4.1 Introduction

Different gas lift installations contain different combinations of downhole equipment: gas lift valves, packers, mandrels, nipples and subs, etc. The type of gas lift installation is mainly governed by the type of lift used: continuous flow or intermittent lift. Equipment selection is based on original well conditions but should provide for the necessary flexibility to reduce the number of future workover operations. A proper gas lift installation design, therefore, assures trouble-free operation for the entire productive life of a well. ^[1], ^[2]

The usual gas lift installation types are classified in two broad categories: tubing flow and casing flow installations. In a tubing flow installation, lift gas is injected in the casing-tubing annulus, and production occurs through the tubing string; whereas a casing flow installation allows gas injection through the tubing string, and the well is produced from the annulus. The following sections present detailed discussions of the most common versions of gas lift installations.

4.2 Tubing Flow Installations

In these cases, lift gas from the surface is injected down the casing-tubing annulus, and liquid production takes place up the tubing string. Except in wells with extremely large liquid production rates, tubing flow installations are generally recommended because of their many advantages: no corrosive and/or abrasive liquids flow in the casing string,...