Modeling, simulation and optimization of continuous gas lift systems for deepwater offshore petroleum production

Abstract

This paper proposed a framework for the analysis of continuous gas lift systems using an optimization algorithm coupled to a stationary two-phase flow network model. The objective function can consider the annualized capital costs on compressor, turbine and gas pipelines, the operating costs related to fuel and the revenue from produced oil. The interaction among wells, production lines and riser is properly evaluated by a stationary two-phase flow simulator for pipe networks composed by mass balances at network elements and momentum balances at pipes using the Beggs and Brill empirical correlation. The solution of the optimization problem can estimate important information for the conceptual design phase of a petroleum production system: (i) the injected gas flow rates that guarantees maximum oil production, (ii) the injected gas flow rates for maximum profit and (iii) optimal design of gas lift system considering capital costs of compressor, turbine and gas pipelines. Case studies of single and multiple wells with different complexities describe some applications of the proposed framework. At the first case study, an offshore petroleum well with gas lift artificial elevation is simulated – to determine the behavior of petroleum production as a function of the injected gas flow rate for different reservoir pressures and different wellbore diameters – and optimized—to determine the maximum production considering different productivity indexes. At the second case study, a complex petroleum production system with multiple wells is simulated and optimized to obtain the optimal design considering annualized costs of compressor, turbine driver, gas pipelines and fuel gas consumption.