Study improves our understanding of the lifecycle of hydraulic fracturing fluids

The study, conducted through CSIRO’s Gas Industry Social and Environmental Research Alliance (GISERA), sought to address community concerns about the potential impacts of hydraulic fracturing on groundwater in the Beetaloo Sub-basin, Northern Territory. Researchers investigated selected chemical compounds used in hydraulic fracturing fluids, in addition to geogenic compounds (those originating from earth’s geological processes) that are found in flowback water and industry facilities.

The process of hydraulic fracturing requires the injection of fracturing fluids into a gas well. The fluids are usually a combination of locally sourced water, chemical additives (less than 1%) with proppant (often sand) being added as required to maintain open fractures.

Researchers focused on four chemical compounds, either with known high toxicity or that had knowledge gaps about their behaviour in the environment. The researchers conducted experiments using samples taken from gas industry sites to learn more about how these chemical compounds move and degrade in subsurface environments. Additionally, they examined how those chemical and geogenic compounds behave if they return to the surface in flowback water.

The chemical compounds selected were two biocides: glutaraldehyde and tributyl tetradecyl phosphonium chloride (TTPC), and two surfactants: ethyoxylated/propoxlated alcohols (AEP) and cocoalkyl dimethyl amine oxide (CDAO).

Results demonstrated that three of the four chemical compounds examined (glutaraldehyde, AEP and CDAO) either degraded abiotically in the subsurface, adsorbed to the formation in the subsurface or are rapidly biodegraded at the surface in water holding tanks. These results indicated that glutaraldehyde, AEP and CDAO likely pose little to no risk when used as intended and pose limited risk to the broader environment.

TTPC resisted degradation in the subsurface but was found to be highly immobile as it tended to readily adsorb to formation rocks. Similarly, on its return to the surface in flowback waters, TTPC was comparatively resistant to biological decomposition and was still detected in water samples from holding ponds, at reduced concentrations, after three months.

In controlled laboratory experiments, CSIRO researchers added 13 parts per million (ppm) of TTPC to water sourced from a surface‑facility water tank. After three months of incubation, TTPC concentration in the sample was 0.13 ppm, representing degradation of 99% of the added TTPC.

Even though the residual TTPC represents 1% of the original dose, its persistence after three months suggests that further studies into its behaviour in the subsurface and in surface facilities may be required if it is intended for wider use in the Beetaloo Sub-basin.

The study also demonstrated that the majority of organic geogenic compounds returned in flowback water were rapidly degraded, although this depends on the individual compounds, and some may be more resistant to decomposition than others.

This research has increased our understanding of the lifecycle of chemical compounds used in hydraulic fracturing fluids, and the project results provide key information to help assess chemical risks associated with hydraulic fracturing in the region.

More information about this project is available on the GISERA website.

To learn more about our work in surface and groundwater research and projects undertaken in the Northern Territory, visit our website.