Development and Field Applications of Shaly Sand Petrophysical Models.

Abstract

A new, theoretically derived model expressing shaly sand conductivity is presented. The proposed model is based on dual water and cation exchange capacity concepts. The new model is based on the Waxman and Smits concept of supplementing the water conductivity with a clay counterions conductivity. The model also utilizes the dual water theory, which relates each conductivity term to a particular type of water, each occupying a specific volume of the total pore space. The proposed model, however, assumes that the counterion conductivity can be represented by a hypothetical electrolyte. The properties of this electrolyte were derived from electrochemical and irreversible thermodynamics theory. From the conductivity model a spontaneous potential model was also developed. Both models have been tested using accurate core data published by Wasman and Smits. The conductivity and spontaneous potential models were also validated by log data. They have been successfully applied to the interpretation of multiple intervals of 15 wells. The use of newly developed models is the first shaly sand interpretation technique based on sound scientific principles, which determines hydrocarbon potential as well as shale and formation water electrical properties directly from well logs readings obtained within the formation analyzed.