Integrating petrophysical attributes with saturation data in a geological framework, Permian–Triassic reservoirs of the central Persian Gulf

Abstract

In this research, an integrated geological and petrophysical approach was applied to understanding the most critical factors affecting the water saturation exponent in the Permian–Triassic Kangan and Dalan carbonate formations in the central Persian Gulf in Iran. Economically, water saturation has a fundamental role in reservoir characterisation. A total of 8 sedimentary facies were recognised with multiple diagenetic phases. Diagenetic processes include marine cementation, moldic dissolution, early dolomitisation, recrystallisation, anhydrite cementation, compaction, and fracturing, which have influenced reservoir properties. Four third-order sequences were distinguished in the study area accompanied by nine fourth-order sequences. Petrographic analysis, scanning electron microscopy, petrophysical core analysis, wireline log data as well as mercury injection tests integrated through flow zone indicator, Lucia classes, and Lorenz plot approaches. Consequently, 4 integrated rock types (IRTs) were identified with particular depositional and diagenetic features. IRT1 with dominant interparticle pore type and strong porosity–permeability correlation (average 9.1% porosity and 27 mD permeability, R2 = 0.98), has a high saturation exponent (n = 2.2). IRT4 with grain-to mud-dominated facies, low porosities (average 1.4%), and a mean value of 4.54 mD permeability has the lowest saturation exponent (n = 1.07). Moldic dissolution with low pore connectivity is the dominant pore type in IRT2 and IRT3 which have a medium and relatively high saturation exponent, respectively (IRT2 n = 1.53 and IRT3 n = 1.78). Accordingly, a conceptual model was suggested for saturation exponent variations in a high-frequency sequence stratigraphic framework. In order to evaluate the heterogeneity of the studied formations and its impact on the reservoir properties, the characteristics of the determined rock units were studied. This study integrates microscopic to macroscopic geological and petrophysical factors to understand the saturation exponent distribution in a heterogeneous carbonate reservoir, leading to obtaining a more accurate water saturation estimation of such reservoirs.