Chapter 11 - Gas lift

Abstract

This chapter gives a complete overview of gas lift. Gas lift is an artificial lift method whereby external gas is injected into the produced flow stream at some depth in the well bore. The additional gas augments the formation gas and reduces the flowing bottom hole pressure, thereby increasing the inflow of produced fluids. For dewatering gas wells, the volume of injected gas is designed so that the combined formation and injected gas will be above the critical rate for the well bore, especially for lower liquid producing gas wells. For higher liquid rates, much of the design procedure may more closely mirror producing oil well gas lift techniques. In addition, gas lift may not lower the flowing pressure as much as an optimized pumping system; there are several advantages of a gas lift system that often make gas lift the artificial lift method of choice. For gas wells in particular, when producing a low amount of liquids, the producing bottom hole pressure with gas lift may compare well with other methods of dewatering. For higher liquid rates, the achievable producing BHP may be higher than pumping techniques. Of all artificial lift methods, gas lift most closely resembles natural flow and has long been recognized as one of the most versatile artificial lift methods. Because of its versatility, gas lift is a good candidate for removing liquids from gas wells under certain conditions. The two fundamental types of gas lifts used in the industry today are continuous flow and intermittent flow, and these are briefly explained in this chapter.