Optimizing drainage strategy is an important part of petroleum reservoir management, and has to be implemented as a dynamic process. This work describes a unique combination of standalone and coupled reservoir simulation modeling as well as production decline curve analysis and tracer data interpretation to establish optimal gas injection strategy in Smørbukk and Smørbukk Sør fields in the Norwegian Sea for improved reservoir management in terms of reserves and economy.

The drainage strategy challenge of Smørbukk and Smørbukk Sør fields is how to prioritize gas export from the fields and how to allocate the remaining gas in the efficient injectors for enhanced condensate recovery. The results triggered a change in injection strategy to rank gas disposition internally in optimized locations both in Smørbukk and Smørbukk Sør fields, and to split the injection between the two fields.

The results showed that gas-oil-ratio development of producers, gas injection efficiency (GIF), well to well tracer communication and produced water-gas ratio development are the key factors. Reservoir segments with lower produced gas-oil ratio and higher water-gas ratio development have shown the most favorable locations for gas injection. It is demonstrated also that injection efficiency decreases by time; accordingly the drainage strategy consists in two phases: Optimized gas cycling period into efficient injectors in Smørbukk and Smørbukk Sør fields and a blowdown phase including converting injectors to producers when the injection is not efficient. The work addresses the workflow and methodology for drainage strategy, main challenges and related lessons associated to reservoir simulation results, compared with production data and tracer results. The paper will shed light on the future of reservoir management and forecasting of drainage strategy for matured complex fields.

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