Investigation and prediction of pore type system by integrating velocity deviation log, petrographic data and mercury injection capillary pressure curves in the Fahliyan Formation, the Persian Gulf Basin

Detecting and understanding the pore types and pore geometries as two crucial attributes of the porous media based on geophysical logs is an essential step in reservoir properties mapping. The Fahliyan Formation is considered as one of the prolific carbonate reservoir3s in the Persian Gulf. In this study, the velocity deviation log and the capillary pressure curves were employed as an efficient way for the quantitative estimation of pore system properties of the Fahliyan Formation. Based on the petrographic studies and velocity log calculations, the Fahliyan Formation is characterized by negative velocity deviations (interconnected pores & vugs), zero deviations (intercrystalline and micropores) and positive velocity deviations (isolated or moldic pores). Integration of petrographic data with velocity deviation log led to the identification of five pore facies (PFs) or hydraulic flow units (HFU), with reservoir quality being increased from PF1 to PF5. Finally, 3D model of pore types and pore facies distribution was prepared by quantifying the well log-derived pore types and their validation with the core data. The results indicate that the reservoir quality of the Fahliyan Formation was affected by the sedimentary and diagenetic processes, but in general, diagenesis has a more significant contribution in developing complex pore types and determining reservoir quality. The best rock types are about the touching vugs and interparticle pores. Based on the velocity deviation log and petrographic analyses, the Fahliyan Formation is divided into the best reservoir unit (equivalent to Manifa), the main reservoir unit (equivalent to middle Yamama), and the low reservoir quality unit (equivalent to upper Yamama). [GRAPHICS]