Gas lift is a flexible artificial lift method, which requires continuous monitoring to identify diverse ways of production optimization. Gas lift systems optimization is a dynamic process throughout well production life in order to maximize the overall field production. Traditional gas lift valve installation standards were replaced by a new strategy, at which valves were converted to smaller port sizes, dummy and Venturi ones. A mature offshore field, with more than 460 gas lifted wells and limited gas availability, undergoes depletion phase. Most of the gas lift design bases were initiated during the production start-up and has standardization set of large gas lift valve port sizes with narrow spacing. Inconstancy of the well flow condition during reservoir depletion added complications to the system and made its operability incompatible with the initial design. Therefore, a screen-out model was created to select candidate wells for downsizing and for dummy and Venturi valves changing-out. After screening, 70 wells were selected for applying the new strategy.
A successful optimization in gas lift system was carried out after selecting 70 candidate wells. The gas lift valve change-out (GLVCO) operation included changing valves from normal unloading valves to dummy ones, downsizing to smaller port sizes, changing valves from edge-orifice operating to Venturi valves and applying new gas lift design approach in order to increase closing pressures of shallower valves by considering ambient the temperature effect. Improvement in wells performances was evaluated using real-time monitoring system, multi-phase flow meters and portable well testing package. Applying the new strategy resulted in exceptional improvements in 47 wells by injecting gas from deeper valves, decreasing the downstream pressure to prevent re-opening of shallower valves, optimizing gas lift injection rate and enhancing gas lift system stability. Accordingly, more than 7000 BOPD were added to the production stream and led to saving more than 10 MMSCFPD of injection gas to be used for other wells and mitigating flow assurance difficulties regarding scale precipitation due to excessive cooling.
This paper reveals the effectiveness of smaller port sizes, dummy and Venturi valves in enhancing the gas lift performance and maximizing the recovery. It provides an improvement philosophy for managing the gas lift wells from the design concept to field application.