Visualization Of Deformation In Unconsolidated Athabasca Oil Sand

Abstract

Abstract 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. Introduction The Athabasca deposit in northern Alberta, Canada, contains 0.2 × 1012 m3 of bitumen in place. The reservoir is the unconsolidated McMurray sand which dips to the south from its outcrop location near Fort McMurray. Because of its shallow depth and lack of consolidation, the understanding of its geomechanical properties under low effective stress is important for designing recovery processes. Many triaxial compression tests have been done in the past. However, the distribution of porosity and shear zones in the sheared samples has not been extensively studied. This paper presents a technique to visualize and quantify the porosity distribution in the sample. Four McMurray sand core samples were taken from the well 11-36-90-10W4M at a depth of about 70 meters. The 7 cm diameter cores were kept frozen until they were ready for the triaxial tests. One sample was used as a control and the other three were tested under 5, 50 and 750 kPa confining stresses. P. 637