Advanced membranes, unusual solvents and new drilling processes could clean up and recycle a growing flood of contaminated water
?| May 25, 2012?|
FRACKED WATER: Hydraulic fracturing requires millions of liters of water, and some way of coping with the dirty water that results.
Image: ? David Biello
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The nation's oil and gas wells produce at least nine billion liters of contaminated water per day, according to an Argonne National Laboratory report. And that is an underestimate of the amount of brine, fracking fluid and other contaminated water that flows back up a well along with the natural gas or oil, because it is based on incomplete data from state governments gathered in 2007.
The volume will only get larger, too: oil and gas producers use at least 7.5 million liters of water per well to fracture subterranean formations and release entrapped hydrocarbon fuels, a practice that has grown in the U.S. by at least 48 percent per year in the last five years, according to the Energy Information Administration. The rise is quickest in places such as the oil-bearing Bakken Formation in North Dakota or the natural gas-rich Marcellus Shale underlying parts of New York State, Pennsylvania, Ohio and West Virginia.
The problem is that the large volumes of water that flow back to the surface along with the oil or gas are laced with everything from naturally radioactive minerals to proprietary chemicals. And there are not a lot of cost-effective options for treating it, other than dumping it down a deep well. But as certain states that are experiencing drought begin to restrict industrial water usage, fossil-fuel companies are experimenting with traditional and untraditional water treatment chemistries and technologies to try to clean this dirty water?or limit its use in the first place.
Recycling is not enough
The first option is to reuse wastewater in whatever ways possible. For fracking, "to the extent possible, fracturing fluid is recovered and recycled for reuse in future fracturing operations," says Reid Porter, a spokesman for the American Petroleum Institute, an industry group. "Recycling of flow-back water reduces demand for freshwater and reduces the need for disposal of wastewater."
But that water still has to be cleaned before it is reused, otherwise it loses the ability to do its subterranean dirty work. Simply dumping it improperly is not an option, because the high levels of salts and minerals will poison a river, stream or aquifer or it will render land incapable of supporting life for generations, like the salt pans of Utah or the ancient farm fields of Carthage salted by the Roman army. The cleansing technologies employed range from high-tech membranes that selectively filter out specific contaminants to the crude solution of boiling away the water, leaving scales of salts and other minerals behind on the walls of the boiler.
"Most of what we get out of the water are salts and a low-level of organics" (hydrocarbons and other contaminating carbon-based molecules), explains environmental engineer Steve Hopper, executive vice president of the industrial business group at Veolia Water, which is helping oil and gas companies cope with such "produced" water. "We have an example in California where we treated the water until it was so pure we had to add minerals back into it to be able to discharge it." The problem, thus far, has been cost, although Hopper argues Veolia's technologies add only "5 percent" to the cost of a given well.
A diversity of waters
To add to the challenge of sheer volume, the water produced by each oil and gas well is often different?with varying levels of acidity, saltiness or types of contaminants, whether dissolved hydrocarbons or heavy metals leached from the surrounding rock.
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