Investigating the depositional history of the Sarvak Formation using microfacies analysis and sequence stratigraphy in two oil wells of the Abadan plain, southwestern Iran

Document Type : Research Paper

Authors

1 Department of Soft Rock, Faculty of Geology, University of Tehran, Tehran, Iran.

2 Department of Soft Rock, Faculty of Geology, University of Tehran, Tehran, Iran

Abstract

A precise evaluation of the depositional history and stratigraphic architecture of carbonate reservoirs is vital for the development of hydrocarbon fields. The Sarvak Formation, of late Albian–Turonian age, is recognized as one of the most important hydrocarbon reservoirs in the Zagros Basin and the Middle East. This formation has also been influenced by sea-level fluctuations and complex diagenetic processes. The present study aims to reconstruct the depositional environment and establish a sequence stratigraphic framework for this formation in the Abadan Plain area (southwest Iran). Based on the integrated analysis of 313.6 m of core and 850 thin sections from two exploration wells, eight distinct microfacies were identified, indicating sediment deposition on a homoclinal carbonate ramp (comprising inner, middle, and outer ramp sectors). The investigations show that zones with favorable reservoir quality are primarily concentrated in the inner ramp belt, particularly in shoal and reef-debris facies (grain-supported rudstones containing rudists). T-R sequence stratigraphic analysis led to the recognition of four third-order sequences, within which the Cenomanian–Turonian (CT-ES) and middle Turonian (mT-ES) exposure surfaces play a key role. By creating subaerial exposure and promoting meteoric diagenesis, these events caused extensive dissolution and a significant improvement in porosity and permeability. Correlation of this framework across the Zagros zone and the Arabian Plate demonstrates a unified tectono-eustatic control on reservoir architecture and provides an efficient model for predicting the lateral distribution of high-quality facies in the region's exploration programs.

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