The impact of micro-to macro-scale geological attributes on Archie's exponents, an example from Permian Triassic carbonate reservoirs of the central Persian Gulf

Enormous and inherent heterogeneity of carbonate reservoirs causes problems in the estimation of their geological and petrophysical attributes. The major part of this heterogeneity is due to the various pore types and structures of these reservoirs. Water saturation is economically one of the most important characteristics of any producing reservoir. Archie introduced practical exponents, which are fundamental parameters for saturation calculation. In this research, the effect of geological factors controlling Archie's exponents including depositional and diagenetic characteristics in a sequence stratigraphic framework in Permian Triassic carbonates of Persian Gulf Basin was carried out. Rock typing approach has been used for assigning reservoir characteristics to geological parameters. Five digenetic facies that were determined according to petrographic studies, wire line logs, SEM and conventional core analysis as well as mercury injection tests, were grouped into four rock types using Lucia diagram. Archie's exponents were calculated for different rock types. Results showed that porosity value and pore type have an important effect on the exponents. This effect could be traced vertically in macro-scale using sequence stratigraphic concept. Grainstone facies with high m values are located in early HST and late TST. Tight grainstone or mud-dominated facies with low m values are located in early TST and late HST.