Technical Paper: Glass Transition and Heavy Oil Dynamics at Low Temperature

Society: Other
Paper Number: WHOC11-596
Presentation Date: 2011


In disordered materials, the velocities of thermal motions slow dramatically with decreasing temperatures. If there is no crystallization, the molecules will rearrange so slowly that they will cool before reaching a stable configuration necessary to form an amorphous solid, or glass. The behaviors of such liquids in terms of viscosity and relaxation time, determined in temperatures that are very close to the glass transition, have led to their classification as glasses with extremes between “strong” and “fragile.” Previous works studied this presence of a glass transition for bitumen and successfully applied modeling that considers this transition to the temperature dependence of some heavy oil viscosities. However, the glass transition for oils and heavy oils and the molecular dynamics at ambient to low temperatures are still not fully understood. In this study, we aim to provide a better understanding of the heavy oil dynamics and the temperature-dependence of the viscosity. The glass transition of heavy oils was characterized with differential scanning calorimetry measurements and the rheological characterization of several heavy oils at ambient to low temperatures was undertaken through shear rate sweeps and small-strain oscillatory measurements. Such a viscoelastic characterization at low temperature was undertaken in order to observe the glass-like behavior experimentally and also to construct the reservoir fluid master curves thanks to the time-temperature superposition principles, which states that at lower temperatures and longer time the fluid behaves the same. These rheological measurements in the linear viscoelastic regimes can then be understood as a response of a structure, represented by the spectrum, to the mechanical stimulation. As expected, the rheology results show that the widely used Arrhenius model cannot fit the experimental data at low temperature and that the heavy oils are highly fragile. Discussions include some comparisons of the structural and dynamics aspects of the heavy oils studied.

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