The studied field is a relatively homogeneous giant carbonate field composed of three stacked isolated reservoirs, having produced for nearly 50 years through a series of pressure maintenance methods. Chronologically, the implemented methods include gravity-driven dumpflood water injection, peripheral water injection and immiscible crestal gas injection. As the historical and on-going pressure maintenance oriented development is reaching its limitation in sustaining the oil production, it is necessary to move towards a sweep oriented development to further extend the plateau and increase final recovery.

A robust full field improved oil recovery (IOR) development plan is proposed with a smooth transition from pressure maintenance to sweep oriented development. The key questions to be answered in the IOR development are (a) when to migrate to sweep oriented development, (b) how to configure the pattern, (c) how to manage voidage replacement and decide the split between water and gas injection, and (d) how to resolve associated common issues with pattern water injection and crestal gas injection. The workflow includes dividing the field into three zones based on reservoir quality and current maturity to water flood. Dedicated sweep oriented strategy is defined for different zones respectively and its efficiency is evaluated through reservoir simulations by incorporating practical drilling campaign, well completion type, surface facility constraints and interference with historical development.

According to simulation results of the IOR plan, it can be concluded that the developed strategy (a) efficiently sweeps the oil without bypassed regions, effectively recovering down to residual oil saturation, (b) is quite robust with respect to the change of well count, (c) extends the plateau with efficient pressure support in the field and (d) is a reasonable approach towards yet undefined tertiary enhanced oil recovery (EOR) application.

This paper discusses the approach used to develop this IOR plan for the near and far future development of this giant carbonate field, focusing in particular on the solution of the above mentioned key questions.

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