Case study: Multifrequency Dielectric Dispersion Service Distinguishes Heavy Oil from Freshwater

Dielectric Scanner service’s high-resolution dielectric permittivity and conductivity identify oil despite lack of resistivity contrast

Challenge: Accurately estimate heavy oil saturation in reservoirs with low-salinity formation water in Kern River field.

Solution: Run Dielectric Scanner multifrequency dielectric dispersion service to determine oil saturation in high resolution for reservoirs with either fresh formation water or unknown salinity.

Result: Identified heavy oil reservoir with low water saturation from dielectric dispersion measurements despite the lack of resistivity contrast between the oil and water zones.

Freshwater ambiguity

Low-salinity formation water makes it difficult to identify water zones on triple-combo logs from Kern River field. Invasion profiles are masked by the similar resistivities of the drilling mud and formation water, making clay content a major influence on the resistivity measurement. A further complication is the inability of conventional logs to distinguish producible from immovable oil. Chevron had to resort to collecting fullbore and sidewall cores to identify fluid contacts and potential oil-producing formations in some Kern River wells.

Dielectric dispersion insight

Dielectric Scanner multifrequency dielectric dispersion service measures dielectric permittivity and conductivity at four different frequencies. Inversion of the measurements provides salinity-insensitive water-filled porosity and water salinity at two depths of investigation along with textural information for determining the Archie exponents mn in carbonates and the cation exchange capacity (CEC) in siliciclastics. Previously, these parameters had to be estimated from log analysis or measured by laboratory core analysis. Pressure, temperature, and borehole mudcake permittivity and conductivity are also measured to correct for environmental effects.

Accurate oil volume measurement

The resistivity logs in Track 2 cannot differentiate oil from the low-salinity formation water, and as a result, all the sands are indicated as having the same water saturation. In this freshwater environment, the clay content—not fluid volumes—drives the resistivity responses. However, the oil volume derived from Dielectric Scanner service’s measurements clearly differentiates the oil reservoir. The dielectric-based saturations in Track 4 are confirmed by carbon/oxygen logs obtained with the RSTPro reservoir saturation tool after the well was cased. The differences in response are due to the much greater vertical resolution of the Dielectric Scanner service’s measurements.

Download: Multifrequency Dielectric Dispersion Tool Distinguishes Heavy Oil from Freshwater (1.14 MB PDF)

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