Shiranish formation in Sazaba Oil fields region had been divided by Petrology study and well Logs measurements to three major members (lower – middle – upper). Then these members have been divided to lithostratigraphic units and subunits. This study showed that the lower member is formed of clayey - limestone rocks rich in planktonic foraminifera and glaconitic sand. The middle member consists of organic limestone facies, dolomitic-limestone, sometimes clayey - limestone rocks with crystals of pyrite and glaconitic sand. Organic- limestone rocks and detrital limestone are predominant in the upper member interbeded by dolomitic-limestone and rare clayey – limestone. This facies contains pelagic and planktonic foraminifera. The role of diagenes phenomenon is evident on Shiranish’s facies through: dolomitization according to burial and miksing processes. It is also clear through chemical compaction, mechanical compaction, cemenation, micretisation and silisification.