Rock typing and reservoir zonation of the Asmari Formation in a gas field, Persian Gulf

In this study, the geological and petrophysical methods were combined to investigate the reservoir characteristics of the Asmari Formation in one of the gas fields in the Persian Gulf. The key focus of this study is to categorize rock types and define reservoir zonation. Initially, sedimentary facies were identified through the analysis of the core samples and the petrographic studies. Subsequently, the depositional environments of each facies were interpreted. After assessing the reservoir quality of sedimentary facies, various rock typing methods, including FZI, R35, and Lucia methods, were used to categorize the reservoir rocks. Finally, reservoir zonation was carried out based on the integration of information and the NCRQI method. According to this study, the Asmari Formation in the studied field consists of 10 sedimentary facies deposited in a carbonate ramp environment during the Rupelian and Chattian stages. From the perspective of frequency, coralgal reef facies play a significant role in this platform, while from a reservoir standpoint, the thin-bedded ooid grainstones are the most important reservoir facies. The high variability in porosity and permeability data for each facies indicates the importance of diagenetic changes in reservoir quality and porosity distribution. A comparative analysis of rock typing methods revealed that the reservoir rock is composed of five reservoir rock types, associated with different sedimentary facies, pore sizes, and reservoir properties. Finally, based on the integration of geological and petrophysical information, the reservoir rock was divided into five reservoir zones, with reservoir zones As-2 and As-4 being the most important due to their relatively high porosity and permeability.