An integrated approach for heterogeneity analysis of carbonate reservoirs by using image log based porosity distributions, NMR T2 curves, velocity deviation log and petrographic studies: A case study from the South Pars gas field, Persian Gulf Basin

Abstract

Reservoir quality, pore types and heterogeneity study in carbonate reservoirs are considered as major concerns for choosing an economic reservoir in oil and gas industry. The optimized production rate and hydrocarbon recovery also needs a reservoir architecture evaluation. Therefore, having an accurate knowledge about the complexity of carbonate formations leads the hydrocarbon exploration and production projects to a more reliable achievement.In the current study, the Permo-Triassic aged carbonate formations of Dalan and Kangan in the world's largest not-associated gas field, South Pars, are selected as the target reservoirs. A comprehensive petrophysical evaluation in an appraisal well of the field resulted in interpretation of lithology and main reservoir quality parameters (porosity and permeability) using conventional and advanced magnetic resonance (NMR) logs. For more accurate understanding of lithology, rock fabric and fluid flows, heterogeneity is measured by applying Lorenz plot and coefficient of variation (CV) methods based on the petrophysical logs. In the next step, reservoir rock typing separated the productive and non-productive zones in different lithological intervals including K1, K2, K3, and k4. Finally, pore types and heterogeneities were investigated by porosity histograms received from formation resistivity image logs, porosity distributions of nuclear magnetic resonance, velocity deviation logs and thinsection studies. Histogram modalities and distributions of the image log bin porosities confirmed by NMR log, velocity deviation log and thin sections show that formation resistivity images are considerable tools for carbonate heterogeneity studies. The results of this study suggest that the paleoenvironmental conditions and diagenetic processes including dolomitization and dissolution controlled the porous media complexity in the K2 and K4 units, the major reservoir intervals of South Pars field.