(230l) Using Microfluidic Device to Study Rheological Properties of Heavy Oil

Using Microfluidic
Device to Study Rheological Properties of Heavy Oil

Microfluidics is
an emerging technology that deals with flow of fluid in micro-scale channels
[1]. Microfluidic chips are used as a good representative of porous media to
evaluate dynamic aspects of fluid flow at pore-scale [2]. There are few
works on application of microfluidic chips on heavy oil and bitumen and
understanding of their pore-scale rheology [3]. There are some advantages of their
application such as direct visualization of phenomena, reduced consumption of
samples, low cost of fabrication, and accurate controlling of operating condition
[4].

Capillary
action drives fluid motion in microchannel without external driving forces. Capillary
driven flow refers to spontaneous movement of interface due to curved
liquid-liquid or gas-liquid interface [5]. Fluid viscosity, pore geometry,
wettability, and surface tension are important parameters that influence the
capillary filling kinetics. Capillary filling speed in rectangular microchannel is
evaluated by classical Lucas-Washburn-Riedel (LWR) equation [6].

 
Where r is the hydraulic radius, σ the air-fluid interfacial tension (IFT),
θ_c the
fluid advancing contact angle, and μ the viscosity of the fluid. Based on the
equation, there is a linear relation between position of advancing liquid and
square root of time. In this study, glass etched microchannels with depth of 10
µm and width of 40 µm were used. Capillary filling speed of methanol, ethanol, and
solutions of bitumen in heptol (80:20) are experimentally monitored using
inverted microscope with a digital charged coupled device (CCD) camera (Figure.
1). As
illustrated in Figure. 1, there are six parallel microchannels on each chip which
enable us to conduct several experiments with the similar experimental
condition. This is important for repeatability of the data and having average
values for each run.

For
all samples linear relation between propagation distance and square root of
time was found as expected in the case of Newtonian fluids. Theoretical
viscosity of each sample was calculated with the assumption of constant contact
angle which was then compared with experimental bulk viscosities. It is noteworthy
to mention that in
our previous work [3] capillary filling kinetics of bitumen solutions in
nanochannel (depth ~ 47 nm) was investigated where theoretical results were
significantly deviated from experimental values specially for higher
concentrations of bitumen samples. It seems that sharp variation of advancing
contact angle and interface shape is the reason of deviation (Figure 2). In
fact, advancing contact angle is completely different from bulk contact angle and
considering a constant value is not a reliable approach for high viscosity
fluids. Therefore, classical model failed to explain filling kinetics of high
viscosity fluids in the nanochannel. These findings further suggest that
channel size affect the wettability, where decreased wettability in nano-scale
separations leads to large deviation between theoretical and experimental
results. On the other hand, experimental results of microchannels were in good
agreement with classical model. Microchannels have the same
size of real pore and pore throat that make them suitable for fluid flow study
in porous media.

All in
all, nanochannels were not suitable for monitoring of heavy oil and bitumen
flow while microchannel enables us to study capillary filling kinetics of the
high viscose fluids. Filling
kinetics of viscous fluids in micro-scale require more study in order to have
better prediction of real porous media structure.                                            

References:

[1] D.
Sinton, Energy: the microfluidic frontier, Lab Chip, 2014, 14, 3127–3134

[2] M.
P. Rossi, H. Ye, Y. Gogotsi, S. Babu, P. Ndungu and J. C. Bradley,”
Environmental Scanning Electron Microscopy Study of Water in Carbon Nanopipes”,
Nano Lett., 4 989–993 (2004).

[3] S.
Mozaffari, “heology of Bitumen at the Onset of Asphaltene Aggregation and its
Effects on the Stability of Water-in-Oil Emulsion”, M.Sc Thesis, University of
Alberta, (2015).

[4]
JC. McDonal, DC. Duffy, JR. Anderson, DT. Chiu, H. Wu, OJ. Schueller, GM.
Whitesides, “Fabrication of microfluidic systems in poly(dimethylsiloxane)”,
Electrophoresis. 21(1) 27-40 (2000).

[5]
J.N. Kuo, Y.K. Lin, Capillary-Driven Dynamics of Water in Hydrophilic
Microscope Coverslip Nanochannels, Japanese Journal of Applied Physics, 51
(2012).

[6] E.
W. Washburn, "The Dynamics of Capillary Flow," Physical Review, 17 p.
273 (1921).

Figure. 1.
Schematic of experimental setup

Figure. 2.
Capillary filling of 40% bitumen diluted in heptol (8:20) [6]