Duke University’s Nicholas School of the Environment recently announced the results of a study analyzing the flowback and produced waters from hydraulically fractured unconventional oil and gas wells. The study, titled “Quantity of flowback and produced waters from unconventional oil and gas exploration,” was published in the peer-reviewed journal Science of The Total Environment and is available here. Significantly, the study found that the vast majority — over 92% — of the flowback and produced water (“wastewater”) is derived from naturally occurring brines that are extracted along with the gas and oil. Fracking fluids on the other hand, which are injected into wells at the start of production, only account for 4 to 8% of the wastewater generated.
Avner Vengosh, professor of geochemistry and water quality at Duke and a study co-author, explained the importance of these findings: “Much of the public fear about fracking has centered on the chemical-laden fracking fluids . . . and the potential harm they could cause if they spill or are disposed of improperly into the environment. Our new analysis, however, shows that . . . [m]ost of the fracking fluids injected into these wells do not return to the surface; they are retained in the shale deep underground. This means that the probability of having environmental impacts from the man-made chemicals in fracking fluids is low, unless a direct spill of the chemicals occurs before the actual fracking.”
The study team used statistical techniques to quantify the volume of wastewater generated from unconventional oil and gas wells in six areas of the country: the Bakken formation in North Dakota; the Marcellus formation in Pennsylvania; the Barnett and Eagle Ford formations in Texas; the Haynesville formation in Arkansas, Louisiana and East Texas; and the Niobrara field in Colorado and Wyoming.
While the study showed only low amounts of fracking fluid in the returned wastewater, the authors point out that brines may carry their own risks, including that they contain varying levels of salts, heavy metals and naturally occurring radioactive elements. Some of this wastewater could be treated, however, particularly in the West where the brines are much less saline than those in the East. For example, following treatment, the brines could be used for agricultural irrigation in drought-prone areas.
The study further determined that the median volume of wastewater produced by an unconventional oil or gas well ranges from 1.7 to 14.3 million liters per year over the first 5 to 10 years of production. The volume of produced water coming from these wells declines over time, while its salinity increases. Specifically, the salt levels rise much faster than the volume declines, resulting in a high volume of saline wastewater during the first 6 months of production. The volume of wastewater then typically drops, along with its hydrocarbon output.
Here at Weil’s Product Liability Monitor, we will continue to keep a close eye on fracking-related developments and report on them.