Improved Stable, Optimal Production in Gas Lift Wells: Exploiting Additional Degrees of Freedom

Typical production objectives in lift gas assisted oil wells include stable and optimal production. These objectives are normally daunted by the presence of unstable dynamic behavior resulting from interplay between the energies in the casing head and tubing head of the wells. Moreover, realistic constraints on compressor power and sufficient lift gas availability need to be considered to determine the optimal production from the wells. This paper proposes an alternate optimization formulation to reflect these realistic constraints and exploit the additional degree of freedom associated with the production choke opening. It is demonstrated that a co-ordinated functioning of the choke with the lift gas flow can result in improved and stable production. To overcome the limitations of corrupt measurements in the uncertain downhole environment, we propose the use of a statistical estimator. Validation results involving the simulation model of Jahanshahi et al., (2012) point to the efficacy of the proposed optimization model as well as the soft-sensing approach for estimating downhole pressures.