Industrial & Engineering Chemistry Research, Vol.50, No.5, 2971-2980, 2011
Gas-Lift Optimization with Choke Control using a Mixed-Integer Nonlinear Formulation
This paper presents an extension to the iterative offline-online procedure proposed by Rashid(4) to efficiently optimize gas-lifted production networks. In particular, this work extends the original scheme to additionally include a single subsurface choke in each of the production wells. Hence, a revised offline formulation is presented that encompasses dual control in each well, comprising both lift-gas injection and a choke setting. As the latter can be discrete (on/off), have fixed positions or be treated as continuous, a mimed-integer nonlinear program (MINLP) result's, necessitating the use of a suitable MINLP solver. The open source Bonmin solver is utilized for this purpose. Moreover, as chokes enable better field pressure and constraint management, in addition to well activation and closure, a broader spectrum of production optimization scenarios can be tackled. Significantly, the paper demonstrates that not only does the offline-online methodology enable the application of a MINLP solver, but the results are obtained in an extremely efficient manner, as per the initial development. Results from a 26-well production network are presented, with and without the imposition of additional operating constraints.