In 2007, when the shale revolution was still in its infant stages, the U.S. oil and gas industry was already producing more than 20 billion barrels of waste water per year, according to researchers at the Argonne National Laboratory (“Produced water volumes and management practices in the United States”, 2009).

The industry’s daily output was 5 million barrels of oil, 67 billion cubic feet of natural gas, and 55 million barrels of water, according to federal government statistics.

Argonne estimated that more than 7.5 barrels of water were produced for every barrel of crude, and 260 barrels of water for every million cubic feet of natural gas, based on state and federal records for onshore oil and gas production.

If offshore production is included, the figures drop slightly to 5.3 barrels for every barrel of crude and 182 barrels for every million cubic feet of natural gas.

But all these numbers are likely to understate the water-to-oil and water-to-gas ratios, since some of the most important states, including Texas, did not report their production statistics in sufficient detail to compute ratios accurately.

Older wells produce a higher proportion of water, so states with a long history of oil and gas production and large numbers of aging stripper wells tend to have the highest volumes of water production and the highest water-to-oil and water-to-gas ratios.

The five old oil- and gas-producing states of Texas (7.4 billion barrels of water), California (2.6 billion), Oklahoma (2.2 billion), Kansas (1.2 billion) and Louisiana (1.1 billion) accounted for almost three quarters of water production in 2007.

California oil wells produced more than 10 barrels of water for every barrel of oil, rising to 22 barrels in Kansas and 43 barrels in Illinois. In contrast, North Dakota reported just 134 million barrels of produced water in 2007, an average of three barrels of water for every one of oil.

Unfortunately, there are no more-recent comprehensive nationwide estimates. But the amount of produced water being handled is now much higher thanks to the shale revolution.

In Pennsylvania, for example, gas production rose from 0.20 trillion cubic feet in 2006 to 2.26 trillion in 2012, and the amount of produced water quadrupled from 6.6 million barrels to 24.4 million, according to the Pennsylvania Department of Environmental Protection.

Across the United States, water production is now probably between 60 million and 70 million barrels every day, based on the rise in oil and gas output.

Yet the issue of produced water commands hardly any attention compared with the enormous media interest shown in the much smaller volumes of water employed in fracking operations.

RE-USE AND DISPOSAL

Much of the water produced from offshore wells, which accounted for around 590 million barrels in 2007, just 3 percent of the total, is treated and discharged at sea, subject to strict controls enforced by the U.S. Environmental Protection Agency.

From onshore oil and gas wells, small quantities of waste water are cleaned up and put to beneficial uses irrigating crops, watering livestock, de-icing roads, and in aquaculture, power plants, dust suppression and fire prevention.

But the vast majority of water from onshore oil and gas wells, accounting for more than 92 percent of all produced water, is re-injected underground to maintain pressure in the reservoir (71 percent) or into non-producing formations for disposal (21 percent).

Produced water is the technical term used by engineers and regulators to describe all the water brought to the surface from a hydrocarbon well.

Some is flowback water, which was originally injected during the fracking phase and then returns to the surface in the first few days and weeks of the well’s production.

But most is formation water, which is naturally present along with oil and gas in petroleum-bearing rock formations and comes to the surface with the oil and gas.

Because the flowback and formation water has been in contact with the hydrocarbon-bearing formations, it picks up some of the chemical characteristics of the formations and the hydrocarbons, as Argonne explains.

SAFETY ISSUES

Flowback water contains traces of the chemicals injected into the well along with the water and proppant during fracking operations.

The chemical additives include anti-microbials, anti-coagulants, corrosion and scale inhibitors, emulsion breakers and solvents.

The chemicals have become a prominent target for anti-fracking campaigners, who fear they could contaminate underground drinking water supplies or surface water when they return to the surface.

In practice, these additives comprise less than 0.5 percent of the volume of liquid injected into a typical well.

Most are chemically identical to those found in common household cleaning products, cosmetics, antifreeze and food, according to North Dakota’s Department of Mineral Resources, which regulates the state’s oil and gas industry (“North Dakota Rural Water”, July 2012).

By contrast, the much larger quantity of produced formation water has received much less attention, probably because the industry has been managing it without major controversy for decades.

Formation water contains large amounts of dissolved grease and other organic compounds, as well as salts and radioactive substances found in the Earth’s crust.

Most produced waters are more saline than seawater, which limits their use in agriculture or power plants, where corrosion is an important consideration.

Some of the trace elements are commercially useful. Iodide recovered from produced water in Oklahoma is the largest source of iodine in the United States, according to USGS.

Other elements are more potentially problematic, however. In some parts of the United States, including Pennsylvania, produced water contains high concentrations of radionuclides such as radium and strontium formed by the decay of uranium and thorium naturally occurring underground.

That hasn’t stopped states in the Northeast and Midwest, including New York, Pennsylvania, Ohio and Michigan, from spreading produced water on the roads to suppress dust in summer and de-ice them in winter, according to the U.S. Geological Survey (“USGS investigations of water produced during hydrocarbon reservoir development”, November 2014).

RISK EVALUATION

By and large, the petroleum industry has dealt with the problem of produced water safely. High-risk practices that were once common, such as giant surface evaporation ponds, have mostly been banned.

There is a huge disparity between the media attention given to the environmental and safety issues linked to water used in fracking, the volumes injected underground, and the chemical additives used, and the much larger volumes of formation water handled by the industry every day.

On average, it takes 2 million to 4 million gallons of water to fracture a new oil well in North Dakota, according to the state regulator, which is between 50,000 and 100,000 barrels. But the United States was handling 55 million barrels of produced water every day in 2007, the latest available data for the country as a whole.

In a classic case of not putting the risks from industrial processes into proper perspective, campaigners have focused on the threat of contamination and earthquakes from the relatively small amounts of water being employed in pressure pumping operations while ignoring the much larger volume of produced water being handled, mostly safely, by the rest of the industry.

(Editing by Dale Hudson)