quickly recover the accumulated water in the wellbore, reduce the bottom hole pressure, and increase the production of gas wells.Due to the poor stability of the foam in the wellbore, the liquid phase will migrate downward along the wellbore wall after the foam is broken, reducing the efficiency of the foam drainage.In order to further improve the efficiency of foam drainage, this paper studied the retention mechanism of liquid in wellbore through numerical simulation combined with laboratory experiment, and analyzed the retention effect of different structures of relocators on reflux liquid.In addition, we designed a foaming device with a crack structure, and used the reflux liquid to foam again, so as to improve the efficiency of foam drainage and gas recovery.The results show that the wavy retaining apparatus has strong water retention capacity in the process of foam drainage and gas recovery.During the simulation time, the liquid phase volume fraction is relatively stable, remaining between 82.8% and 83.4%, indicating that there is no significant change in the liquid phase in the reentrant, which can prevent the water phase from settling to the bottom of the well.The pressure comparison of the three kinds of arrester inlet is as follows: wavy arrester < rectangular arrester < zigzag arrester.The pressure at the entrance of the wave-shaped redetention shows a fluctuating increase and remains at about 2.5–4 Pa, indicating that the flow resistance in the wave-shaped redetention is relatively low and cannot greatly increase the pipe flow resistance in the wellbore.After the high-speed airflow passed through the reentrant with water phase, dispersed bubbles were produced in combination with the secondary foaming device. The foaming effect of rectangular foaming device and pulsed trapezoidal foaming device was the best, and 8 bubble particles were produced within 500 ms.The addition of secondary retained foam structure can effectively reuse the water phase after foam breaking. The injection pressure is up to 19 mm/min at 2.5mpa, and the drainage speed is increased by 200%-240%, indicating that the foam breaking in the wellbore seriously affects the drainage efficiency. This study can effectively solve the problem of wellbore fluid accumulation in natural gas Wells, which is of great significance to the efficient development of natural gas Wells.