Depositional dynamics of the Devonian rocks and their influence on the distribution patterns of liptinite in the Sifa-1X well, Western Desert, Egypt: Implications for hydrocarbon generation

Abstract Samples from the Devonian succession in the Sifa-1 well located mid-way between the Egyptian Faghur Basin and the Libyan Cyrenaica Platform were examined in this study. The distribution of liptinite group macerals was investigated under reflected and transmitted light microscopy. Diverse and abundant liptinite of terrigenous and marine origin were identified. The palynological investigations included analysis of the miospores assemblages and palynofacies categories by multiple statistical approaches in addition to calculation of the sedimentation rates. These analyses signified four miospores biotopes and three palynofacies biotopes that were used to assess the ramps of paleoclimatological and paleoenvironmental changes during sedimentation. These biotopes were used to define a model of liptinite maceral distribution throughout the Devonian in the study area. The model suggested two different phases of basinal dynamics in terms of climate, sea level, and sedimentation rates, namely an Early-Middle Devonian transgressive phase and a Late Devonian regressive phase. Conditions during the Early-Middle Devonian transgressive phase were oxic to dysoxic with low sedimentation rates and oxic during the Late Devonian regressive phase. Oxygen depletion was above the threshold required to induce significant preservation of the quantity and quality of organic matter, including liptinite macerals. The redox conditions were confirmed by trace elements analysis. The high oxygen level affected both the quantity and quality of the liptinite macerals and greatly reduced the preservation of the amorphous organic matter. The quality of the organic matter varied from kerogen type I, II, mixed types II/III and type III. The mixture of these kerogen types was assessed by organic elemental and pyrolysis gas chromatography analyses. In addition, the entire Devonian succession in the Sifa-1 well is in the oil window, as also indicated by miospore coloration. This indicates that the organic matter in the Devonian strata have the potential to generate oil and gas.