Contaminated water in 2 states linked to faulty shale gas wells

Faulty well integrity, not hydraulic fracturing deep underground, is the primary cause of drinking water contamination from shale gas extraction in parts of Pennsylvania and Texas, according to a new study by researchers from five universities.

The scientists from Duke, Ohio State, Stanford, Dartmouth and the University of Rochester
published their peer-reviewed study Sept. 15 in the Proceedings of the National Academy of Sciences. Using noble gas and hydrocarbon tracers, they analyzed the gas content of more than 130 drinking water wells in the two states.

“We found eight clusters of wells — seven in Pennsylvania and one in Texas — with contamination, including increased levels of natural gas from the Marcellus shale in Pennsylvania and from shallower, intermediate layers in both states,” said Thomas H. Darrah, assistant professor of earth science at Ohio State, who led the study while he was a research scientist at Duke.

“Our data clearly show that the contamination in these clusters stems from well-integrity problems such as poor casing and cementing,” Darrah said.

“These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared,” said Avner Vengosh, professor of geochemistry and water quality at Duke.

In four of the affected clusters, the team’s noble gas analysis shows that methane from drill sites escaped into drinking water wells from shallower depths through faulty or insufficient rings of cement surrounding a gas well’s shaft. In three clusters, the tests suggest the methane leaked through faulty well casings. In one cluster, it was linked to an underground well failure.

“People’s water has been harmed by drilling,” said Robert B. Jackson, professor of environmental and earth sciences at Stanford and Duke. “In Texas, we even saw two homes go from clean to contaminated after our sampling began.”

“The good news is that most of the issues we have identified can potentially be avoided by future improvements in well integrity,” Darrah stressed.

Using both noble gas and hydrocarbon tracers — a novel combination that enabled the researchers to identify and distinguish between the signatures of naturally occurring methane and stray gas contamination from shale gas drill sites — the team analyzed gas content in 113 drinking-water wells and one natural methane seep overlying the Marcellus shale in Pennsylvania, and in 20 wells overlying the Barnett shale in Texas. Sampling was conducted in 2012 and 2013. Sampling sites included wells where contamination had been debated previously; wells known to have naturally high level of methane and salts, which tend to co-occur in areas overlying shale gas deposits; and wells located both within and beyond a one-kilometer distance from drill sites.

Noble gases such as helium, neon or argon are useful for tracing fugitive methane because although they mix with natural gas and can be transported with it, they are inert and are not altered by microbial activity or oxidation. By measuring changes in ratios in these tag-along noble gases, researchers can determine the source of fugitive methane and the mechanism by which it was transported into drinking water aquifers — whether it migrated there as a free gas or was dissolved in water.

“This is the first study to provide a comprehensive analysis of noble gases and their isotopes in groundwater near shale gas wells,” said Darrah, who is continuing the analysis in his lab at Ohio State. “Using these tracers, combined with the isotopic and chemical fingerprints of hydrocarbons in the water and its salt content, we can pinpoint the sources and pathways of methane contamination, and determine if it is natural or not.”

Gas leaks from faulty wells linked to contamination in some groundwater

A study has pinpointed the likely source of most natural gas contamination in drinking-water wells associated with hydraulic fracturing, and it’s not the source many people may have feared.

What’s more, the problem may be fixable: improved construction standards for cement well linings and casings at hydraulic fracturing sites.

A team led by a researcher at The Ohio State University and composed of researchers at Duke, Stanford, Dartmouth, and the University of Rochester devised a new method of geochemical forensics to trace how methane migrates under the earth. The study identified eight clusters of contaminated drinking-water wells in Pennsylvania and Texas.

Most important among their findings, published this week in the Proceedings of the National Academy of Sciences, is that neither horizontal drilling nor hydraulic fracturing of shale deposits seems to have caused any of the natural gas contamination.

“There is no question that in many instances elevated levels of natural gas are naturally occurring, but in a subset of cases, there is also clear evidence that there were human causes for the contamination,” said study leader Thomas Darrah, assistant professor of earth sciences at Ohio State. “However our data suggests that where contamination occurs, it was caused by poor casing and cementing in the wells,” Darrah said.

In hydraulic fracturing, water is pumped underground to break up shale at a depth far below the water table, he explained. The long vertical pipes that carry the resulting gas upward are encircled in cement to keep the natural gas from leaking out along the well. The study suggests that natural gas that has leaked into aquifers is the result of failures in the cement used in the well.

“Many of the leaks probably occur when natural gas travels up the outside of the borehole, potentially even thousands of feet, and is released directly into drinking-water aquifers” said Robert Poreda, professor of geochemistry at the University of Rochester.

“These results appear to rule out the migration of methane up into drinking water aquifers from depth because of horizontal drilling or hydraulic fracturing, as some people feared,” said Avner Vengosh, professor of geochemistry and water quality at Duke.

“This is relatively good news because it means that most of the issues we have identified can potentially be avoided by future improvements in well integrity,” Darrah said.

“In some cases homeowner’s water has been harmed by drilling,” said Robert B. Jackson, professor of environmental and earth sciences at Stanford and Duke. “In Texas, we even saw two homes go from clean to contaminated after our sampling began.”

The method that the researchers used to track the source of methane contamination relies on the basic physics of the noble gases (which happen to leak out along with the methane). Noble gases such as helium and neon are so called because they don’t react much with other chemicals, although they mix with natural gas and can be transported with it.

That means that when they are released underground, they can flow long distances without getting waylaid by microbial activity or chemical reactions along the way. The only important variable is the atomic mass, which determines how the ratios of noble gases change as they tag along with migrating natural gas. These properties allow the researchers to determine the source of fugitive methane and the mechanism by which it was transported into drinking water aquifers.

The researchers were able to distinguish between the signatures of naturally occurring methane and stray gas contamination from shale gas drill sites overlying the Marcellus shale in Pennsylvania and the Barnett shale in Texas.

The researchers sampled water from the sites in 2012 and 2013. Sampling sites included wells where contamination had been debated previously; wells known to have naturally high level of methane and salts, which tend to co-occur in areas overlying shale gas deposits; and wells located both within and beyond a one-kilometer distance from drill sites.

As hydraulic fracturing starts to develop around the globe, including countries South Africa, Argentina, China, Poland, Scotland, and Ireland, Darrah and his colleagues are continuing their work in the United States and internationally. And, since the method that the researchers employed relies on the basic physics of the noble gases, it can be employed anywhere. Their hope is that their findings can help highlight the necessity to improve well integrity.

Natural gas saves water, even when factoring in water lost to hydraulic fracturing

For every gallon of water used to produce natural gas through hydraulic fracturing, Texas saved 33 gallons of water by generating electricity with that natural gas instead of coal (in 2011). -  University of Texas at Austin
For every gallon of water used to produce natural gas through hydraulic fracturing, Texas saved 33 gallons of water by generating electricity with that natural gas instead of coal (in 2011). – University of Texas at Austin

A new study finds that in Texas, the U.S. state that annually generates the most electricity, the transition from coal to natural gas for electricity generation is saving water and making the state less vulnerable to drought.

Even though exploration for natural gas through hydraulic fracturing requires significant water consumption in Texas, the new consumption is easily offset by the overall water efficiencies of shifting electricity generation from coal to natural gas. The researchers estimate that water saved by shifting a power plant from coal to natural gas is 25 to 50 times as great as the amount of water used in hydraulic fracturing to extract the natural gas. Natural gas also enhances drought resilience by providing so-called peaking plants to complement increasing wind generation, which doesn’t consume water.

The results of The University of Texas at Austin study are published this week in the journal Environmental Research Letters.

The researchers estimate that in 2011 alone, Texas would have consumed an additional 32 billion gallons of water – enough to supply 870,000 average residents – if all its natural gas-fired power plants were instead coal-fired plants, even after factoring in the additional consumption of water for hydraulic fracturing to extract the natural gas.

Hydraulic fracturing is a process in which water, sand and chemicals are pumped at high pressure into a well to fracture surrounding rocks and allow oil or gas to more easily flow. Hydraulic fracturing and horizontal drilling are the main drivers behind the current boom in U.S. natural gas production.

Environmentalists and others have raised concerns about the amount of water that is consumed. In Texas, concerns are heightened because the use of hydraulic fracturing is expanding rapidly while water supplies are dwindling as the third year of a devastating drought grinds on. Because most electric power plants rely on water for cooling, the electric power supply might be particularly vulnerable to drought.

“The bottom line is that hydraulic fracturing, by boosting natural gas production and moving the state from water-intensive coal technologies, makes our electric power system more drought resilient,” says Bridget Scanlon, senior research scientist at the university’s Bureau of Economic Geology, who led the study.

To study the drought resilience of Texas power plants, Scanlon and her colleagues collected water use data for all 423 of the state’s power plants from the Energy Information Administration and from state agencies including the Texas Commission on Environmental Quality and the Texas Water Development Board, as well as other data.

Since the 1990s, the primary type of power plant built in Texas has been the natural gas combined cycle (NGCC) plant with cooling towers, which uses fuel and cooling water more efficiently than older steam turbine technologies. About a third of Texas power plants are NGCC. NGCC plants consume about a third as much water as coal steam turbine (CST) plants.

The other major type of natural gas plant in the state is a natural gas combustion turbine (NGCT) plant. NGCT plants can also help reduce the state’s water consumption for electricity generation by providing “peaking power” to support expansion of wind energy. Wind turbines don’t require water for cooling; yet wind doesn’t always blow when you need electricity. NGCT generators can be brought online in a matter of seconds to smooth out swings in electricity demand. By combining NGCT generation with wind generation, total water use can be lowered even further compared with coal-fired power generation.

The study focused exclusively on Texas, but the authors believe the results should be applicable to other regions of the U.S., where water consumption rates for the key technologies evaluated – hydraulic fracturing, NGCC plants with cooling towers and traditional coal steam turbine plants – are generally the same.

The Electric Reliability Council of Texas, manager of the state’s electricity grid, projects that if current market conditions continue through 2029, 65 percent of new power generation in the state will come from NGCC plants and 35 percent from natural gas combustion turbine plants, which use no water for cooling, but are less energy efficient than NGCC plants.

“Statewide, we’re on track to continue reducing our water intensity of electricity generation,” says Scanlon.

Hydraulic fracturing accounts for less than 1 percent of the water consumed in Texas. But in some areas where its use is heavily concentrated, it strains local water supplies, as documented in a 2011 study by Jean-Philippe Nicot of the Bureau of Economic Geology. Because natural gas is often used far from where it is originally produced, water savings from shifting to natural gas for electricity generation might not benefit the areas that use more water for hydraulic fracturing.

Study offers 7 safeguards for hydraulic fracturing

A new report by Duke University researchers offers several health and environmental measures for North Carolina lawmakers to consider as they debate legalizing horizontal drilling and hydraulic fracturing for natural gas.

The study, which has been accepted for publication in the Duke Environmental Law and Policy Forum journal, looks at potential environmental hazards and how lawmakers in other states are factoring health and environmental risks into regulatory approaches targeting the natural gas extraction method.

“If North Carolina legalizes shale gas extraction, we need to consider what’s worked best in other states and avoid what hasn’t,” said Rob Jackson, Nicholas professor of global environmental change at the Nicholas School of the Environment. “That’s the only way to get it right.”

Legislation passed earlier this year has moved North Carolina closer to producing shale gas, and is directing the Department of Environment and Natural Resources to complete a study on the effects of hydraulic fracturing, often called “fracking,” by May, 2012.

The authors of Duke’s own study say if North Carolina legislators allow natural gas production through hydraulic fracturing, they should consider seven measures to help avoid and mitigate any possible negative effects. These include:

  • Securing baseline data on groundwater prior to shale gas production and at each stage of the drilling process
  • Funding for regulatory programs and an agency to carry them out
  • Planning for withdrawals from area water supplies related to the production
  • Minimizing the risks of spills and contamination caused by equipment failure and human error by implementing safety requirements
  • Thinking through options for the disposal and treatment of wastewater resulting from the hydraulic fracturing process
  • Assessing the impacts on air quality and assuring attainment of federal ground-level ozone standards
  • Requiring some degree of disclosure regarding the chemicals used in fracturing fluid

“Lawmakers have the unique opportunity to decide whether or not hydraulic fracturing is appropriate for the state,” said Jonas Monast, director of the climate and energy program for the Nicholas Institute for Environmental Policy Solutions. “Before making a decision, we need to understand the full range of potential economic, environmental and health impacts.

Unconventional natural gas reservoir poised to dramatically increase U.S. production





PSU geoscientist Terry Engelder shows natural fractures in a piece of shale. - Photo By: Greg Grieco, Penn State Public Information
PSU geoscientist Terry Engelder shows natural fractures in a piece of shale. – Photo By: Greg Grieco, Penn State Public Information

Natural gas distributed throughout the Marcellus black shale in northern Appalachia could conservatively boost proven U.S. reserves by trillions of cubic feet if gas production companies employ horizontal drilling techniques, according to a Penn State and State University of New York, Fredonia, team.



“The value of this science could increment the net worth of U.S. energy resources by a trillion dollars, plus or minus billions,” says Terry Engelder, professor of geosciences, at Penn State.



The Marcellus shale runs from the southern tier of New York, through the western portion of Pennsylvania into the eastern half of Ohio and through West Virginia. In Pennsylvania, the formation extends from the Appalachian plateau into the western valley and ridge. This area has produced natural gas for years, but the Marcellus shale, a deep layer of rock, is officially identified as holding a relatively small amount of proven or potential reserves. However, many gas production companies are now interested in the Marcellus.



Engelder, working with Gary Lash, professor of geoscience, SUNY Fredonia, has conservatively estimated that the Marcellus shale contains 168 trillion cubic feet of natural gas in place and optimistically suggests that the amounts could be as high as 516 trillion cubic feet.



“Conservatively, we generally only consider 10 percent of gas in place as a potential resource,” says Engelder. “The key, of course, is that the Marcellus is more easily produced by horizontal drilling across fractures, and until recently, gas production companies seemed unaware of the presence of the natural fractures necessary for magnifying the success of horizontal drilling in the Marcellus.”



The U.S. currently produces roughly 30 trillion cubic feet of gas a year, and these numbers are dropping. According to Engelder, the technology exists to recover 50 trillion cubic feet of gas from the Marcellus, thus keeping the U.S. production up. If this recovery is realized, the Marcellus reservoir would be considered a Super Giant gas field.



Engelder, who has studied this area of the U.S. for most of his career and began looking into fractures under a National Science Foundation grant 25 years ago, has identified and mapped natural fractures in the Marcellus shale. He and Lash will present some of their recent work at the 2008 American Association of Petroleum Geologists Annual Convention and Exhibition this spring.



The researchers look at the patterns of fractures in the shale and determine which are important for gas production. Fractures that correlate with the folding of the ridge and valley system are less common in black shale. However, because of their orientation, the fractures that formed prior to the folding will release gas if the wells cross the fracture zones.


These fractures, referred to as J1 fractures by Engelder and Lash, run as slices from the northeast to the southwest in the Marcellus shale and are fairly close together. While a vertical well may cross one of these fractures and other less productive fractures, a horizontally drilled well aimed to the north northwest will cross a series of very productive J1 fractures.



“It takes $800,000 to drill a vertical well in the Marcellus, but it takes $3 million to drill a horizontal well,” says Engelder.



Companies that drill gas wells need to be certain that horizontal drilling will produce the gas they expect and the work by Engelder and Lash suggests that it will.



“We know that the Marcellus shale appears as an outcrop near Batavia, N.Y., east of Buffalo,” says Engelder. “And we can see the fractures in the Marcellus in the exposed sections of the ridge and valley areas to the southeast. Because we see them going through the folded areas, we know they were there before the folding. If it happened earlier, then we know they have to be in the intervening basin as well.”



The natural fractures in the Marcellus shale are the key to recovering large amounts of gas. As heavily organic sediments were laid down 365 million years ago, the black shale of the Marcellus formed. As the organic material decayed and degraded, methane and other components of natural gas formed and dispersed through the pores in the rock. About 300 million years ago, the pressure of the gas caused fractures to form in the shale. It was not until 280 million years ago that the eastern portion of Pennsylvania was pushed into the folding of the ridge and valley province that makes up that area. Gas that occurs in pockets underground is considered a conventional reservoir; gas that is distributed throughout the rock, like the Marcellus, is called an unconventional reservoir.



The Penn State-Fredonia approach is not restricted to production of the Marcellus shale, but can be applied to any gas-bearing shale with this type of fracture. Because the approach begins with a vertical well and then drills horizontally in the direction that will crosscut the productive fractures, old vertical wells can be reused.



“We can go back to wells that are already drilled and played out, and then drill horizontal from there,” says Engelder. “Reusing old wells has both economic and environmental value.”



Engelder and Lash are principals in Appalachian Fracture Systems Inc., a consulting firm.