Scientists Discover New Ways Bubbles Form in Foam

A new study published in the journal Soft Matter includes two new previously unknown ways in which bubbles form in foam.

The discoveries not only have implications for makers of foam, whether it be shaving cream or insulation, but for companies looking to extract every last drop of oil from a reservoir through the use of thick foam to displace it.

Led by Sibani Lisa Biswal of Rice University, the scientists used microfluidic devices and high-speed imaging to capture images of bubbles transforming as they pass through tight spaces.

In doing so, they uncovered new mechanisms that, the researchers say, could be used by engineers looking to manipulate foam for specific tasks.

"In the classic descriptions of bubble formation, there's what we call snap-off, lamella division and leave-behind," Biswal said in a press release.

According to the press release regarding the study, "Snap-off bubbles are created when liquid accumulates by capillary action in a narrow section of a pore and forms a liquid slug separating two bubbles. A lamella division bubble happens when the lamella (a thin film of liquid) moves through a branch in the flow path and becomes two lamella. Leave-behind happens when a gas enters two adjoining, parallel pores and the liquid between the two pores thin down to a lamella."

In the case of the newly observed processes, the bubbles form before gas passes through the constriction rather than after -- a behavior the researcher has named "pinch-off."

"No one has seen these mechanisms," she said, adding that they "found neighboring bubbles that are basically karate-chopping a third one as it tries to go through."

According to co-author George Hirasaki, a Rice research professor of chemical and biomolecular engineering, the smaller the bubbles, the more companies will be able to recover oil.

"We're trying to understand how foam behaves in porous media because it is a way of making gas act like a more viscous fluid," Hirasaki explained. "Normally, gas has very low viscosity and it tends to flow through rock and not displace oil and water. Once it finds a path, usually along the top of a reservoir, the rest of the gas tends to follow. If there were some way to make gas act more like a liquid, to make it more viscous, then it would contact much more of the reservoir and would push the fluids out."