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An important carbonate oil field, located onshore Abu Dhabi, has been producing from the Upper Cretaceous (Maastrichtian) Simsima Formation since 1983. To optimize and increase production of the field, seismic and high-resolution sequence stratigraphy was integrated by tying fourth-order, high-frequency sequences identified from core to 3-D seismic data. To establish the sequence stratigraphic framework, a new detailed sedimentological and high-resolution sequence stratigraphy study had been carried out, integrating approximately 7,000 feet of core material, approximately 3,500 thin sections, and all available well-log data from 46 wells. Core description, together with semi-quantitative petrographic examination of thin sections, established a new depositional model for the Simsima Formation. Sixteen lithofacies types (LF1 to LF16) representing a wide variety of depositional environments, ranging from upper ramp, rudist-bioclastic shoals to open marine mid to outer ramp mud-dominated settings. The newly developed, high-resolution sequence stratigraphic framework suggested that the Simsima Formation comprises one complete third-order composite sequence and the transgressive systems tract of an overlying second third-order composite sequence. These third-order composite sequences include seventeen high-frequencies, fourth-order sequences (HFS). HFS-1 to HFS-12 build the older third-order composite sequence, HFS-13 to HFS-17 form the transgressive system tract of the overlying, younger third-order composite sequence. 3-D seismic cross-sections show that fourth-order high-frequency sequences HFS-1 to HFS-6 of the older third-order composite sequence clearly show onlap on a pre-existing high (pre-Simsima unconformity surface), whereas the top part of the Simsima Formation (high-frequency sequences HFS-13 to HFS-17) show various degree of erosion. The established high-resolution sequence stratigraphic framework provides the layering scheme for the next generation Simsima 3-D static model, which will be used as input for the reservoir flow (dynamic) model. Introduction Large oil accumulations have been discovered and produced from the Upper Cretaceous (Maastrichtian) Simsima Formation in Abu Dhabi since 1983. The Simsima Formation was deposited on an actively growing paleo-high in shallow marine environment. It is capped by the basal shale member of the Umm Er Radhuma Formation and overlies the crest of partly eroded former structure of the Aruma Group. It ranges in thickness from 323 ft in the crest of the field structure to 628 ft in the flank. Recently, approximately 7,000 feet of core and 3,500 thin sections along with well-log data from 46 wells were studied. A total of sixteen lithofacies types were identified. As a result of the core study, seventeen high-resolution fourthorder sequences were established. They constitute a complete third-order composite sequence and the transgressive systems tract of an overlying second third-order composite sequence. The high-resolution sequence stratigraphy identified from cores was integrated with the 3-D seismic by tying the fourth-order sequences to the seismic data. An integrated layering scheme will be used for the next generation Simsima 3-D static model, which will be used as input for reservoir flow (dynamic) model.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMajor contribution to oil production has been mostly from the highly prolific upper Southern units in a giant complex carbonate reservoir in the middle-east region. The water front advanced much faster in highly permeable upper units than the lower units and has created uneven water sweep in southern part of the field. Reservoir management program has been implemented to reduce production from wells that are located near the water finger area to achieve an even water flood advance. However, the current situation has raised some issues concerning the optimization of recoverable reserves in lower units due to water slumping from upper to lower units, uneven areal and vertical sweep, and uncertainty in the effectiveness of dense intervals within the lower subunits. But opportunity still exists to improve the recovery from these units.

The ultimate success of an offshore field startup depends on the strategy and integration within an organization. Even more challenging is managing the dynamic interface of subsurface and surface project delivery through the design, construction, hookup, commissioning, and startup operations. This paper presents the case study of a new field startup in Abu Dhabi from the early concept selection through the critical startup phases. Integrated multi-discipline approach underpinned the successful startup when the field achieved first oil production ahead of schedule on February 2015 and exceeded expectation despite the backdrop of global sharp decline in oil price. This paper highlights the technical and functional preparation put in place by the subsurface and surface teams to ensure full integrated readiness and plan-in-place for production start-up. It also outlines the challenges encountered to achieve operational performance and the major lessons learned from the journey. The results demonstrated in this paper shows that an integrated and cooperative approach is key in dealing with delays, prioritization, execution of processes, projects and operations. The lessons learned from subsurface and surface technical preparation, through surface project engineering and delivery phases are presented. Successful management was critical in handling the drilling rigs and barge logistics, offshore installation and commissioning phases, and simultaneous operations during the production start-up and ramp-up of the field. In addition, while encountering pressures to minimize rig time and execute the extensive data gathering program, good team synergy ensured that the milestones were successfully met even with the additional limitation of skilled technical resources. Finally, illustrated in this paper are best practices applicable for new offshore field startups. This proves that even with the financial-demanding outlook and market-down conditions, the successful startup of a new field is essential and visible.

In the paper, we will briefly review the pilot design and demonstrate the utility of applying the EM imaging to the pilot. We will also show the benefit of the optimized casing material on the resolution of the crosswell EM resistivity images and describe the methods employed for monitoring the fluid flow and show preliminary results of the modeling process. This crosswell EM technique which has been successfully employed and proven in other geographical areas is being implemented first time in UAE. The EMI technology is being deployed in southern part of a complex carbonate reservoir in the middle-east where an uneven flood front advance has been observed in different reservoir units. It has been observed that water front has advanced much faster in the highly permeable upper reservoir units as compared to lower reservoir units. In order to understand the horizontal and vertical fluid flow behavior, an inverted 5-spot water injection pilot pattern is being implemented. The pilot will address the issues of the uneven sweep efficiency, bypassed oil and effectiveness of stylolites across different units. The pilot results and observed data will be used in the simulation to design an optimum development scheme for the lower reservoir units in the southern part of the field. The current dynamic simulations predicted that the injected water will reach producers after 7 to 10 years. However, the decision on field developments have to be taken early enough to avoid the slumping of water from upper to lower units and loss of reserves in the lower units. Early imaging of the injected water from the injection well into the reservoir is paramount in assessing the success of the pilot and future field development issues. It is anticipated that this tomographic Cross-well Electro-magnetic (EM) resistivity technique will provide sufficient imaging information to track the water flood movement between wells. The most favorable conditions to acquire reliable formation resistivity distribution information, EMI require at least one kilometer distance or separation between wells. Prior to the field deployment, simulations were run to confirm the applicability of the technique and define the parameters for the survey with objectives; 1) to check the sensitivity of EM technique to the reservoir conditions and injected fluids, and 2) to carry out actual EM tool simulation and check the quality of tool response. The study concluded; 1) cross-well EM resistivity technique is well suited for tracking the water front in the current reservoir conditions, 2) the injected fluids create enough resistivity contrast to be easily picked up by the technique, and 3) the flood front progress can be captured by conducting the surveys in a time-lapse mode. As part of this project, lab tests were conducted to choose a material that would limit the attenuation at high frequency as much as possible at source and receiver locations. Introduction Peripheral water flooding as pressure maintenance method was commenced within few years of the discovery of the giant complex carbonate reservoir in the middle-east region. Although initially quite successful, the field has experienced uneven distribution of water flood front, vertical and lateral sweep due to reservoir complexity. Detailed simulation modeling was performed to delineate optimum strategy for maximizing reserves in the lower two oil bearing units of reservoir thereby controlling the process at a more local level (Ref. 1). The benefits of this process are more efficient and faster recovery. The potential drawbacks are greater costs and higher local pressures which could induce uneven flows.