Facies analysis, depositional environment and diagenetic processes of the Lower Cretaceous Yamama Formation, Riyadh, Saudi Arabia

This research article presents a comprehensive work on sedimentological study of the Yamama Formation in the Saudi Arabia, aiming to enhance understanding of its depositional environments, diagenetic evolution, and reservoir properties of the formation. Integrated field and petrographic studies are used to interpret microfacies, depositional environment and diagenetic history of the Yamama Formation near Riyadh, Saudi Arabia. Field investigations show that the formation is thin- to thick-bedded, massive to nodular limestone with small patches of shale and marl. Petrographic studies show four distinct microfacies, i.e., mudstone MF-I, wackestone MF-II, packstone MF-III, grainstone MF-IV. The microfacies and their associations represent homoclinal ramp depositional setting designated on the basis of the relative percentage of allochems and orthochems. The diagenetic history, which includes eogenetic, mesogenetic, and telogenetic stages, is discussed as follows: The eogenetic stage includes burrowing, micrtization, neomorphism, and drusy mosaic cementation; the mesogenetic stage includes compaction (mechanical and chemical) and dissolution. The telogenetic stage is evident from calcite-filled fracture veins crosscutting the rock unit. The reservoir properties are directly dependent on both depositional and diagenetic processes. The reservoir quality of the formation has been significantly reduced by the precipitation of different types of cements during the diagenetic processes, as observed in the detailed paragentic sequence; however, during the late stage, fracturing has enhanced the reservoir quality significantly during the late stage.