Case study: Dielectric Scanner Service’s Measurements Reveal Additional 150 ft of Pay

Previously masked by low resistivity, identified producible heavy oil confirmed by sidewall samples

Challenge: Identify producible heavy oil in a laminated reservoir, where formation evaluation is biased by resistivity reduced by conductive clay content, high-viscosity oil prevents direct oil identification on nuclear magnetic resonance (NMR) logs, and rugose borehole compromises measurement by conventional dielectric tools.

Solution: Run Dielectric Scanner multifrequency dielectric dispersion service to obtain high-resolution measurements for accurately determining water volume and formation water salinity insensitive to clay content, oil viscosity, and poor hole conditions.

Result: Identified an additional 150 ft of pay, as confirmed by sidewall samples and subsequent tests.

Low-resistivity formation hides oil

The production potential of a reservoir in the Orinoco belt of Venezuela could not be fully determined with conventional logs. Thinly bedded shale and sand layers decreased resistivity measurements, masking pay zones and resulting in pessimistic interpretations of hydrocarbon volume. In this heavy oil reservoir, NMR logs measured a reduced oil signal, which in turn adversely affected fluid saturation determinations.

Dielectric dispersion differentiates moveable hydrocarbons from water

Dielectric Scanner multifrequency 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 independent of salinity. The conductivity measurements provide reconstructed resistivity and water saturation for the invaded zone.

Dielectric Scanner service also provides textural information for determining the Archie exponents mn for carbonates and cation exchange capacity (CEC) for siliciclastics instead of relying on potentially incorrect estimations from conventional 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.

Accurate saturations identify an additional 150 ft of pay

As shown by the caliper log in Track 1, the borehole was highly rugose, but the pad maintained good contact with the formation, and the measurements by Dielectric Scanner service were not compromised. The high resistivity in Track 5 in the oil-bearing interval from approximately X,430 to X,500 ft had been observed in other wells in the area. However, resistivity values below this interval are uniformly low. The NMR log in Track 7 has a strong oil signature in the upper interval, but the apparent porosity is reduced with increasing depth.

The Dielectric Scanner service’s log dispelled uncertainty about the reservoir quality of the lower interval, revealing moveable oil over a 150-ft section, from X,560 to X,650 ft and again from X,690 to X,720 ft (Track 6). Sidewall samples confirmed Dielectric Scanner service’s measurements, recovering oil at X,447 and X,574 ft, oil and some water near the oil/water contact at X,701.5 ft, and water at X,818 ft.

Download: Dielectric Scanner Dispersion Measurements Reveal Additional 150 ft of Pay (1.63 MB PDF)

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