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

SOLUTIONObtain Dielectric Scanner* multifrequency dielectric dispersion measurements to determine the oil saturation independently of conventional resistivity measurements and the influence of salinity.

RESULTSConfirmed up to 95% residual hydrocarbon and used the dielectric-derived Archie saturation equation parameters to improve reservoir understanding.

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

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

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

CASE STUDY

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Dielectric Pro* interpretation and quality control software performs robust radial interpretations, integrates measurements for multimineral analysis, and applies petrophysical models in an efficient workflow.

X10

X20

X30

X40

X50

Illite (dry)

Lithology

0 10

Epsilon Matrixfrom Lithology

1 3.5

Archie mn

0 ft3/ft3 1

Dielectric Scanner

Oil

Residual OilSaturation

1 m3/m3

Depth, m

0

Porosity

0 ft3/ft3 1

Archie

Difference

Bound Water

Oil

Water

0.2 ohm.m 2,000

HRLA* True Resistivity

0.5 m3/m3 0Dielectric Scanner Water-Filled Porosity

Freq. 0 – Freq. 1

Freq. 2 – Freq. 3

Freq. 2 – Freq. 1

Freq. 1 – Freq. 2

Freq. 3 – Freq. 2

Freq. 0 – Freq. 1

Permittivity

Dispersion Image

Conductivity

0.5 m3/m3 0ELAN* Total Porosity

Hydrocarbon

Porosity

0.2 ohm.m 2,000

Dielectric Scanner Invaded Zone Resistivity

0.2 ohm.m 2,000

Invaded Zone Resistivity

0.2 ohm.m 2,000

Array Laterolog Resistivity

Resistivity

6 in 16

Caliper

Calcite

Dolomite

www.slb.com/ds

*Mark of SchlumbergerCopyright © 2014 Schlumberger. All rights reserved. 10-FE-0067

CASE STUDY: Fluid saturations in high-porosity carbonate, Middle East

Dielectric Scanner service’s resistivity curve in Track 4 confirms the conventional Rxo measurements of 95% residual hydrocarbon in the carbonate reservoir.

Textural variation accounted for in saturation determinationThe 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.

Dielectric 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, as shown by the red shading.

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.