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Estimation of the Sealing Capacity of the Zubair Formation in Selected Oil Fields in Southern Iraq


E-mail:[email protected]* The lower Cretaceous Zubair Formation is one of the most important and prolific oil reservoirs in the southern Iraq region. This study attempts to improve the understanding of the nature of pressure distribution within the Zubair formation, and to show which factors such as seals, barriers and baffles are responsible for controlling that pressure distribution. The current study examines the impact of clay mineralogy and diagenetic processes on seal capacity of the formation within the Mesopotamia Basin. The seal is mapped to investigate geometry and continuity, and distribution of overpressures across the area. Work has also been undertaken to characterize the reservoir unit itself, investigating reservoir petrophysics and heterogeneity. A large data set was used to accomplish this work comprising cores, logs and pressure data. SEM, EDX and XRD analyses were performed using data collected from six wells taken from sand /shale contacts. The clay mineralogy of the sand/shale contacts revealed the abundance of authigenic illite, illite /chlorite and chlorite in the Zubair shales at greater depths, with kaolinite is present in only a few samples. The economic viability of the Zubair Formation will be greatly increased by the improved understanding of reservoir sealing and compartmentalization, allowing for better reservoir management and improved recovery.