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US researchers have demonstrated that enhanced oil recovery using foam could be more effective than existing techniques that use water, gas or surfactants.
Oil rarely sits in a pool underground waiting to be pumped out and is often contained in formations of rock and sand in small cracks and crevices. Enhanced oil recovery (EOR) techniques are used by industry to pump various substances downhole to loosen and either push or carry oil to the surface are used to extract more oil.
A research team at Rice University in Houston, Texas, used an experimental rig that housed microfluidic models of rock formations to see how the use of foam compared to other materials in removing as much oil as possible. By pushing various fluids, including foam, into the test formations, the researchers could see how the foam removes 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 use of foam left 25% percent of oil from low-permeability regions after four minutes of pushing it through a test rig, versus 53% for water and gas and 98.3% for water flooding, demonstrating the efficient use of injected fluid with foam to recover oil.
The less-viscous fluids appeared to displace oil in high-permeability regions while blowing right by the smaller cracks that retain deposits. But foam offers mobility control, which means a higher resistance to flow near large pores.
Sibani Lisa Biswal, associate professor of chemical and biomolecular engineering at Rice University, said: “The borders between individual bubbles, the foam's lamellae, add extra resistance to the flow. Water and gas don't have that ability, so it's easy for them to find the 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 that the foam tends to dry out as it progresses through the model. He said: "The bubbles don't actually break. It's more that the liquid drains away and leaves them behind.”
Drying slows the progress of the foam further and allows surfactant from the lamellae to drain into low-permeability zones, where it forces oil out. Foam may also cut the sheer amount of material that may have to be sent downhole.
However a key challenge will be the development of a way to generate the foam deep underground within a reservoir.
The researchers are to test foam on core samples that more closely mimic the environment underground next.