Impacts of Depositional Facies and Diagenesis on Reservoir Quality: A Case Study from the Rudist-bearing Sarvak Formation, Abadan Plain, SW Iran

An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells. Eight main facies are recognized and categorized in five facies groups: lagoon, shoal, rudist-biostrome, slope, and shallow open marine, deposited on a shelf carbonate platform. Given the distribution of diagenetic products and their effects on pore systems, three diagenetic facies namely, (DF-1) low dissolution and cementation; (DF-2); high dissolution; and (DF-3) high cementation are differentiated. The initial sedimentary characteristics in combination with distribution of diagenetic products play an important role in reservoir quality heterogeneity. The effect of diagenetic processes related to disconformities mainly depends on the facies nature below these surfaces. Grain-dominated facies of shoal and rudist debris, observed below the Cenomanian–Turonian disconformity, are mostly characterized by high dissolution and interconnected pore systems. Finally, depositional and diagenetic facies in the studied wells are correlated by petrophysical well log data, leading to distribution of the reservoir zones. Data obtained can be utilized for efficient reservoir characterization of the Sarvak Formation and its equivalent units in the Arabian Plate.