The challenges to effectively manage a field with stacked reservoirs that are in known hydraulic communication are enormous. Conventional management of such fields can result in many undesired outcomes such as premature water production caused by cross-communication from different reservoirs, inefficient pressure support to some of the individual reservoirs, or large volumes of bypassed oil. The major challenge is to identify the reasons and magnitude of inter-reservoir communication, and accurately capture these in the models which are utilized for optimized well placement and efficient field development. This paper discusses an integrated multi-disciplinary approach to identify and model inter-reservoir communication in a giant offshore carbonate field from UAE. Tracer study conducted for several years combined with detailed seismic interpretation suggest that the cross-flow of reservoirs due to fault juxtapositions is the major cause of inter-reservoir communication. This observation is further supported by pressure-transient analysis, logs, cores, drilling reports and regional structural studies. Hence, it becomes absolutely essential to build a robust static and dynamic model that can accurately capture the communication between different reservoirs. This paper proposes a novel approach to build a full-field integrated framework that allows coupling of multiple reservoirs that have been previously modeled independently. The methodology includes; detailed reinterpretation of faults and key chronostratigraphic surfaces, qualitative/ quantitative attribute analysis using reprocessed 3D seismic (post-stack time migrated) data, interpretation of pressure transit analysis, logs, surveillance data and regional structural history studies. The updated framework ensures accurate fault throw and fault extension in order to capture fault juxtapositions. The ability of the new model to allow inter-reservoir communication has been tested and confirmed in dynamic simulation model. This was achieved through series of simulation sensitivities where tracers injected in wells targeting specific reservoirs were successfully sampled from different reservoirs due to inter-reservoir communication through fault juxtaposition. Based on the results of sensitivity test, it is expected that the new integrated framework will provide a much improved history match in faulted areas where cross-communication across reservoir is very prominent. The improved model will lead to a better understanding of field and possibly will be used as guidance for field development plan.

The ability to identify subtle structural and paleo geomorphological features within carbonates may significantly reduce wide range of drilling challenges including stuck pipe, breakouts, casing failure, lost circulation, hole collapse, washouts, etc. Current study emphasis on integrated approach to discuss drilling challenges, their possible mitigations and subsurface risk assessment. This study is a multi-disciplinary application of integrated borehole and advanced seismic attributes to identify hazards, mainly linked with drilling problems. In this regards, paleo structure mapping is initially utilized to broadly outline areas in the field that may be associated with potential karst collapse features development. These karst collapse features are mainly responsible for dynamic mud losses and may also cause other problems (e.g., casing failure, etc.). One of the main challenges observed to confidently characterize karst collapse and other subtle features is that seismic data contains a lot of overburden noise hence an improved approach is proposed to eliminate seismic noise and enhance S/N ratio. Advanced seismic attribute volumes are then produced to capture full field lateral as well as vertical distribution of subtle features. Integrated results are calibrated with borehole image, core, logs, PLT, mud losses, Hall plot and CUM injection in vicinity. A novel approach is introduced to calculate unmonitored injection area of influence and other associated subsurface risks assessment. An improved Integrated approach used in this paper shows promising results. Full field distribution of karst collapse features is outlined confidently and results are validated with dynamic data and diffraction seismic imaging. Vertical extent of karstified zone is clearly captured in cross sectional view, which ties with petrophysical zonation, PLT, core and dynamic mud losses. Furthermore, the novel approach of Injection area of influence calculation improves subsurface understanding and highlight other challenges e.g. pressure anomalies or future disposal wells planning, etc. Two examples are presented in this paper for reference. An approach defined in this paper improves confidence in subsurface hazards identification, well plan optimization and minimizing unexpected costs associated with mud losses, sidetracks, etc.