  The Ilam Formation Cenomanian to Santonian in age is considered one of the
main rock reservoirs of the Bangestan Group in the southwest of Iran. This
formation mostly consists of carbonate rocks. To examine the sedimentary
environment, diagenesis, sequence stratigraphy, and reservoir quality of Ilam
Formation in Dezful embayment and Abadan Plain, four subsurface sections in
wells, were studied. The lithology of the Ilam Formation in the studied wells
is limestone with interbedded shale and argillaceous limestone. Considering the
abundance of allochems and various fabrics in these deposits, twelve
microfacies and one shale petrofacies of the Ilam Formation were recognized in
these four wells. These microfacies were deposited in three facies belts,
namely lagoon, shoal, and open marine, in a homoclinal carbonate ramp setting.
These deposits have been influenced by meteoric, marine, and burial diageneses.
Sequence stratigraphy of the Ilam Formation reveals that the studied wells
consist of a third-order sedimentary sequence. The sea-level fluctuations in
this area are the same as the global sealevel fluctuations. During the study of
the Ilam Formation reservoir quality based on the results of diagenesis, mainly
porosity and permeability data in one of studied wells,six flow units were
identified. Flow unit number five has the most potential reservoir quality, and
flow unit number 6 has the undesirable flow unit.
