Controls of depositional and diagenetic processes on the distribution of reservoir rock types in carbonate reservoirs; a case from the Sarvak Formation in the Dezful Embayment

The Sarvak Formation was deposited on shallow-marine carbonate platforms under the controls of tectonic and eustatic changes during the Upper Cretaceous in the Zagros area. It forms on of the most important reservoir intervals in SW Iran. Complex depositional setting and diagenesis history have resulted in a heterogeneous carbonate reservoir. This study, integrates the results of petrographic (facies and diagenesis) studies with petrophysical and reservoir data (core porosity-permeability and wireline logs) to evaluate the controls of depositional and diagenetic processes on the distribution of reservoir quality in the Sarvak Formation. Ten hydraulic flow units are determined using the FZI concept. Twelve reservoir and non-reservoir (baffle and barrier) units are identified using the Lorenz approach. Finally, dominant depositional facies and diagenetic alterations are evaluated in each HFU and reservoir zone. Results of this study showed that meteorically-dissolved rudist-dominated facies and high-energy facies of shoal complexes formed the best reservoir units in the Sarvak Formation. In sequence stratigraphic point of view, these zones are located in the RSTs of third-order sequences, beneath the disconformity (paleoexposure) surfaces. In contrast, the compacted and cemented mud-dominated facies concentrated in the TSTs and around the maximum flooding surfaces (MFS) formed the non-reservoir units of the Sarvak Formation.