Michael Lev Litvak

Gas Lift Optimization for Long-Term Reservoir Simulations

Although various gas-lift optimization algorithms have been proposed in literature, few of them is suitable for long-term reservoir development studies, which require the gas-lift optimizer to be highly efficient, flexible and powerful enough to handle complicated fluid flows and operational constraints, and have low impact on simulator convergences. This paper investigated methods to address these important issues. The gas-lift optimization problem considered in this paper is to maximize the daily hydrocarbon production by selecting optimally the well production and lift gas rates subject to pressure and rate constraints in nodes of the surface pipeline network and to the amount of lift gas available. The problem is regarded as a well management problem in a commercial reservoir simulator capable of simulating multiphase compositional fluid flow in reservoirs, well tubing strings, surface pipeline network systems, and separation facilities. The problem is solved in selected iterations of a reservoir simulation time step. This paper proposed a method for the described gas-lift optimization problem and investigated its performance against multiple existing methods. Case studies showed that the new method is capable of producing high quality results while requires less CPU time for optimization and has smaller impact on reservoir simulator convergence. This paper also applied the concept of multiobjec tive optimization to smooth the rate oscillation between adjacent iterations by sacrificing a certain amount of oil production. In certain cases, this method reduces the simulation time significantly.