A Rice University laboratory has provided proof that foam may be the right stuff to maximize enhanced oil recovery (EOR) increasing production. With over half of all the oil found so far still in the ground this may develop into very important news.

The Rice team demonstrated that foam may be a superior means to displace and extract tough-to-reach oil. In their tests the foam pumped into an experimental rig that mimicked the flow paths deep underground proved better at removing oil from formations with low permeability than common techniques involving water, gas, surfactants or combinations of the three.

The team’s paper, which is openly accessible, has been published online by the Royal Society of Chemistry journal Lab on a Chip.

Crude oil rarely sits in an underground pool waiting to be pumped out to the surface. Oil usually exits in formations of rock and sand and hides in small cracks and crevices that have proved devilishly difficult to tap. Oil producers pump various substances down the hole to loosen and either push or carry oil to the surface.

Rice scientist Sibani Lisa Biswal working with George Hirasaki have learned a great deal about how foam forms. With an eye toward EOR, she and her colleagues created microfluidic models of formations – they look something like children’s ant farms – to see how well foam stacks up against other materials in removing as much oil as possible.

The lab’s formations are not much bigger than a postage stamp and include wide channels, large cracks and small cracks. By pushing various fluids, including foam, into test formations, the Rice team can visualize the ways by which foam is able to remove oil from hard-to-reach places. They can also measure the fluid’s pressure gradient to see how it changes as it navigates the landscape.

The team determined the numbers are strongly in foam’s favor. Foam dislodged all but 25.1 percent of oil from low-permeability regions after four minutes of pushing it through a test rig. This compares to 53 percent for water and gas and 98.3 percent for water flooding; this demonstrated efficient use of injected fluid with foam to recover oil. This technology vastly improves upon water flooding by 73.2%!

The less-viscous fluids like water appear to displace oil in high-permeability regions while blowing right by the smaller cracks that retain their treasure. But foam offers mobility control, which means a higher resistance to flow near large pores.

Biswal, an associate professor of chemical and biomolecular engineering explains, “The foam’s lamellae (the borders between individual bubbles) add extra resistance to the flow. Water and gas don’t have that ability, so it’s easy for them to find paths of least resistance and move straight through. Because foam acts like a more viscous fluid, it’s better able to plug high-permeable regions and penetrate into less-permeable regions.”

Charles Conn, a Rice graduate student and lead author of the paper, said foam tends to dry out as it progresses through the model. “The bubbles don’t actually break. It’s more that the liquid drains away and leaves them behind,” he said.

Drying has two effects: It slows the progress of the foam even further and allows surfactant from the lamellae to drain into low-permeability zones, where it forces oil out. Foam may also cut the total amount of material that may have to be sent down the well hole.

One of the challenges will always be to get the foam to the underground formation intact. “It’s nice to know that foam can do these things, but if you can’t generate foam in the reservoir, then it’s not going to be useful,” Conn said. “If you lose the foam, it collapses into slugs of gas and liquid. You really want foam that can regenerate as it moves through the pores.”

Biswal said the lab plans to test foam on core samples that more closely mimic the environment underground.

Foam technology has been idea flirted with for a few years now. The Rice team has finally came up with an experimental system that produces real data. The data looks really interesting. Perhaps industrial researchers and academics will be able now to hasten the work and progress.


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