Case study: Accurate Heavy Oil Volume in Shaly Sands with Variable Water Resistivity

Resistivity- and salinity-independent measurements from Dielectric Scanner service provide accurate hydrocarbon volume in Canadian oil sands

Challenge: Determine the bulk mass fraction of oil (weight percent bitumen) in oil sands with variable formation water resistivity in Canada.

Solution: Obtain Dielectric Scanner multifrequency dielectric dispersion measurements to accurately calculate water-filled porosity insensitive to water salinity instead of estimating Archie parameters or waiting months for laboratory core analysis.

Result: Accurately determined weight percent bitumen months in advance of laboratory analysis in oil sand reservoirs where shale intervals and variable formation water salinity complicate conventional porosity and resistivity analysis.

Interpretation ambiguity introduced by varying water salinity

Canadian operators needed a more efficient approach to the formation evaluation of heavy oil reservoirs that include some thin-bedded shaly sections. Because the salinity of the formation water varies, current industry practice is to evaluate oil volume using Dean Stark core analysis, and the operators may have to wait several months for the core analysis results. The results are used to determine the parameters required to make conventional  saturation calculations match the core data to fill in intervals that were not cored.

Saturation determination independent of water salinity

Dielectric Scanner service delivers dielectric dispersion measurements at a 1-in [2.54-cm] vertical resolution based on nine attenuation and phase-shift measurements at four frequencies. These multifrequency high-resolution measurements are radially inverted to obtain permittivity and conductivity at each frequency. The resulting determination of water-filled porosity is salinity insensitive because the permittivity of water is readily differentiated from that of rock matrix or hydrocarbons. The conductivity measurements provide reconstructed resistivity and water saturation for the invaded zone. Dielectric Scanner service’s measurements also yield useful textural information.

Dielectric Scanner service’s articulated pad greatly improves contact with the formation in rugose boreholes, a condition that previous mandreltype electromagnetic propagation tools were sensitive to.

Accurate fluid volumes without waiting for laboratory analysis

In Well 1, the variying formation water resistivity produced discrepancies in the conventional analysis based on the Archie equation, leading to a pessimistically high calculation of water saturation. The weight percent bitumen calculated from Dielectric Scanner service’s measurements is salinity independent and shows excellent agreement to core analysis results.

In Well 2, the high-resolution weight percent bitumen calculated from Dielectric Scanner service’s measurements also shows excellent agreement to the core analysis results, even in the thin shale intervals identified in the core photograph by the lighter colors within the black bitumen-rich core. Water saturation and hydrocarbon volume calculated from the salinity-insensitive measurements of Dielectric Scanner service provide higher resolution, more accurate answers than those dervied from the Archie equation or NMR data.

Dielectric Scanner service analysis is available within a few days, providing critical information months before typical core analysis turnaround. With the accuracy and speed of these answers, Canadian operators can confidently consider a reduction in coring frequency and the number of core analysis points for their multiwell projects.

Download: Accurate Heavy Oil Volume in Shaly Sands with Variable Water Resistivity (4.10 MB PDF)

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