Integrated sedimentological and petrophysical analyses for improved reservoir characterization in the sequence stratigraphy framework, Fahliyan Formation, southwest Iran

Abstract

Fahliyan Formation is one of the important hydrocarbon reservoirs in south-western Iran. This study employs a comprehensive and integrated approach to reservoir characterization of this formation by combining petrographic, petrophysical, and sequence stratigraphic analyses. Various data types, including core descriptions, thin sections, well logs, and advanced clustering techniques, are utilized to enhance the accuracy of the analysis. By integrating these methodologies, this research provides a more detailed understanding of the reservoir properties, improving predictive capability for hydrocarbon exploration and development. For this purpose, petrographic and petrophysical data in two wells were used. Based on petrographic studies, six microfacies have been identified and grouped into three facies belts (lagoon, shoal and open marine). Fahliyan Formation has experienced various diagenetic processes including dissolution, cementation and dolomitization that have occurred in marine, meteoric and burial diagenetic environments. Four 3rd order sedimentary sequences have been identified (Sq- I is assigned to Manifa Member, Sq- II and III are associated with the Middle Yamama Member and Sq-IV corresponds to the Upper Yamama Member). Sequence boundaries determined through integrated prediction error filter analyses (INPEFA) and changes in microfacies. Reservoir zonation using the multi-resolution graph-based clustering method led to the identification of 6 electrofacies. In addition, based on K-means clustering by applying the Elbow method, three distinct hydraulic flow units (HFU) were determined. The comparison of results indicates that electrofacies 1 and 2, along with HFU 1, exhibit the lowest reservoir quality and are prevalent in the Upper Yamama Member. These electrofacies correspond to the sedimentary sub-environment of the lagoon and the mud-dominant microfacies. On the other hand, electrofacies 5 and 6 and HFU 2, 3 have the highest reservoir quality and are the most abundant in the Manifa and Middle Yamama members. These electrofacies and HFUs correspond to the sedimentary sub-environment of the shoal complex and the grain-dominant microfacies. In general, the regressive systems tracts have better reservoir quality than the transgressive systems tracts. This integrated analysis not only enhances the understanding of the Fahliyan Formation's reservoir characteristics but also serves as a valuable template for similar studies in other hydrocarbon reservoirs worldwide. The methodologies and findings presented here can be applied to improve reservoir characterization.