Classification of carbonate reservoir rocks using combination of electrical-elastic properties: a new rock typing approach

The information provided by electrical and elastic properties of porous media has highlighted the need for investigating the methods of their evaluation to optimize both operational and economic aspects of geoscience surveys. Geo-electrical properties represent valuable geometric characteristics of pore network and water content, while acoustic waves can be applied for identification of lithology and seismic modeling of subsurface structures. The present study attempts to introduce combined electrical-elastic rock typing technique by defining a new parameter as electrical-elastic efficiency (η_ee). Authors believe that samples with similar electrical-elastic efficiency establish an electrical-elastic rock type (EERT). A dataset comprising 93 calcite-dominated rocks was employed to examine the applicability of the proposed method. Five EERTs were extracted properly with highly efficient correlations between formation resistivity factor and compressional wave velocity (in saturated conditions). These regression models were also validated by Hashin and Shtrikman bounds. Moreover, the average properties of porous media were investigated through the proposed rock typing method. Average wave velocities (dry/wet), acoustic tortuosity, and pore throat diameter were inversely related to average η_ee. In contrast, average electrical tortuosity and cementation factor showed an increasing trend with respect to average η_ee. Furthermore, applying the proposed method leads to prediction of average permeability using average compressional velocity of dry rock. The resulting relationships of each aforementioned correlation had high determination coefficients (R ² > 0.90). The findings of this work provide a new approach for combined electrical-elastic investigations by suggesting a time-saving and economically efficient process, compared to laboratory and in situ measurements.