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'''Hydraulic fracturing''' is the propagation of fractures in a rock layer caused by the presence of a pressurized fluid. Hydraulic fractures form naturally, as in the case of [[Vein (geology)|vein]]s or [[dike]]s, and is one means by which gas and petroleum from [[source rock]]s may migrate to [[reservoir rock]]s.
 
'''Hydraulic fracturing''' is the propagation of fractures in a rock layer caused by the presence of a pressurized fluid. Hydraulic fractures form naturally, as in the case of [[Vein (geology)|vein]]s or [[dike]]s, and is one means by which gas and petroleum from [[source rock]]s may migrate to [[reservoir rock]]s.
   
However oil and gas companies may attempt to accelerate this process in order to release [[petroleum]], [[natural gas]], [[coal seam gas]], or other substances for extraction, where the technique is often called '''fracking'''{{ref label|a|a|none}} or '''hydrofracking'''.<ref name="Charlez">Charlez, Philippe A. (1997). ''Rock Mechanics: Petroleum applications'', Editions Technip.</ref> This type of fracturing, known colloquially as a '''frack job''' (or '''frac job'''),<ref>[http://www.glossary.oilfield.slb.com/Display.cfm?Term=frac%20job "frac job"], Schlumberger Oilfield Glossary</ref><ref>[http://www.fracktrack.org "frac job"] Pennsylvania Marcellus Shale GIS Database</ref> is done from a [[wellbore]] drilled into reservoir rock formations. The energy from the injection of a highly-pressurized [[fracking fluid]]<ref>Schlumberger Oilfield Glossary, describing [http://www.glossary.oilfield.slb.com/Display.cfm?Term=fracturing%20fluid fracking fluids]</ref> creates new channels in the rock which can increase the extraction rates and ultimate recovery of fossil fuels. When done in already highly-permeable reservoirs such as [[sandstone]]-based wells, the technique is known as '''well stimulation'''. Operators typically try to maintain ''fracture width'' or slow its decline following treatment by introducing a [[proppant]]<ref name="proppant">Schlumberger Oilfield Glossary, definition of [http://www.glossary.oilfield.slb.com/Display.cfm?Term=proppant proppant]</ref> into the injected fluid, a material, such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped. Consideration of proppant strengths and prevention of proppant failure becomes more important at deeper depths where pressure and stresses on fractures are higher.
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However oil and gas companies may attempt to accelerate this process in order to release [[petroleum]], [[natural gas]], [[coal seam gas]], or other substances for extraction, where the technique is often called '''fracking'''{{ref label|a|a|none}} or '''hydrofracking'''.<ref name="Charlez">Charlez, Philippe A. (1997). ''Rock Mechanics: Petroleum applications'', Editions Technip.</ref> This type of fracturing, known colloquially as a '''frack job''' (or '''frac job'''),<ref>[http://www.glossary.oilfield.slb.com/Display.cfm?Term=frac%20job "frac job"], Schlumberger Oilfield Glossary</ref><ref>[http://www.fracktrack.org "frac job"] Pennsylvania Marcellus Shale GIS Database</ref> is done from a [[wellbore]] drilled into reservoir rock formations. The energy from the injection of a highly-pressurized [[fracking fluid]]<ref>Schlumberger Oilfield Glossary, describing [http://www.glossary.oilfield.slb.com/Display.cfm?Term=fracturing%20fluid fracking fluids]</ref> creates new channels in the rock which can increase the extraction rates and ultimate recovery of [[fossil fuel]]s. When done in already highly-permeable reservoirs such as [[sandstone]]-based wells, the technique is known as '''well stimulation'''. Operators typically try to maintain ''fracture width'' or slow its decline following treatment by introducing a [[proppant]]<ref name="proppant">Schlumberger Oilfield Glossary, definition of [http://www.glossary.oilfield.slb.com/Display.cfm?Term=proppant proppant]</ref> into the injected fluid, a material, such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped. Consideration of proppant strengths and prevention of proppant failure becomes more important at deeper depths where pressure and stresses on fractures are higher.
 
Distinction can be made between low-volume hydraulic fracturing used to stimulate high-permeability reservoirs, which may consume typically 20,000 to 80,000 gallons of fluid per well, with high-volume hydraulic fracturing, used in the [[well completion|completion]] of [[tight gas]] and [[shale gas]] wells; high-volume hydraulic fracturing can use as much as two to three million gallons of fluid per well.<ref>{{cite web|author=Andrews, Anthony et. al. |url=http://www.fas.org/sgp/crs/misc/R40894.pdf |title=Unconventional Gas Shales: Development, Technology, and Policy Issues |publisher= Congressional Research Service |date=2009 |accessdate=Jan. 16, 2012}}</ref>
 
This latter practice has come under scrutiny internationally due to concerns about the [[environment]]al impact, [[health and safety]], and has been suspended or banned in some countries.<ref>{{cite web|author=Post a Job |url=http://www.businessweek.com/news/2011-10-04/france-to-keep-fracking-ban-to-protect-environment-sarkozy-says.html |title=France to Keep Fracking Ban to Protect Environment, Sarkozy Says |publisher=Businessweek |date=2011-10-04 |accessdate=2011-11-02}}</ref>
 
 
==Mechanics==
 
Fracturing in rocks at depth is suppressed by the [[Pressure#Liquid pressure or pressure at depth|confining pressure]], particularly in the case of tensile (Mode 1) fractures which require the walls of the fracture to move apart. Hydraulic fracturing occurs when the [[effective stress]] is reduced sufficiently by an increase in the pressure of fluids in the rock such that the minimum principal stress becomes tensile and exceeds the [[tensile strength]] of the material.<ref name="Price">{{cite book|last1=Price|first1=N.J.|last2=Cosgrove|first2=J.W.|title=Analysis of geological structures|url=http://books.google.co.uk/books?id=80gYS1IzUWsC&pg=PA32&dq=%22hydraulic+fracture+mechanism%22+price+cosgrove&hl=en&ei=xl-1TpTsF8zq8QPYlczuBA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CDkQ6AEwAA#v=onepage&q&f=false|accessdate=5 November 2011|year=1990|publisher=[[Cambridge University Press]]|isbn=9780521319584|pages=30&ndash;33}}</ref> Fractures formed in this way will typically be oriented perpendicularly to the minimum principal stress and for this reason, induced hydraulic fractures in wellbores are sometimes used to determine stress orientations. In natural examples, such as dikes or vein-filled fractures, their orientations can be used to infer past stress states.
 
 
==Natural examples==
 
Rocks often contain evidence of past hydraulic fracturing events, where fluids have passed through tensile fractures. {{cn|date=December 2011}}
 
 
===Veins===
 
Most vein systems are a result of repeated hydraulic fracturing during periods of relatively high pore fluid pressure. This is particularly clear in the case of 'crack-seal' veins, where the vein material can be seen to have been added in a series of discrete fracturing events, with extra vein material deposited on each occasion.<ref name="Laubach">{{cite journal|last=Laubach|first=S.E.|coauthors=Reed R.M., Olson J.E., Lander R.H. & Bonnell L.M.|year=2004|title=Coevolution of crack-seal texture and fracture porosity in sedimentary rocks: cathodoluminescence observations of regional fractures|journal=Journal of Structural Geology|publisher=[[Elsevier]]|volume=26|issue=5|pages=967–982|doi=10.1016/j.jsg.2003.08.019|url=http://www.sciencedirect.com/science/article/pii/S0191814103001858|accessdate=5 November 2011}}</ref> One mechanism to explain such examples of long-lasting repeated fracturing, is the effects of seismic activity, in which the stress levels rise and fall episodically and large volumes of fluid may be expelled from fluid-filled fractures during earthquakes, a process referred to as 'seismic pumping'.<ref name="Sibson">{{cite journal|last=Sibson|first=R.H.|coauthors=Moore J. McM. & Rankin A.H.|year=1975|title=Seismic pumping--a hydrothermal fluid transport mechanism|journal=Journal of the Geological Society|publisher=[[Geological Society]]|location=London|volume=131|pages=653–659|doi=10.1144/gsjgs.131.6.0653|url=http://jgs.geoscienceworld.org/cgi/content/abstract/131/6/653|accessdate=5 November 2011}}</ref>
 
 
===Dikes===
 
High-level minor intrusions such as dikes propagate through the crust in the form of fluid-filled cracks, although in this case the fluid is [[magma]]. In sedimentary rocks with a significant water content the fluid at the propagating fracture tip will be steam.<ref name="Gill">{{cite book|last=Gill|first=R.|title=Igneous rocks and processes: a practical guide|url=http://books.google.co.uk/books?id=vgpmAcu_M-AC&pg=PA102&lpg=PA102&dq=dyke+propagation+tip+steam&source=bl&ots=V7ircv_EZH&sig=5ylSJH4hbKnJhajuhPRSJQca9Ic&hl=en&ei=HlS1ToSMIMK38gPn9JH_BA&sa=X&oi=book_result&ct=result&resnum=5&sqi=2&ved=0CEkQ6AEwBA#v=onepage&q=dyke%20propagation%20tip%20steam&f=false|accessdate=5 November 2011|year=2010|publisher=John Wiley and Sons|isbn=9781444330656|page=102}}</ref>
 
 
==Induced hydraulic fracturing==
 
The technique of hydraulic fracturing is used to increase or restore the rate at which fluids, such as [[oil]], [[water]], or [[natural gas]] can be produced from subterranean natural reservoirs. Reservoirs are typically porous sandstones, limestones or [[dolomite]] rocks, but also include 'unconventional reservoirs' such as [[shale]] rock or [[coal]] beds. Hydraulic fracturing enables the production of natural gas and oil from rock formations deep below the earth's surface (generally 5,000–20,000 feet or 1,500–6,100 m). At such depth, there may not be sufficient [[porosity]], [[Permeability (earth sciences)|permeability]] or reservoir pressure to allow natural gas and oil to flow from the rock into the wellbore at economic rates. Thus, creating conductive fractures in the rock is essential to extract [[shale gas|gas from shale reservoirs]] because of the extremely low natural permeability of shale, which is measured in the micro[[darcy]] to nanodarcy range.<ref>{{cite web
 
|title=The Barnett Shale
 
|url=http://www.nknt.org/Exhibits/Barnett_shale_points2.pdf
 
|format=PDF
 
|publisher=North Keller Neighbors Together
 
}}</ref> Fractures provide a conductive path connecting a larger area of the reservoir to the well, thereby increasing the area from which natural gas and liquids can be recovered from the targeted formation. So-called 'super fracking'—creating longer, deeper cracks in the earth to release more oil and gas—will allow companies to frack more efficiently.<ref name="BW 19.01.2012">{{cite news |url=http://www.businessweek.com/magazine/like-fracking-youll-love-super-fracking-01192012.html |title=Like Fracking? You'll Love 'Super Fracking' |author=David Wethe |date=19 January 2012 |newspaper=Businessweek |accessdate=22 January 2012}}</ref>
 
 
While the main industrial use of hydraulic fracturing is in stimulating production from [[Oil well|oil and gas wells]],<ref>Gidley, J.L. et al. (editors), "Recent Advances in Hydraulic Fracturing", SPE Monograph, SPE, Richardson, Texas, 1989.</ref><ref>Yew, C.H., "Mechanics of Hydraulic Fracturing", Gulf Publishing Company, Houston, Texas, 1997.</ref><ref>Economides, M.J. and K.G. Nolte (editors), "Reservoir Stimulation", John Wiley & Sons, Ltd., New York, 2000.</ref> hydraulic fracturing is also applied to:
 
* Stimulating [[groundwater]] wells<ref>{{cite journal
 
|first=David |last=Banks
 
|coauthors=Odling, N.E., Skarphagen, H., and Rohr-Torp, E.
 
|title=Permeability and stress in crystalline rocks
 
|journal=Terra Nova
 
|volume=8 |issue=3 |doi=10.1111/j.1365-3121.1996.tb00751.x
 
|month=May|year=1996
 
|pages=223–235
 
}}</ref>
 
* Preconditioning rock for caving or inducing rock to cave in [[mining]]<ref>Brown, E.T., "Block Caving Geomechanics", JKMRC Monograph 3, JKMRC, Indooroopilly, Queensland, 2003.</ref>
 
* As a means of enhancing waste remediation processes, usually hydrocarbon waste or spills<ref name=hazmat40.2>{{cite journal
 
|url=http://www.sciencedirect.com/science/article/B6TGF-3YS8C2K-C/2/236451dcf9e7265b12548b83a2025e0f
 
|title=Remediation of low permeability subsurface formations by fracturing enhancement of soil vapor extraction
 
|journal=Journal of Hazardous Materials
 
|volume=40 |issue= 2
 
|work=Soil Remediation: Application of Innovative and Standard Technologies
 
|date=February 1995
 
|pages=191–201
 
|issn= 0304-3894 |doi=10.1016/0304-3894(94)00069-S
 
|author=Frank, U.; Barkley, N.
 
}}</ref>
 
* Dispose of waste by injection into deep rock formations
 
* As a method to measure the stress in the earth
 
* For heat extraction to produce electricity in an [[Enhanced geothermal system|enhanced geothermal systems]] <ref>{{cite web|url=http://www1.eere.energy.gov/geothermal/egs_animation.html |title=Geothermal Technologies Program: How an Enhanced Geothermal System Works |publisher=.eere.energy.gov |date=2011-02-16 |accessdate=2011-11-02}}</ref>
 
 
===Method===
 
A hydraulic fracture is formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increase pressure downhole to exceed that of the fracture gradient of the rock. {{cn|date=December 2011}} The rock cracks and the fracture fluid continues farther into the rock, extending the crack still farther, and so on. To keep this fracture open after the injection stops, a solid proppant,<ref name="proppant"/> commonly a sieved round sand, is added to the fluid. The propped fracture is permeable enough to allow the flow of formation fluids to the well. Formation fluids include gas, oil, salt water, fresh water and fluids introduced to the formation during completion of the well during fracturing. {{cn|date=December 2011}}
 
 
The location of one or more fractures along the length of the borehole is strictly controlled by various different methods which create or seal-off holes in the side of the wellbore. Typically, hydraulic fracturing is performed in [[Casing (borehole)|cased]] wellbores and the zones to be fractured are accessed by [[Perforation (oil well)|perforating]] the casing at those locations. {{cn|date=December 2011}}
 
 
====Well types====
 
While hydraulic fracturing is many times performed in vertical wells, today it is also performed in horizontal wells. [[Horizontal drilling]] involves wellbores where the terminal drillhole is completed as a 'lateral' that extends parallel with the rock layer containing the substance to be extracted. For example, laterals extend 1,500 to 5,000 feet in the [[Barnett Shale]] basin in Texas, and up to 10,000 feet in the [[Bakken formation]] in North Dakota. In contrast, a vertical well only accesses the thickness of the rock layer, typically 50–300 feet. Horizontal drilling also reduces surface disruptions as fewer wells are required. Drilling usually induces damage to the pore space at the wellbore wall, reducing the permeability at and near the wellbore. This reduces flow into the borehole from the surrounding rock formation, and partially seals off the borehole from the surrounding rock. Hydraulic fracturing can be used to restore permeability. {{cn|date=December 2011}}
 
 
Hydraulic fracturing is commonly applied to wells drilled in low permeability reservoir rock. An estimated 90 percent of the natural gas wells in the United States use hydraulic fracturing to produce gas at economic rates. {{cn|date=December 2011}}
 
 
====Fracturing====
 
The fluid injected into the rock is typically a slurry of water, proppants, and chemical additives. Additionally, gels, foams, and compressed gases, including [[nitrogen]], [[carbon dioxide]] and air can be injected. Various types of proppant include silica sand, resin-coated sand, and man-made ceramics. These vary depending on the type of permeability or grain strength needed. Sand containing naturally radioactive minerals is sometimes used so that the fracture trace along the wellbore can be measured. Chemical additives are applied to tailor the injected material to the specific geological situation, protect the well, and improve its operation, though the injected fluid is approximately 98-99.5% percent water,<ref>Hydraulic Fracturing Fluids - Composition and Additives (Republished from: Modern Shale Gas Development in the United States by the U.S. Department of Energy). http://geology.com/energy/hydraulic-fracturing-fluids/. 2009.</ref> varying slightly based on the type of well. The composition of injected fluid is sometimes changed as the fracturing job proceeds. Often, acid is initially used to scour the perforations and clean up the near-wellbore area. Afterward, high pressure fracture fluid is injected into the wellbore, with the pressure above the fracture gradient of the rock. This fracture fluid contains water-soluble gelling agents (such as guar gum) which increase viscosity and efficiently deliver the proppant into the formation.<ref>{{cite news |title=Unconventional Gas Shales: Development, Technology, and Policy Issues |author=Anthony Andrews et al. |url= |newspaper=Congressional Research Service |date=30 October 2009 |accessdate=17 January 2012}}</ref> As the fracturing process proceeds, viscosity reducing agents such as oxidizers and enzyme breakers are sometimes then added to the fracturing fluid to deactivate the gelling agents and encourage flowback.<ref>{{cite web|author=Andrews, Anthony et. al. |url=http://www.fas.org/sgp/crs/misc/R40894.pdf |title=Unconventional Gas Shales: Development, Technology, and Policy Issues |publisher= Congressional Research Service |date=2009 |accessdate=Jan. 17, 2012}}</ref> The proppant's purpose is primarily to provide a permeable and permanent filler to fill the void created during the fracturing process. At the end of the job the well is commonly flushed with water (sometimes blended with a friction reducing chemical) under pressure. Injected fluid is to some degree recovered and is managed by several methods, such as underground injection control, treatment and discharge, recycling, or temporary storage in pits or containers while new technology is being developed to better handle wastewater and improve reusability.<ref>Modern Shale Gas Development in the United States: A Primer.http://www.netl.doe.gov/technologies/oil-gas/publications/epreports/shale_gas_primer_2009.pdf. April 2009. Pg. ES-4.</ref> Although the concentrations of the chemical additives are very low, the recovered fluid may be harmful due in part to hydrocarbons picked up from the formation.
 
 
Hydraulic fracturing equipment used in oil and natural gas fields usually consists of a slurry blender, one or more high pressure, high volume fracturing pumps (typically powerful triplex, or quintiplex pumps) and a monitoring unit. Associated equipment includes fracturing tanks, one or more units for storage and handling of proppant, high pressure treating iron, a chemical additive unit (used to accurately monitor chemical addition), low pressure flexible hoses, and many gauges and meters for flow rate, fluid density, and treating pressure. Fracturing equipment operates over a range of pressures and injection rates, and can reach up to 100 [[Pascals|MPa]] (15,000 [[Pounds per square inch|psi]]) and 265 L/s (100 barrels per minute). {{cn|date=December 2011}}
 
 
====Fracture monitoring====
 
Measurements of the pressure and rate during the growth of a hydraulic fracture, as well as knowing the properties of the fluid and proppant being injected into the well provides the most common and simplest method of monitoring a hydraulic fracture treatment. This data, along with knowledge of the underground geology can be used to model information such as length, width and conductivity of a propped fracture. {{cn|date=December 2011}}
 
 
For more advanced applications, [[Microseismic]] monitoring is sometimes used to estimate the size and orientation of hydraulically induced fractures. Microseismic activity is measured by placing an array of [[geophone]]s in a nearby wellbore. By mapping the location of any small seismic events associated with the growing hydraulic fracture, the approximate geometry of the fracture is inferred. [[Tiltmeter]] arrays, deployed on the surface or down a well, provide another technology for monitoring the strains produced by hydraulic fracturing. {{cn|date=December 2011}}
 
 
Emission of gases displaced by hydraulic fracturing into the atmosphere may be detected via atmospheric gas monitoring, and can be quantified directly via the [[eddy covariance]] flux measurements. {{cn|date=December 2011}}
 
 
====Horizontal completions====
 
Since the early 2000s, advances in [[Oil well#Drilling|drilling]] and [[Completion (oil and gas wells)|completion]] technology has made drilling horizontal wellbores much more economical. Horizontal wellbores allow for far greater exposure to a formation than a conventional vertical wellbore. This is particularly useful in shale [[Tight oil|oil]] and [[Tight gas|gas]] formations which do not have sufficient permeability to produce economically with a vertical well. Such wells when drilled onshore are now usually hydraulically fractured many times, especially in North America. The type of wellbore completion used will affect how many times the formation is fractured, and at what locations along the horizontal section of the wellbore.<ref>{{cite journal
 
|last=Seale |first= Rocky
 
|date=July/August 2007
 
|url=http://drillingcontractor.org/dcpi/dc-julyaug07/DC_July07_PackersPlus.pdf
 
|format=PDF
 
|title=Open hole completion systems enables multi-stage fracturing and stimulation along horizontal wellbores
 
|magazine=Drilling Contractor
 
|accessdate= October 1, 2009
 
|edition=Fracturing stimulation
 
}}</ref>
 
 
In North America, tight reservoirs such as the [[Bakken Formation|Bakken]], [[Barnett Shale]], [[Montney Formation|Montney]] and [[Haynesville Shale]] are drilled, completed and fractured using this method. The method by which the fractures are placed along the wellbore is most commonly achieved by one of two methods, known as 'plug and perf' and 'sliding sleeve'. {{cn|date=December 2011}}
 
 
The wellbore for a plug and perf job is generally composed of standard joints of steel casing, either cemented or uncemented, which is set in place at the conclusion of the drilling process. Once the drilling rig has been removed, a [[Wireline (cabling)|wireline truck]] is used to [[Perforation (oil well)|perforate]] near the end of the well, following which a fracturing job is pumped (commonly called a stage). Once the stage is finished, the wireline truck will set a plug in the well to temporarily seal off that section, and then perforate the next section of the wellbore. Another stage is then pumped, and the process is repeated as necessary along the entire length of the horizontal part of the wellbore. {{cn|date=December 2011}}
 
 
The wellbore for the sliding sleeve technique is different in that the sliding sleeves are included at set spacings in the steel casing at the time it is set in place. The sliding sleeves are usually all closed at this time. When the well is ready to be fractured, using one of several activation techniques, the bottom sliding sleeve is opened and the first stage gets pumped. Once finished, the next sleeve is opened which concurrently isolates the first stage, and the process repeats. For the sliding sleeve method, wireline is usually not required. {{cn|date=December 2011}}
 
 
These completion techniques may allow for more than 30 stages to be pumped into the horizontal section of a single well if required, which is far more than would typically be pumped into a vertical well. {{cn|date=December 2011}}
 
 
===Terminology===
 
;Fracture Gradient: The pressure to fracture the formation at a particular depth divided by the depth. A fracture gradient of 18 kPa/m (0.8 psi/foot) implies that at a depth of 3&nbsp;km (10,000 feet) a pressure of 54 MPa (8,000 psi) will extend a hydraulic fracture.
 
;ISIP — Initial Shut In Pressure: The pressure measured immediately after injection stops. The ISIP provides a measure of the pressure in the fracture at the wellbore by removing contributions from fluid friction.
 
;Leakoff: Loss of fracturing fluid from the fracture channel into the surrounding permeable rock.
 
;Fracturing fluid: The fluid used during a hydraulic fracture treatment of oil, gas, or water wells. The fracturing fluid has two major functions:
 
#Open and extend the fracture.
 
#Transport the proppant along the fracture length.
 
;Proppant: Suspended particles in the fracturing fluid that are used to hold fractures open after a hydraulic fracturing treatment, thus producing a conductive pathway that fluids can easily flow along. Naturally occurring sand grains or artificial ceramic material are common proppants used.
 
;Concise slang: "Fracing" (sometimes spelled "fracking"<ref>Quillen, Ed (June 25, 2009). [http://www.hcn.org/blogs/goat/fracking-fracing-or-fraccing "Fracking, fracing or fraccing?"]. ''[[High Country News]]''.</ref> primarily in media) is a shortened version of fracturing.
 
 
==Environmental concerns==
 
Environmental concerns with hydraulic fracturing include the potential contamination of [[ground water]], risks to [[air quality]], the potential migration of gases and hydraulic fracturing chemicals to the surface, the potential mishandling of waste, and the health effects of these.<ref name="house1">{{cite web
 
|url=http://democrats.energycommerce.house.gov/sites/default/files/documents/Hydraulic%20Fracturing%20Report%204.18.11.pdf
 
|publisher=Committee on Energy and Commerce U.S. House of Representatives
 
|title=Chemicals Used in Hydraulic Fracturing
 
|date=April 18, 2011}}</ref><ref name="HeatOnGas"/>
 
A 2004 study by the [[United States Environmental Protection Agency|Environmental Protection Agency]] (EPA) concluded that the injection of hydraulic fracturing fluids into coalbed methane (CBM) wells posed minimal threat to underground drinking water sources.<ref>{{cite web
 
|url=http://www.epa.gov/ogwdw/uic/pdfs/cbmstudy_attach_uic_final_fact_sheet.pdf
 
|publisher=U.S. EPA
 
|title=Evaluation of Impacts to Underground Sources of Drinking Water by Hydraulic Fracturing of Coalbed Methane Reservoirs; National Study Final Report
 
|date=June 2004}}</ref>
 
This study has been criticised for only focusing on the injection of fracking fluids, while ignoring other aspects of the process such as disposal of fluids, and environmental concerns such as water quality, fish kills and acid burns; the study was also concluded before public complaints of contamination started emerging.<ref name="DammelNotes">{{cite article |year=2011 |last=Dammel |first=Joseph A. |title=Notes From Underground: Hydraulic Fracturing in the Marcellus Shale |journal=Minnesota Journal of Law, Science and Technology |issue=12(2)}}</ref>{{rp|780}} Largely on the basis of this study,{{fact|date=December 2011}} in 2005 hydraulic fracturing was exempted by US Congress from any regulation under the [[Safe Drinking Water Act]].
 
 
With the explosive growth of natural gas wells in the US, researcher Valerie Brown predicted in 2007 that "public exposure to the many chemicals involved in energy development is expected to increase over the next few years, with uncertain consequences."<ref name="HeatOnGas">{{cite article|last=Brown |first=Valerie J. |title=Industry Issues: Putting the Heat on Gas |date=February 2007 |journal=Environmental Health Perspectives |publisher=US National Institute of Environmental Health Sciences |issue=115(2) |http=http://ehp03.niehs.nih.gov/article/browseIssue.action?issue=info:doi/10.1289/issue.ehp.v115.i02}}</ref>
 
As development of natural gas wells in the U.S. since the year 2000 has increased, so too have claims by private well owners of water contamination. This has prompted EPA and others to re-visit the topic.
 
 
While the EPA recognizes the potential for contamination of water by hydraulic fracturing, EPA Administrator Lisa Jackson testified in a Senate Hearing Committee "I'm not aware of any proven case where the fracking process itself has affected water...".<ref>{{cite web
 
|url=http://epw.senate.gov/public/index.cfm?FuseAction=PressRoom.PressReleases&ContentRecord_id=23EB85DD-802A-23AD-43F9-DA281B2CD287
 
|publisher=U.S. Senate
 
|title=Pathways To Energy Independence: Hydraulic Fracturing And Other New Technologies
 
|date=May 6, 2011}}</ref> There are, however, documented incidents of contamination. In 2006 drilling fluids and [[methane]] were detected leaking from the ground near a gas well in [[Clark, Wyoming]]; 8 million cubic feet of methane were eventually released, and shallow groundwater was found to be contaminated.<ref name="HeatOnGas"/> In the town of [[Dimock, Pennsylvania]], 13 water wells were contaminated with methane (one of them blew up), and the gas company, [[Cabot Oil & Gas]], had to financially compensate residents and construct a pipeline to bring in clean water; the company continued to deny, however, that any "of the issues in Dimock have anything to do with hydraulic fracturing".<ref name="DammelNotes"/><ref name="DarkSide">{{cite article |title=Dark Side of a Natural Gas Boom |last=Mouawad |first=Jad |otherauthors=Krauss, Clifford |http=http://www.nytimes.com/2009/12/08/business/energy-environment/08fracking.html?pagewanted=all |journal=The New York Times |date=December 7, 2009 |page=B1}}</ref><ref name="Bloomberg 10.01.2012">{{cite news |url=http://www.bloomberg.com/news/2012-01-10/pennsylvania-fracking-foes-fault-epa-over-tainted-water-response.html |title=Pennsylvania Fracking Foes Fault EPA Over Tainted Water Response |author=Jim Snyder |coauthor=Mark Drajem |date=10 January 2012 |newspaper=Bloomberg |accessdate=19 January 2012}}</ref> The devices needed to prevent such water contamination cost as little as $600.<ref name="Bloomberg 23.12.2011">{{cite news |url=http://www.bloomberg.com/news/2011-12-23/fracking-opens-fissures-among-states-as-drillers-face-many-rules.html |title=Fracking Opens Fissures Among States as Drillers Face Many Rules |author=Jim Efstathiou Jr. |coauthor=Mark Niquette |date=23 December 2012 |newspaper=Bloomberg |accessdate=19 January 2012}}</ref>
 
 
In January 2012, a group of doctors called for a moratorium on fracking in populated areas until its health effects are better understood.<ref name="BW 19.01.2012"/><ref name="Bloomberg 11.01.2012">{{cite news |url=http://www.bloomberg.com/news/2012-01-11/fracking-s-political-support-unshaken-by-doctors-call-for-ban.html |title=Fracking Political Support Unshaken by Doctors' Call for Ban |author=Mark Drajem |date=11 January 2012 |newspaper=Bloomberg |accessdate=19 January 2012}}</ref>
 
 
====Air emissions and pollution====
 
One group of emissions associated with natural gas development and production, are the emissions associated with combustion. These emissions include particulate matter, nitrogen oxides, sulfur oxide, carbon dioxide and carbon monoxide. Another group of emissions that are routinely vented into the atmosphere are those linked with natural gas itself, which is composed of methane, ethane, liquid condensate, and [[volatile organic compounds]] (VOCs). The VOCs that are especially impactful on health are [[benzene]], [[toluene]], [[ethyl benzene]], and [[xylene]] (referred to as a group, called BTEX). Health effects of exposure to these chemicals include neurological problems, birth defects, and cancer.<ref>{{cite journal
 
|url=http://www.epa.gov/region04/foiapgs/readingroom/hercules_inc/toxicological_and_human_health_effects_following_exposure_3v.pdf
 
|publisher=US EPA
 
|title=Toxicology and human health effects following exposure to oxygenated or reformulated gasoline
 
|date=May 2001}}</ref>
 
 
VOCs, including BTEX, mixed with nitrogen oxides from combustion and combined with sunlight can lead to [[ozone]] formation. Ozone has been shown to impact lung function, increase respiratory illness, and is particularly dangerous to lung development in children.<ref>{{cite journal
 
|url=http://www.pasdegazdeschistes.rd-h.fr/wp-content/uploads/NaturalGasManuscriptPDF09_13_10-Th%C3%A9o-Colborn.pdf
 
|publisher=Internal Journal of Human and Ecological Risk Assessment
 
|title=Natural Gas Operations from a Public Health Perspective
 
|date=September 2010}}</ref> In 2008, measured ambient concentrations in the rural [[Sublette County, Wyoming]] where ranching and natural gas are the main industries were frequently above the National Ambient Air Quality Standards (NAAQS) of 75ppb and have been recorded as high as 125 ppb.<ref>{{cite web
 
|url=http://trib.com/news/state-and-regional/article_d1b0ff92-d3a0-5481-a9fc-e3ca505fbe12.html
 
|publisher=Wyoming's Online News Source
 
|title=Ozone mitigation efforts continue in Sublette County, Wyoming
 
|date=March 2011}}</ref>
 
 
===Groundwater contamination===
 
A Duke University study published in ''Proceedings of the National Academy of Sciences'' in 2011 examined methane in groundwater in [[Pennsylvania]] and [[New York]] states overlying the [[Marcellus Shale]] and the [[Utica Shale]]. It determined that groundwater tended to contain much higher concentrations of methane near fracking wells, with potential explosion hazard; the methane's [[isotopic signature]]s and other geochemical indicators were consistent with it originating in the fracked deep shale formations, rather than any other source.<ref>{{cite journal
 
|last=Osborn |first=Stephen G.
 
|last2=Vengosh |first2=Avner
 
|last3= Warner |first3= Nathaniel R.
 
|last4=Jackson |first4= Robert B.
 
|title=Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing
 
|date= 2011-05-09
 
|accessdate=2011-10-14
 
|journal= Proceedings of the National Academy of Sciences
 
|doi= 10.1073/pnas.1100682108
 
|url=http://www.pnas.org/content/early/2011/05/02/1100682108}}</ref> Complaints from a few residents on water quality in a developed natural gas field prompted an EPA groundwater investigation in Wyoming. The EPA reported detections of methane and other chemicals such as phthalates in private water wells.<ref>{{cite web
 
|url=http://www.epa.gov/region8/superfund/wy/pavillion/PavillionAnalyticalResultsReport.pdf
 
|publisher=U.S. EPA Region 8
 
|title=Expanded Site Investigation - Analytical Results Report, Pavillion Area Groundwater Report
 
|date=August 30, 2010}}</ref>
 
 
In [[Pavillion, Wyoming]], the EPA discovered traces of methane and foaming agents in several water wells near a gas rig, though it suggested these chemicals might have come from cleaning products.<ref name="DarkSide"/> In [[DISH, Texas]], elevated levels of [[disulphide]]s, [[benzene]], [[xylene]]s and [[naphthalene]] have been detected in the air, alongside numerous local complaints of headaches, diarrhea, nosebleeds, dizziness, muscle spasms and other problems. {{cn|date=December 2011}} Additionally, the Colorado Oil & Gas Conservation Commission has found some wells containing thermogenic methane due to oil and gas development upon investigating complaints from residents.<ref>{{cite web|title=Gasland Correction Document|url=http://cogcc.state.co.us/library/GASLAND%20DOC.pdf|publisher=Colorado Oil & Gas Conservation Commission|accessdate=25 January 2012}}</ref>
 
 
Groundwater contamination doesn't come directly from injecting fracking chemicals deep into Shale rock formations well below water aquifers but from waste water evaporation ponds and poorly constructed pipelines taking the waste water and chemicals to processing facilities. The evaporation ponds allow the volatile chemicals in the waste water to evaporate into the atmosphere and when it rains these ponds tend to overflow and the runoff eventually makes its way into groundwater systems. Another way groundwater gets contaminated relating to fracking is from the temporary, and poorly constructed pipelines to transport the waste water to water treatment plants. These pipelines can leak and in some cases break in a section all together allowing the waste water and fracking chemicals to flow into groundwater systems. The transportation by trucks and storage of fracking chemicals allows for groundwater to become contaminated when accidents happen during transportation to the fracking site or to its disposal destination.{{citation needed|date=December 2011}}
 
 
Epidemiological studies that might confirm or rule out any connection between these complaints and fracking are virtually non-existent. Individuals "smell things that don't make them feel well, but we know nothing about cause-and-effect relationships in these cases."<ref name="schmidt1">{{cite journal |title=Blind Rush? Shale Gas Boom Proceeds Amid Human Health Questions |last=Schmidt |first=Charles W. |journal=Environmental Health Perspectives |issue=119(1)}}</ref> In [[Garfield County, Colorado]], another area with a high concentration of drilling rigs, [[volatile organic compound]] emissions increased 30% between 2004 and 2006; during the same period there was a rash of health complaints from local residents. The health effects of VOCs are largely unquantified, so any causal relationship is difficult to ascertain; however, some of these chemicals are suspected carcinogens and neurotoxins.<ref name="HeatOnGas"/> Investigators from the Colorado School of Public Health performed a study in Garfield regarding potential adverse health effects, and concluded that residents near gas wells might suffer chemical exposures, accidents from industry operations, and psychological impacts such as depression, anxiety and stress. This study (the only one of its kind to date) was never published, owing to disagreements between community members and the drilling company over the study's methods.<ref name="schmidt1"/>
 
 
In 2010 the film ''[[Gasland]]'' premiered at the Sundance Film Festival. The filmmaker claims that chemicals including toxins, known carcinogens, and heavy metals polluted the ground water near well sites in Pennsylvania, Wyoming, and Colorado.<ref>{{cite web
 
|url=http://www.pbs.org/now/shows/613/index.html
 
|title=Gasland
 
|year=2010}}</ref>
 
 
A 2011 report by the Massachusetts Institute of Technology addressed groundwater contamination, noting "There has been concern that these fractures can also penetrate shallow freshwater zones and contaminate them with fracturing fluid, but there is no evidence that this is occurring. There is, however, evidence of natural gas migration into freshwater zones in some areas, most likely as a result of substandard well completion practices by a few operators. There are additional environmental challenges in the area of water management, particularly the effective disposal of fracture fluids". This study encourages the use of industry best practices to prevent such events from recurring.<ref>{{cite journal
 
|url=http://web.mit.edu/mitei/research/studies/documents/natural-gas-2011/NaturalGas_ExecutiveSummary.pdf
 
|publisher=MIT Energy Initiative
 
|title=The Future of Natural Gas: An Interdisciplinary MIT Study
 
|date=June 2011}}</ref>
 
 
Directed by Congress, the U.S. EPA announced in March 2010 that it will examine claims of water pollution related to hydraulic fracturing.<ref>{{cite web
 
|url=http://water.epa.gov/type/groundwater/uic/class2/hydraulicfracturing/index.cfm
 
|publisher=U.S. EPA
 
|title=Hydraulic Fracturing
 
|date=March 2010}}</ref>
 
 
====Radioactive contamination====
 
The [[New York Times]] has reported radiation in hydraulic fracturing wastewater released into rivers in [[Pennsylvania]]. Sand containing naturally mild radioactive minerals are used on rare occasions to trace and measure fractures. According to a Times report in February 2011, wastewater at 116 of 179 deep gas wells in Pennsylvania "contained high levels of radiation," but its effect on public drinking water supplies is unknown because water suppliers are required to conduct tests of radiation "only sporadically".<ref>[http://www.post-gazette.com/pg/11064/1129908-113.stm#ixzz1eAXuAwtw Radiation-fracking link sparks swift reactions] By Don Hopey, 5 March 2011 Pittsburgh Post-Gazette</ref> The Times stated "never-reported studies" by the [[EPA]] and a "confidential study by the drilling industry" concluded that radioactivity in drilling waste cannot be fully diluted in rivers and other waterways.<ref>{{cite journal |title=Documents: Natural Gas's Toxic Waste |url=http://www.nytimes.com/interactive/2011/02/27/us/natural-gas-documents-1.html#document/p533/a9948
 
|publisher=New York Times
 
|date=February 26, 2011}}</ref> Despite this, as of early 2011 federal and state regulators did not require sewage treatment plants that accept drilling waste (which is mostly water) to test for radioactivity. In Pennsylvania, where the drilling boom began in 2008, most drinking-water intake plants downstream from those sewage treatment plants have not tested for radioactivity since before 2006.<ref>{{cite journal |title=Regulation Lax as Gas Wells’ Tainted Water Hits Rivers |url=http://www.nytimes.com/2011/02/27/us/27gas.html?pagewanted=all
 
|publisher=New York Times
 
|date=February 26, 2011}}</ref>
 
 
The [[New York Post]] stated that the [[Pennsylvania Department of Environmental Protection]] reported that all samples it took from seven rivers in November and December 2010 "showed levels at or below the normal naturally occurring background levels of radioactivity", and "below the federal drinking water standard for Radium 226 and 228.".<ref>[http://www.nypost.com/p/blogs/capitol/shocker_new_york_times_report_is_cLlp6sP8ohc3mZIXbFT7EM#ixzz1eAZWwuju Shocker: New York Times radioactive water report is false] March 8, 2011 ι Abby Wisse Schachter. Report is from a [[Rupert Murdoch]] tabloid, [[The New York Post]]</ref> However the samples taken by the state at at least one river, (the [[Monongahela River|Monongahela]], a source of drinking water for parts of [[Pittsburgh]]), were taken upstream from the sewage treatment plants accepting drilling waste water.<ref>{{cite journal |title=E.P.A. Steps Up Scrutiny of Pollution in Pennsylvania Rivers |url=http://www.nytimes.com/2011/03/08/science/earth/08water.html
 
|publisher=New York Times
 
|date=March 7, 2011}}</ref> Furthermore, the New York Times has implicated the DEP in industry-friendly inactivity, such as only making a "request — not a regulation" of gas companies to handle their own flowback waste rather than sending them to public water treatment facilities.<ref name=griswold>{{cite news|last=Griswold|first=Eliza|title=The Fracturing of Pennsylvania|url=http://www.nytimes.com/2011/11/20/magazine/fracking-amwell-township.html?pagewanted=all|accessdate=21 November 2011|newspaper=[[The New York Times Magazine]]|date=17 November 2011}}</ref>
 
 
===Chemicals used in fracturing===
 
 
Water is by far the largest component of fracking fluids. The initial drilling operation itself may consume from 65,000 gallons to 600,000 gallons of fracking fluids. Over its lifetime an average well will require up to an additional 5 million gallons of water for the initial fracking operation and possible restimulation frac jobs.<ref>{{cite web
 
|title=Water Usage
 
|url=http://www.hydraulicfracturing.com/Water-Usage/Pages/Information.aspx
 
|publisher=Chesapeake Energy site hydraulicfracturing.com}}</ref><!--Not a good citation. This is very specific -->
 
 
Chemical additives used in fracturing fluids typically make up less than 2% by weight of the total fluid<ref>http://www.hydraulicfracturing.com/Fracturing-Ingredients/Pages/information.aspx</ref>. Over the life of a typical well, this may amount to 100,000 gallons of chemical additives. These additives (listed in a U.S. House of Representatives Report<ref name="house1"/>) include biocides, surfactants, viscosity-modifiers, and emulsifiers. They vary widely in toxicity: Many are used in household products such as cosmetics, lotions, soaps, detergents, furniture polishes, floor waxes, and paints,<ref>{{cite web
 
|url=http://hpd.nlm.nih.gov/
 
|publisher=U.S. Department of Health and Human Services
 
|title=Household Products Database}}</ref> and some are used in food products. Although some of the chemicals pose no known health hazards, some are known carcinogens, some are toxic, some are neurotoxins. For example: benzene (causes cancer, bone marrow failure), lead (damages the nervous system and causes brain disorders), ethylene glycol (antifreeze, causes death), methanol (highly toxic), boric acid (kidney damage, death), 2-butoxyethanol (causes hemolysis).
 
 
The 2011 US House of Representatives investigative report on the chemicals used in hydraulic fracturing shows that of the 750 compounds in hydraulic fracturing products “[m]ore than 650 of these products contained chemicals that are known or possible human carcinogens, regulated under the Safe Drinking Water Act, or listed as hazardous air pollutants” (12). The report also shows that between 2005 and 2009 279 products (93.6 million gallons-not including water) had at least one component listed as “proprietary” or “trade secret” on their Occupational Safety and Health Administration (OSHA) required Material Safety Data Sheet (MSDS).
 
 
The MSDS is a list of chemical components in the products of chemical manufacturers, and according to OSHA, a manufacturer may withhold information designated as “proprietary” from this sheet. When asked to reveal the proprietary components, most companies participating in the investigation were unable to do so, leading the committee to surmise these “companies are injecting fluids containing unknown chemicals about which they may have limited understanding of the potential risks posed to human health and the environment” (12).<ref>Chemicals Used in Hydraulic Fracturing. U.S. House of Representatives Committee on Energy and Commerce Minority Staff. April 2011. http://democrats.energycommerce.house.gov/sites/default/files/documents/Hydraulic%20Fracturing%20Report%204.18.11.pdf</ref> Third-party laboratories are performing analysis on soil, air, and water near the fracturing sites to measure the level of contamination by each of the chemicals. Each state has a contact person in charge of such regulation.
 
<ref>{{cite web
 
|url= "http://www.caslab.com/Fracking-Regulations/"
 
|title= Fracking Regulations}}</ref> A map of these contact people can be found at FracFocus.org as well.<ref>About Gas: Regulation. http://www.aboutgas.com.au/regulation.html.</ref>
 
 
Another study in 2011, titled “Natural Gas Operations from a Public Health Perspective” and published in ''Human and Ecological Risk Assessment: An International Journal'' identified 632 chemicals used in natural gas operations. Only 353 of these are well-described in the scientific literature; and of these, more than 75% could affect skin, eyes, respiratory and gastrointestinal systems; roughly 40-50% could affect the brain and nervous, immune and cardiovascular systems and the kidneys; 37% could affect the endocrine system; and 25% were carcinogens and mutagens. The study indicated possible long-term health effects that might not appear immediately. The study recommended full disclosure of all products used, along with extensive air and water monitoring near natural gas operations; it also recommended that fracking's exemption from regulation under the US Safe Drinking Water Act be rescinded.<ref>{{cite journal |title=Natural Gas Operations from a Public Health Perspective |journal=Human and Ecological Risk Assessment: An International Journal |last=Colborn |first=Theo |last2=Kwiatkowski |first2=Carol |last3=Schultz |first3=Kim |last4=Bachran |first4=Mary |pages=1039–1056 |issue=17:5 |year=2011}}</ref>
 
 
=== Earthquakes ===
 
A report in the UK concluded that fracking was the likely cause of some small earth tremors that happened during shale gas drilling.<ref>[http://www.bbc.co.uk/news/uk-england-lancashire-15550458 Fracking tests near Blackpool 'likely cause' of tremors]</ref><ref>[http://www.cuadrillaresources.com/cms/wp-content/uploads/2011/11/Final_Report_Bowland_Seismicity_02-11-11.pdf Geomechanical Study of Bowland Shale Seismicity]</ref> In addition the [[United States Geological Survey]] (USGS) reports that "Earthquakes induced by human activity have been documented in a few locations" in the United States, Japan, and Canada; "the cause was injection of fluids into deep wells for waste disposal and secondary recovery of oil, and the use of reservoirs for water supplies."<ref>[http://earthquake.usgs.gov/learn/faq/?categoryID=1&faqID=1Q: "FAQs - Earthquakes, Faults, Plate Tectonics, Earth Structure: Can we cause earthquakes? Is there any way to prevent earthquakes?"] USGS. October 27, 2009.</ref> The disposal and injection wells referenced are regulated under the Safe Drinking Water Act and UIC laws and are not wells where hydraulic fracturing is generally performed.
 
 
Several earthquakes, that happened throughout 2011 in Youngstown, Ohio, USA are likely linked to a disposal well for injecting wastewater used in the hydraulic fracturing process, say seismologists at [[Columbia University]].<ref>[http://www.ldeo.columbia.edu/news-events/seismologists-link-ohio-earthquakes-waste-disposal-wells "Ohio Quakes Probably Triggered by Waste Disposal Well, Say Seismologists", Lamont-Doherty Earth Observatory Institute, Columbia University, January 6, 2012]</ref>
 
 
===Greenhouse gas emissions===
 
The use of natural gas rather than oil or coal is often viewed as a way of alleviating [[global warming]]: natural gas burns more cleanly, and gas power stations can produce up to 50% less greenhouse gases than coal stations.<ref>{{cite journal| title=Should Fracking Stop? Extracting gas from shale increases the availability of this resource, but the health and environmental effects may be too high. Counterpoint: No, It's Too Valuable. |last=Engelder |first=Terry |pages=271–275 |issue=477 |date=15 September 2011| journal=Nature}}</ref> However, an analysis by Howarth et al. of the well-to-consumer lifecycle of fracked natural gas concluded that 3.6–7.9% of the methane produced by a well will be leaked into the atmosphere during the well's lifetime. According to the analysis, methane is such a potent [[greenhouse gas]], this means that over short timescales, shale gas is actually worse than coal or oil. Methane gradually breaks down in the atmosphere, forming carbon dioxide, so that over very long periods it is no more problematic than [[carbon dioxide]]; in the meantime, even if shale gas is burnt in efficient gas power stations, its greenhouse-gas footprint is still worse than coal or oil for timescales of less than fifty years.<ref>{{cite journal| title=Should Fracking Stop? Extracting gas from shale increases the availability of this resource, but the health and environmental effects may be too high. Point: Yet, it's too high risk |last=Howarth |first=Robert W. |last2=Ingraffea |first2=Anthony |pages=271–275 |issue=477 |date=15 September 2011| journal=Nature}}</ref> This analysis by Howarth et al. refers to the 2011 study by the same authors published in Climatic Change Letters in which they controversially claimed that the extraction of shale gas may lead to the emission of as much or more greenhouse gas emissions than oil or coal.<ref>Howarth RW, Santoro R, and Ingraffea A (2011). Climatic Change Letters, DOI: 10.1007/s10584-011-0061-5, [http://www.springerlink.com/content/e384226wr4160653/fulltext.pdf]</ref> However, numerous studies have pointed out critical flaws with that paper and/or come to completely different conclusions, including assessments by experts at the U.S. Department of Energy,<ref>Timothy J. Skone, "Life Cycle Greenhouse Gas Analysis of Natural Gas Extraction & Delivery in the United States." National Energy Technology Laboratory, May 12, 2011 [http://cce.cornell.edu/EnergyClimateChange/NaturalGasDev/Documents/PDFs/SKONE_NG_LC_GHG_Profile_Cornell_12MAY11_Final.pdf]</ref>, peer-reviewed studies by Carnegie Mellon University<ref>Mohan Jiang et al. (2011), "Life cycle greenhouse gas emissions of Marcellus shale gas." Environmental Research Letters, DOI: 10.1088/1748-9326/6/3/034014, [http://iopscience.iop.org/1748-9326/6/3/034014/fulltext/]</ref> and the University of Maryland<ref>Hultman et al (2011), "The greenhouse impact of unconventional gas for electricity generation." Environmental Research Letters, DOI: 10.1088/1748-9326/6/4/044008, [http://iopscience.iop.org/1748-9326/6/4/044008]</ref>, and even the [[Natural Resources Defense Council]], which concluded that the Howarth et al. paper's use of a 20-year time horizon for global warming potential of methane is "too short a period to be appropriate for policy analysis."<ref>Dan Lashof, "Natural Gas Needs Tighter Production Practices to Reduce Global Warming Pollution," April 12, 2011 [http://switchboard.nrdc.org/blogs/dlashof/natural_gas_needs_tighter_prod.html]</ref> In January 2012, Howarth's own colleagues at [[Cornell University]], Lawrence Cathles et al., responded with their own peer-reviewed assessment, noting that the Howarth paper was "seriously flawed" because it "significantly overestimate[s] the fugitive emissions associated with unconventional gas extraction, undervalue[s] the contribution of 'green technologies' to reducing those emissions to a level approaching that of conventional gas, base[s] their comparison between gas and coal on heat rather than electricity generation (almost the sole use of coal), and assume[s] a time interval over which to compute the relative climate impact of gas compared to coal that does not capture the contrast between the long residence time of CO2 and the short residence time of methane in the atmosphere."<ref>Cathles et al. (2011), [http://www.springerlink.com/content/x001g12t2332462p/]</ref> The author of that response, Lawrence Cathles, concludes that "shale gas has a GHG footprint that is half and perhaps a third that of coal," based upon "more reasonable leakage rates and bases of comparison."
 
 
==Public relations==
 
The considerable opposition against fracking activities in local townships has led companies to adopt a variety of public relations measures to assuage fears about fracking, including the admitted use of "mil­i­tary tac­tics to counter drilling oppo­nents". At a conference where public relations measures were discussed, a senior executive at [[Anadarko Petroleum]] was recorded on tape saying, ''"Download the US Army / Marine Corps Counterinsurgency Manual, because we are dealing with an insurgency"'', while referring to fracking opponents. Matt Pitzarella, spokesman for the most important fracking company in Pennsylvania, [[Range Resources]], also told other conference attendees that Range employed [[psychological warfare]] operations veterans. According to Pitzarella, the experience learnt in the Middle East has been valuable to Range Resources in Pennsylvania, when dealing with emotionally-charged township meetings and advising townships on zoning and local ordinances dealing with fracking.<ref name=psyops>{{cite news|last=Javers|first=Eamon|title=Oil Executive: Military-Style 'Psy Ops' Experience Applied|url=http://www.cnbc.com/id/45208498|newspaper=[[CNBC]]|date=8 Nov 2011}}</ref><ref>{{cite news|last=Phillips|first=Susan|title=‘We’re Dealing with an Insurgency,’ says Energy Company Exec of Fracking Foes|url=http://stateimpact.npr.org/pennsylvania/2011/11/09/were-dealing-with-an-insurgency-says-energy-company-exec-of-fracking-foes/|newspaper=[[National Public Radio]]|date=9 Nov 2011}}</ref>
 
 
==Hydraulic fracturing by country==
 
Hydraulic fracturing has become a contentious environmental and health issue with France banning the practice and a moratorium in place in New South Wales (Australia), Karoo basin (South Africa), Quebec (Canada), and some of the states of the US.<!-- Need to dig out a better ref than this --><ref>Stewart, Rachel (July 25, 2011). [http://www.stuff.co.nz/taranaki-daily-news/opinion/5332967/Editorial-A-fracking-scandal-on-our-back-doorstep "Editorial A fracking scandal on our back doorstep"]. Stuff.co.nz. ''Taranaki Daily News''.{{dubious|date=September 2011}}</ref>
 
 
===Australia===
 
Up until the mid 2000s, hydraulic fracturing was generally limited to conventional oil and gas wells in the [[Cooper Basin]] and limited to one, two or sometimes zero ongoing fracturing operations. However more recently, it has spread and grown in Queensland as coal seam gas drilling and production in the [[Surat Basin|Surat]] and [[Bowen Basin|Bowen]] basins has rapidly increased. However the vast majority of coal seam gas wells have not been hydraulically fractured as the wells presently being drilled are in coal seams that have good natural permeability.
 
 
On 21 February 2011, the [[Australian Broadcasting Corporation|ABC]]'s investigative journalism program [[Four Corners (TV program)|Four Corners]] aired a program showing incidents of wellhead gas leaks (unrelated to hydraulic fracturing) and alleged aquifer contamination near [[Chinchilla, Queensland]] at wells owned by [[QGC]], some of which had been hydraulically fractured.<ref>{{Cite episode
 
| title = The Gas Rush
 
| series = [[Four Corners (TV program)|Four Corners]]
 
| url = http://www.abc.net.au/4corners/content/2011/s3141787.htm
 
| credits = Reporter: Matthew Carney, Presenter: Kerry O'Brien
 
| network = [[Australian Broadcasting Corporation|ABC]]
 
| city = [[Chinchilla, Queensland]]
 
| airdate = February 21, 2011
 
| minutes = 0:43}}</ref>
 
 
There is currently a moratorium in place on the practice of hydraulic fracturing in the state of [[New South Wales]].{{citation needed|date=November 2011}}. The moratorium will not affect exploration, drilling core holes and getting core samples. The NSW Government's restrictions on hydraulic fracturing apply to new licences only. The NSW Government has banned [[BTEX]] chemicals as additives. {{cn|date=December 2011}} It also requires companies to hold a water licences for extraction of more than three megalitres per year and has banned the use of evaporation ponds. {{cn|date=December 2011}}
 
===Bulgaria===
 
A number of protests occurred in Bulgaria after the government's decision to grant an approval for [[Chevron Corporation]] to research the possibilities of [[shale gas]] extraction in the country's northeast in 2011. After a nationwide protest in January 2012, the government decided to ban the hydraulic fracturing technology.<ref>[http://thesofiaecho.com/2012/01/17/1746998_bulgaria-says-chevron-cannot-use-fracking-to-search-for-shale-gas Bulgaria says Chevron cannot use fracking to search for shale gas], The Sofia Echo, 17 January 2012</ref>
 
 
===Canada===
 
Fracking has been in use in Canada at an industrial level since the 1990s. Concerns about fracking began in late July 2011, when the [[Government of British Columbia]] gave [[Talisman Energy]] a long-term water licence to draw water from the [[BC Hydro]]-owned [[Williston Lake]] [[reservoir]], for a twenty year term. Fracking has also received criticism in [[New Brunswick]] and [[Nova Scotia]], and the Nova Scotia government is currently reviewing the practice, with recommendations expected in March 2012. The practice has been temporarily suspended, in [[Quebec]], pending an environmental review. The [[Canadian Centre for Policy Alternatives]] has also expressed concern.<ref>{{cite news|url=http://www.cbc.ca/news/technology/story/2011/07/29/bc-talisman-fracking.html|title=Northern B.C. fracking licence concerns critics |date=July 29, 2011 |publisher=[[CBC.ca]] |accessdate=2011-07-30}}</ref>
 
 
===France===
 
Hydraulic fracturing was banned in France in 2011 after public pressure.<ref>{{cite web|url=http://www.bloomberg.com/news/2011-07-01/france-vote-outlaws-fracking-shale-for-natural-gas-oil-extraction.html |title=France Vote Outlaws ‘Fracking’ Shale for Natural Gas, Oil Extraction |publisher=Bloomberg.com |date=July 1, 2011 }}</ref>
 
 
===Ireland===
 
In Ireland, Tamboran Resources have a licence for gas exploration and plan to proceed hydraulic fracturing in the [[Lough Allen]] basin area of [[County Leitrim]]. The CEO of Tamboran Resources has declared a “zero-chemical hydraulic fracturing” pledge. The Protest group "No Fracking Ireland" has been set up by locals of counties Leitrim, [[County Roscommon|Roscommon]] and [[County Sligo|Sligo]] and petitions against hydraulic fracturing are still ongoing. .<ref>{{cite news|url=http://www.leitrimobserver.ie/news/zero_chemical_promise_on_fracking_is_not_enough_1_3019372|title=|date=September 1, 2011 |publisher=[[CBC.ca]] |accessdate=2012-01-03}}</ref>
 
 
===New Zealand===
 
In [[New Zealand]], hydraulic fracturing is part of petroleum exploration and extraction on a small scale mainly in Taranaki and concerns have been raised by environmentalists.<ref>{{cite news| last = Maetzig| first = Rob| title = Anti-frackers 'need to get real'| newspaper = Taranaki Daily News| accessdate = 2011-07-27| date = July 27, 2011| url = http://www.stuff.co.nz/taranaki-daily-news/news/5344522/Anti-frackers-need-to-get-real
 
}}</ref><ref>{{cite news
 
|url= http://www.stuff.co.nz/taranaki-daily-news/news/5379486/Concern-as-gas-drilling-intensifies |title=Concern as gas drilling intensifies
 
|first=Rob |last=Maetzig
 
|newspaper=Taranaki Daily News
 
|date= August 3, 2011
 
|accessdate=2011-08-14}}</ref>
 
 
===South Africa===
 
There is currently a moratorium on hydraulic fracturing in South Africa's [[Karoo]] region despite the interest of several energy companies.<ref>{{cite web|url=http://www.reuters.com/article/2011/04/21/us-safrica-fracking-idUSTRE73K45620110421 |title=S.Africa imposes "fracking" moratorium in Karoo |publisher=Reuters.com |date=April 21, 2011 }}</ref>
 
 
===United Kingdom===
 
Hydraulic fracturing is currently proceeding in the United Kingdom operated by Cuadrilla and a number of other companies. In [[Lancashire]], operations were suspended after two small earthquakes subsequent to drilling operations.<ref>{{cite web|url=http://www.bbc.co.uk/news/uk-england-lancashire-13700575|title=Shale gas fracking: MPs call for safety inquiry after tremors |publisher=BBC |date=June 8, 2011 }}</ref>
 
 
Several protest groups have started to oppose hydraulic fracturing in the UK such as nationwide groups like [[Frack Off]] and local groups like Ribble Estuary Against Fracking and The Vale Says No <ref>{{cite web|last=Melley |first=James |url=http://www.bbc.co.uk/news/science-environment-15021328 |title=BBC News - New groups protest at shale gas |publisher=Bbc.co.uk |date=2011-09-28 |accessdate=2011-11-02}}</ref>
 
 
===United States===
 
{{Main|Hydraulic fracturing in the United States}}
 
 
Hydraulic fracturing is most commonly used in the United States to extract natural gas from shale formations. Because of the impermeability of shale, the gas industry of the 1970s could not economically extract shale gas<ref>[http://www.aapg.org/explorer/2011/09sep/fredonia0911.cfm "Proceedings from the 2nd Annual Methane Recovery from Coalbeds Symposium"]</ref><ref>[http://www.netl.doe.gov/newsroom/100yr/NETL-A_Century_of_Innovation.pdf National Energy Technology Laboratory. "A Century of Innovation: A history of NETL from the U.S. Bureau of Mines to the National Energy Technology Laboratory (1910-2010)."]</ref>. Following direct investments in R&D and demonstration in massive hydraulic fracturing, directional drilling, and microseismic 3-dimensional imaging by the Department of Energy and other federal agencies<ref>[http://www.washingtonpost.com/opinions/a-boom-in-shale-gas-credit-the-feds/2011/12/07/gIQAecFIzO_story.html Michael Shellenberger and Ted Nordhaus. "A boom in shale gas? Credit the feds." Washington Post, December 16, 2011.]</ref><ref>[http://thebreakthrough.org/blog/2011/12/new_investigation_finds_decade.shtml The Breakthrough Institute. "New Investigation Finds Decades of Government Funding Behind Shale Revolution." December 2011.]</ref>, Mitchell Energy applied an innovative technique called slick-water fracturing to achieve the first economical well for the extraction of shale gas in 1998<ref>[http://thebreakthrough.org/blog/2011/12/interview_with_dan_steward_for.shtml The Breakthrough Institute. Interview with Dan Steward, Former Mitchell Energy Vice President. December 2011.]</ref>.
 
 
Hydraulic fracturing for the purpose of oil, natural gas, and geothermal production was exempted under the Safe Drinking Water Act.<ref>{{cite web
 
|url=http://water.epa.gov/type/groundwater/uic/class2/hydraulicfracturing/wells_hydroreg.cfm
 
|title= Regulation of Hydraulic Fracturing by the Office of Water
 
|publisher=US EPA
 
|date=October 6, 2011
 
|accessdate=October 14, 2011}}</ref> This was a result of the signage of the Energy Policy Act of 2005, also known as the Halliburton Loophole because of former Halliburton CEO Vice President Dick Cheney’s involvement in the passing of this exemption. The result of a 2004 EPA study on coalbed hydraulic fracturing was used to justify the passing of the exemption; however EPA whistleblower Weston Wilson and the Oil and Gas Accountability Project found that critical information was removed from the final report.<ref>Sumi, Lisa. "Our Drinking Water at Risk What EPA and the Oil And Gas Industry Don’t Want Us to Know About Hydraulic Fracturing." www.earthworks.org. Oil and Gas Accountability Project & Earthworks, n.d. Web. 16 Oct. 2011.<http://www.earthworksaction.org/pubs/DrinkingWaterAtRisk.pdf>.</ref> Halliburton is the No. 1 provider of fracking services in the United States.<ref name="BW 19.01.2012"/>
 
 
Opposers of hydraulic fracturing in the US have focused on this 2005 exemption; however the more primary risk to drinking water is the handling and treatment of wastewater produced by hydraulic fracturing. The EPA and the state authorities do have power “to regulate discharge of produced waters from hydraulic operations” (EPA, 2011) under the Clean Water Act, which is regulated by the National Pollutant Discharge Elimination System (NPDES) permit program<ref>Regulation of Hydraulic Fracturing Under the Safe Drinking Water Act. http://water.epa.gov/type/groundwater/uic/class2/hydraulicfracturing/wells_hydroreg.cfm. US EPA.October 31, 2011. Retrieved November 7, 2011. OR "Hydraulic Fracturing." www.epa.gov. Environmental Protection Agency, n.d. Web. 5 Oct. 2011. <http://water.epa.gov/type/groundwater/uic/class2/hydraulicfracturing/index.cfm>.</ref> "Treatment and Disposal of Wastewater from Shale Gas Extraction | NPDES."www.epa.gov/npdes. Environmental Protection Agency, n.d. Web. 15 Oct. 2011. <http://cfpub.epa.gov/npdes/hydrofracturing.cfm>.. Although this waste is regulated, oil and gas exploration and production (E&P) wastes are exempt from Federal Hazardous Waste Regulations under Subtitle C of the Resource Conservation and Recovery Act (RCRA) despite the fact that wastewater from hydraulic fracturing contains toxins such as total dissolved solids (TDS), metals, and radionuclides.<ref>Exemption of Oil and Gas Exploration and Production Wastes from Federal Hazardous Waste Regulations." www.epa.gov. Environmental Protection Agency, n.d. Web. 15 Oct. 2011. <http://www.epa.gov/osw/nonhaz/industrial/special/oil/oil-gas.pdf></ref><ref>Natural Gas Drilling in the Marcellus Shale NPDES Program Frequently Asked Question." epa.gov/npdes. Environmental Protection Agency, 16 Mar. 2011. Web. 15 Oct. 2011. <http://www.epa.gov/npdes/pubs/hydrofracturing_faq.pdf>.</ref>
 
About 750 chemicals have been listed as additives for hydraulic fracturing in a report to the US Congress in 2011. However, well-specific information can be found on FracFocus.org and it can be noted that significantly fewer chemicals are actually used in the hydraulic fracturing operation. <ref>FracFocus.org</ref>
 
<ref>{{cite web
 
|url= http://www.propublica.org/article/fracking-chemicals-cited-in-congressional-report-stay-underground/single
 
|title= Fracking Chemicals Cited in Congressional Report Stay Underground
 
|publisher= ProPublica
 
|date= April 8, 2011
 
|accessdate= July 11, 2011}}</ref>
 
 
==See also==
 
*[[ExxonMobil Electrofrac]]
 
*''[[Gasland]]'', a 2010 documentary by Josh Fox claim that hydraulic fracturing has many environmental impacts
 
*[[Eddy covariance]], a method to directly measure emissions of gases displayed by hydraulic fracturing into the atmosphere
 
*[[Cost of electricity by source]]
 
*[[Environmental impact of the oil shale industry]]
 
*[[Environmental impact of petroleum]]
 
*[[Environmental concerns with electricity generation]]
 
 
==Notes==
 
:a. {{note_label|a|a|none}} Also spelled "fraccing"<ref>[http://www.appea.com.au/images/stories/Policy_CSG/APPEA_Fraccing_chemicals_-_FINAL.pdf "Chemicals that may be used in Australian CSG fraccing fluid"] [[Petroleum industry in Western Australia|Australian Petroleum Ptoduction & Exploration Association Limited]]</ref> or "fracing".<ref>{{cite web |url=http://stocks.investopedia.com/stock-analysis/2010/Will-The-EPA-Crack-Down-On-Fracking-HAL-APC-NBL-COG-EOG-CHK-UPL-XOM0712.aspx
 
|title=Will The EPA Crack Down On 'Fracking'?
 
|publisher=Investopedia
 
|date=Jul 12, 2010
 
|author=Stephen D. Simpson}}</ref><ref>{{cite web|url=http://www.hydraulicfracturing.com |title=HydraulicFracturing.com |publisher=HydraulicFracturing.com |date= |accessdate=2011-07-13}}</ref>
 
 
==References==
 
{{Reflist|2}}
 
 
==External links==
 
*[http://www.earthworksaction.org/FracingDetails.cfm Hydraulic Fracturing slanted toward environmental issues] at Earthworks
 
*[http://www.propublica.org/series/fracking Fracking] collected news and commentary at ''[[ProPublica]]''
 
*{{Guardiantopic|environment/shale-gas|Shale gas and fracking}}
 
*[http://fracfocus.org/ FracFocus] Site indicating chemical composition of fracking fluid of individual wells
 
*[http://www.youtube.com/user/Shell#p/u/21/vO82b2auSdo Hydraulic fracturing shale gas extraction] at [[YouTube]]
 
 
{{Shale gas|technology=yes}}
 
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{{redirect|Fracking|the expletive|Frak (expletive)}}
 
'''Hydraulic fracturing''' is the propagation of fractures in a rock layer caused by the presence of a pressurized fluid. Hydraulic fractures form naturally, as in the case of [[Vein (geology)|vein]]s or [[dike]]s, and is one means by which gas and petroleum from [[source rock]]s may migrate to [[reservoir rock]]s.
 
 
However oil and gas companies may attempt to accelerate this process in order to release [[petroleum]], [[natural gas]], [[coal seam gas]], or other substances for extraction, where the technique is often called '''fracking'''{{ref label|a|a|none}} or '''hydrofracking'''.<ref name="Charlez">Charlez, Philippe A. (1997). ''Rock Mechanics: Petroleum applications'', Editions Technip.</ref> This type of fracturing, known colloquially as a '''frack job''' (or '''frac job'''),<ref>[http://www.glossary.oilfield.slb.com/Display.cfm?Term=frac%20job "frac job"], Schlumberger Oilfield Glossary</ref><ref>[http://www.fracktrack.org "frac job"] Pennsylvania Marcellus Shale GIS Database</ref> is done from a [[wellbore]] drilled into reservoir rock formations. The energy from the injection of a highly-pressurized [[fracking fluid]] <ref>Schlumberger Oilfield Glossary, describing [http://www.glossary.oilfield.slb.com/Display.cfm?Term=fracturing%20fluid fracking fluids]</ref> creates new channels in the rock which can increase the extraction rates and ultimate recovery of fossil fuels. When done in already highly-permeable reservoirs such as [[sandstone]]-based wells, the technique is known as '''well stimulation'''. Operators typically try to maintain ''fracture width'' or slow its decline following treatment by introducing a [[proppant]]<ref name="proppant">Schlumberger Oilfield Glossary, definition of [http://www.glossary.oilfield.slb.com/Display.cfm?Term=proppant proppant]</ref> into the injected fluid, a material, such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped. Consideration of proppant strengths and prevention of proppant failure becomes more important at deeper depths where pressure and stresses on fractures are higher.
 
   
 
Distinction can be made between low-volume hydraulic fracturing used to stimulate high-permeability reservoirs, which may consume typically 20,000 to 80,000 gallons of fluid per well, with high-volume hydraulic fracturing, used in the [[well completion|completion]] of [[tight gas]] and [[shale gas]] wells; high-volume hydraulic fracturing can use as much as two to three million gallons of fluid per well.<ref>{{cite web|author=Andrews, Anthony et. al. |url=http://www.fas.org/sgp/crs/misc/R40894.pdf |title=Unconventional Gas Shales: Development, Technology, and Policy Issues |publisher= Congressional Research Service |date=2009 |accessdate=Jan. 16, 2012}}</ref>
 
Distinction can be made between low-volume hydraulic fracturing used to stimulate high-permeability reservoirs, which may consume typically 20,000 to 80,000 gallons of fluid per well, with high-volume hydraulic fracturing, used in the [[well completion|completion]] of [[tight gas]] and [[shale gas]] wells; high-volume hydraulic fracturing can use as much as two to three million gallons of fluid per well.<ref>{{cite web|author=Andrews, Anthony et. al. |url=http://www.fas.org/sgp/crs/misc/R40894.pdf |title=Unconventional Gas Shales: Development, Technology, and Policy Issues |publisher= Congressional Research Service |date=2009 |accessdate=Jan. 16, 2012}}</ref>
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