Paleo weathering effect on detrital composition of Adigrat sandstone from Ogaden Basin and Kella area, Ethiopia: Insight for reservoir quality prediction

Ogaden basin is one of the five major sedimentary basins in Ethiopia; and Kella is one of the areas in Ethiopia where pre-Tertiary sedimentary rocks can be found, though it is not among the major sedimentary basins. Detrital composition analysis is a powerful tool for understanding the paleo-climate, paleo-weathering conditions, and provenance. The purpose of this research is to investigate the paleo-weathering effect on the detrital composition of Adigrat sandstone from the Kella area and Ogaden Basin, which are understudied compared to the contemporaneous deposits in Mekele and Blue Nile Basins. Twenty core samples from the Ogaden basin and nine outcrop samples from Kella area were collected. Laboratory analysis including petrographic, XRD, and XRF were employed for the study. The QLF ternary plot analysis indicates that the majority of the Kella area and Ogaden Basin samples are quartz-rich, with a significant proportion falling within the quartzarenite and subarkose fields. The provenance analysis indicates felsic and intermediate igneous rock sources. The Kella samples, with higher CIA and CIW values, indicate intense chemical weathering under warm and humid climate conditions, potentially leading to reservoir quality reduction. Conversely, the Ogaden Basin well samples, with lower CIA and CIW values, suggest less weathering under arid climate conditions suggesting better reservoir quality. However, the presence of less stable minerals like plagioclase could lead to mineral dissolution and porosity loss over time. Using the analyzed data, the link among the reservoir quality, paleo-weathering processes, paleo-climate, and provenance of the Adigrat sandstone was established, which is very crucial in reducing future exploration risks particularly in the frontier Basins, like the Blue Nile Basin.