Bubbles split about how best to empty oil wells

Abstract

A better understanding of how bubbles form in a foam may enable the extraction of every last drop from an oil reservoir, say US scientists. Industry currently struggles to fully drain oil reservoirs, finding it technically difficult and expensive to do so. Gas – such as carbon dioxide – together with foam is often used to flush out some of the hard-to-reach oil. But a proportion of it remains elusive. Sibani Lisa Biswal and her team at Rice University used microfluidic channels and high-speed imaging to watch how gas bubbles change as they move through small spaces such as those found in the permeable rock containing oil reservoirs. These observations may help in the design of foams better able to fully extract oil wells. ‘Typically, it is difficult to recover oil from the tight pores in the lower permeable regions of the rock,’ explains Biswal. Ideally, a foam would block all the channels in the highly permeably sections of the rock, forcing pressure to flow through the regions of lower permeability flushing out any oil trapped there. ‘Foam able to block high permeable regions will lead to better recovery of oil in the low permeable regions,’ she says. The Soft Matter paper [Liontas, et al., Soft Matter (2013), doi:10.1039/c3sm51605a] described two previously unknown mechanisms through which gas bubbles split as they flow through a constriction such a pore in a rock. ‘We fabricated a microfluidic channel with a narrow constriction and flowed foam through it at different rates,’ Biswal told Materials Today. ‘We captured the events using a high-speed camera and then analyzed the resulting images.’ By taking 10 000 pictures per second, the team saw that a bubble pinched between another bubble and the wall would split in to two smaller bubbles just before it entered the 20 mm wide channel. They also saw that a bubble squeezed and pinched between two other bubbles would also split in two before going into the channel. ‘We found neighboring bubbles that are basically karate-chopping a third one as it tries to go through,’ Biswal explains. ‘No one has seen these mechanisms [before]’. The next step in the quest for improved foams for oil extraction is to develop microfluidic models that allow the visualization of how foams displace oil in porous rocks, she says.