The use of PDMS micromodels to study CO2
foam transport in porous media
Kun Ma, George J. Hirasaki, Sibani Lisa Biswal
Department of Chemical & Biomolecular Engineering
Rice University, Houston, TX
04/26/2011
Reservoir conditions for multi-phase flow
Structure
Wettability
water-wet(0-80°)
8%
strongly oil-wet (160180°)
15%
intermediate wettability
(80-100°)
12%
oil-wet (100-160°)
65%
Pores1 and vugs2 in reservoir rock
1. Image Source: U.S. Department of Energy
2. Image Source: www.slb.com/Schlumberger
Wettability of carbonate reservoir rocks
(water contact angle,161 samples1)
3. Chilingar, G. V.; Yen, T. F., Energy Sources 1983, 7, (1),
67-75.
Microchannels in porous media
Microfluidics in EOR process1
1.
2.
Source: http://www.oil-gas-news.com
Source: this study
Bubble break-up in microchannels2
Goals of this work
1. To tune and pattern
wettability in micromodels;
500 μm
2. To investigate foam flow in
heterogeneous porous media.
Microchannel and photolithography
Photoresist
Silicon wafer
SU-8 photoresist mold
PDMS
Silicon wafer
PDMS curing on SU-8 mold
PDMS
1.
Cubaud, T., U. Ulmanella, and C.M. Ho, Fluid
Dynamics Research, 2006. 38(11): p. 772-786.
PDMS after peeling it off the
mold
PDMS surface modification by UV-Ozone
Ozone
[1]
1. Berdichevsky Y, et al, Sensors and Actuators B-Chemical 2004, 97, (2-3), 402-408.
Wettability control by water immersion
Wettability maintenance by keeping UV-ozone-treated PDMS (1-hour curing at 80
°C) surface in contact with DI water.
Schematic of the two-step process of wettability control
An example of wettability patterning
(a) Top view of the porous medium in Device A.
(b) Top view of the porous medium in Device B.
Left: initially saturated with dye solution; Right: after 2 min air injection at a volumetric
flow rate of 1.0 ml/hr. The red scale bar at the upper left corner represents 500 μm.
Design of a heterogeneous micromodel
2.57 cm
Porous medium
1.19 cm
Foam generator
Foam generator
surfactant
150 μm
gas
bubbles
surfactant
Heterogeneous porous media
High permeable layer:
grain radius 150 μm;
pore throat 60 μm;
porosity 0.45.
Low permeable layer:
grain radius 50 μm;
pore throat 20 μm;
porosity 0.45.
100% air injection to dye solution
CO2 is only able to flow through the high permeability region leaving the aqueous
solution trapped in the low permeability region
Played at 1 frames per second, captured at 10 frames per second.
Injected gas flow rate 5.0 ml/hr, injected liquid flow rate 0.0 ml/hr.
90% air injection to dye solution
Adding surfactant to the foam allows the aqueous solution to be swept from both the
high and low permeability regions
Played at 1 frames per second, captured at 10 frames per second.
Injected gas flow rate 4.5 ml/hr, injected liquid (0.2% wt coco betaine) flow rate 0.5 ml/hr.
Image processing by MATLAB
Only targeting the
aqueous (green dye)
solution
Coworked with Dichuan Li, Rice University.
Comparison of saturation profiles
1.1 sec (gas breakthrough)
2.7 sec (gas breakthrough)
Conclusions
★ PDMS-based microfluidic devices provide a facile way to study the
effect of wettability and heterogeneity on multi-phase flow in porous
media;
★ A simple method has been demonstrated to tune and pattern the
wettability of polydimethylsiloxane (PDMS) to generate microfluidic
mimics of heterogeneous porous media;
★ Preliminary results in micromodels show that pre-generated foam is
able to greatly improve sweep in low permeable region in a
heterogeneous porous medium.
Future work
Understand the mechanism of foam propagation in heterogeneous
porous media:
- permeability dependence
- cross flow
- effect of surfactants
- effect of foam quality
- shear thinning effect