Micromechanical and microstructural DEM modeling of the viscoelastic behavior of oil sands

摘要

Oil sand is a composite material of quartz aggregates, bitumen, water, and air void in which the bitumen exhibits a time and temperature dependent behavior under loading. The soil skeleton (quartz aggregates) comprises dense, highly incompressible, and uncemented fine interlocked grains exhibiting low in-situ void ratio, and high shear strengths and dilatancy under low normal stresses. In this work, a 2D discrete element method (DEM) is developed to model the viscoelastic response of an oil sand formation. A digital sample of the oil sand with varying particle shapes and sizes were built using the discrete element software PFC2D. The oil sand microstructure was captured from a scanning electron microscope image of a 14.5% bitumen content Athabasca oil sand. The micromechanical approach is based on discretizing the oil sands microstructure and modeling particle interactions (contacts) of its constituents at microscale. The quartz aggregates, water, and bitumen included in the digital samples were modeled using different contact models. Rheological data for the bitumen was obtained from a stress/strain controlled rheometer equipped with a parallel plate. This data was used to calibrate the parameters of the viscoelastic contact models among the different material phases. The resulting parameters of Burger’s model were used to simulate the micromechanical behavior of the material. A 2D DEM model with two temperatures and three loading frequencies subjected to a constant amplitude sinusoidal compression tests was simulated. The results of the study show a good agreement between the model prediction and the measured dynamic modulus and phase angle. This indicates that the linear viscoelastic DEM model developed is capable of simulating time-dependent behavior of oil sands material. Additionally, the effect of rate of loading and temperature on the deformational mechanics of the material was evident in the dynamic modulus determination.