Geochemical evaluation of oils from the Asmari reservoir of the Qale-Nar Oilfield, implication for field-scale reservoir compartmentalization

The Qale-Nar Oilfield is an asymmetric two-humped anticline located in the northernmost part of the Dezful Embayment, in which the fractured Asmari carbonates are the main reservoir rock. In this study, for the first time, the organic geochemistry of oils produced from the Asmari reservoir are used to investigate the reservoir continuity and possible compartmentalization. For this end, geological information from the studied oilfield were combined with bulk geochemistry (e.g., ˚API gravity) and molecular characteristics (e.g., GC and GCMS data) of produced oils. Two oil samples obtained from well # 6 and well # 10 of the studied oil field indicate significant differences in terms of their bulk and molecular geochemical properties. Accordingly, a scenario was presented to better explain the reservoir charging and compartmentalization in the Qale-Nar Oilfield. In this scenario, low-maturity hydrocarbon pulses first charge the eastern culmination of the Qale-Nar Oilfield. The activity of a fault plane located between well # 6 and well # 10 could induce a barrier between the two wells. Consequently, the late hydrocarbon charges with higher maturity could only charge the compartment belonging to well # 6. Therefore, well # 10 could not receive these high-maturity hydrocarbon pulses due to the lack of lateral connectivity. The information obtained from this study can be of great help in future reservoir studies with important implications for field development projects and enhanced-recovery plans.