The paper presents an integrated reservoir modeling (IRM) of a giant complex fractured carbonate reservoir to get insights about the reservoir's displacement process. Historically the field has undergone many recovery mechanisms, nowadays two still remains: Gas-Oil Gravity Drainage (GOGD) and waterflood. A major change in understanding the vertical connectivity of the different reservoir units henders the future development options. A decision-based approach was followed to select an economically feasible field development option. Selection of economically feasible development option need; field performance review, full frame structure and geological model is built, ideal conceptual sector models sliced from the full frame structural model and numerical dynamic simulation is carried out with different development options (water injection (WI), gas oil gravity drainage (GOGD) and mixture of WI and GOGD).

Understanding the fluid flow behavior in fractured carbonate reservoirs is complex and challenging. The complexity directly linked to the understanding of the fracture hierarchy and connectivity. The field development plan at the time of analyzing the field data was water injection with very good recovery factor that cannot be explained by the injected water pore volume. Applying the integrated reservoir modeling (IRM) procedures, full filed performance review is carried out, update of subsurface models with different fracture model realizations and run numerical dynamic simulations over idealized conceptual models with different development options. Full filed history match is carried out on the selected development option.

Front Loading and data analysis is key for successful modeling strategy, the main uncertainty is the fracture distribution, better understanding of the reservoir units cross flow, understand the effect of different development options on recovery factor in significantly short time and create reasonable scenarios of subsurface.

Well performance showed some effects of water injection. Gas oil gravity is the dominant recovery process. Gas recirculation of shallow wells have negative effects on the GOGD process. Adding water injectors with continuous gas injection has negative effects on the recovery factor.

The fracture hierarchy is key to understand the subsurface. All the studied reservoir units are in communication via fracture corridors. The main recovery mechanism is gas oil gravity drainage (GOGD). WI may have local effects but as development concept it will not add value. Well location relative to fracture corridors is critical to achieve better history match. Water injection has negative effect on field recovery and operationally (WRFM). Filed operation optimization (optimize gas injection) can result in maintain the same rate with lower CPEX and OPEX (Capital spending efficiency).

This paper presents significant importance understanding the integration and clear vision of the modeling strategy that saves effort and money.

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