Chapter 5 - Total system analysis applied to gas lift design

Abstract

Several ways of calculating the depth of the operating point of injection is presented at the beginning of the chapter with the objective of explaining the role that each component of the gas lift system plays in the performance of a gas lifted well. The theory behind many operational analyses that can be performed with commercially available software is presented in detail: (1) total system analyses, (2) pressure and temperature profile determination, (3) multiphase flow correlation comparison, (4) nodal analysis, (5) outlet pressure as a function of the liquid flow rate (well performance curves), (6) liquid production and injection gas flow rate calculation for a given set of surface gas injection pressure and seat diameter, (7) calculation of the deepest point of injection depth for a given injection gas flow rate using the equilibrium curve concept (the behavior of constant-injection-gas-flow-rate equilibrium curves is illustrated with the use of pressure–depth diagrams), and (8) Bracketing. Several diagrams are presented to illustrate the effect that different gas lift system’s components or fluid properties (water cut, API gravity, gas/oil ratio, reservoir pressure, productivity index, separation pressure, injection point depth, and production tubing diameter) might have on the liquid production of a well on gas lift. Finally, the preliminary calculations that are needed before performing a gas lift design are illustrated in examples using data from typical gas lifted wells.