Bitumen–Toluene Mutual Diffusion Coefficients Using Microfluidics

Abstract

In this paper, we present a microfluidic approach to measure liquid solvent diffusivity in Athabasca bitumen. The method has three distinguishing features: (a) a sharp initial condition enabled by the high wettability of the solvent; (b) one-dimensional diffusive transport (in the absence of convection) ensured by microscale confinement; and (c) visible-light-based measurement enabled by the partial transparency of the bitumen at small scales. The method is applied to measure the diffusion of toluene into bitumen by imaging transmitted light profiles over time, and relating intensities to the mass fractions. Plotting toluene mass fraction versus distance/sqrt(time), results in a tight superposition of all curves (time-dependent mass fractions) demonstrating the diffusion dominated nature of the system and the robustness of the method. The diffusion transport equations were solved and fit to a constant diffusion coefficient as well as a variety of concentration-dependent diffusion coefficient relations found in the literature. For intermediate toluene mass fractions (0.2–0.8), a constant diffusion coefficient of 2.0 × 10–10 m2/s provides an appropriate representation. However, at low toluene mass fractions (<0.2), significantly reduced diffusive transport is observed, and endpoint analysis indicates diffusion coefficients trending toward 4.3 × 10–11 m2/s. At high toluene mass fractions (>0.8), the values trend toward 1.5 × 10–10 m2/s. This microfluidic method provides an inexpensive and rapid mutual diffusion coefficient evaluation, with significantly improved spatial/composition resolution vis-à-vis competing measurement methods.

Fickian and Non-Fickian Diffusion in Heavy Oil + Light Hydrocarbon Mixtures

“…et al13 for the same mixture. The two groups used subsamples from the same master sample, but variations in subsequent storage, handling, and sample pretreatment affect the details…”

Critical review of mutual diffusion coefficient measurements for liquid solvent + bitumen/heavy oil mixtures

“…Fadaei et al [15] claimed that the Beer-Lambert law closely predicted their calibration curve (maximum error of 4 %), although for such non-homogeneous colloidal solutions (asphaltene monomers), greater deviation would be expected. In a fraction of a second, air that was initially in contact with the bitumen was displaced with toluene due to strong wettability, providing a sharp initial condition for the one-dimensional diffusion of toluene into bitumen.…”

“…The expansion of Equation (15) to allow for the variation of density and the mutual diffusion coefficient with composition and rearrangement for mutual diffusion coefficient results in: The expansion of Equation (15) to allow for the variation of density and the mutual diffusion coefficient with composition and rearrangement for mutual diffusion coefficient results in:…”

Functionalization of micromodels with kaolinite for investigation of low salinity oil-recovery processes

“…18 Recently, glass and silicon microfluidic devices with representative pore-scale geometries have enabled the study of fluid behavior in petroleum related applications. 26,[28][29][30][31] In particular, Buchgraber et al, 2012, described the creation of twodimensional microfluidic devices (micromodels) with a porescale geometry that is identical to real rocks using thin section images obtained with a scanning electron microscope (SEM). 26,[28][29][30][31] In particular, Buchgraber et al, 2012, described the creation of twodimensional microfluidic devices (micromodels) with a porescale geometry that is identical to real rocks using thin section images obtained with a scanning electron microscope (SEM).…”