At the root of the liquid-lifting problem is droplet size. At high gas flow rates, liquids break into droplets of sufficiently small size for lifting by the gas. With decreasing gas flow rate, both the droplet creating capacity and the droplet lifting capacity decrease. This idea was succinctly stated by Turner, Hubbard, and Dukler (1969) in their expression for critical gas velocity ­ the minimum velocity for dispersing and lifting liquid as droplets. If the velocity of gas declines below the critical velocity, then liquid accumulation begins.

In 1994, we began research at CSM on new approaches for stimulating production of droplets at gas velocities below the critical velocity. In the past two years, we have tested vibrational (sonic and ultrasonic) devices, rotational devices, and two-fluid nozzles for stimulating droplet production. This testing has shown qualitatively that small droplets can be transported for large vertical distances, and that ultrasonic devices are most promising for field application ­ they generate droplet sizes that are most easily lifted.

Our research objectives are to develop an ultrasonic device for lifting liquids from gas wells, and to numerically simulate the performance of gas wells with interactions of accumulated water in the wells and the surrounding reservoir.