Integrated Petrophysical and Heterogeneity Assessment of the Karstified Fahliyan Formation in the Abadan Plain, Iran

This study aimed to investigate the petrophysical properties and heterogeneity rate of the Fahliyan Formation in the Abadan Plain, southwestern Iran. Thin section slides, core analysis results, scanning electron microscope (SEM), and computed tomography (CT) images were studied in association with petrophysical log data to describe pore types, hydraulic flow units, and log facies in the Fahliyan reservoir. Our analysis revealed that the meteorically dissolved mud dominated low energy lagoonal facies (Layer-3) are the best reservoir intervals in the Fahliyan Formation. In contrast, intensively cemented, and physically and chemically compacted facies formed the tight zones in this reservoir (Layer-1). Comparison of depositional texture and sedimentary setting with the flow units and reservoir quality clearly revealed the major role of diagenesis in reservoir quality of the Fahliyan Formation. Heterogeneity assessment through statistical analysis revealed that Layer-1 is the most heterogeneous unit in the Fahliyan Formation, while Layer-2 and Layer-3 exhibit relatively similar behavior, with very close heterogeneity values. However, porosity distribution histograms showed that pore types and network are more heterogeneous in Layer-3, presenting multimodal distribution. Image log-derived porosity distribution provided by thin sections, SEM and CT images, and velocity deviation log showed that pores are homogeneous in Layer-1 and heterogeneous in Layer-3, in light of extensive dissolution and development of molds, vugs, and solution enlarged fractures. Finally, different sources of heterogeneity were considered by combining various datasets including petrophysical logs, core analysis data, and geological attributes.