IMPROVED WATER SATURATION ESTIMATION IN SHALY SANDSTONE THROUGH CLAY MINERALS ELECTROCHEMICAL STUDY

Petrophysical interpretation in shaly sandstone is a complex process. Previous studies suggested that excess conductivity from clay minerals causes different conductivity characteristic in shaly sandstone, hence the Archie’s Law for formation factor-porosity correlation is no longer applicable. This study aims to propose an improvement to the mathematical correlation of formation factor-porosity in shaly sandstone. The equation was derived based on the physical theory of clay surface conduction in combination with geometric effect. It furnishes a variable cementation factor m that explains the data deviation from Archie’s straight line on the log-log plot of formation factor versus porosity; thus providing possible solution for the non-linear part of shaly sandstone conductivity curve. The proposed mathematical equation provides good estimation of shaly sandstone formation factor F* for different types of data used for validation i.e established core data, field core data at overburden pressure from different regions and experimental data of collected shaly sandstone samples.