Sedimentology and reservoir characteristics of delta plain reservoirs: An example from Messinian Abu Madi Formation, Nile Delta

Abstract

Delta plain sandstones represent one of the major deltaic hydrocarbon reservoir compartments. The present research provides integrated sedimentological, petrophysical, and petrographical analyses of delta plain reservoirs using an example from the gas-bearing Messinian Abu Madi in the central part of the Nile Delta. The Abu Madi reservoir is interpreted as a tidally-influenced, fluvial-dominated delta plain, and it is subdivided into four sedimentological architectural elements: distributary channel, crevasse channel (straight and meandering), crevasse splays, and interdistributary bay fill. Although the distributary channel has the best reservoir quality (HFU 4 and HFU 5), it is characterized by a high degree of heterogeneity due to the complex interaction between fluvial discharge and tidal currents; straight crevasse channels (HFU 3 and HFU 4) are similar to the distributary channel but have relatively fine grain size and small sand body volume. The meandering crevasse channels are of low reservoir quality (HFUs 1 and 2) due to the formation of point bar muddy inclined heterolithics. According to the results, the delta plain reservoirs are microscopically dominated by quartzose, and litho- and feldspathic quartzose microfacies. The common mud-matrix and poorly sorted fabric due to rapid deposition as well as reworking by tidal/wave currents, that represent the main depositional controls on reservoir quality. Meanwhile, dissolution, anhydrite, quartz, and calcite as well as authigenic kaolinite and chlorite clays are the main diagenetic control factors on reservoir quality.