Quantitative analysis of geological attributes for reservoir heterogeneity assessment in carbonate sequences; a case from Permian–Triassic reservoirs of the Persian Gulf

Abstract

This study integrates quantitative analysis of reservoir properties with geological parameters to discriminate the reservoir heterogeneities in the Permian–Triassic sequences of the Persian Gulf. To achieve this goal, geological analysis of core samples and thin sections were integrated with petrophysical logs and porosity–permeability data. For quantitative assessment of reservoir heterogeneity, Coefficient of Variation (CV), Dykstra-Parsons Coefficient (VDP) and Lorenz Coefficient (VLC) were used along with the concept of Hydraulic Flow Units (HFU). Depositional facies, diagenetic alterations and sequence stratigraphic framework of the reservoir were used as a basis for the interpretation of geological heterogeneities. Accordingly, 14 microfacies types and 5 facies belts have been defined and indicate a low-angle (homoclinal) ramp model. Complex diagenesis history of these sequences includes marine, hypersaline and shallow to deep burial diagenesis that considerably altered the primary distribution of reservoir properties. A comparison of tested methods revealed that the CV is the best approach for quantification of heterogeneity in targeted reservoir. Consequently, the K4 and K2 are proposed as the most homogeneous units with a dominance of grain-supported facies of shoal setting, intense effects of hypersaline dissolution and lesser effect of compaction and cementation. The K3 and K1 units show high levels of heterogeneity resulting from the combined facies changes and diagenetic alterations (dolomitization, cementation and compaction). Finally, sequence stratigraphic framework of reservoir heterogeneities is discussed for all reservoir units and can be used as a basis for ongoing reservoir studies of the Permian–Triassic sequences in the Persian Gulf and the Middle East.