Dense unconsolidated Athabasca oil sand exhibits significant dilation in triaxial compression tests at low confining stresses of 5 to 750 kPa. This paper presents an innovative method which can visualize and calculate the porosity distribution in a sheared sample.

Thin sections from the sheared sample were made to quantify the porosity within and outside the shear zones. Porosity was determined using image analysis on back scattered scanning electron microscopy (SEM) images of the thin sections. These porosity data were used to calibrate computer assisted tomography scan (CAT scan) images of the whole core sample so that the porosity distribution in the sheared sample could be mapped. The calculated average porosity of each of the four samples agreed very well with porosity measured by Dean-Stark analysis.

In the CAT scan images, shear dilation was seen to be concentrated along and within multiple, localized shear bands. However, the porosity distribution within each sample had a very narrow range compared to the overall increase in porosity, implying the sheared samples were essentially uniformly dilated.

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