In this study, a computerized integrated production model was developed for a gas lift system in a mature oilfield located off the east coast of Trinidad. The model included the compressor station, injection manifold, three producing strings, the producing manifold and the low pressure separator, and utilized reservoir pressure-volume-temperature data and injection data. It was used to analyze and provide the optimal allocation of available gas lift gas, over the entire network of wells, using nodal analysis.

Gas lift systems are a well-known form of artificial lift which is used to improve oil production rates. The high-pressure gas injected mixes with the oil column to reduce its density which in return reduces the flowing bottomhole pressure, creating a drawdown large enough for the well to flow. The main operating constraints at this mature field are the fixed amount of gas available for compression to the wells, and the operating pressure of the compressor. Given these constraints, one has to optimally utilize the available lift gas to allow maximum recovery while considering the economics of the project.

The results indicated that using the optimized gas injection rates, an increase in oil production would be realized. An economic evaluation of the optimized system also indicated improved project economics due to a decrease in gas utilization and operational costs.

The work presented in this study is of great value since it was geared towards solving a real industry-based problem. The model which was built can also be used for reservoir management since it is capable of making future predictions. It can also be continuously updated to reflect new operating conditions and changes to the surface piping or the downhole completion. This study shows that integrated asset/production modelling can be quite effective in production optimization.

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