The Numbi field is located approximately 20 miles offshore of the Cabinda enclave of Angola. The main producing reservoir in the Numbi field, the 57-05 Upper Vermelha reservoir, is comprised of a stacked sequence of near shore deposits approximately 550 FT thick. The reservoir is highly stratified and faulted, containing a hydrocarbon column that consists of a 200-FT thick oil column overlain by a 240-FT thick gas cap.

The field was discovered in 1982 and placed on production in 1987. A peripheral waterflood project was implemented in 1991 to maintain the reservoir pressure and to improve the ultimate oil recovery. The field reached a peak production rate of over 85,000 BOPD after water injection was initiated. However, poor injectivity, formation sand back-flow into the injection wells, and poor injection profiles prevented the desired level and distribution of water injection from being achieved. These imbalances in injection caused gas cap expansion in some areas, and oil migration into the primary gas cap in others.

Cabinda Gulf Oil Company recently implemented fundamental changes to the reservoir management strategy of the Numbi field to maximize the field's ultimate recovery. Crestal waterflood injection wells have been drilled into the gas cap to balance the distribution of water injection, to increase the voidage replacement ratio (VRR), and to serve as a buffer to prevent the migration of oil into the gas cap. The new injection wells have been successfully completed as screenless frac packs employing curable resin-coated proppant (RCP) for sand control and incorporating multiple packers with injection mandrels for mechanical injection profile control. Pre-job laboratory evaluations were performed with manifold objectives including selection of the optimum curable RCP to be compatible with the proposed fracturing fluid. This was done to provide a frac pack with the greatest conductivity and sufficient compressive strength to withstand the impacts of stress-cycling due to periodic water injection shut-downs. Three dimensional fracture simulations were used to optimize the fracture geometry during the design and implementation of the frac-packs. While the evaluation of the success of these completions is ongoing, results thus far show that the target injection rates are being achieved and that the injection profiles are balanced. The success of this well design is critical for achieving the reservoir management objectives at Numbi.

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