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40160-AC9
Petrophysical Characterization and Hydraulic Properties of Unconsolidated Reservoir Sands from Spectral Electrical Response Measurements

Fred Boadu, Duke University

Hydraulic Conductivity of Soils from Spectral Electrical Measurements: Laboratory Experiments and Models             Hydraulic conductivity governs the movement of fluids through pore spaces and networks in porous media such as soils and rocks. Estimates of hydraulic conductivity are essential for the characterization of the transport properties and flow processes in the earth’s subsurface. Non-invasive characterization of hydraulic conductivity using geophysical methods (e.g., electrical and electromagnetic methods) may provide an alternative cost-effective tool to delineate preferential flow paths for hydrocarbon exploration or environmental applications. Knowledge of saturated hydraulic conductivity is as well, useful in predicting the unsaturated hydraulic conductivity via pedo-transfer functions. Non-invasive prediction of the saturated hydraulic conductivity can be very useful when the petrophysical information is needed over a wide area and non-destructive requirements are imposed on the project area.

            The spectral electrical response (SER) of soils contains useful information that can be linked to flow and transport properties. The SER of twenty-two natural soils with wide variability in physical and textural properties have been measured in a laboratory environment in the frequency range 0.01Hz to 10 kHz. For each soil, the hydraulic conductivity (K) was also measured and qauntified. An equivalent circuit model described by six circuit parameters has been used to model the electrical behavior of the soils. Relationships between the parameters and the textural and saturated hydraulic properties of the soils were investigated. The frequency exponent (η) increases with decrease in K, increase in porosity and increase in fines content. The relaxation time (τ) increases with an increase in K, a decrease in porosity and a decrease in fines. The bulk resistivity (ρ₀ ) increases with an increase in K, an increase in porosity and a decrease in fines. The relationships between the other circuit parameters and K are not strong, but when their interdependencies are exploited in multi-variate regression models, they help to predict saturated hydraulic conductivity of the soils reasonably

            Multiple regression models were developed using the circuit parameters to predict the hydraulic conductivities of the soils with reasonable success. The regression model obtained using only four selected influential electrical parameters, ρ0, τ, d_r and D_i produced the most useful prediction. It was shown that bulk resistivity plays an important role in the prediction models.

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