Abstract

The JG field is an oil & gas producing field located in Abu Gharadig Basin. The Lower Safa Member is the main reservoir representing the lower member of Khattatba Formation and it is subdivided into two reservoir units "A and C" separated by non-reservoir unit "B". During the next development phase of Lower Safa "A" by it is necessary to avoid drilling dry holes or wells with low reservoir quality, and so, it was essential to understand the reason behind drilling 6 wells with low reservoir quality and the re-evaluation of the available data used to re-identify geometry was of high importance.

Lower Safa "A" had been cored in three wells with total length of about 46m. The sedimentological description of these cores highlighted several features pointing to a tidal dominated estuarine environment of deposition as abundance of carbonaceous material, channel erosion surfaces and paleosols, rapid changes of lateral and vertical facies, and mix of terrestrial and marine micro fossils.

The previous development strategy of JG field was to drill wells on crestal position along the main bounding fault which extended about 8 km in the East-West direction, assuming extension of estuarine system in the North-South direction.

Based on this study after re-evaluating available data estuarine system subdivisions clearly reflected in Lower Safa "A" unit and delineated from log characters and core features, it was proven that this unit was deposited in tidal dominated estuarine environment but extended in the East-West direction parallel to the fault, and the wells which encountered low reservoir quality were drilled in the low energy central zone and marches of estuary.

According to this study, it is recommended while developing Lower Safa "A" unit to drill within eastern and western areas i.e. the inner and outer parts of the estuarine system, which are characterized by good reservoir quality and to avoid drilling in the central part where the reservoir is low quality.

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