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Case study: Accurate Resistivity and Hydrocarbon Saturation in Washed-Out Zones in a Heavy Oil Reservoir

Dielectric Scanner service’s high-resolution, salinity-insensitive measurements accurately characterize heavy oil reservoir

Challenge: Obtain measurements for petrophysical analysis that are not biased by washed-out intervals in a heavy oil reservoir in Cymric field.

Solution: Run Dielectric Scanner multifrequency dielectric dispersion service to measure water-filled porosity to determine hydrocarbon volume insensitive to washouts, fluid salinity, and other environmental effects.

Result: Corrected a pessimistic water saturation measurement that was too high by 23% by using dielectric-derived saturation measurements, confirmed by sidewall core analysis.

Ambiguous measurements in washed-out hole

Washed-out borehole intervals in a heavy oil reservoir in Cymric field, California, USA, were adversely affecting logging. The mudcake-filled washouts were causing separation in the resistivity curves that could be confused with invasion. Typically little invasion occurs in heavy oil reservoirs, in which case the oil saturations of the uninvaded and invaded zones are approximately equal. A further complication in determining saturation was that the porosity measurements from a conventional, mandrel-type electromagnetic propagation tool were suspect because the tool would not have been able to maintain good contact in these rugose conditions.

Robust water-filled porosity measurement and textural information from dielectric dispersion

Dielectric Scanner service measures high-resolution permittivity and conductivity at multiple depths and 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. Pressure, temperature, and the permittivity and conductivity of the borehole mudcake are also measured to correct for environmental effects.

Rock textural information is also obtained by Dielectric Scanner service for determining the Archie exponents mn in carbonates and the cation exchange capacity (CEC) for siliciclastics instead of relying on potentially incorrect estimations or waiting for core analysis.

Measurements free of environmental effects

The accuracy of the Dielectric Scanner service’s porosity and water saturation measurements was confirmed from laboratory measurement of sidewall core samples, which closely track Dielectric Scanner service’s log.

 


Download: Accurate Resistivity and Hydrocarbon Saturation in Washed-Out Zones (1.18 MB PDF)

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