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

1. Image Source: U.S. Department of Energy2. Image Source: www.slb.com/Schlumberger

WettabilityWettabilityStructureStructure

Pores1 and vugs2 in reservoir rock

3. Chilingar, G. V.; Yen, T. F., Energy Sources 1983, 7, (1), 67-75.

Wettability of carbonate reservoir rocks (water contact angle,161 samples1)

Microchannels in porous media

1. Source: http://www.oil-gas-news.com2. Source: this study

Microfluidics in EOR process1 Bubble break-up in microchannels2

Goals of this work

1. To tune and pattern wettability in micromodels;

2. To investigate foam flow in heterogeneous porous media.

500 μm

Microchannel and photolithography

Silicon wafer

Silicon wafer

PDMS

PDMS

Photoresist

SU-8 photoresist mold

PDMS curing on SU-8 mold

PDMS after peeling it off the mold1. Cubaud, T., U. Ulmanella, and C.M. Ho, Fluid

Dynamics Research, 2006. 38(11): p. 772-786.

PDMS surface modification by UV-Ozone

1. Berdichevsky Y, et al, Sensors and Actuators B-Chemical 2004, 97, (2-3), 402-408.

Ozone[1]

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

1.19 cm

Foam generator

Porous medium

Foam generator

150 μm

surfactant

surfactant

gas bubbles

Heterogeneous porous media

Low permeable layer: grain radius 50 μm; pore throat 20 μm; porosity 0.45.

High permeable layer: grain radius 150 μm; pore throat 60 μm; porosity 0.45.

100% air injection to dye solution

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.

CO2 is only able to flow through the high permeability region leaving the aqueous solution trapped in the low permeability region

90% air injection to dye solution

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.

Adding surfactant to the foam allows the aqueous solution to be swept from both the high and low permeability regions

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