The obstructing implications of the deteriorating diagenetic factors on the reservoir quality and flow capacity of the gas-bearing siliciclastic sequence in the Obaiyed Field, northern Western Desert, Egypt

Abstract

The Obaiyed Gas Field is a significant gas-producing field in the northern Western Desert of Egypt. It is considered a tight gas reservoir because of its highly compact nature resulting from its intensive diagenetic history. This study presents a profound investigation and an integrated assessment of petrophysical and geological data, comprising core measurements, well logs for formation evaluation, sedimentological studies, and diagenetic modifications. The investigation focuses on characterizing the heterogeneous reservoirs of the siliciclastic sequences of the Lower Paleozoic-Middle Jurassic sequence, intending to aid in the exploration and development of hydrocarbon reservoirs in the Obaiyed Field. Several petrophysical parameters, such as the discrete rock type, reservoir quality index, normalized porosity index, flow zone indicator, and effective pore throat radius, were calculated to assess the quality of the reservoirs being studied. Seven microfacies were identified and summed into 5 reservoir rock types (RRTs). The quartz arenite and kaolinitic quartz arenite of the Lower Safa Member had the best reservoir quality. The micaceous clayey and siliceous quartz arenite of the Shifah Formation have the lowest quality. The main dominant key diagenetic features that control reservoir quality are compaction, cementation, quartz overgrowth, dispersed authigenic minerals, fracturing, and dissolution. Reservoir zonation shows that the Shifah Formation is not as promising as the Lower Safa Member because of its highly heterogeneous nature. The southeastern and central regions of the field exhibit a significant increase in the reservoir quality. The applied workflow is applicable to the other gas/condensate fields in the Western Desert and NE Africa, which are similar in the same stratigraphic and structural settings. • The Obaiyed Gas Field is characterized by varied lithology, lateral facies changes, variable reservoir properties, and complex structure. • This research is considered integrated petrophysical (Core and Well logging) and petrographical study. • siliciclastic sequences of the Lower Paleozoic Shifah Fm and the Middle Jurassic Lower Safa Mb are the most potential reservoirs in this field. • The DRT, RQI, NPI, FZI, and R 35 are estimated to help in evaluation the reservoir properties of this sequence. • The sequence is classified into five RRTs; where compaction, cementation, authigenic minerals, fracturing, and dissociation are the dominant diagenetic features.