Dielectric Logging for Heavy-Oil Reservoirs

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  • Formation evaluation plays an important role in managing heavy-oil reservoirs. The ability to estimate oil saturation, oil mobility and formation texture provides invaluable information for evaluating these reservoirs. Information obtained from array dielectric logging at multiple depths of investigation used with the correct set of petrophysical assumptions and interpretation methods can provide more accurate formation evaluation results in these reservoirs. Dielectric logging provides water saturation and water resistivity as its main petrophysical output. Consequently, its advantage over traditional resistivity methods is more apparent, especially in formations where the water resistivity changes over a short distance or is drastically different from borehole fluid and cannot be assumed as known. This work discusses various assumptions made or methods used for the different aspects of dielectric logging. Each assumption and method is considered at length, pitfalls are highlighted, and the effects of misconceptions on the petrophysical outputs are emphasized. The methods and assumptions discussed include processing the compensated phase measurements, mixing models used for obtaining effective permittivity, single versus multiple frequency measurements and obtaining textural parameters.  For each case, possible alternate methods are proposed to avoid inaccuracy in quantifying petrophysical properties.   Interpretation of dielectric logging when performed correctly with full knowledge of important factors involved can be a powerful tool in formation evaluation. This work provides best-practice guidelines for avoiding common mistakes for multi-frequency array dielectric interpretation.