Sequence Stratigraphy of lower zones of Asmari Formation in Marun Oilfield by using of microfacies analysis, isolith maps and γ- Ray log

The Oligo- Miocene Asmari Formation is one of the most important reservoir units of the Marun Oilfield in Dezful Embayment SW Iran، deposited in Zagros foreland basin. The goal of this study is to interpret depositional environment and sequence stratigraphy of lower zones of the Asmari Formation in Well No. 281، 342 and 312in Marun Oilfield based on changes in the shape of γ- Ray، isolith maps and microfacies properties. Accordingly، identification of 9 carbonate microfacies and 2 siliciclastic petrofacies were identified that are deposited in four depositional environment including open marine، barrier، lagoon and tidal flat in a homoclinal ramp (consisting of outer، middle and inner ramp). Also، based on the shape of γ- Ray log، There sediment were deposited in marine environment. In open marine and barrier environments، The shape of γ- Ray log is serrated bell-shaped، serrated funnel-shaped، left bow-shaped، serrated shape and right boxcar shape، Whole in the beach environment it is cylinder and funnel shape and in lagoon and tidal flat environment can be seen on right bow to cylinder-shaped. Based on the isolith maps، sandstone of lower zones of the Asmari Formation in Marun Oilfield expanded by deltaic system along the southwestern margin of the basin and influenced by changes in sea level constantly. Sequence stratigraphic analysis led to identification of three third- order (DS1، DS2 and DS3) depositional sequences.