Integrating routine and novel methods for a comprehensive analysis of heterogeneity in Persian Gulf's Permian-Triassic carbonate reservoirs

Abstract

This study investigates the interplay between depositional environments and diagenetic processes in controlling the reservoir heterogeneity of Permian–Triassic carbonate platform of the Persian Gulf. Understanding this framework is crucial for identifying and characterizing reservoir heterogeneity at both micro and macro scales. A combined approach of integrated data (thin section analysis, petrophysical measurements, FMI and DT logs) used to evaluate reservoir heterogeneity of the upper Dalan and Kangan formations. Detailed analysis of sedimentary properties revealed a homoclinal ramp depositional environment, leading to minimal inherent heterogeneity within facies. Facies were subsequently classified into two main groups: mud-dominated and grain-dominated. Diagenetic processes, including dissolution, dolomitization, anhydritization, and cementation, further influenced these facies. This resulted in the creation of two distinct classes: mud-dominated facies (Class I) with low porosity and permeability, and grain-dominated facies (Class II) with high porosity and permeability. FMI log analysis highlighted the role of stylolites and conductive seams in shaping the heterogeneity within these two classes. Open stylolites in Class II have increased pore connectivity and enhanced permeability, while having minimal impact on Class I. Finally, core porosity data combined with the DT log enabled a more comprehensive assessment of pore types and their influence on reservoir heterogeneity within each class. DT logs identified two distinct facies groups. The first group exhibited high porosity and permeability with connected pores, representing grain-dominated facies. The second group showed low porosity and permeability with disconnected pores, representing mud-dominated facies. This approach provides valuable insights into the factors governing heterogeneity in carbonate reservoirs, offering a framework for improved reservoir characterization and development strategies.