Carbonate reservoirs in the Middle East are characterized by strong heterogeneity, fairly subtle barriers and baffles, which result in low water flood swept volume and poor displacement efficiency. Therefore, optimum well pattern deployment is critical for high-efficiency development of such reservoirs. This paper focuses on a giant carbonate reservoir and discusses the application of highly inclined well to optimizing the deployment of well pattern.

In this paper, first, based on the productivity formulae of slanted and horizontal wells proposed by Besson, the adaptability of highly inclined well in giant carbonate reservoir was evaluated. Then, the well design parameters were optimized by using numerical simulation. Finally, the optimum well pattern of "water injection in vertical well and oil production in highly inclined well" was established, and sound development strategies were determined. This provided us the foundation to propose customized water flooding plan. The successful application of this development scheme for M carbonate reservoir in Iraq validated the technical feasibility, which achieved considerable economic benefits.

The results indicate that highly inclined well has advantages in productivity and adaptability of well type to this kind of reservoirs. The production of top low-permeability layers and bottom low-permeability layers in M reservoir with inclined interval and horizontal interval respectively makes full use of highly inclined well, which balances injectivity and productivity of different reservoir properties. The proper length of highly inclined well is 2953∼3281 feet, and the ratio of inclined interval to horizontal interval is about 2. The optimized well pattern of "water injection in vertical well and oil production in highly inclined well" improves water injection sweep efficiency and recovery factor. The M reservoir in Iraq has achieved an annual yield of more than 1.5 million barrels.

The water injection development for large-scale carbonate reservoirs in the Middle East is still at exploration stage and lack of mature experience. The proposed development pattern in this paper provides a methodology for the efficient development of similar reservoirs.

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