Sandstone reservoir quality in light of depositional and diagenetic processes of the Messinian Qawasim Formation, onshore Nile Delta, Egypt

Abstract

• Sandstone in the upper part of the Qawasim Formation is the main reservoir in the El Tamad field. • Primarily, the sandstone is arenite in composition, well sorted with sub-rounded to rounded grains. • Diagenesis enhanced the reservoir quality of the sandstone with low-cement content, poor compaction and weak fracturing. • Clastic rocks of the Qawasim Formation were deposited in a shelf environment as stacked barrier-island bars. • Carbonate rocks of the Qawasim Formation were deposited in a shelf lagoon with open circulation. The Nile Delta region is the main gas-producing province in Egypt. Late Miocene sediments are the target of drilling in the onshore Nile Delta where it has the potentiality to store and produce hydrocarbons. Five wells of the Messinian Qawasim Formation at El Tamad Field were selected for the present study. Detailed petrographic investigations were carried out to reveal the depositional and diagenetic features of the Qawasim Formation rock units. Two main facies were distinguished in the studied formation: clastic and carbonate facies. The clastic rocks include conglomerate, sandstone and shale, while the carbonate rocks include limestone and dolostone. Depositional, diagenetic and petrophysical parameters of the sandstones of the Qawasim Formation reflect that this rock unit an excellent reservoir for hydrocarbon. These microfacies display depositional features such as well sorting, open packing and poor cementation in both coarse and fine-grained microfacies. The porosity of sandstone was enhanced by diagenetic processes such as dolomitization of calcite cement and low compaction that resulted in grain cracking, while the dissolution of feldspars had a subordinate impact on increasing porosity due to their low abundance and the resultant authigenic clay minerals.