Design and Operational Characteristics Study of Gas-Driven Reciprocating Pumps for Drainage and Gas Recovery

In view of bottomhole fluid accumulation in low-pressure water-producing gas wells, a natural gas-driven pump for drainage and gas recovery was designed, featuring a simple structure, stable performance, high reliability, and no need for an external power source. The effects of the outer diameter of different cylinder pistons and high-pressure water pump pistons, stroke lengths, flow channel diameters, different hanging pump depths, and pressure differences of different gas source on the movement law of natural gas-driven pumps were studied through AMESim aero-hydraulic simulation and experiments. The results show that increasing the diameter of the cylinder piston will increase the average speed and maximum instantaneous flow but it will reduce the cycle. The influence of the diameter of the high-pressure water pump piston on the movement law is just the opposite of the influence of the diameter of the cylinder piston. The piston stroke is positively correlated with the peak velocity and cycle but negatively correlated with the average velocity and liquid discharge volume. The channel diameter is positively correlated with the peak velocity, average velocity, liquid discharge volume, and instantaneous flow rate. Compared with the air source pressure, the hanging pump depth has a greater impact on the working characteristics of the water pump. Based on this, the following parameters are selected: the diameter of the cylinder piston is 55.0 mm; the diameter of the high-pressure water pump piston is 30.0 mm; the stroke is 370.0 mm, and the channel diameter is 10.0 mm. Finally, the laboratory test on the natural gas-driven pump proves that the structure design is reasonable, and the drainage and gas recovery function can be achieved.