Shale Gas Production and Water Resources
March 1, 2012
Following are excerpts from a statement by David Ross, the U.S. Geological Survey’s (USGS) northeast regional executive, to the Senate Energy and Natural Resource Committee, on Oct. 20, 2011:
The USGS conducts research and assessments of the undiscovered, technically recoverable oil and gas resources of the United States. Advances in drilling technologies and subsurface geophysical imaging techniques over the last 20 years have enabled a new class of petroleum systems – primarily coal, shale and tight sands – to become more easily accessible and economically viable as petroleum sources. These unconventional systems lack traditional oil- and gas-trapping structures, are regional in extent, occur in rock of extremely low permeability, and, therefore, require artificial stimulation such as hydrofracturing to produce the gas or oil.
The Marcellus Shale is one of a number of shale formations that occur across a considerable area in the Appalachians. In August 2011, the USGS released a new assessment of undiscovered oil and gas resources of the Marcellus Shale. Results from the assessment found that there is a mean value of 84 trillion cubic feet of gas within the Marcellus Shale system, an amount that is significantly higher than the 2 trillion cubic feet estimate provided in an USGS assessment conducted in 2002 before the application of modern hydrofracturing and horizontal drilling technologies. By comparison, according to the Department of Energy, the total natural gas consumption for the United States in 2010 was about 24.1 trillion cubic feet. The USGS recently completed and is preparing for release a new assessment of the unconventional natural gas and natural gas liquid resources in the Mesozoic Basins of the eastern United States. The geological and ground water characteristics of various shale gas formations vary significantly across the region, and can affect production economics and potential environmental impacts in different ways. USGS is conducting research that should allow for an improved understanding of the local and regional variations in gas abundance, composition and quality. The results could serve to guide exploration strategies and the resultant need and locations of water resources to support future gas and oil development efforts.
USGS activities on potential environmental effects of shale gas exploration and production is focused on three primary topics:
- research to protect water supply and water
- measurement of baseline water-quality conditions,
- research leading to improved management of short-term and cumulative impacts to land quality and terrestrial and aquatic ecosystems.
The USGS currently is focusing on documenting and understanding the conditions of water quality and availability, and habitat conditions prior to land disturbance and shale gas development. In the Marcellus Shale gas area, the USGS is focusing on the potential effects of hydrofracturing and gas production on water quality and the occurrence of natural gas in private water wells (so-called “stray gas”). Concerns about the possible presence of gas and hydrofracturing chemicals in private water wells have been raised by citizens living in areas where shale gas production is underway.
Ground Water ProtectionThe possibility of surface and ground water contamination from drilling practices at the well pad, accidents, ground water transport, and the construction of pipelines and support facilities to collect and convey gas has been a prevailing topic in public discussion. Drilling regulations and permits issued by federal and state agencies and water basin commissions, as well as industry best-management practices, are designed to minimize these potential problems. However, whether these practices and regulations are adequate to protect water supplies and water quality during drilling and production still are a concern. Some of the key water supply and quality concerns related to Marcellus Shale gas production include:
- effect of water withdrawal for well construction and
hydrofracturing on local water resources,
- effects of land disturbance from road, bridge and drill pad
development, and from heavy equipment travel on stream sedimentation and small
- safe storage and disposal of the large quantities of fluids
recovered from the wells, which may contain salt and radioactive elements,
- composition and fate of chemicals introduced into the wellbore during hydrofracturing, and the potential effect of these chemicals on public drinking water supplies, ground water, wetlands and sensitive habitats.
Planned USGS ResearchThe USGS plans to use its modeling capabilities to develop a regional ground water flow model for specific areas of the Marcellus Shale gas play to evaluate the fate of injected hydrofracture waters that do not return up the wellbore to the surface as flowback waters (a relatively small proportion of the water in Marcellus wells currently returns to the surface). Additional research is needed to fully understand the potential fate of the injected waters, particularly in areas where hydrofracturing and resource production from shale beds as shallow as 2,000 feet from the surface is permitted. For example, a recently published USGS study shows that artificially injected deep gas can and does migrate into shallow water wells in the Marcellus Shale gas area.
Because natural gas can and does emanate from a variety of subsurface rock and alluvial formations (for example, organic shales, abandoned coal mines, conventional oil- and gas-bearing rocks, landfills and river valley alluvial fills), baseline monitoring for natural gas occurrence is needed for research purposes prior to, concurrent with, and following gas exploration and production activities in order to detect and/or distinguish among these gas sources. Given the challenge of conducting such monitoring that would cover the entire extent of the Marcellus Shale gas area with sufficient instrumentation for meaningful analysis, USGS recommends that several representative pilot areas be instrumented to support the collection of baseline water quality and gas data. It is important that the monitoring be maintained for an extended period of time to ensure a scientifically adequate sample size to detect water-quality anomalies and determine possible trends. USGS is conducting a number of baseline surface water and ground water quality studies,
- Ground water quality baseline monitoring and simulation of
ground water sources to wells is underway at the USGS Northern Appalachian
Research Lab in Wellsboro, Pa.
- Improvements to the USGS water-quality monitoring network in
Pennsylvania have been made to enhance monitoring in headwater streams near
drilling operations. Through support from the Pennsylvania Department of
Environmental Protection, 11 new sampling sites were added in small headwater
streams during 2011, and the frequency of sample collection and analysis was
increased at existing sites. Ten new continuous monitors were added for
temperature, dissolved oxygen, specific conductance and pH that will improve the
baseline of water quality.
- Baseline water quality in National Park units within the Marcellus
and Utica Shale gas plays is being assessed. This work is characterizing the
existing water quality and radiochemistry of National Park supply wells or
public wells serving these park units in Pennsylvania, New York and West
Virginia in order to provide a basis of comparison with future conditions,
including identification of the potential effects of
- Construction of several observation wells near an Environmental
Protection Agency prospective research site in western Pennsylvania is underway
to provide background data on ground water quality prior to the drilling of a
primary Marcellus Shale gas well nearby. This project is part of USGS’s
national study regarding the potential impacts of hydrofracturing operations on
drinking water supplies.
- USGS is monitoring baseline surface water and ground water quality in the Lycoming Creek watershed in northeastern Pennsylvania and in Blair County in central Pennsylvania. A more comprehensive regional monitoring, assessment and research program would provide the data and information to understand the relations among hydrofracturing, environmental setting, and management factors on water resources of the area.
Short-and Long-term ImpactsPotential impacts to biological resources and the water resources available to sustain them due to activities associated with shale gas development also are being investigated. The use of large volumes of freshwater for drilling, completion of shale gas wells, and for hydrofracturing purposes will result in a net loss of available freshwater. To reduce freshwater use, most companies recycle fracture water that has been rehabilitated after initial use, however, impacts to freshwater resources may remain. Additionally, fragmentation of the forest canopy due to Marcellus Shale gas development in the region potentially could create challenges for plants and wildlife, and open avenues for invasive species. For biological resources, landscape-scale research is important to quantify responses of key species and ecological communities to the impacts resulting from development of energy resources within the Marcellus Shale, and to develop best management practices to identify and mitigate impacts. In addition to traditional biological and ecological research, new interdisciplinary approaches linking ecology, economics and geospatial modeling frameworks can be applied to assess impacts across the full suite of ecosystem services and provide the science decision-makers the information they need to prioritize management decisions.
As a first step, USGS research on potential impacts of shale gas production on biological resources is focused on using remotely sensed airborne imagery to assess forest fragmentation and effects of shale gas activities on land-use patterns, and the abundance of migratory bird populations in key areas where shale gas production is underway. Research also is addressing the effects of habitat change on key aquatic species in the region affected by Marcellus Shale production, including eastern brook trout and the federally endangered dwarf wedge mussel.
General R&D NeedsThere are a variety of important issues related to water resources and shale gas production that warrant investigation by the appropriate agency, institution or industry. These include:
- Characterization of the physical processes by which rock fractures
are formed and propagate during the hydrofracturing pressurization process. The
USGS previously has conducted research on hydrofracturing in an effort to
characterize the Earth’s natural stress fields as part of its Earthquake
Hazards Reduction Program. Controlling the propagation of induced fractures is
important to limiting water use required in hydrofracturing, minimizing the
potential for the formation of large contiguous fracture sets that potentially
could serve as conduits to transmit hydrofracturing fluids to or near aquifers
and/or the Earth’s surface, and maximizing the yield of gas from the
- Assessment of water requirements necessary to re-hydrofracture gas
wells that are declining in gas production. This research would address the
important topic of re-use of existing wells, thereby reducing the need to drill
new wells, and minimizing additional impacts on the environment. Important
components of this research would be the application of advanced microseismic
techniques to better understand how the original fractures formed during the
hydrofracturing process, and whether re-hydrofracturing might simply open up
existing fractures rather than generate new ones, which would significantly
reduce the potential gas yield from the well.
- Investigation of the effects of water flowing through fractures
generated by hydrofracturing on gas yield. As gas production in a well
diminishes over time, there is reduced gas pressure in the fractures, so the
water in the fractures could act as a flow retardant. Pressure, however, is
necessary to drive water and gas out of the rock and into the well. The
research would address mechanisms to enhance gas flow.
- Understanding induced seismicity triggered by the injection of shale gas waste fluids into the subsurface. The USGS has conducted research on induced seismicity as part of the Earthquake Hazards Reduction Program. USGS has partnered with the Arkansas State Geological Survey to evaluate a series of earthquakes during the past year, and assess whether they may have been generated by waste water fluid injection in wells in the Fayetteville Shale gas play area.