A Study of microfacies and diagenetic processes of the Asmari Formation in Khesht Oil Field with emphasis on reservoir characteristic: a case study from Zagros basin, Fars, SW Iran

Abstract

The Oligo-Miocene Asmari Formation is a most famous oil reservoir in southwest of Iran and the world. In the present study, in order to understand the reservoir quality controlling factors of the Asmari Formation, the detailed petrographic studies were carried out in the Khesht Oil Field to identify microfacies, diagenetic processes affecting these microfacies and their paragenetic sequence. Six carbonate microfacies indicated based on one hundred eighty three microscopic thin section analysis from core samples in this field, which are deposited in tidal flat and lagoon sub-environments along a ramp type platform. The results of this study show that important diagenetic processes have affected the Asmari Formation carbonates are included micritization, cementation (marine, meteoric, and burial cements), dissolution (meteoric and burial dissolution), neomorphism, mechanical and chemical compaction, fracturing, dolomitization (dolomicrite, dolomicrosparite, dolosparite and dolomite cement) and anhydritization (in different types). Dissolution and fracturing have enhanced porosity and permeability values, while cementation and compaction have decreased the reservoir potential of the Asmari Formation by occluding the pore spaces. Dolomitization had a dual impact on reservoir quality of the Asmari Formation.