Rock typing using geological and petrophysical data in the Asmari reservoir, Aghajari Oilfield, SW Iran

The Oligo-Miocene Asmari Formation, which extends over the entire Zagros foreland basin, is one of the most important hydrocarbon reservoirs in the Middle East. The Aghajari Field is one of the largest oilfields in the Zagros basin with the Asmari Formation being the major reservoir rock. We used petrophysical and geological data, by means of the neural network clustering technique, to identify rock types in the Asmari reservoir. Using petrophysical logs, such as gamma ray, sonic, density and neutron, along with calculated reservoir data (water saturation and effective porosity) from 20 wells (5 cored and 15 uncored wells) and their correlation with capillary pressure (Pc) curves, led to recognition of 5 electrofacies (EF1-EF5). These electrofacies were used to extend our interpretations to 60 uncored wells. The link between electrofacies and geological data (obtained from 1100 m cores and 2500 thin sections) indicate that both sedimentary and diagenetic processes controlled the reservoir quality of the Asmari Formation. Porosity, permeability, water saturation, and reservoir quality index (RQI) were used to estimate reservoir quality of each electrofacies. EFs 1 and 2 with low porosity and permeability, high water saturation and low RQI are considered as non-reservoir that are related to sedimentary textures (argillaceous nature of wackestone-packstones) and effect of destructive diagenetic processes (cementation, physical and chemical compaction). EFs 3 and 4 show high values of porosity, permeability, RQI, and low percent of water saturations, which characterizes them as good reservoirs rocks. Vuggy, growth framework and interparticle porosities are major in EF-3, while the intercrystaline porosity is the major type in EF-4. Finally, EF-5 is the only electorfacies in the siliciclastic parts of the Asmari Reservoir, which is composed of rounded and well-sorted quartz grains that are slightly cemented. The latter is the best reservoir electrofacies in the Asmari Formation of the Aghajari oilfield due to its' high values of porosity, permeability, and RQI and low percent of water saturation. Based on vertical distribution of EFs in the Asmari Formation, zones 1, 2, 3 and 4 are the best zones for drilling new productive wells around the oilfield. The results of this research can be useful in the development of the field, taking a decision and proper strategy in the connection of hydrocarbon production and recovery in the future of this field and similar fields.