Greening Up Fracking

Although hydraulic fracturing, or fracking, has been a boon to the energy industry, the technique, which extracts oil and natural gas from underground deposits by breaking up rock with millions of gallons of pressurized fluid, has been under fire because of its heavy environmental impact. To address the concerns, scientists have been developing more eco-friendly fracking fluids.

One such fluid, which transforms into an expandable hydrogel when it interacts with carbon dioxide, was created this year by a team led by Carlos A. Fernandez of Pacific Northwest National Laboratory. The group found that the expansion process produces enough force to fracture rock, suggesting that the hydrogel could reduce the amount of water and chemical additives required for fracking.

The new switchable fluid builds on a range of green chemical systems developed over the past decade in which CO toggles the properties of solvents, surfactants, or catalysts back and forth to facilitate reactions and separations. Using the hydrogel would involve pumping an aqueous solution of polyallylamine into a fracking well followed by CO₂. When CO₂ interacts with the polymer’s amine groups and water to form the hydrogel, the material expands to more than twice its volume, creating pressure for fracturing hydrocarbon-laden rock deep underground.

The researchers showed that the hydrogel can bust open rock samples in the lab. Releasing the CO₂ pressure or adding a weak acid breaks the hydrogel (Green Chem. 2015, DOI: 10.1039/c4gc01917b). Besides reducing the amount of the water needed, the reusable hydrogel has low toxicity and the amine groups function as a built-in biocide and corrosion inhibitor, which would reduce the number of fluid additives needed.