Iranian Researchers Study Persian Gulf’s Oil, Gas Reservoirs
In a recent study led by Hamzeh Mehrabi, a faculty member of the Faculty of Geology of the University of Tehran, in collaboration with Zahra Pouyafard and Mohammad Bahrevar, master’s degree graduates from the University of Tehran, and a professor from the University of Windsor, Canada, various models of dolomitization and its impact on the quality of oil and gas reservoirs in the Persian Gulf have been investigated.
“Dolomite is a type of sedimentary carbonate rock containing large amounts of the mineral dolomite (CaMg(CO3)2). One of the geological processes in parts of the Persian Gulf has been dolomitization, or the formation of dolomite rocks. This process has affected the reservoir quality of the Darian Formation in three oil/gas fields in the Persian Gulf. In this study, the dolomitization process in this formation was investigated by petrographic studies of core samples and thin sections with a cathodoluminescence microscope, carbon and oxygen isotopic analyses, and studies of the fluids involved,” Mehrabi said.
Elaborating on the dolomitization phenomenon, he stated, “In the hydrothermal dolomitization process, saddle dolomites are formed that fill fractures and cavities. Stylolite-related dolomitization occurs in the dominant mud facies and is concentrated as fine to medium-sized crystals with an opaque center and a clear margin, mainly along dissolution seams and stylolites. Bacterial dolomitization has been identified in algal facies, indicating a microbially mediated role in their formation.”
“This study shows that the dolomitization process specifically improves permeability, in a way that the highest reservoir quality is found in the dolomitized facies of the lower carbonate part of the Darian Formation,” Mehrabi said.
Dolomitization, the process of converting limestone to dolostone by the replacement of calcium with magnesium, can occur through various models, including seepage reflux, mixing zone, burial, and hydrothermal models.
Each model is characterized by distinct geochemical signatures and spatial distribution patterns, which can be deciphered through detailed petrographic and geochemical analyses.
Previous studies have shown that dolomitization can enhance or degrade reservoir properties depending on the timing and conditions of dolomite formation.
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