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Microfacies are defined as a study and interpretation of all observable specifications of a rock in thin section. An initial accurate biostratigraphy and chronostratigraphy threshold is necessary.Microfacies interpretation application is very common in Petroleum geology, because most of carbonate rocks have the biogenetic origin; therefore changes in carbonate microfaices have close relationship with biotic evolution. Ahwaz oil field is one of the gaint oil fields in Dezful Embayment South West of Iran, which produces oil from Asmari limestone reservoir of Oligocene-Miocene and Bangestan of Middle Cretaceous. The Dezful Embayment is a tectonic feature in the South-western edge of the Zagros Basin. The embayment comprises Iran's major oil fields. It is the center of South-western Iranian oil province, which geologically belongs to the Northern part of the Arabian plate.
The present research work is based on the selected six wells in Ahwaz oil field. Microfacies of Ilam and Sarvak formations of Bangestan group of above wells have been studied. In carbonate rocks series of Ilam and Sarvak formations, in a sedimentary model and in a lateral changes in facieses, the three microfacies have been distinguished: A and B are related to open-marine and C to middle shelf. Microfacies of an open- marine group contain A 1, A2 for continental slope and B1, B2 for the upper part of open- marine and B3 relates to shallow ridges (Shoal ridges). Microfacies, of group C related to lagoon (Mid- continental Shelf). Microfacies, A1 for example, consists of wackstone/packstone (very fine-medium grains) with Echinoderm fragments of Crinodis sp.(10-15%), small Rotalids(2-10%), Ostracoda, (0-2%) and Saccocoma sp., Calcisphaeres (5-10) These microfacies are for an open-marine slope. Calcisherula Bonet genus and Calcisphaerula innominata Bonet species belong to Upper Albian, Coniacian- Santonian ages.
The age, lithology, grain type, porosity, interpretation of diagenetic processes and paleo-depth curves have been shown in various wells in regard to depth curve and vertical microfacie changes in Ilam and Sarvak formations , Bangestan reservoirs. Besides, the sedimentary environment of 3D diagrams of the above formations have been illustrated and discussed in detail.
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