Case study: Dielectric Scanner Service’s Measurements Confirm 95% Residual Hydrocarbon Saturation

Dielectric logging provides new insight to Middle East carbonate reservoir texture and residual oil saturation

Challenge: Quantify the amount of residual high-viscosity oil in a high-porosity carbonate reservoir in the Middle East with varying Archie exponents.

Solution: Obtain Dielectric Scanner multifrequency dielectric dispersion service measurements to determine the oil saturation independently of conventional resistivity measurements and the influence of salinity.

Result: The dielectric-derived resistivity and saturation values confirm up to 95% residual hydrocarbon and provided Archie saturation equation parameters to improve reservoir understanding.

Confirmation needed for resistivity-based saturations

An operator wanted to improve understanding of the fluid saturations in a high-porosity carbonate reservoir where textural variation raised uncertainty in conventional interpretation. Conventional logging measurements were also ambiguous because of the effect of the 180,000-ppm [-ug/g] mud filtrate salinity.

Accurate water-filled porosity and textural information from dielectric dispersion measurements

Dielectric Scanner dielectric dispersion service measures high-resolution permittivity and conductivity at four frequencies to provide dielectric dispersion at a 1-in [2.54-cm] vertical resolution. Because there is a large difference in the permittivity of water from that of rock matrix or hydrocarbons, the resulting determination of water-filled porosity is insensitive to salinity. The conductivity measurements provide reconstructed resistivity and water saturation in the invaded zone. Dielectric Scanner service also provides textural information for determining the Archie exponents mn for carbonates and the cation exchange capacity (CEC) for siliciclastics instead of relying on potentially incorrect estimations from log analysis or waiting for core analysis.

The articulated pad of Dielectric Scanner service greatly improves contact with the formation in rugose boreholes, a condition that previous mandrel-type electromagnetic propagation tools were sensitive to.

Textural variation accounted for in saturation determination

The porosity data are presented in Track 5, with the difference between the total porosity and the water-filled porosity from Dielectric Scanner service indicating the volume of residual hydrocarbon.

Dieletric Scanner service’s hydrocarbon saturation in Track 2 accounts for variation in the Archie exponents across the reservoir and confirms up to 95% residual hydrocarbon. Conventional saturation determination using constant values of the Archie exponents is not as accurate.

In Track 4, Dielectric Scanner service’s invaded zone resistivity Rxo is in good agreement with Rxo obtained with conventional resistivity logging, confirming up to 95% residual hydrocarbon.

Download: Dielectric Scanner Measurements Confirm 95% Residual Hydrocarbon Saturation (1.93 MB PDF)

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Multifrequency dielectric dispersion measurements speak volumes about carbonates, shaly sands, and heavy oil. Visit the Dielectric Scanner webpage