Reservoir rock typing of the Asmari Formation using integrating geological and petrophysical data for unraveling the reservoir heterogeneity: a case study from the Ramshir oilfield, southwest Iran

The Asmari Formation with Oligo-Miocene in age and a carbonate-siliciclastic lithology is considered as one of the main hydrocarbon reservoirs in the Zagros Basin of Iran. In this research, with the target of unraveling the reservoir heterogeneity, a comprehensive rock typing was performed using all available geological and petrophysical data. The procedure for reservoir rock typing was started with the identifying of sedimentary rock types derived from the description of cored intervals and the study of thin sections from 7 cored wells. These studies led to the identifying and classification of 12 sedimentary facies related to the inner, middle, and outer parts of a carbonate ramp platform. The statistical clustering algorithms were applied using Multi-Resolution Graph-based Clustering approach on well log data, resulting in the recognition of five electrofacies (EFs). Accordingly, five hydraulic flow units (HFUs), based on the flow zone indicator method were defined in the reservoir interval. A compatible relationship between EFs and HFUs demonstrates that changes in petrophysical attributes are mainly controlled by diagenetic features. By examining special core analysis data, appropriate capillary pressure curves were correlated with the identified reservoir rock types. The methodology used in this study shows the reservoir heterogeneity in addition to primary depositional texture is controlled by the effect of diagenetic processes such as compaction, cementation, dissolution, dolomitization, and fracturing. Dolomitization, dissolution, and fracturing are the main diagenetic processes, showing significant effect on increasing and improving the reservoir quality. According to the results, among different reservoir zones of the Asmari, zones 1, 2, 3, and 4 are considered as the most favorable zones from the reservoir quality and production point of view in the studied field.