Diagenetic controls on the porosity of adigrat sandstone formation in the Dejen-Gohatsion section of the Blue Nile Basin, Central Ethiopia

Abstract

The Adigrat Sandstone Formation, representing the siliciclastic assemblage of the Lower Mesozoic succession, underlies the Gohatsion Formation in the Blue Nile Basin. Despite its stratigraphic and geological significance, the impact of diagenesis on the porosity value of the Adigrat sandstone remains poorly understood. By analyzing a detailed field description of two stratigraphic logs, along with the associated thin sections and additional correlated well data, the environment of deposition has been interpreted. The petrographic analysis was carried out to 30 sandstone samples collected from five selected outcrops, and complemented by the two stratigraphic columns. The main diagenetic processes affecting the Adigrat sandstone porosity were compaction, cementation, mineral dissolution, replacement, authigenesis, and recrystallization. The framework grain and cement relationship suggests an early quartz cement precipitation, followed by partial or intense calcite and hematite development in some samples as the second cementation phase. Feldspar alteration to lath-shaped kaolinite clusters causes kaolinite to act as a pore-lining and pore-filling cement, thereby reducing porosity. Conversely, the fracture and dissolution of some samples enhanced the fluid storage capacity. The estimated existing optical porosity (EOP) varies between 1 and 8%, with a mean value of 5%, of which 70% of the samples possess catenary and cul-de-sac porosities. Based on petrographic analysis, the sandstone is mineralogically categorized as sub-mature to mature. These findings significantly contribute to understanding the diagenetic evolution of the Adigrat Sandstone Formation, providing valuable insights for reservoir characterization and exploration strategies in the Blue Nile Basin (BNB).