Show the flow

When it comes to teaching, seeing is a key to believing, or at least understanding.

That's is the guiding principle of a new class, 1.079 (Rock-on-a-Chip), dedicated to exploring multiphase flow in porous media.

“This course is an opportunity to teach this subject in a completely different way, by visualizing the physics of flow,” says instructor Ruben Juanes, the ARCO Associate Professor in Energy Studies.

Juanes introduced 1.079 in the spring of 2017, seeking to kick-start an energy resources track within the Department of Civil and Environmental Engineering. “The class plays a very nice role in the curriculum, filling a gap in a subject that is crucial to many energy technologies,” he says.

Flows in porous media come into play in a range of real-world applications, from oil and gas recovery and groundwater resource management to seismic activity mapping and energy storage technology. These flows are frequently multiphase, composed of gases, solids, and liquids in diverse mixes. For example, hydrocarbon reservoirs simultaneously host water, oil, and gas; and fuel cells feature a porous layer next to the cathode where water vapor may condense into liquid water.

However, the processes by which liquids and gases move underground often take place out of sight. Rainwater infiltrates soil, displacing air. Oil and water compete as they seep through rock reservoirs. It has been difficult to observe and capture in scientific detail what Juanes calls “the marvelous physics and chemistry of multiphase flows.” 

But recently, Juanes figured out a way of elucidating these subterranean processes. Employing 3-D printing and methods borrowed from the field of microfluidics, he created a multiphase flow laboratory on a chip. 

The device consists of a microfluidic flow cell patterned with vertical posts using soft lithography, sandwiched between two thin layers of a transparent polymer. When one fluid is introduced to displace another, the chip permits direct visualization of fundamental physical mechanisms at the scale of actual rock and soil pores. Juanes can now study in vivid close-up the critical properties and porous media conditions that hamper, or hasten, underground flows.

What Juanes calls a “new approach to an old problem” proves especially effective in the classroom.

“With transparent porous media, you can demonstrate the process of oil recovery, filtration of water, extraction of gases,” he says. “You can’t really understand these applications without knowledge of the physics, and here, an image is worth a thousand words.”

Lubna Barghouty SM ’17, whose graduate research focused on predicting the flow of oil from rock reservoirs containing both oil and water, calls 1.079 a “one-of-a-kind class.”

“I had been reading about the concepts and trying to imagine these phenomena, and finally I was able to see them,” she says.

Rafael Villamor Lora, a graduate student in civil engineering and geomechanics, is studying rock permeability and fluid flow inside rock fractures. He says he found that 1.079 offered “a unique approach to presenting very difficult physics, making it clear and understandable.”

Juanes divides class time between lectures focused on theory and labs that brought theory to life, a mix that students found both intellectually challenging and practical.  

“I love experimenting and doing things hands-on,” says Omar Al-Dajani SM ’16, a petroleum engineer for Saudi Aramco now pursuing a doctoral degree in civil and environmental engineering. But sometimes his experiments failed. “It was amazing how Professor Juanes could change a few things on the fly so the experiment would run successfully,” he says. “He goes through derivations, formulates problems in a very elegant way, and comes up with the right solution for whatever problem comes up in the lab.”

Barghouty says she was anxious when she initially discovered that she would be responsible for fabricating her own lab tools.

“We did whole experiments from A to Z, including cutting sheets of acrylic glass with lasers and using 3-D printers to etch pores in these chips,” she says. “I am now confident that I have the skills necessary for experimental work and that I can apply those skills to other kinds of research.”

Lab-on-a-chip experiments that required hours of preparation might take mere moments to run. One experiment demonstrated the power of capillary forces. After filling their microfluidic chips with a fluid, students flipped them 180 degrees, expecting the fluid to flow down in response to gravity. 

“In my cell, the fluid hung, and my jaw dropped,” recalls Al-Dajani. Surface tension made the fluid stick to the many tiny posts inside the chip, fabricated to simulate rock pores. When he added a drop of soap, suddenly the surface tension disappeared and the fluid dropped. “We saw the physics in action, the competition between gravity and capillary forces, which also takes place inside oil reservoirs,” he says.

Several labs featured Juanes’s research pursuits. “I asked students to change the wettability of the microfluidic cell and to look at displacement of multiphase flow under different wetting conditions,” says Juanes. Understanding and altering wettability — a measure of a substance’s attraction to or repulsion of water — is essential to fluid extraction applications. 

“There are ways wettability could be modulated to recover more oil and gas in existing reservoirs,” Juanes notes. “There is a big margin for improvement in both fracking and conventional drilling.”

While he hopes to drive home the real-world applications of laboratory work, Juanes intends for the class to accomplish a broader pedagogical goal. 

“When you perform an experiment not knowing the outcome, you are forced to make sense of what happens, especially something unexpected,” he says. “Moments like these captivate your attention, really allowing you to dig deep and giving you a better understanding of physics at play.”

The Rock-on-a-Chip class was developed with funding from the S.D. Bechtel, Jr. Foundation. It will be an elective for the energy studies minor starting in 2018. 

This article appears in the Autumn 2017 issue of Energy Futures, the magazine of the MIT Energy Initiative.

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