A gas-lift system assembled with the production tubing string to provide a means of deploying gas-lift valves. The position or depth of the gas lift valves is crucial to the efficient operation of the entire system. Consequently, proper assembly of the gas lift mandrels within the completion tubulars is essential. A port in the gas-lift mandrel provides communication between the lift-gas supply in the tubing annulus and the production- tubing conduit.
Source: IADC UBO / MPD Glossary, December 2011. Global Standards