Stabilization of gas-lift oil wells using topside measurements

Abstract

Highly oscillatory flow regimes that can occur in gas-lift oil wells have been successfully treated using conventional linear control. However, these control systems rely on downhole pressure measurements which are unreliable or even unavailable in some cases. In this paper we propose a solution based on a high gain observer for the state of the process. The estimates are used to compute the downhole pressure, that is the controlled variable considered in the feedback control. Moreover, we propose an estimator to extend a nonlinear observer already presented in the literature, and then we compare the performances. The key feature of the solution proposed is its simplicity and that it relies only on measurements easily obtainable from the top of the single well, and thus it is immediately applicable to multiple-well systems where, since there is often one common outflow manifold, it would be hard to see from the outflow measurements which well is operating in an oscillatory regime.