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Workreport 2016-42



EDZ Study Area in ONK-TKU-3620: Association Analysis of Petrophysical and Rock Mechanics Data


Kiuru, R.



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Physical and mechanical properties of drill core specimens were determined as a part of investigations into excavation damaged in the dedicated study area in ONK-TKU-3620. The main goal of this study was to find indicators of excavation in the form of anomalous physical properties linked to increased porosity or lower mechanical strength. Geophysical indicators are desired for their ease, speed and cost-effectiveness. The secondary goal was to find associations between dynamic and static elastic properties, to allow estimation of rock mechanical properties using geophysical measurements.

The parameters most sensitive to the presence of (saline) pore space fluid showed depth dependencies. Resistivity showed abnormally low values in the first 0.2 m, and an increase with depth in the first 0.7 m from the study area surface. S-velocity, shear impedance, shear modulus and Young’s modulus all showed abnormally low values in the first 0.2 m from the study area surface.

Specimens in the first 0.7 m from the study area surface showed increased proportion of elevated (> 0.5 %) porosity values. Combinations of high porosity/shallow depth, low resistivity/shallow depth, high porosity/low resistivity, low IP/shallow depth and low IP/high porosity also seem to separate anomalous specimens. S-velocity, P/S -ratio, Poisson’s ratio and all three impedances in respect to depth separated anomalous specimens. Abnormally high S-velocity in respect to other elastic properties also seemed to separate anomalous specimens. On one of the anomalous specimens, the presence of an EDZ feature was confirmed by Posiva geologist. This specimen could be identified based on S-velocity, P/S -ratio, Poisson’s ratio and all three impedances.


Best indicators for excavation damage based on this study would appear to be resistivity, S-velocity, shear impedance, shear modulus and Young’s modulus. Most of the other elastic parameters in conjunction with other parameters could be used to identify anomalous specimens. The results support the use of electrical and seismic methods to identify excavation damage. Estimation of static elastic properties based on dynamic elastic properties does not appear possible based on this study. Saturation water salinity had a clear effect decreasing measured resistivity.


petrophysics, rock mechanics, physical properties of rocks, laboratory testing, statistical analysis, ONKALO, excavation damage, EDZ study area


Appendix_G (xls) (6.2 MB)
WR 2016-42_web (pdf) (28.5 MB)


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