Controls on depositional facies in Upper Cretaceous carbonate reservoirs in the Zagros area and the Persian Gulf, Iran

In the Zagros area and the Persian Gulf, Upper Cretaceous carbonate sequences are among the most important hydrocarbon reservoirs. In this study, facies analysis and stratigraphic interpretation of these sequences, Cenomanian-Santonian in age, have been carried out in subsurface sections from various parts of the Zagros area (including the Dezful Embayment and Fars Province) and the Persian Gulf. To have a better understanding about the facies variations at the regional scale, depositional facies of these formations have been determined and grouped as facies associations. Frequency analyses of depositional facies and their characteristics reveal considerable variations in the study area. These are interpreted to have resulted from the combined effects of paleoenvironmental conditions and platform configuration. The overall depositional model of these formations is that of a carbonate ramp, which was likely homoclinal for the Sarvak and distally-steepened for the Ilam Formation. The isopach maps of the studied intervals are depicted based on the available data from hundreds of drilled wells, surface sections and seismic interpretations. Large scale variations in facies and thicknesses of the studied formations are interpreted to be controlled by regional tectonic evolution and sea-level fluctuations during the Upper Cretaceous.