The most important reason for studying any oil reservoir is the more efficient use of the production parts of the reservoir and the first step in identifying the reservoir is its zoning. Zoning is determined based on lithological changes by combining production data and petrophysical logs in each reservoir. In order to improve and accelerate the zoning of oil reservoirs, like other branches of science, the use of software has become common in recent years. One of the most powerful of these software's is Cyclolog. The science of using this software is cyclostratigraphy, which can be used to separate reservoir zones based on sedimentary cycles and their knowledge. Cyclolog software with the help of petrophysical logs taken from the wellbore and especially gamma diagram (GR) allows subsurface matching and preparation of matching charts in selected wells. In this study, in the three oil fields studied (Karanj, Paranj and Parsi) using cyclolog software, a total of seven positive timelines (Pb3000, Pb2000, Pb1500, Pb1000, Pb500, Pb400, and Pb300) as well as five negative timelines (Nb4000, Nb3000, Nb2000, Nb1000, and Nb500) were detected. Accordingly, the Pb1500 timeline is the separator and the boundary of the Chattian and Aquitanian peaks, which in the wells of all three studied fields almost cross the boundary of reservoir zones 3 and 4. The Nb4000, Nb3000, and Nb2000 timelines are also Chattian age. The Nb3000 timeline in Karanj oil field has crossed the boundaries of zones 4 and 5 in most of the wells due to calibration with biometric evidence (biostratigraphy) and indicates the top of the formation. The age of the Nb500 timeline is Burdigalian and passes through the middle of their reservoir zone 1 in the study area. The boundary between the Aquitanian and Burdigalian peaks is defined by the Nb1000 timeline. This timeline crosses the boundaries of zones 1 and 2 in all three fields studied
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