Study of Rock Types and Diagenetic Facies based on Velocity Deviation Log for Unraveling the Reservoir Heterogeneity in a Mixed Siliciclastic-Carbonate Reservoir, Southwest of Iran

Abstract

Investigating depositional and diagenetic factors that control pore systems properties of reservoir rocks is essential for unraveling reservoir heterogeneity and interpreting reservoir rock types. In this respect, utilization of petrophysical well logs provides enormous information about reservoir properties, which can be interpreted continuously throughout the reservoir interval. In this study, the velocity deviation log derived from the Wyllie time-average equation has been used to differentiate reservoir rock types of the Oligo-Miocene Asmari Formation with a mixed siliciclastic-carbonate lithology from the field in the southwestern of Iran. As a result, four rock types were identified and interpreted throughout the reservoir interval. Each carbonate rock type with certain pore types and reservoir property signifies a specific diagenetic facies. Variation from a siliciclastic (sandstone-shale) environment in lower parts of the reservoir interval to a carbonate system in upper parts, as well as a transition interval (interlayers of carbonate and clastic facies) between them, shows a high degree of reservoir heterogeneity. This could be described by different zones and interpreted in the framework of sequence stratigraphy. The results indicated that the carbonates due to the complex pore systems have the main control on vertical reservoir heterogeneity, reflected by wide variations in velocity deviation. However, the sandstones control the horizontal reservoir heterogeneity through the variability in thickness and lateral continuity of reservoir zones. The findings of this research can be correlated with dynamic reservoir data for the identification and investigation of production zones in the field.

Keywords

• reservoir heterogeneity
• pore system
• diagenesis
• reservoir rock types
• velocity deviation log