University of Pittsburgh professor Eric Beckman and his colleague Bob Enick have been intent on solving a decades-old mystery: how to increase the viscosity of liquid CO2 so it can better extract oil from its hiding spots inside the pores of underground sandstone. Now, with a $1.3 million grant from the National Energy Technology Laboratory, the researchers are pursuing a promising lead.
In the U.S., each gallon of crude oil we produce requires, on average, anywhere from two to 5.5 gallons of water according to a study from Argonne National Library (pdf). It is a much more water-intensive process than hydraulic fracturing, or fracking, which attracts far more attention.
“If you’re going to push something down under the ground it’s better that it be CO2 than water,” Beckman says. “Water is too valuable to be stuffing underground.”
Water is too valuable to be stuffing underground
So finding a way to use CO2 could have an enormous benefit. But many other researchers—and oil companies—left that trail for dead long ago.
Toward a gooier CO2
In its most common form, liquid CO2 can weaken oil’s hold on a rock, but it’s not powerful enough to push it out. So instead, oil companies alternate injections of liquid CO2 to loosen the oil with injections of water—millions of gallons of water—to extract it. That water comes back to the surface contaminated and needs to be treated. Gooier liquid CO2 would solve two problems, reducing or eliminating the need for water and staying put underground when it displaces the oil it pushes out.
But liquid CO2 has been notoriously hard to thicken. “The biggest challenge is that liquid CO2 is a terrible solvent and very, very few things dissolve in liquid CO2,” says Beckman. “In the past people figured ‘If I want to make CO2 gooier, I’ll try strategies that work for conventional liquids.’ Like if I want to make acetone gooier, there are things you can do. One strategy is to dissolve polymers in these conventional liquids. But high molecular weight polymers will not dissolve in any quantity in CO2.”
So they are working with little molecules—attempting to design a compound that will dissolve in CO2 and associate enough in solution that it will, as Beckman says, “fake the system out.” He explains: “We want to make the system believe that there’s high molecular weight material in solution when there really isn’t. It’s a strategy developed over long experiences.”
Future CO2 Solutions
While carbon capture at power plants is nearly nonexistent in the U.S. – aside from one gasification plant in North Dakota called the Great Plains Synfuels Plant owned by the Dakota Gasification Company – injecting captured CO2 back into the earth to better extract oil, or natural gas, could provide a means of CO2 sequestration.
Currently, the CO2 being used for petroleum extraction comes from underground reservoirs. But, says Beckman, “you could capture it from a power plant and use that as well, it’s the same stuff.” The captured CO2 from the Great Plains plant is piped to Canada for injection into oil fields.
“If we can elevate the viscosity of CO2, the first application would be oil production, but it could be used to displace the water for fracturing used in natural gas production as well,” Beckman says. And unlike water which dissolves salt, minerals, bitumen and other materials in large quantities, CO2, as Beckman and Enick know well, doesn’t dissolve anything very well.
Top image: Taladro-H104-OilDriller courtesy/Nestor Galina