Characterization of sedimentary microfacies and depositional dynamics of the upper cretaceous hartha formation in the X oil field, Middle East

Abstract There is a lack of continuous distribution of reef facies in carbonate gentle slopes, which is accompanied by pronounced reservoir heterogeneity and ambiguous development patterns. This complexity necessitates a detailed analysis of sedimentary microfacies and their changing trends to effectively delineate favorable facies zones for resource exploration and development. Previous studies on the sedimentary facies of the Hartha Formation in the EBS oilfield in Iraq were based on secondary tectonic units or adjacent oilfield blocks, limiting the understanding and development of oil and gas reservoirs within the oilfield. Utilizing an integrated approach that combines core analyses, thin section petrography, well logging, and seismic data with regional geological backgrounds, this study conducts a comprehensive sequence stratigraphic analysis of the Hartha Formation. First, a unified sequence stratigraphic framework is established, thereby facilitating a detailed examination of the characteristics and evolutionary trajectories of each depositional sequence and the development of a corresponding depositional model. Key findings include the following: (1) The division of the Hartha Formation into two complete third-order sequences and eight fourth-order sequences; (2) The identification of ten distinct carbonate microfacies types (MF1-MF10), with each corresponding to specific depositional environments in the outer, middle, and inner ramps; (3) The effective restoration of the paleogeography for each depositional period using the residual thickness method, which highlights the critical role of sea-level fluctuations in influencing the spatial distribution of shoals and facies zones; (4) A clear depiction of the depositional progression from the outer ramp through to the inner ramp, thus underscoring the dynamic nature of sedimentary processes within the Hartha Formation.