Researchers have created a hydraulic fluid that transforms into an expandable hydrogel on interacting with carbon dioxide. The expansion process produces enough force to fracture rock. The hydrogel could reduce the amount of water and chemical additives required for hydraulic fracturing used to generate underground reservoirs for geothermal energy production or for oil and natural gas extraction.
The research paper reporting the promising technology, published in the journal Green Chemistry, has created a stir among scientists about whether fracking for oil and gas ought to ever be considered green.
A team led by Carlos A. Fernandez of Pacific Northwest National Laboratory developed the process, which would involve pumping an aqueous solution of polyallylamine into the ground followed by CO2. The CO2 interacts with the polymer’s amine groups and water to form a hydrogel that expands to more than twice its volume, creating pressure for fracking. The researchers showed that this expansion could break rock samples in the lab. Releasing the CO2 pressure or adding a weak acid breaks the hydrogel (Green Chem. 2015, DOI: 10.1039/c4gc01917b).
This switchable fluid builds on a range of green chemical systems developed over the past decade in which CO2 toggles the properties of solvents, surfactants, or catalysts back and forth to facilitate reactions and separations. The new fluid would use only a fraction of the water typically required for fracking, Fernandez and coworkers say, and it can be recovered and reused. In addition, the polymer has low toxicity and the amine groups function as a built-in biocide and corrosion inhibitor, which would reduce the number of additives normally included in fracking fluids.
“This paper is particularly strong in that the researchers evaluated the performance in rock at realistic conditions,” says Philip G. Jessop of Queen’s University, in Kingston, Ontario, whose group has helped lead development of the switchable chemistry concept.
“Fracking is understandably not well loved in the green chemistry community, and whether green chemistry can or should be brought to bear to decrease fracking’s impact is highly controversial,” Jessop adds. “The researchers give reasonable arguments for why their fluid would be green, but that point won’t be decided definitively until a cradle-to-grave life-cycle analysis is used to fully compare the environmental impacts with conventional fluids.”
Green Chemistry’s editorial board chair, Walter Leitner of RWTH Aachen University, in Germany, wrote an editorial to explain the editors’ dilemma on whether to publish the paper. “One may raise the fundamental question of whether an increased exploitation of fossil resources is inherently incompatible with the Principles of Green Chemistry,” Leitner writes.
The editors decided to give the paper the benefit of the doubt and forged ahead. The reviewers agreed that the authors’ work is sound and that the data presented might help lower the environmental impact of the fracking industry, Leitner explains.
“We need to continue our efforts to contribute with fundamentally new approaches to a sustainable chemical industry,” Leitner continues. “However, we also recognize that things are not always black or white and there are more than 50 shades of green.”