LAUSR

Abstract Evaluation of tight gas sandstone (TGS) reservoirs and estimation of their reserves are associated with significant uncertainties. Indeed, estimation of electrical properties, such as cementation factor (m), is one of the main challenges in TGS characterization. Well known Archie's formula is applied to determine water saturation and therefore hydrocarbon saturation. Diagenetic processes and presence of fractures and slot-like pore throats in TGS reservoirs cause that m varies in a wide range. Furthermore, correlations which have been developed for a specific formation, generally cannot be applied for prediction of cementation factor in other formations. Besides, several studies of cementation factor in conventional reservoirs show that classification of the reservoir rocks based on a common parameter may result in an appropriate estimation of m. In this paper, electrical efficiency ( η e ) was presented as a basis for classification of rock samples into distinct electrical rock types. Indeed, all rock samples with similar electrical efficiency lie on the same straight line with slope of (−1) and intercept of 1 η e in the log-log plot of formation resistivity factor (F) versus porosity ( φ ) . Moreover, in this study a new theoretical equation was developed for prediction of m versus porosity. This equation shows that for each electrical rock type, m versus 1 l n φ has a linear trend and its intercept is one. To verify this electrical rock typing approach, a large dataset from Byrnes' et al. work related to Mesaverde tight gas sandstone was used. These samples were classified into five different groups based on the proposed technique of electrical rock typing. Additionally, results revealed that values of cementation factor of each electrical rock type properly satisfy in the new established linear equation of m versus 1 l n φ .