Diagenetic history and reservoir quality based on petrographic and geochemical properties of Upper Member of Sarvak Formation in Bangestan anticline, SW Iran

Sarvak Formation of Bangestan Group (Cenomanian-Turonian) is a carbonate sequence of Cretaceous system in the Zagros Basin. In this research، an outcrop of this formation in Tang-e-Bulfares، about 60 Km east of Ramhormoz (Khuzestan Province) and in southern part of Bangestan anticline، has been studied. Diagenetic processes that have affected Sarvak Formation were evaluated using polarizing and cathodoluminescence microscopes and the paragenetic sequence of were interpreted. The most important diagenetic processes which have involved limestones of upper part of Sarvak Formation include: micritization، neomorphism، cementation، mechanical compaction، chemical compaction، dissolution، fracturing and development of calcitic veins. In general، processes such as dissolution، fracturing and in specific conditions stylolitization have increased reservoir quality in the studied section and the processes of micritization، cementation، compaction and development of calcitic veins have decreased the potential of this formation as a suitable petroleum reservoir. The results of this research reveal that destructive processes have had more influence and so the reservoir quality of the upper part of Sarvak Formation has been reduced by diagenesis. Also، study of major and minor elements reveals a closed to semi-closed diagenetic system and probably the high Mg-calcite was a primary mineralogy for carbonate rocks of the studied formation. Based on the Sr/Na versus Mg graph، palaeoclimatic conditions during deposition of the Sarvak Formation may have been similar to the present-time temperate regions.