Stray gases found in water wells near shale gas sites

Homeowners living within one kilometer of shale gas wells appear to be at higher risk of having their drinking water contaminated by stray gases, according to a new Duke University-led study.

Duke scientists analyzed 141 drinking water samples from private water wells across northeastern Pennsylvania’s gas-rich Marcellus shale basin. Their study documented not only higher methane concentrations in drinking water within a kilometer of shale gas drilling — which past studies have shown — but higher ethane and propane concentrations as well.

Methane concentrations were six times higher and ethane concentrations were 23 times higher at homes within a kilometer of a shale gas well. Propane was detected in 10 samples, all of them from homes within a kilometer of drilling.

“The methane, ethane and propane data, and new evidence from hydrocarbon and helium isotopes, all suggest that drilling has affected some homeowners’ water,” said Robert B. Jackson, a professor of environmental sciences at Duke’s Nicholas School of the Environment. “In a minority of cases, the gas even looks Marcellus-like, probably caused by faulty well construction.”

The ethane and propane contamination data are “new and hard to refute,” Jackson stressed. “There is no biological source of ethane and propane in the region and Marcellus gas is high in both, and higher in concentration than the Upper Devonian gas found in-between.”

The team examined which factors might explain their results, including topography, distance to gas wells and distance to geologic features. “Distance to gas wells was, by far, the most significant factor influencing gases in the drinking water we sampled,” said Jackson.

The peer-reviewed findings will appear this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

Hydraulic fracturing, also called hydrofracking or fracking, involves pumping water, sand and chemicals deep underground into horizontal gas wells at high pressure to crack open hydrocarbon-rich shale and extract natural gas. Accelerated shale gas drilling and hydrofracking in recent years has fueled concerns about contamination in nearby drinking water supplies.

Two previous peer-reviewed studies by Duke scientists found direct evidence of methane contamination in water wells near shale-gas drilling sites in northeastern Pennsylvania, as well as possible connectivity between deep brines and shallow aquifers. A third study conducted with U.S. Geological Survey scientists found no evidence of drinking water contamination from shale gas production in Arkansas. None of the studies have found evidence of contamination by fracking fluids.

“Our studies demonstrate that distances from drilling sites, as well as variations in local and regional geology, play major roles in determining the possible risk of groundwater impacts from shale gas development,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School. “As such, they must be taken into consideration before drilling begins.”

“The helium data in this study are the first from a new tool kit we’ve devised for identifying contamination using noble gas isotopes,” said Duke research scientist Thomas H. Darrah. “These tools allow us to identify and trace contaminants with a high degree of certainty.”

Fracking requires a minimum distance of at least 0.6 kilometers from sensitive rock strata

This is Professor Richard Davies. -  Durham University
This is Professor Richard Davies. – Durham University

The chances of rogue fractures due to shale gas fracking operations extending beyond 0.6 kilometers from the injection source is a fraction of one percent, according to new research led by Durham University.

The analysis is based on data from thousands of fracking operations in the USA and natural rock fractures in Europe and Africa.

It is believed to be the first analysis of its type and could be used across the world as a starting point for setting a minimum distance between the depth of fracking and shallower aquifers used for drinking water.

The new study, published in the journal Marine and Petroleum Geology, shows the probabilities of ‘rogue’ fractures, induced in fracking operations for shale gas extraction, extending beyond 0.6 kilometres from the injection source is exceptionally low. The probability of fractures extending beyond 350 metres was found to be one per cent.

During fracking operations, fractures are created by drilling and injecting fluid into the rock strata underground to increase oil and gas production from fine-grained, low permeability rocks such as shale. These stimulated fractures can significantly increase the rate of production of oil and gas from such rocks.

Fracking operations in the USA are growing in number and many countries across the world are looking at shale gas as a potential energy resource. The process of fracking has come under increasing scrutiny. A recent test well in the UK near Blackpool, Lancashire, was stopped after some minor earthquakes were felt at the surface. The UK government is allowing the test fracking to resume but critics have also warned of other possible side-effects including the contamination of groundwater.

Researchers from Durham University, Cardiff University and the University of Tromsø looked at thousands of natural and induced fractures from the US, Europe and Africa. Of the thousands artificially induced, none were found to exceed 600 metres, with the vast majority being much less than 250 metres in vertical extent.

Fracture heights are important as fractures have been cited as possible underground pathways for deep sources of methane to contaminate drinking water. But the likelihood of contamination of drinking water in aquifers due to fractures when there is a separation of more than a kilometer is negligible, the scientists say.

Professor Richard Davies, Director of Durham Energy Institute, Durham University, said: “Based on our observations, we believe that it may be prudent to adopt a minimum vertical separation distance for stimulated fracturing in shale reservoirs. Such a distance should be set by regulators; our study shows that for new exploration areas where there is no existing data, it should be significantly in excess of 0.6 km.

“Shale gas exploration is increasing across the world and sediments of different ages are now potential drilling targets. Constraining the maximum vertical extent of hydraulic fractures is important for the safe exploitation of unconventional hydrocarbons such as shale gas and oil, and the data from the USA helps us to understand how fracturing works in practice.

“Minimum vertical separation distances for fracturing operations would help prevent unintentional penetration of shallow rock strata.”

Professor Davies’ team looked at published and unpublished datasets for both natural and stimulated fracture systems in sediment of various ages, from eight different locations in the USA, Europe and Africa.

Professor Richard Davies said: “Sediments of different types and ages are potential future drilling targets and minimum separation depths are an important step towards safer fracturing operations worldwide and tapping into what could be a valuable energy resource.

“We need to keep collecting new data to monitor how far fractures grow in different geological settings.”

The team accepts that predicting the height and behavior of fractures is difficult. They now hope that the oil and gas industry will continue to provide data from new sites across the globe as it becomes available to further refine the probability analysis.

Analysis of new sites should allow a safe separation distance between fracking operations and sensitive rock layers to be further refined, the scientists say. In the meantime, the researchers hope that governments and shale gas drilling companies will use the analysis when planning new operations.

Managing the seismic risk posed by wastewater disposal

The debate over hydraulic fracturing has recently focused on the rise in seismicity throughout the primarily stable interior of the United States. These intraplate regions, though not unfamiliar with earthquakes, have been experiencing an increased amount of seismic activity in the last decade. This unusual increase is likely to be caused in part by wastewater disposal practices related to natural gas production. With such a sensitive issue it is important to keep the facts in perspective: No earthquake triggered by fluid injection has ever caused serious injury or significant damage. Moreover, approximately 140,000 wastewater disposal wells have been operating safely and without incident in the U.S. for many decades. Nevertheless, minor seismicity can occur, and it is important to recognize that with proper planning, monitoring and response the occurrence of small-to-moderate earthquakes associated with fluid injection can be reduced and the risks associated with such events effectively managed.

What steps can we take in order to safely practice wastewater injection? In the April issue of EARTH Magazine, Mark D. Zoback, professor of geophysics at Stanford University puts forward five steps that can be taken to reduce the probability of triggering seismicity associated with fluid injection. Zoback argues that through proper study and planning prior to injection, careful monitoring in areas where seismicity might be triggered, and careful training of operators and regulators will help to manage the seismic risk posed by wastewater disposal. To learn more, read the full article online at http://www.earthmagazine.org/article/managing-seismic-risk-posed-wastewater-disposal.

Read this story and more in the April issue of EARTH magazine, available online at http://www.earthmagazine.org/. Explore the archaeology, volcanoes and hot springs of the Northern Atacama Desert; Probe the limits of the solar system with Voyager 1; and, unearth the mechanics of crustal thinning.

Cary Institute Hydrofracking Forum

On Saturday, May 5th from 9AM to noon join the Cary Institute of Ecosystem Studies in Millbrook, N.Y. for a special forum exploring hydrofracking. The event’s goal is to provide citizens and decision makers with current information on the natural gas extraction technique, which involves injecting a high-pressure mix of chemically treated water and sand thousands of feet underground to release gas trapped in shale.

Hydrofracking has been the focus of environmental and economic discussions in New York State, with conversations centering on the future of the Marcellus Shale formation. There is currently a moratorium on hydrofracking in New York, while a task force appointed by the governor investigates the economic and environmental impacts of the drilling practice. Several of the speakers are from Pennsylvania-where hydrofracking in the Marcellus Shale is already underway; one sits on the peer-review panel for the EPA’s hydrofracking study.

Topics to be covered include groundwater contamination, the treatment of hydrofracking wastewater, human health effects, industry innovations, and the social impact that rapid gas booms have on small communities.

Speakers will include:

  • William Schlesinger, Ph.D., President, Cary Institute, Introduction

  • Avner Vengosh, Ph.D., Nicholas School of the Environment, Duke University, Methane and Water Contamination Associated with Shale Gas Development and Hydrofracking
  • Radisav Vidic, Ph.D., P.E., Chairman of the Department of Civil and Environmental Engineering, University of Pittsburgh, Wastewater Quality, Quantity, and Management: Lessons from the Marcellus Shale Region
  • Bernard Goldstein, M.D., Dean Emeritus, University of Pittsburgh Graduate School of Public Health, Potential Public Health Impacts of Hydraulic Fracturing
  • Mark Boling, J.D., Executive Vice President and General Counsel of Southwestern Energy, Hydraulic Fracturing Operations-Separating Fact from Fiction
  • Simona Perry, Ph.D., Science and Technology Studies, Rensselaer Polytechnic Institute, Rapid Shale Gas Developments and Stress Factors in Northern Appalachian Communities
  • Emma Rosi-Marshall, Ph.D., Aquatic Ecologist, Cary Institute; Moderator, Q&A Session

Free and open to the public, the event will be held in the Cary Institute’s auditorium, located at 2801 Sharon Turnpike (Rte. 44) in Millbrook, New York. RSVP is required, name tags will be provided at sign in. Information and registration is available online at: http://www.caryinstitute.org/fracking.html.