(297e) The Effect of Surface Wettability On Foam Stability

The stability of carbon dioxide (CO2) foam is important due to its application in enhanced oil recovery. However, the rheological behavior of foam in porous media is complex and still not well characterized. Here we describe our studies on foam generation, propagation and coalescence using microfluidic channels to mimic the porous network found in reservoir conditions. Moreover, we describe a novel technique which can be used to alter the surface properties of microchannels[1], which is beneficial to investigate multi-phase transport phenomena in accordance with surface conditions of oil reservoir formation.

It is well known that at small pore diameters, the wettability of the walls play an important role in gas-liquid two-phase flow at low Reynolds number and low capillary number [2,3]. Under such conditions, capillary forces dominate over inertial forces. It is generally accepted that foam is unstable in oil-wet porous media, but a quantitative understanding of how wettability affects foam stability is still imperative. For example, capillary snap-off through a constricted pore, one of the primary mechanisms of foam generation in porous media, does not occur when the advancing contact angle of the aqueous phase is above ~70°[4].

By taking advantage of UV/ozone modification of polydimethylosiloxane (PDMS) microfluidic channels, one can precisely control the wettability of channel surface, with water equilibrium contact angle ranging from 0° to 98°. In our experiments, different wettability results in different flow patterns, under the condition that the other variables were kept the same, including the flow rate of aqueous phase, the in-flow pressure of CO2 and the channel dimensions. Additionally, the CO2 bubble pinch-off mechanism is also studied in this geometry, by comparing different partial wetting systems of aqueous phase. After CO2 bubbles have invaded into the downstream channel, it is found that corner flow of the wetting phase, which is affected by dynamic contact angle in the CO2-liquid-PDMS system, is an important factor in determining CO2 bubble size and break-up frequency.