Hydrocarbon saturation and viscosity estimation from NMR logging in the Belridge diatomite

C. E. Morriss, R. Freedman, C. Straley, M. Johnston, H. J. Vinegar, P. N. Tutunjian

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86 Scopus citations


Nuclear magnetic resonance (NMR) logs have been recorded in Shell's North Belridge diatomite and Brown shale using an experimental logging tool, the CMR2 Combinable Magnetic Resonance tool. The CMR tool successfully logged porosity and T2 distributions over 1,500 ft of formation. In the diatomite and Brown shale formations, the CMR porosity is a measure of the total liquid-filled porosity even in this tight lithology because of the high signal-to-noise ratio and short interecho spacing (320 μs). CMR porosity values were in good agreement with core porosity, even in zones with appreciable gas saturation, which indicated complete flushing of the gas within the depth of investigation of the tool. T2 distributions from both the borehole and laboratory measurements are distinctly bimodal, with the shorter T2 peak at about 10 ms originating from water in contact with the diatom surface and a longer T2 peak at about 150 ms originating from the light oil. The T2 of the oil peak correlates roughly with oil viscosity. This indicates that the diatomite is predominantly water wet. The water and oil peaks are well separated in the light oil zones, which allows estimation of oil saturation by integrating the T2 distribution beyond a certain cutoff. The assignment of the oil peak and selection of the T2 cutoff were determined by laboratory NMR measurements on native-state cores after diffusing in D2O to eliminate the water signal. Because of the tight lithology and good fluid-loss control, estimates of oil saturation from the shallow-reading CMR tool are in good agreement with resistivity logs and core analysis. T2 distributions have been measured on 31 crude oil samples from Belridge spanning a range of viscosities from 2.7 to 4,300 cp. The CMR estimate of oil T2 correctly predicts oil viscosity and shows that the upper 150 ft of diatomite formation in this well undergoes a transition to heavier oil.

Original languageEnglish
Pages (from-to)44-59
Number of pages16
JournalLog Analyst
Issue number2
StatePublished - 1 Mar 1997
Externally publishedYes

ASJC Scopus subject areas

  • Process Chemistry and Technology


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