Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


In this dissertation, a new theoretical conductivity model for shaly sands is developed. The model is based on dual water concepts. In addition, the equivalent counterion conductivity changes as the diffuse electrical double layer expands and is then a function of temperature, shaliness, and of the conductivity of the far water. The formation resistivity factor used in the model is independent of shaliness. A method to calculate the equivalent counterion conductivity is proposed. This method is based on treating the double layer region as a hypothetical electrolyte, the properties of which are derived from basic electrochemistry theory. The new model was used to calculate conductivities of specific shaly sand samples 25(DEGREES)C. The calculated values display an excellent agreement with published experimental data. The new model is shown to be superior in predicting core conductivities to the two models currently accepted by the industry. The developed model has been extended to represent hydrocarbon bearing formations as well as to predict membrane potentials in shaly sands. Calculated water saturation and membrane potential values from the new model also show excellent agreement with accurate experimental data obtained at laboratory conditions. The effect of temperature on the conductive behavior of shaly sands has been revised under the basis of the new model. The representativity of conductivities predicted by the new model for temperatures up to 200(DEGREES)C warrants its application under actual field conditions. Several new concepts useful in the analysis of shaly sands are introduced in this work. In addition, the new model is used to enhance the interpretation of the SP log in shaly environments. Finally, a new interpretation technique for shaly sands is proposed. This interpretation tool is based on the new conductivity model and makes use of log derived data. It allows the proper evaluation of the potential of a reservoir formation.