The impact of carbonate precursor mineralogy and heterogeneity stemming from diagenetic process on reservoir characteristics, cases from Permo-Triassic and upper Jurassic intervals of the Persian Gulf

The Permo-Triassic Dalan-Kangan and upper Jurassic Arab formations are important carbonate-evaporate reservoirs resulted from depositional and diagenetic heterogeneities. The objectives of the study are comparison precursor mineralogy, identification of dominant pore types and clarify the role of diagenetic processes on petrophysical characteristics and reservoir quality of the Dalan-Kangan and Arab formations in the Persian Gulf. To achieve this goal core description and petrographic study and core poroperm data from two hydrocarbon fields in the Persian Gulf were integrated. Pore system studies show that different pore types contribute to the fluid flow and production within the Dalan-Kangan and Arab formations. These pore types are inter-granular, intercrystalline, touch and non-touch vugs and microspores. The initial mineralogy of the components had a significant effect on pores system distribution and trend of the diagenesis of the two studied intervals. During the Permo-Triassic and upper Jurassic, the composition of ocean waters has been suitable for deposition of non-skeletal components with aragonite and calcite mineralogy, respectively. Thus, moldic pores in the Dalan and Kangan reservoirs and intercrystalline and inter-granular pores in the Arab Formation occur as the dominant pore types. In Dalan and Kangan formations, micropores are more frequent than the Arab Formation, which is attributed to the dominance of mud-dominated facies during the Permo-Triassic periods. Detailed diagenetic studies indicate that the studied intervals were exposed to dissolution, cementation, anhydrite mineralization, dolomitization, physical and chemical compaction and fracturing after deposition. Dissolution, anhydrite mineralization and cementation seem to have exerted the main effect on pore system properties