Schlumberger

Dielectric Scanner Multifrequency Dielectric Dispersion Service

Dielectric dispersion science

The heart of Dielectric Scanner service is its short, multispacing antenna array pad. As the electromagnetic waves travel from the transmitters to the receivers, changes occur in amplitude and phase that are directly related to the dielectric permittivity and conductivity of the formation. Because there is a large contrast between the permittivity of water and that of oil and of rock, the tool makes a direct measurement of the water volume that is independent of the water salinity.

Depending on the texture of the rock, the permittivity and conductivity differ for different frequencies of the electromagnetic waves. This phenomena of the variation of formation dielectric properties as a function of the frequency is known as dielectric dispersion. Dielectric dispersion cannot be measured by conventional single-frequency electromagnetic tools.

The permittivity and conductivity measurements made by Dielectric Scanner service at each frequency are interpreted using a petrophysical model. The output parameters of the model are water-filled porosity (hence water saturation if the total porosity is known), water salinity, and textural effects. In carbonate reservoirs, dielectric dispersion is related to the cementation and saturation factors that are represented by the exponents m and n in the Archie saturation equation. In shaly sands dielectric dispersion is related to the shale volume, represented by the cation exchange capacity (CEC).

Dielectric Scanner Comparison Log

Previous-generation single-frequency electromagnetic propagation tools, emulated in the log on the left by single-frequency processing, cannot account for textural variation, resulting in the overestimation of invaded zone resistivity Rxo (Track 3). In the log on the right from Dielectric Scanner service, multifrequency mixing analysis correctly matches the water-filled porosity to the total porosity in this water-filled sand in Track 4, as confirmed by the matching Rxo values of the Dielectric Scanner service and resistivity tools in Track 3.

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See How Dielectric Science Quantifies Fluid Content

Dielectric Scanner Animation
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