Researchers identify two novel ways bubbles form in foam; potential benefit for enhanced oil recovery
A new study led by Rice chemical and biomolecular engineer Sibani Lisa Biswal and published in the journal Soft Matter describes two previously unknown ways that bubbles form in foam. The findings may enable more effective enhanced oil recovery operations using foam.
|Neighboring bubbles pinch a third into two before it enters a constriction like those found in oil-bearing reservoirs. Courtesy of the Biswal Lab. Click to enlarge.|
|A bubble is split before entering a constriction by a neighboring bubble and the wall. Courtesy of the Biswal Lab. Click to enlarge.|
Biswal and her team used microfluidic devices and high-speed imaging to capture images of how bubbles transform as they pass through tight spaces such as those found in permeable rock deep underground. They discovered mechanisms that should help engineers understand how foam can be manipulated for specific tasks.
Classic processes of bubble formation include “snap-off”, “lamella division” and “leave-behind,” Biswal said. 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 lamellae. 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 newly observed bubble-making processes, which Biswal calls “pinch-off” behaviors, the bubbles form before gas passes through the constriction, not after.
In one pinch-off, a bubble caught between a neighboring bubble and the wall would split as it entered the channel. In the second, she said, “We found neighboring bubbles that are basically karate-chopping a third one as it tries to go through.”
The smaller the bubbles in the foam, the better it may serve enhanced oil recovery, said George Hirasaki, a Rice research professor of chemical and biomolecular engineering and co-author of the paper.
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. 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.—George Hirasaki
Ideally, foam would pack the channels inside high-permeable regions and force pressure to flow through rocks with low permeability, flushing out the hard-to-get oil often trapped there.
The Biswal lab built devices that mimic what happens in porous rock, squeezing mixtures of gas and surfactant through 20 micrometer-wide channels. They filmed what happened under a range of pressures at either end of the channel at 10,000 frames per second.
We want to offer the oil industry more mobility control. What we mean by that is the ability to drive fluids through areas that vary in their permeability. We want fluids to move through the entire path, not just the path of least resistance.—Sibani Biswal
Lead authors are Rice alumna Rachel Liontas, currently a graduate student at Caltech, and former graduate student Kun Ma, currently a reservoir engineer at Total E&P USA.
The Abu Dhabi National Oil Company, the Abu Dhabi Oil R&D Sub-Committee, the Abu Dhabi Company for Onshore Oil Operations, the Zakum Development Co., the Abu Dhabi Marine Operating Company), the Petroleum Institute of the United Arab Emirates and the US Department of Energy funded the research.
Rachel Liontas, Kun Ma, George J. Hirasaki and Sibani Lisa Biswal (2013) “Neighbor-induced bubble pinch-off: novel mechanisms of in situ foam generation in microfluidic channels”, Soft Matter doi: 10.1039/C3SM51605A