Facies determination of the Kazhdumi Formation in Solabdar and Chilingar oil wells which are the oldest Iranian oil wells is very important since the Kazhdumi was known as a source rock in these fields. Lithological composition of this formation is limestone, shale and glauconite bearing sandstone in the base which is an obvious sign of disconformity between Kazhdumi and Dariyan formations. The Diagenetic effective processes in this area include: dissolution, substitution (hematitization, glauconitization), micritization and bioturbation, cementation, compaction, stylolitization and porosity (interapartical, moldic, intercrystaline, channel). These processes are in relation to diagenetic environments such as meteoric, marine phreatic and deep burial. Kazhdumi Formation in the studied fields is composed of seven carbonate facies and two clastic facies (shale and sandstone) as follows: bioclast wackestone/ packstone- bioclast packstone– bioclast wackestone/packstone–sandstone (lagoon facies) and bioclast wackestoneglobigerin, wackestone (planktonic wackestone)/crinoidal globigerina wackestone –oligosteginid wackestone (open marine facies).