Incorporating microthermometry and fluorescence spectroscopy of oil-bearing fluid inclusions into the geochemical modeling: a case study of Asmari and Bangestan carbonate reservoirs in the Dezful embayment, Zagros oil Province
摘要
The Dezful embayment is considered as one of the largest petroleum basins of the Middle East, hosting the Asmari and Bangestan reservoirs. This study integrates fluid inclusion analysis with burial-thermal history modeling to better understand oil migration and charging histories in the Asmari and Sarvak Formations. Key findings include the following: (1) Primary and secondary fluid inclusions were identified as single-phase liquid (L), two-phase liquid-rich (L + V), and immiscible three-phase (L1 + L2 + V) types, with salinities ranging from 4.9 to 20 wt% NaCl equiv. in both formations. Homogenization temperatures ranged from 60 to 140 °C and 50–170 °C for the Asmari and Sarvak Formations. (2) Fluorescence microscopy detected both yellow and blue oils. Blue fluorescence signifies lighter, mature oils (API 50–40), while yellow indicates heavier, immature oils (API 30–20). The coexistence of these signals suggests multiple hydrocarbon sources and complex diagenetic processes. (3) Basin modeling results indicate that oil migration into the Sarvak reservoir occurred around 9 million years (Ma) ago (with ~ 2300 m of overburden), mainly sourced from the Kazhdumi Formation. In contrast, petroleum charging of the Asmari reservoir took place later, at approximately 5 Ma ago (with ~ 1000 m of overburden), with contributions from both the Kazhdumi and Pabdeh formations. Therefore, the differing fluid inclusion characteristics and migration timings point to multiple oil sources and dynamic migration histories within these reservoirs. This research advances understanding of their diagenetic evolution and petroleum systems, providing valuable guidance for future exploration and reservoir management in the Dezful Embayment.