Abstract
Gas lift is deplored when the natural lift energy for matured well provides flow rate below the required value. Casing-heading instability removal, fault-tolerant control (FTC) and general operation of the system require the system model and its analysis. In this article, we present a simple approach to gas lift modelling from a tutorial perspective. We derive these gas-lifted system models comparing the models with existing models in the process. We also derive the pressure profile in the annulus and tubing. A simplified approach to the linearisation of the gas-lifted system that is a differential algebraic equation (DAE) system is also presented. The linearised result is used in simulation and analysis of the gas-lifted system where the phase portrait and the stability of the linearised system were considered. Also considered were behaviour of the linearised system and the nonlinear counterpart. The difference of 4kg, 4kg and 30kg corresponding to percentage difference of 0.16%, 0.29% and 2.38% respectively between the linearised and the nonlinear states observed implies convergence. The key objective of this work is to present a simplified approach to the modelling and analysis of the gas-lifted system.
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