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Hydraulic fracturing
Process type	Mechanical
Industrial sector(s)	Mining
Main technologies or sub-processes	Fluid pressure
Product(s)	Natural gas; Petroleum
Inventor	Floyd Farris; J.B. Clark (Stanolind Oil and Gas Corporation)
Year of invention	1947

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Hydraulic fracturing is the propagation of fractures in a rock layer, as a result of the action of a pressurized fluid. Some hydraulic fractures form naturally—certain veins or dikes are examples—and can create conduits along which gas and petroleum from source rocks may migrate to reservoir rocks. Induced hydraulic fracturing or hydrofracking, commonly known as fraccing or fracking, is a technique used to release petroleum, natural gas (including shale gas, tight gas and coal seam gas), or other substances for extraction.^[a]^[1]

The first use of hydraulic fracturing was in 1947 but the modern fraccing technique that made the extraction of shale gas economical was first used in 1997 in the Barnett Shale in Texas.^[1]^[2]^[3] The energy from the injection of a highly pressurized fracking fluid creates new channels in the rock which can increase the extraction rates and ultimate recovery of hydrocarbons.

Proponents of fraccing point to the vast amounts of formerly inaccessible hydrocarbons the process can extract.^[4] Opponents point to potential environmental impacts, including contamination of ground water, risks to air quality, the migration of gases and hydraulic fracturing chemicals to the surface, surface contamination from spills and flowback and the health effects of these.^[5]

Schematic depiction of hydraulic fracturing for shale gas, showing potential environmental effects.

Geology

Mechanics

Fracturing in rocks at depth tends to be suppressed by the confining pressure, due to the load caused by the overlying rock strata. This is particularly so in the case of "tensile" (Mode 1) fractures, which require the walls of the fracture to move apart, working against this confining pressure. Hydraulic fracturing occurs when the effective stress is reduced sufficiently by an increase in the pressure of fluids within the rock, such that the minimum principal stress becomes tensile and exceeds the tensile strength of the material.^[6]^[7] Fractures formed in this way will in the main be oriented in a plane perpendicular to the minimum principal stress and for this reason induced hydraulic fractures in wellbores are sometimes used to determine the orientation of stresses.^[8] In natural examples, such as dikes or vein-filled fractures, the orientations can be used to infer past states of stress.^[9]

Veins

Most vein systems are a result of repeated hydraulic fracturing during periods of relatively high pore fluid pressure. This is particularly noticeable 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.^[10] One mechanism to demonstrate 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. This process is referred to as "seismic pumping".^[11]

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.^[12]

History

Fracturing as a method to stimulate shallow, hard rock oil wells dates back to the 1860s. It was applied by oil industries in Pennsylvania, New York, Kentucky, and West Virginia by using liquid and later also solidified nitroglycerin. Later the same method was applied to water and gas wells. The idea to use acid as a nonexplosive fluid for a well stimulation was introduced in the 1930s. Due to acid etching, created fractures would not close completely and therefore enhanced productivity. The same phenomenon was discovered with water injection and squeeze cementing operations.^[13]

The relationship between well performance and treatment pressures was studied by Floyd Farris of Stanolind Oil and Gas Corporation. This study became a basis of the first hydraulic fracturing experiment, which was conducted in 1947 at the Hugoton gas field in Grant County of southwestern Kansas by Stanolind.^[1]^[13] For the well treatment 1,000 US gallons (3,800 L; 830 imp gal) of gelled gasoline and sand from the Arkansas River was injected into the gas producing limestone formation at 2,400 feet (730 m). The experiment was not very successful as deliverability of the well did not change appreciably. The process was further described by J.B. Clark of Stanolind in his paper published in 1948. A patent on this process was issued in 1949 and an exclusive license was granted to the Halliburton Oil Well Cementing Company. On March 17, 1949, Halliburton performed the first two commercial hydraulic fracturing treatments in Stephens County, Oklahoma, and Archer County, Texas.^[13] Since then, hydraulic fracturing has been used to stimulate approximately a million oil and gas wells.^[14]

In the Soviet Union, the first hydraulic proppant fracturing was carried out in 1952. In Western Europe in 1977–1985, hydraulic fracturing was conducted at Rotliegend and Carboniferous gas-bearing sandstones in Germany, Netherlands onshore and offshore gas fields, and the United Kingdoms sector of the North Sea. Other countries in Europe and Northern Africa included Norway, the Soviet Union, Poland, Czechoslovakia, Yugoslavia, Hungary, Austria, France, Italy, Bulgaria, Romania, Turkey, Tunisia, and Algeria.^[15]

Due to shale's high porosity and low permeability, technology research, development and demonstration were necessary before hydraulic fracturing could be commercially applied to shale gas deposits. In the 1970s the federal government initiated both the Eastern Gas Shales Project, a set of dozens of public-private hydro-fracturing pilot demonstration projects, and the Gas Research Institute, a gas industry research consortium that received approval for research and funding from the Federal Energy Regulatory Commission.^[16] In 1977, the Department of Energy pioneered massive hydraulic fracturing in tight sandstone formations. In 1997, based on earlier techniques used by Union Pacific Resources (now part of Anadarko Petroleum Corporation), Mitchell Energy (now part of Devon Energy) developed the hydraulic fracturing technique known as "slickwater fracturing" that made the shale gas extraction economical.^[2]^[3]^[17]

In 2011, France became the first nation to ban hydraulic fracturing.^[18]^[19]

Induced hydraulic fracturing

Uses

The technique of hydraulic fracturing is used to increase or restore the rate at which fluids, such as petroleum, 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 (1,500–6,100 m)). At such depth, there may not be sufficient 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 pivotal to extract gas from shale reservoirs because of the extremely low natural permeability of shale, which is measured in the microdarcy to nanodarcy range.^[20] Fractures provide a conductive path connecting a larger volume of the reservoir to the well. So-called "super fracking", which creates cracks deeper in the rock formation to release more oil and gas, will allow companies to frack more efficiently.^[21] The yield for a typical shale gas well generally falls off sharply after the first year or two.^[22]

While the main industrial use of hydraulic fracturing is in arousing production from oil and gas wells,^[23]^[24]^[25] hydraulic fracturing is also applied:

To stimulate groundwater wells^[26]
To precondition or induce rock to cave in mining^[27]
As a means of enhancing waste remediation processes, usually hydrocarbon waste or spills^[28]
To dispose of waste by injection into deep rock formations^[29]
As a method to measure the stress in the earth^[30]
For heat extraction to produce electricity in an enhanced geothermal systems^[31]
To increase injection rates for geologic sequestration of CO₂^[32]

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 (pressure gradient) of the rock.^[33] The fracture gradient is defined as the pressure increase per unit of the depth due to its density and it is usually measured in pounds per square inch per foot or bars per meter. The rock cracks and the fracture fluid continues further into the rock, extending the crack still further, and so on. Operators typically try to maintain "fracture width", or slow its decline, following treatment by introducing into the injected fluid a proppant – a material such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing when the injection is stopped and the pressure of the fluid is reduced. Consideration of proppant strengths and prevention of proppant failure becomes more important at greater depths where pressure and stresses on fractures are higher. 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.^[33]

During the process fracturing fluid leakoff, loss of fracturing fluid from the fracture channel into the surrounding permeable rock occurs. If not controlled properly, it can exceed 70% of the injected volume. This may result in formation matrix damage, adverse formation fluid interactions, or altered fracture geometry and thereby decreased production efficiency.^[34]

The location of one or more fractures along the length of the borehole is strictly controlled by various methods that create or seal off holes in the side of the wellbore. Typically, hydraulic fracturing is performed in cased wellbores and the zones to be fractured are accessed by perforating the casing at those locations.^[35]

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 quintuplex 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.^[36] Fracturing equipment operates over a range of pressures and injection rates and can reach up to 100 megapascals (15,000 psi) and 265 litres per second (9.4 cu ft/s) (100 barrels per minute).^[37]

Well types

A distinction can be made between conventional or low-volume hydraulic fracturing used to stimulate high-permeability reservoirs to frac a single well, and unconventional or high-volume hydraulic fracturing, used in the completion of tight gas and shale gas wells as unconventional wells are deeper and require higher pressures than conventional vertical wells.^[38] In addition to hydraulic fracturing of vertical wells, it is also performed in horizontal wells. When done in already highly permeable reservoirs such as sandstone-based wells, the technique is known as "well stimulation".^[25]

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 (460 to 1,520 m) in the Barnett Shale basin in Texas, and up to 10,000 feet (3,000 m) in the Bakken formation in North Dakota. In contrast, a vertical well only accesses the thickness of the rock layer, typically 50–300 feet (15–91 m). Horizontal drilling also reduces surface disruptions as fewer wells are required to access a given volume of reservoir rock. 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.^[39]

Fracturing fluids

Introduction

The two main purposes of fracturing fluid is to extend fractures and to carry proppant into the formation, the purpose of which is to stay there without damaging the formation or production of the well. Two methods of transporting the proppant in the fluid are used – high-rate and high-viscosity. High-viscosity fracturing tends to cause large dominant fractures, while with high-rate (slickwater) fracturing causes small spread-out micro-fractures.^{[citation needed]}

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. Typically, of the fracturing fluid over 98–99.5% is water and sand with the chemicals accounting to about 0.5%.^[33]^[40]

Hydraulic fracturing may use between 1.2 and 3.5 million US gallons (4.5 and 13.2 Ml) of fluid per well, with large projects using up to 5 million US gallons (19 Ml). Additional fluid is used when wells are refractured; this may be done several times.^[41]^: 7, 33

Proppants

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. The most commonly used proppant is silica sand, though proppants of uniform size and shape, such as a ceramic proppant, is believed to be more effective. Due to a higher porosity within the fracture, a greater amount of oil and natural gas is liberated.^[42]

High-rate fracturing

In slickwater hydraulic fracturing a fracturing fluid containing a limited amount of sand, friction reducers and other chemical additives, to improve the efficiency of fracturing, is pumped at a high rate to ensure the rate of the fluid carries the proppant down the well, through the perforations, and into the formation. The friction reducer is usually a polymer, the purpose of which is to reduce pressure loss due to friction, thus allowing the pumps to pump at a higher rate without having greater pressure on the surface. The process does not work well at high concentrations of proppant thus more water is required to carry the same amount of proppant. Slickwater fracturing is the preferred method on shale formations, but it is not always used in such cases.^{[citation needed]} For slickwater it is common to include sweeps or a reduction in the proppant concentration temporarily to ensure the well is not overwhelmed with proppant causing a screen-off.^{[citation needed]}

High-viscosity fracturing

A variety of chemicals that can be used to increase the viscosity of the fracturing fluid. With any viscosity increase, some type of gelling chemical must be used first.^[43] Viscosity is used to carry proppant into the formation, but when a well is being flowed back or produced, it is undesirable to have the fluid pull the proppant out of the formation. For this reason, a chemical known as a breaker is almost always pumped with all gel or crosslinked fluids to reduce the viscosity. This chemical is usually an oxidizer or an enzyme. The oxidizer reacts with the gel to break it down, reducing the fluid's viscosity and ensuring that no proppant is pulled from the formation. An enzyme acts as a catalyst for the breaking down of the gel. Sometimes pH modifiers are used to break down the crosslink at the end of a hydraulic fracture job, since many require a pH buffer system to stay viscous.^{[citation needed]} The rate of viscosity increase for several gelling agents is pH-dependent, so that occasionally pH modifiers must be added to ensure viscosity of the gel.^{[citation needed]} Typical fluid types are:

Conventional linear gels. These gels are cellulose derivatives (carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, hydroxypropyl cellulose, methyl hydroxyl ethyl cellulose), guar or its derivatives (hydroxypropyl guar, carboxymethyl hydroxypropyl guar) based, with other chemicals providing the necessary chemistry for the desired results.
Borate-crosslinked fluids. These are guar-based fluids cross-linked with boron ions (from aqueous borax/boric acid solution). These gels have higher viscosity at pH 9 onwards and are used to carry proppants. After the fracturing job the pH is reduced to 3–4 so that the cross-links are broken and the gel is less viscous and can be pumped out.
Organometallic-crosslinked fluids zirconium, chromium, antimony, titanium salts are known to crosslink the guar based gels. The crosslinking mechanism is not reversible. So once the proppant is pumped down along with the cross-linked gel, the fracturing part is done. The gels are broken down with appropriate breakers.^[41]
Aluminium phosphate-ester oil gels. Aluminium phosphate and ester oils are slurried to form cross-linked gel. These are one of the first known gelling systems. They are very limited in use currently, because of formation damage and difficulty in cleanup.^{[citation needed]}

Other chemical additives

Chemical additives are applied to tailor the injected material to the specific geological situation, protect the well, and improve its operation, 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.^[41] 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.^[41] 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 continually being developed and improved to better handle wastewater and improve reusability.^[33] Although the concentrations of the chemical additives are very low, the recovered fluid may be harmful due in part to minerals picked up from the formation.^{[citation needed]} Over the life of a typical gas well, up to 100,000 US gallons (380,000 L; 83,000 imp gal) of chemical additives may be used.^[44]

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.^[33]

Injection of radioactive tracers, along with the other substances in hydraulic-fracturing fluid, is sometimes used to determine the injection profile and location of fractures created by hydraulic fracturing.^[45]

The radiotracer is chosen to have the readily detectable radiation, appropriate chemical properties, minimal radiotoxicity, and a half life that will minimise residual contamination with initial activity that is as low as reasonably achievable.^[46] For example, plastic pellets coated with 10 GBq of Ag-110mm may be added to the proppant ^[46] or the sand labelled with Ir-192 [1] so that the proppant's progress can be monitored. Sand containing naturally radioactive minerals is sometimes used for this purpose.

Radiotracers such as Tc-99m and I-131 are also used to measure flow rates.^[46] The Nuclear Regulatory Commission publishes guidelines which list a wide range of radioactive materials in solid, liquid and gaseous forms that may be used as tracers and limit the amount that may be used per injection and per well of each radionuclide.^[47]

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 geophones 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.^{[citation needed]}

Horizontal completions

Since the early 2000s, advances in drilling and completion technology have 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 formations which do not have sufficient permeability to produce economically with a vertical well. Such wells when drilled onshore are now usually hydraulically fractured in a number of stages, 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.^[48]

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 truck is used to 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.^[49]

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.^[50]

Increased recovery

Hydraulic fracturing has been seen as one key methods of extracting unconventional oil and gas resources. According to the International Energy Agency, the remaining technically recoverable resources of shale gas are estimated to amount to 208 trillion cubic metres (7.3 quadrillion cubic feet), tight gas to 76 trillion cubic metres (2.7 quadrillion cubic feet), and coalbed methane to 47 trillion cubic metres (1.7 quadrillion cubic feet). As a rule, formations of these resources have lower permeability than conventional gas formations and therefore, depending on the geological characteristics of the formation, specific technologies, such as hydraulic fracturing, are required. Although there are also other methods to extract these resources, such as conventional drilling or horizontal drilling, hydraulic fracturing is one of the key methods making their extraction technically viable. The multi-stage fracturing technique has facilitated shale gas and light tight oil production development in the United States and is believed to do so in the other countries with unconventional hydrocarbon resources. Significance of the extraction of unconventional hydrocarbons lies also in the fact that these resources are less concentrated than of conventional oil and gas resources.^[4]

Environmental impact

Hydraulic fracturing has raised environmental concerns and is challenging the adequacy of existing regulatory regimes.^[51] These concerns have included ground water contamination, risks to air quality, migration of gases and hydraulic fracturing chemicals to the surface, mishandling of waste, and the health effects of all these.^[5]^[33]^[44]

A University of Texas study listed water contamination and consumption, blowouts, explosions, spill management, atmospheric emissions, and health effects as associated problems.^[14] The UT study described the environmental impact of each part of the hydraulic fracturing process, which included:^[52]^[53]

Drill pad construction and operation
Construction, integrity, and performance of the wellbores
Injection of the fluid once it is underground (which proponents consider the actual "fracking")
Flowback of the fluid back towards the surface
Blowouts, often unreported, which spew hydraulic fracturing fluid and other byproducts across surrounding area
Integrity of other pipelines involved
Disposal of the flowback, including waste water and other waste products

All but the injection stage were reported to be sources of contamination.^[14]

Because hydraulic fracturing originated in the United States,^[54] its history is more extensive there than in other regions. Most environmental impact studies have therefore taken place there.

Research issues

Several organizations, researchers, and media outlets have reported difficulty in conducting and reporting the results of studies on hydraulic fracturing due to industry^[55]^[56]^[57] and governmental pressure, and expressed concern over possible censoring of environmental reports.^[55]^[58]^[59] Researchers have recommended requiring disclosure of all hydraulic fracturing fluids, testing animals raised near fracturing sites, and closer monitoring of environmental samples.^[60] After court cases concerning contamination from hydraulic fracturing are settled, the documents are sealed. The American Petroleum Institute deny that this practice has hidden problems with gas drilling, while others believe it has and could lead to unnecessary risks to public safety and health.^[61]

One New York Times report claimed that the results of a 2004 United States Environmental Protection Agency (EPA) study were censored due to political pressure.^[55] An early draft of the study had discussed the possibility of environmental threats due to fracking, but the final report omitted this.^[55] The study's scope had been narrowed so that it only focused on the injection of fracking fluids, while omitting other aspects of the process.^[62] The 2012 EPA Hydraulic Fracturing Draft Plan was also narrowed thusly.^[56]^[58]^[63]^[64]

As of May 2012, the US Institute of Medicine and US National Research Council were preparing to review the potential human and environmental risks of hydraulic fracturing.^[65]^[66]

Air

The air emissions from hydraulic fracking are related to methane leaks originating from wells, and emissions from the diesel or natural gas powered equipment such as compressors, drilling rigs, pumps etc.^[33]

Shale gas produced by hydraulic fracturing causes higher well-to-burner emissions than conventional gas. This is mainly due to the gas released during completing wells as some gas returns to the surface, together with the fracturing fluids. Depending on their treatment, the well-to-burner emissions are 3.5%–12% higher than for conventional gas.^[51] According to a study conducted by professor Robert W. Howarth et al. of Cornell University, "3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the lifetime of a well." The study claims that this represents a 30–100% increase over conventional gas production.^[67] Methane gradually breaks down in the atmosphere, forming carbon dioxide, which contributes to greenhouse gasses more than coal or oil for timescales of less than fifty years.^[67]^[68] Several studies suggest that this paper is flawed,^[69]^[70]^[71]^[72] and Howarth's colleagues at Cornell agreed.^[73] Howarth et al. responded, "The latest EPA estimate for methane emissions from shale gas falls within the range of our estimates but not those of Cathles et al, which are substantially lower."^[74]^[75]

In 2008, concentrations near drilling sites in Sublette County, Wyoming were frequently above the National Ambient Air Quality Standards (NAAQS),^[76] though a 2011 study for the city of Fort Worth, Texas "did not reveal any significant health threats" traceable to fracking.^[77]^[78]

In some areas, elevated air levels of harmful substances have coincided with elevated reports of health problems among the local populations. In DISH, Texas, elevated substance levels were detected and traced to fracking compressor stations,^[79] and people living near shale gas drilling sites complained of health problems;^[80] though a causal relationship to fracking was not established.^[80]

The EPA has proposed new regulations for controlling emissions from upstream oil and gas operations. These regulations would reduce emissions from aspects of the oil and gas production process including completions and various fugitive emissions. The regulations are scheduled to go into effect on April 17, 2012. However, the industry has requested a delay in implementation.^[81]

Water

Consumption

The large volumes of water required have raised concerns about fraccing in arid areas, such as Karoo in South Africa.^[54] During periods of low stream flow it may affect water supplies for municipalities and industries such as power generation, as well as recreation and aquatic life. It may also require water overland piping from distant sources.^[82] Over its lifetime an average well requires 3 to 5 million US gallons (11,000 to 19,000 m³) of water for the initial hydraulic fracturing operation and possible restimulation frac jobs.^[33]^[82] Using the case of the Marcellus Shale as an example, fracking accounted for 650 million US gallons per year (2,500,000 m³/a) or less than 0.8% of annual water use in the area overlying the Marcellus Shale as of 2010.^[82] To minimize water consumption, recycling is one possible option.^[51]

Waste water

As the fracturing fluid flows back through the well, it consists of spent fluids and may contain dissolved constituents such as minerals and brine waters. It may account for about 30–70% of the original fracture fluid volume. In addition, natural formation waters may flow to the well and need treatment. These fluids, commonly known as produced water, should be managed by underground injection, wastewater treatment and discharge, or recycling to fracture future wells.^[83] Treatment of produced waters may be feasible through either self‐contained systems at well sites or fields or through municipal waste water treatment plants or commercial treatment facilities.^[83] However, the quantity of waste water needing treatment and the improper configuration of sewage plants have become an issue in some regions of the United States. Much of the wastewater from hydraulic fracturing operations is processed by public sewage treatment plants, which are not equipped to remove radioactive material and are not required to test for it.^[84]^[85]

To mitigate the impact of hydraulic fracturing to groundwater the well and the shale formation itself should remain hydraulically isolated from other geological formations, especially freshwater aquifers.^[51] Several cases of groundwater contamination due to fracking waste water have been suspected.^[86]^[87] In 1987, an EPA report was published that indicated fracture fluid invasion into a well in West Virginia. The well, drilled by Kaiser Exploration and Mining Company, was found to have induced fractures that allowed fracture fluid to contaminate groundwater – though the oil and gas industry, as well as the EPA, questioned the accuracy of the report.^[61] In 2006, over 7 million cubic feet (200,000 m³) of methane were released from a blown gas well in Clark, Wyoming and shallow groundwater was found to be contaminated.^[88] Directed by Congress, the EPA announced in March 2010 that it will conduct a study, set to be released for peer review at the end of 2012, of hydraulic fracturing's impact on drinking water and ground water resources.^[89]

The 2010 film Gasland presented claims that chemicals polluted the ground water near well sites in Pennsylvania, Wyoming, and Colorado.^[90] Energy in Depth, an oil and gas industry group, called the film's facts into question.^[91] In response, a detailed rebuttal of the claims of inaccuracy was posted on Gasland's website.^[92]

Methane

Groundwater methane contamination is also a concern as it has adverse impact on water quality and in extreme cases may lead to potential explosion.^[93] However, methane contamination is not always caused by fracking. Drilling for ordinary drinking water wells can also cause methane release. Some studies make use of tests that can distinguish between the deep thermogenic methane released during gas/oil drilling, and the shallower biogenic methane that can be released during water-well drilling. While both forms of methane result from decomposition, thermogenic methane results from geothermal assistance deeper underground.^[94]^[95]

According to the 2011 study of the MIT Energy Initiative, "there is evidence of natural gas (methane) migration into freshwater zones in some areas, most likely as a result of substandard well completion practices by a few operators."^[96] 2011 studies by the Colorado School of Public Health and Duke University also pointed to methane contamination stemming from fracking or its surrounding process.^[93]^[95] A study by Cabot Oil and Gas examined the Duke study using a larger sample size, found that methane concentrations were related to topography, with the highest readings found in low-lying areas, rather than related to distance from gas production areas. Using a more precise isotopic analysis, they showed that the methane found in the water wells came from both the Marcellus Shale (Middle Devonian) where hydraulic fracturing occurred, and from the shallower Upper Devonian formations.^[94]

Chemicals

While some of the chemicals used in hydraulic fracturing are common and generally harmless, some are known carcinogens or toxic.^[44] The most common chemical used for hydraulic fracturing in the United States in 2005–2009 was methanol, while some other most widely used chemicals were isopropyl alcohol, 2-butoxyethanol, and ethylene glycol.^[44]

The 2011 US House of Representatives investigative report on the chemicals used in hydraulic fracturing states that out of 2,500 hydraulic fracturing products, "more 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".^[44] The report also shows that between 2005 and 2009, 279 products 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).^[44]

Without knowing the identity of the proprietary components, regulators cannot test for their presence. This prevents government regulators from establishing baseline levels of the substances prior to hydraulic fracturing and documenting changes in these levels, thereby making it impossible to prove that hydraulic fracturing is contaminating the environment with these substances.^[97] Third-party laboratories are performing analyses on soil, air, and water near the fracturing sites to measure the level of contamination by some of the known chemicals, but not the proprietary substances, involved in hydraulic fracturing.^{[citation needed]} Each state has a contact person in charge of such regulation.^[98]

Another 2011 study 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.^[99]

Some states have started requiring natural gas companies to "disclose the names of all chemicals to be stored and used at a drilling site", keeping a record on file at the state's environmental agency, such as the case in Pennsylvania with the Department of Environmental Protection and in New York with the Department of Environmental Conservation.^[91] In addition, seven states now require companies report their chemical use through fracfocus.org. However, the continuing concern of some activists who oppose hydraulic fracturing is the lack of information really provided. According to Weston Wilson in Affirming Gasland, "about 50% or so of these MSDS sheets lack a specific chemical name, and some MSDS sheets simply claim 'proprietary' status and list none of the chemicals in that container."^[100] As a result, some activists are calling for specific disclosure of chemicals used, such as the Chemical Abstract Service (CAS) number and specific chemical formulas, and increased access to such information. In his State of the Union address for 2012, Barack Obama stated his intention to force fracking companies to disclose the chemicals they use,^[101] though the subsequent, proposed guidelines were criticised for failing to specify how drillers will disclose the chemicals they use.^[102]

Radioactivity

Radioactive tracers are injected with the other substances in hydraulic-fracturing fluid. ^[45] In addition, hydraulic fracturing fluid might release heavy metals and radioactive materials from the deposit which may reflow to the surface by the flowback.^[103]^[104]^[105]^[106] The New York Times has reported radium and gross alpha radiation in wastewater from natural gas wells, which releases into Pennsylvania rivers,^[85] compiled a map of these wells and their wastewater contamination levels,^[107] and stated that some EPA reports were never made public. They did not measure beta or gamma radiation. The Times' reporting on the issue has come under some criticism.^[108]^[109] Recycling the wastewater has been proposed as a solution but has its limitations.^[110]

The EPA has asked the Pennsylvania Department of Environmental Protection to require community water systems in certain locations, and centralized wastewater treatment facilities to conduct testing for radionuclides.^[111]^[112] Safe drinking water standards have not yet been established to account for possible substances or radioactivity levels known to be in hydraulic fracturing waste water,^[85] and although water suppliers are required to inform citizens of radon and other radionuclides levels in their water,^[113] this doesn't always happen.^[114]

Seismic

Hydraulic fracturing causes induced seismicity called microseismic events or microearthquakes. The magnitude of these events is usually too small to be detected at the surface, although the biggest micro-earthquakes may have the magnitude of about -1.6 (M_w). The injection of waste water from gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude tremors, being registered up to 3.3 (M_w).^[115]

In 1966 -1967 the disposal of waste water under high pressure into deep wells at Rocky Flats Rocky Mountain Arsenal facility outside Denver and Boulder, Colorado was directly connected to earthquakes in the nearby basement rocks. It is thought that the water at high pressure increased the pore pressure across existing faults which then slipped and caused quakes. It should be noted that the water injection released stress already present on these faults and that earthquakes in the 3.0 - 4.0 and larger Richter range are most likely due to the triggering of existing faults as opposed to coming solely from stresses added in fracking.^{[citation needed]}

A report in the UK concluded that fracking was the likely cause of some small tremors that occurred during shale gas drilling.^[116]^[117]^[118] The United States Geological Survey (USGS) reports that earthquakes induced by human measures, including fracking, have been documented in a few locations;^[119] though 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.^[120]

Several earthquakes, including a light 4.0 magnitude quake on New Year's Eve that hit Youngstown, Ohio throughout 2011 are likely linked to a disposal well for injecting wastewater used in the fracking process, according to seismologists at Columbia University.^[121] Consequently, Ohio has since tightened its rules regarding the wells^[122] and is considering a moratorium on the practice.^[122]

Public policy, information, and relations

Governments are developing legislation related to hydraulic fracturing. The US has the longest history with hydraulic fracturing, so its approaches to hydraulic fracturing may be modeled by other countries.^[54] In the US, some states have introduced legislation that limits the ability of municipalities to use zoning to protect citizens from exposure to pollutants from hydraulic fracturing by protecting residential areas. For instance, in Pennsylvania, the new Marcellus Shale Law (House Bill 1950)^[123] requires all municipalities to allow Marcellus Shale well drilling in all zoning districts, including residential, and allow water and wastewater pits in all zoning district, including residential. Compressor stations must be allowed in industrial and agricultural zoning districts, and gas processing plants allowed in industrial zoning districts. Municipalities are no longer permitted to limit the hours of operation of gas related activities. Gas pipelines must be allowed in all zoning districts.^[123] Similar laws have been created in Ohio,^[124] and New York,^[125] Colorado, and Texas are battling over related legislation.^[126] Pennsylvania's Marcellus Shale Law (House Bill 1950) also contains a provision that allows doctors in Pennsylvania access to the list of chemicals in hydraulic fracturing fluid in emergency situations only, and forbids them from ever discussing this information with their patients.^[127]

A number of public information resources have been developed by governments and news sources (see external links section below). The US Environmental Protection Agency has a site labelled Natural Gas Extraction - Hydraulic Fracturing. Other sites include FracFocus, a site indicating the chemical composition of fraccing fluid of individual wells and ProPublica's sites containing collected news, commentary and illustration. The Guardian has posted Shale gas and fracking site. The New York Times also has a page dedicated to hydraulic fracturing.

The considerable opposition against fraccing activities in local townships has led companies to adopt a variety of public relations measures to assuage fears about fraccing, 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 fraccing opponents. Matt Pitzarella, spokesman for the most important fraccing company in Pennsylvania, Range Resources, also told other conference attendees that Range employed psychological warfare operations veterans. According to Pitzarella, the experience learned 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 fraccing.^[128]^[129]

Notes

a. ^{^} Also spelled "fraccing"^[130] or "fracing".^[131]^[132]

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^ Charles Petit (2 March 2011). "Part II of the fracking water problems in PA and other Marcellus Shale country". Knight Science Journalism Tracker. MIT. Retrieved 24 February 2012. {{cite web}}: External link in |author= (help)
^ Urbina, Ian (1 March 2011). "Drilling Down: Wastewater Recycling No Cure-All in Gas Process". The New York Times. Retrieved 22 February 2012.
^ Urbina, Ian (7 March 2011). "E.P.A. Steps Up Scrutiny of Pollution in Pennsylvania Rivers". The New York Times. Retrieved 23 February 2012.
^ "Letter to PADEP re:Marcellus Shale 030711" (Document). EPA. 07 March 2011. several sources of data, including reports required by PADEP, indicate that the wastewater resulting from gas drilling operations (including flowback from hydraulic fracturing and other fluids produced from gas production wells) contains variable and sometimes high concentrations of materials that may present a threat to human health and aquatic environment, including radionuclides.... Many of these substances are not completely removed by wastewater treatment facilities, and their discharge may cause or contribute to impaired drinking water quality for downstream users, or harm aquatic life ... At the same time, it is equally critical to examine the persistence of these substances, including radionuclides, in wastewater effluents and their potential presence in receiving waters. {{cite document}}: Check date values in: |date= (help); Unknown parameter |accessdate= ignored (help); Unknown parameter |authors= ignored (help); Unknown parameter |format= ignored (help); Unknown parameter |url= ignored (help)
^ "Radionuclides in public drinking water". EPA. 8 March 2012. Retrieved 4 May 2012.
^ Bauers, Sandy (21 July 2011). "Cancer patients' urine suspected in Wissahickon iodine-131 levels". Philadelphia inquirer, Carbon County Groundwater Guardians. Retrieved 25 February 2012.
^ Zoback, Mark; Kitasei, Saya; Copithorne, Brad (2010). Addressing the Environmental Risks from Shale Gas Development (PDF) (Report). Worldwatch Institute. p. 9. Retrieved 2012-05-24. {{cite report}}: Unknown parameter |month= ignored (help)
^ "Shale gas fracking: MPs call for safety inquiry after tremors". BBC News. 8 June 2011. Retrieved 22 February 2012.
^ "Fracking tests near Blackpool 'likely cause' of tremors". BBC News. 2 November 2011. Retrieved 22 February 2012.
^ de Pater, C.J.; Baisch, S. (2 November 2011). Geomechanical Study of Bowland Shale Seismicity (PDF) (Report). Cuadrilla Resources. Retrieved 22 February 2012.
^ "FAQs – Earthquakes, Faults, Plate Tectonics, Earth Structure: Can we cause earthquakes? Is there any way to prevent earthquakes?". USGS. 27 October 2009. Retrieved 22 February 2012.
^ "EPA Underground Injection Control Program". Retrieved 2012-04-13.
^ "Ohio Quakes Probably Triggered by Waste Disposal Well, Say Seismologists" (Press release). Lamont–Doherty Earth Observatory. 6 January 2012. Retrieved 22 February 2012.
^ ^a ^b Niquette, Mark (22 March 2012). "Fracking Fluid Soaks Ohio". Bloomberg Businessweek. Retrieved 2 April 2012.
^ ^a ^b "Local zoning provisions in Pa.'s gas drilling law". USA Today. Associated Press. 3 March 2012. Retrieved 23 February 2012. {{cite news}}: Text "Frontpage" ignored (help); Text "newswell" ignored (help); Text "s" ignored (help); Text "text" ignored (help)^{[dead link]}
^ Suddes, Thomasn (14 Jan 2012). "'Fracking' debate exposes weaknesses in Ohio Statehouse – term limits and the death of home rule". The Plain Dealer. Retrieved 26 March 2012.
^ "Recent Court Decisions May Affect Hydraulic Fracturing in New York and Ohio". The National Law Review. McDermott Will & Emery. 2012-04-01. Retrieved 2012-07-03.
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^ Javers, Eamon (8 Nov 2011). "Oil Executive: Military-Style 'Psy Ops' Experience Applied". CNBC.
^ Phillips, Susan (9 Nov 2011). "'We're Dealing with an Insurgency,' says Energy Company Exec of Fracking Foes". National Public Radio.
^ "Chemicals that may be used in Australian CSG fraccing fluid" (PDF). Australian Petroleum Ptoduction & Exploration Association Limited. Retrieved 22 February 2012.
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^ "HydraulicFracturing.com". Chesapeake Energy. Retrieved 2011-07-13.

Cite error: A list-defined reference named "Reis iodine" is not used in the content (see the help page).

External links

FracFocus Site indicating chemical composition of fracking fluid of individual wells
Fracking collected news and commentary at ProPublica
GasLand, a 2010 documentary by Josh Fox exploring the environmental impacts of hydraulic fracturing
Hydraulic Fracturing at Earthworks.
Hydraulic fracturing illustration on ProPublica
Hydraulic fracturing shale gas extraction at YouTube
Shale gas and fracking collected news and commentary at The Guardian

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[Montgomery-13] Montgomery, Carl T.; Smith, Michael B. (2010-12-105). "Hydraulic fracturing. History of an enduring technology" (PDF). JPT Online. Society of Petroleum Engineers: 26–41. Retrieved 13 May 2012. {{cite journal}}: Check date values in: |date= (help)

[UT_Study-14] Energy Institute (2012). Fact-Based Regulation for Environmental Protection in Shale Gas Development (PDF) (Report). University of Texas at Austin. Retrieved 29 February 2012. {{cite report}}: Unknown parameter |month= ignored (help)

[Mader-15] Mader, Detlef (1989). Hydraulic Proppant Fracturing and Gravel Packing. Elsevier. pp. 173–174, 202. ISBN 9780444873521.

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[AutoZV-9-17] The Breakthrough Institute. Interview with Dan Steward, former Mitchell Energy Vice President. December 2011.

[Bweek_31.03.2011-18] Patel, Tara (31 March 2011). "The French Public Says No to 'Le Fracking'". Bloomberg Businessweek. Retrieved 22 February 2012.

[Bweek_04.10.2011-19] Patel, Tara (4 October 2011). "France to Keep Fracking Ban to Protect Environment, Sarkozy Says". Bloomberg Businessweek. Retrieved 22 February 2012.

[AutoZV-2-20] "The Barnett Shale" (PDF). North Keller Neighbors Together. Retrieved 2012-05-14.

[BW_19.01.2012-21] David Wethe (19 January 2012). "Like Fracking? You'll Love 'Super Fracking'". Businessweek. Retrieved 22 January 2012.

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[AutoZV-3-23] Gidley, John L. (1989). Recent Advances in Hydraulic Fracturing. SPE Monograph. Vol. 12. SPE. p. ?. ISBN 9781555630201.

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[Economides-25] Economides, Michael J. (2000). Reservoir stimulation. J. Wiley. p. P-2. ISBN 9780471491927.

[AutoZV-6-26] Banks, David (1996). "Permeability and stress in crystalline rocks". Terra Nova. 8 (3): 223–235. doi:10.1111/j.1365-3121.1996.tb00751.x. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

[AutoZV-7-27] Brown, Edwin Thomas (2007) [2003]. Block Caving Geomechanics (2nd ed.). Indooroopilly, Queensland: Julius Kruttschnitt Mineral Research Centre, UQ. ISBN 978-0-9803622-0-6. Retrieved 2012-05-14.

[hazmat40.2-28] Frank, U.; Barkley, N. (February 1995). "Remediation of low permeability subsurface formations by fracturing enhancement of soil vapor extraction". Journal of Hazardous Materials. 40 (2): 191–201. doi:10.1016/0304-3894(94)00069-S. ISSN 0304-3894. {{cite journal}}: More than one of |work= and |journal= specified (help)

[Bell-29] Bell, Frederic Gladstone (2004). Engineering Geology and Construction. Taylor & Francis. p. 670. ISBN 9780415259392.

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[AutoZV-8-31] "Geothermal Technologies Program: How an Enhanced Geothermal System Works". .eere.energy.gov. 2011-02-16. Retrieved 2011-11-02.

[Miller-32] Miller, Bruce G. (2005). Coal Energy Systems. Sustainable World Series. Academic Press. p. 380. ISBN 9780124974517.

[DOE_primer-33] ^ ^a ^b ^c ^d ^e ^f ^g ^h Ground Water Protection Council; ALL Consulting (2009). Modern Shale Gas Development in the United States: A Primer (PDF) (Report). DOE Office of Fossil Energy and National Energy Technology Laboratory. pp. 56–66. DE-FG26-04NT15455. Retrieved 24 February 2012. {{cite report}}: Unknown parameter |month= ignored (help)

[Penny-34] Penny, Glenn S.; Conway, Michael W.; Lee, Wellington (1985). "Control and Modeling of Fluid Leakoff During Hydraulic Fracturing". Journal of Petroleum Technology. 37 (6). Society of Petroleum Engineers: 1071–1081. doi:10.2118/12486-PA. Retrieved 2012-05-10. {{cite journal}}: Unknown parameter |month= ignored (help)

[Arthur-35] Arthur, J. Daniel; Bohm, Brian; Coughlin, Bobbi Jo; Layne, Mark (2008). Hydraulic Fracturing Considerations for Natural Gas Wells of the Fayetteville Shale (PDF) (Report). ALL Consulting. p. 10. Retrieved 2012-05-07.

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[Love-37] Love, Adam H. (2005). "Fracking: The Controversy Over its Safety for the Environment". Johnson Wright, Inc. Retrieved 2012-06-10. {{cite web}}: Unknown parameter |month= ignored (help)

[bmp-38] "Hydraulic Fracturing". University of Colorado Law School. Retrieved 2 June 2012.

[Renpu-39] Wan Renpu (2011). Advanced Well Completion Engineering. Gulf Professional Publishing. p. 424. ISBN 9780123858689.

[Hartnett-40] Hartnett-White, K. (2011). "The Fracas About Fracking- Low Risk, High Reward, but the EPA is Against it" (PDF). National Review Online. Retrieved 2012-05-07. {{cite journal}}: Cite journal requires |journal= (help)

[CRO_2009-41] Anthony Andrews; et al. (30 October 2009). Unconventional Gas Shales: Development, Technology, and Policy Issues (PDF). Congressional Research Service. p. ?. Retrieved 22 February 2012. {{cite book}}: Explicit use of et al. in: |author= (help)

[AutoZV-12-42] "CARBO ceramics". Retrieved 2011. {{cite web}}: Check date values in: |accessdate= (help)

[43] ttp://www.hydraulicfracturing.com/Fracturing-Ingredients/Pages/information.aspx

[house1-44] ^ ^a ^b ^c ^d ^e ^f Chemicals Used in Hydraulic Fracturing (PDF) (Report). Committee on Energy and Commerce U.S. House of Representatives. April 18, 2011.

[Reis_iodine-45] Cite error: The named reference Reis_iodine was invoked but never defined (see the help page).

[IAEA_2003-46] Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry (PDF) (Report). International Atomic Energy Agency. 2003. pp. 39–40. Retrieved 20 May 2012. Beta emitters including H-3 and C-14 may be used when it is feasible to use sampling techniques to detect the presence of the radiotracer or when changes in activity concentration can be used as indicators of the properties of interest in the system. Gamma emitters, such as Sc-46, La-140, Mn-56, Na-24, Sb-124, Ir-192, Tc-m, I-131, Ag-m, Ar-41, and Xe-133 are used extensively because of the ease with which they can be identified and measured ... In order to aid the detection of any spillage of solutions of the 'soft' beta emitters, they are sometimes spiked with a short half-life gamma emitter such as Br-82

[NRC-47] Jack E. Whitten, Steven R. Courtemanche, Andrea R. Jones, Richard E. Penrod, and David B. Fogl (Division of Industrial and Medical Nuclear Safety, Office of Nuclear Material Safety and Safeguards (June 2000). "Consolidated Guidance About Materials Licenses: Program-Specific Guidance About Well Logging, Tracer, and Field Flood Study Licenses (NUREG-1556, Volume 14)". US Nuclear Regulatory Commission. Retrieved 19 April 2012. labeled Frac Sand...Sc-46, Br-82, Ag-110m, Sb-124, Ir-192{{cite web}}: CS1 maint: multiple names: authors list (link)

[AutoZV-13-48] Seale, Rocky (2007). "Open hole completion systems enables multi-stage fracturing and stimulation along horizontal wellbores" (PDF). Drilling Contractor (Fracturing stimulation ed.). Retrieved October 1, 2009. {{cite journal}}: Unknown parameter |month= ignored (help)

[AutoZV-14-49] [energyfromshale.org "EnergyFromShale"]. EnergyFromShale. 2011. {{cite web}}: Check |url= value (help)

[mooney-50] Mooney, Chris (2011). "The Truth About Fracking". Scientific American (305): 80–85.

[WEO2011full-51] IEA (2011). World Energy Outlook 2011. OECD. pp. 91, 164. ISBN 978 92 64 12413 4.

[vancouversun-52] Munro, Margaret (17 February 2012). "Fracking does not contaminate groundwater: study released in Vancouver". Vancouver Sun. Retrieved 3 March 2012.

[fuelfix-53] Vaughan, Vicki (16 February 2012). "Fracturing 'has no direct' link to water pollution, UT study finds". Retrieved 3 March 2012.

[NYTUrbina30Dec2011-54] Urbina, Ian (30 December 2011). "Hunt for Gas Hits Fragile Soil, and South Africans Fear Risks". The New York Times. Retrieved 23 February 2012. Covering much of the roughly 800 miles between Johannesburg and Cape Town, this arid expanse – its name [Karoo] means "thirsty land" – sees less rain in some parts than the Mojave Desert.

[Urbina_03Mar2011-55] Urbina, Ian (3 March 2011). "Pressure Limits Efforts to Police Drilling for Gas". The New York Times. Retrieved 23 February 2012. More than a quarter-century of efforts by some lawmakers and regulators to force the federal government to police the industry better have been thwarted, as E.P.A. studies have been repeatedly narrowed in scope and important findings have been removed

[EPA_re_study-56] DiCosmo, Bridget (15 May 2012). "SAB Pushes To Advise EPA To Conduct Toxicity Tests In Fracking Study". InsideEPA. Inside Washington Publishers. (subscription required). Retrieved 2012-05-19. But some members of the chartered SAB are suggesting that the fracking panel revise its recommendation that the agency scale back its planned toxicity testing of chemicals used in the hydraulic fracturing, or fracking, process, because of the limited resources and time frame ... Chesapeake Energy supported the draft recommendation, saying that "an in-depth study of toxicity, the development of new analytical methods and tracers are not practical given the budget and schedule limitation of the study."

[Chesapeake-57] Satterfield, John (30 June 2011). "Letter from Chesapeake Energy to EPA" (Document). Inside Washington Publishers. (subscription required). Flowback and Produced water ... Chesapeake agrees that an indepth study of toxicity, the development of new analytic methods and tracers are not practical given the budget and schedule limitations of the study ... Wastewater Treatment and Waste Disposal ... Chesapeake believes there was unjustified emphasis on the surface disposal of produced water to treatment plants in the SAB's Review ... Chesapeake disagrees with the inclusion of water distribution network corrosion and burden of analyzing for contaminants by POTW's into the study. {{cite document}}: Unknown parameter |accessdate= ignored (help); Unknown parameter |format= ignored (help); Unknown parameter |newspaper= ignored (help); Unknown parameter |url= ignored (help)

[NYT_lobbying_docs-58] "The Debate Over the Hydrofracking Study's Scope". The New York Times. 3 March 2011. Retrieved 1 May 2012. While environmentalists have aggressively lobbied the agency to broaden the scope of the study, industry has lobbied the agency to narrow this focus

[NYT_Docs-59] "Natural Gas Documents". The New York Times. 27 February 2011. Retrieved 5 May 2012. The Times reviewed more than 30,000 pages of documents obtained through open records requests of state and federal agencies and by visiting various regional offices that oversee drilling in Pennsylvania. Some of the documents were leaked by state or federal officials.

[Cornellvet03092012-60] Ramanuja, Krishna (7 Martch 2012). "Study suggests hydrofracking is killing farm animals, pets". Cornell Chronicle. Cornell University. Retrieved 9 March 2012. {{cite news}}: Check date values in: |date= (help)

[Urbina_03Aug2011-61] Urbina, Ian (3 August 2011). "A Tainted Water Well, and Concern There May be More". The New York Times. Retrieved 22 February 2012.

[EPA_2004-62] Evaluation of Impacts to Underground Sources of Drinking Water by Hydraulic Fracturing of Coalbed Methane Reservoirs; National Study Final Report (PDF) (Report). EPA. June 2004. Retrieved 23 February 2011.

[Bloomberg_11.01.2012-63] Mark Drajem (11 January 2012). "Fracking Political Support Unshaken by Doctors' Call for Ban". Bloomberg. Retrieved 19 January 2012.

[BW_04Jan2012-64] Alex Wayne (4 January 2012). "Health Effects of Fracking Need Study, Says CDC Scientist". Bloomberg Businessweek. Retrieved 29 February 2012.

[Research_Council_study-65] Mall, Amy (16 May 2012). "Concerns about the health risks of fracking continue to grow". Switchboard: NRDC Staff Blog. Natural Resources Defense Council. Retrieved 2012-05-19.

[Research_Council_study2-66] Hopkinson, Jenny; DiCosmo, Bridget (15 May 2012). "Academies' NRC Seeks Broad Review Of Currently Ignored Fracking Risks". InsideEPA. Inside Washington Publishers. (subscription required). Retrieved 2012-05-19.

[howarth-67] Howarth, Robert W.; Santoro, Renee; Ingraffea, Anthony (13 March 2011). "Methane and the greenhouse-gas footprint of natural gas from shale formations" (PDF). Climatic Change. 106 (4). Springer: 679–690. doi:10.1007/s10584-011-0061-5. Retrieved 2012-05-07.

[howarth2-68] Howarth, Robert W.; Ingraffea, Anthony (15 September 2011). "Should Fracking Stop? Extracting gas from shale increases the availability of this resource, but the health and environmental risks may be too high. Point: Yes, it's too high risk". Nature (477): 271–275. doi:10.1038/477271a.

[Skone-69] Skone, Timothy J. (12 May 2011). "Life Cycle Greenhouse Gas Analysis of Natural Gas Extraction & Delivery in the United States" (PDF). National Energy Technology Laboratory. Retrieved 4 February 2012.

[Jiang-70] Jiang, Mohan; Griffin; Hendrickson, Chris; Jaramillo, Paulina; VanBriesen, Jeanne; Venkatesh, Aranya (2011). "Life cycle greenhouse gas emissions of Marcellus shale gas" (PDF). Environmental Research Letters. 6 (3). IOP Publishing. doi:10.1088/1748-9326/6/3/034014. Retrieved 4 February 2012. {{cite journal}}: Unknown parameter |firat2= ignored (help)

[Hultman-71] Hultman, Nathan; Rebois, Dylan; Scholten, Michael; Ramig, Christopher (2011). "The greenhouse impact of unconventional gas for electricity generation" (PDF). Environmental Research Letters. 6 (4). IOP Publishing. doi:10.1088/1748-9326/6/4/044008. Retrieved 4 February 2012.

[Lashof-72] Lashof, Dan (12 April 2011). "Natural Gas Needs Tighter Production Practices to Reduce Global Warming Pollution". Natural Resources Defense Council. Retrieved 4 February 2012.

[Cathles-73] Cathles, Lawrence M.; Brown, Larry; Taam, Milton; Hunter, Andrew (2011). Climatic Change. doi:10.1007/s10584-011-0333-0. {{cite journal}}: |access-date= requires |url= (help); Missing or empty |title= (help)

[Howarth3-74] Howarth, Robert W.; Santoro, Renee; Ingraffea, Anthony (1 February 2012). "Venting and leaking of methane from shale gas development: Response to Cathles et al" (PDF). Climatic Change. Springer. doi:10.1007/s10584-012-0401-0. Retrieved 4 February 2012.

[ipsnewsShale-75] Stephen Leahy (24 January 2012). "Shale Gas a Bridge to More Global Warming". IPS. Retrieved 4 February 2012.

[tribOzoneWyoming-76] "Ozone mitigation efforts continue in Sublette County, Wyoming". Wyoming's Online News Source. March 2011.

[fortworthtexas-77] Eastern Research Group, Sage Environmental Consulting (July 13, 2011). City of Fort Worth: Natural Gas Air Quality Study (PDF) (Report). City of Fort Worth. Retrieved 2012-05-07.

[starFortWorthNoThreats-78] Hanna, Bill; Smith, Jack Z. (July 15, 2011). "Study: No 'significant health threats' from natural gas sites in Fort Worth". Fort Worth Star-Telegram. Retrieved 2012-05-24.

[DISH_TX_SciAm-79] Biello, David (30 March 2010). "Natural gas cracked out of shale deposits may mean the U.S. has a stable supply for a century – but at what cost to the environment and human health?". Scientific American. Retrieved 23 March 2012.

[DISH_TX_EHP-80] Schmidt, Charles (1 August 2011). "Blind Rush? Shale Gas Boom Proceeds Amid Human Health Questions". Environmental Health Perspectives. 119: a348–a353. doi:10.1289/ehp.119-a348. Retrieved 23 March 2012.

[EPA_standards-81] "EPA Oil and Gas Air Pollution Standards". EPA. Retrieved 11 April 2012.

[ALL-Marcellus-82] Arthur, J. Daniel; Uretsky, Mike; Wilson, Preston (May 5–6, 2010). Water Resources and Use for Hydraulic Fracturing in the Marcellus Shale Region (PDF). Meeting of the American Institute of Professional Geologists. Pittsburgh: ALL Consulting. p. 3. Retrieved 2012-05-09.

[Arthur2-83] Arthur, J. Daniel; Langhus, Bruce; Alleman, David (2008). An overview of modern shale gas development in the United States (PDF) (Report). ALL Consulting. p. 21. Retrieved 2012-05-07.

[Neshaminy_2009-84] David Caruso (2011-01-03). "44,000 Barrels of Tainted Water Dumped Into Neshaminy Creek. We're the only state allowing tainted water into our rivers". NBC Philadelphia. Associated Press. Retrieved 2012-04-28.

[Urbina_26Feb2011-85] Urbina, Ian (26 February 2011). "Regulation Lax as Gas Wells' Tainted Water Hits Rivers". The New York Times. Retrieved 22 February 2012.

[AutoZV-21-86] Mall, Amy (19 December 2011). "Incidents where hydraulic fracturing is a suspected cause of drinking water contamination". Switchboard: NRDC Staff Blog. Natural Resources Defense Council. Retrieved 23 February 2012.

[AutoZV-22-87] Lustgarten, Abrahm (November 2008). "Incidents where hydraulic fracturing is a suspected cause of drinking water contamination". ProPublica. Retrieved 20 March 2012.

[AutoZV-23-88] Blowout brings scrutiny to energy company

[hfstudy-89] "EPA's Study of Hydraulic Fracturing and Its Potential Impact on Drinking Water Resources". EPA. Retrieved 24 February 2010.

[AutoZV-25-90] "Gasland". 2010. Retrieved 2012-05-14.

[indepth-91] "Gasland Debunked" (PDF). Energy in Depth. Retrieved 2012-05-14.

[AutoZV-27-92] "Affirming Gasland" (PDF). 2010-07. Retrieved 2010-12-21. {{cite news}}: Check date values in: |date= (help)

[Duke_study_2010-93] Osborn, Stephen G.; Vengosh, Avner; Warner, Nathaniel R.; Jackson, Robert B. (2011-05-17). "Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 108 (20): 8172–8176. doi:10.1073/pnas.1100682108. Retrieved 2011-10-14.

[molofsky-94] Connor, J.A.; Shahla, K.F.; Wylie, A.S.; Wagner, T. (December 5, 2011). "Methane in Pennsylvania Water Wells Unrelated to Marcellus Shale Fracturing". Oil and Gas Journal. 109 (49). Pennwell Corporation: 54–67. {{cite journal}}: |first1= missing |last1= (help); Unknown parameter |last1s= ignored (help)

[AutoZV-32-95] "Gasland Correction Document" (PDF). Colorado Oil & Gas Conservation Commission. Retrieved 25 January 2012.

[AutoZV-33-96] Moniz, Ernest J.; et al. (2011). The Future of Natural Gas: An Interdisciplinary MIT Study (PDF) (Report). Massachusetts Institute of Technology. Retrieved 1 June 2012. {{cite report}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)

[AutoZV-16-97] Kris Fitz Patrick (November 17, 2011). "Ensuring Safe Drinking Water in the Age of Hydraulic Fracturing".

[AutoZV-17-98] "Fracking Regulations".

[AEHS_2011-99] Colborn, Theo; Kwiatkowski, Carol; Schultz, Kim; Bachran, Mary (2011). "Natural Gas Operations from a Public Health Perspective" (PDF). Human and Ecological Risk Assessment: An International Journal. 17 (5). Taylor & Francis: 1039–1056. doi:10.1080/10807039.2011.605662.

[AutoZV-19-100] Josh Fox, "Affirming Gasland", http://www.gaslandthemovie.com/whats-fracking/affirming-gasland; http://1trickpony.cachefly.net/gas/pdf/Affirming_Gasland_Sept_2010.pdf (cover letter and transcribed panel discussion rebuttal of gas industry response to film Gasland.)

[FT_25.01.2012-101] Ed Crooks (25 January 2012). "US set to require disclosure from 'frackers'". The Financial Times. Retrieved 26 January 2012.

[AutoZV-20-102] Katarzyna Klimasinska (7 February 2012). "Draft Fracking Rule Has 'Good Elements,' Environmentalist Says". Businessweek. Retrieved 22 February 2012. The draft of the measure only says the information "will become a matter of public record." Among his [Dusty Horwitt, senior counsel of the Environmental Working Group] concerns are an exemption from disclosure of trade secrets. "Our concern is whether the exemption would swallow the rule", he said.

[stevens-103] Stevens, Paul (2010). The 'Shale Gas Revolution': Hype and Reality (PDF) (Report). Chatham House. p. 17. ISBN 978 1 86203 239 2. Retrieved 2012-05-28. {{cite report}}: Unknown parameter |month= ignored (help)

[NYT_Waste_Docs_26Feb2011-104] Staff (26 February 2011). "Drilling Down: Documents: Natural Gas's Toxic Waste". The New York Times. Retrieved 23 February 2012.

[Urbina_07Apr2011-105] Urbina, Ian (7 April 2011). "Pennsylvania Calls for More Water Tests". The New York Times. Retrieved 23 February 2012.

[Bucks_Co_Water-106] "Iodine 131 Found in Philadelphia's Drinking Water" (Press release). Bucks County Water & Sewer Authority. 12 April 2011. Retrieved 11 May 2012. In response to these results, PWD is working with the EPA and DEP and taking the following actions: Developing a Joint PADEP, EPA, PWD Action Plan for all Radionuclides; Initiating a focused sampling program for Iodine; Developing an aggressive track down program with EPA and DEP to identify the potential sources of Iodine 131 in our source waters.

[TimesMap-107] White, Jeremy; Park, Haeyoun; Urbina, Ian; Palmer, Griff (26 February 2011). "Toxic Contamination From Natural Gas Wells". The New York Times.

[NYT_letters_05Mar2011-108] "Natural Gas Drilling, the Spotlight". The New York Times. 5 March 2011. Retrieved 24 February 2012.

[Petit_02Mar2011-109] Charles Petit (2 March 2011). "Part II of the fracking water problems in PA and other Marcellus Shale country". Knight Science Journalism Tracker. MIT. Retrieved 24 February 2012. {{cite web}}: External link in |author= (help)

[Urbina_01Mar2011-110] Urbina, Ian (1 March 2011). "Drilling Down: Wastewater Recycling No Cure-All in Gas Process". The New York Times. Retrieved 22 February 2012.

[Urbina_07Mar2011-111] Urbina, Ian (7 March 2011). "E.P.A. Steps Up Scrutiny of Pollution in Pennsylvania Rivers". The New York Times. Retrieved 23 February 2012.

[EPA_letter_to_PADEP-112] "Letter to PADEP re:Marcellus Shale 030711" (Document). EPA. 07 March 2011. several sources of data, including reports required by PADEP, indicate that the wastewater resulting from gas drilling operations (including flowback from hydraulic fracturing and other fluids produced from gas production wells) contains variable and sometimes high concentrations of materials that may present a threat to human health and aquatic environment, including radionuclides.... Many of these substances are not completely removed by wastewater treatment facilities, and their discharge may cause or contribute to impaired drinking water quality for downstream users, or harm aquatic life ... At the same time, it is equally critical to examine the persistence of these substances, including radionuclides, in wastewater effluents and their potential presence in receiving waters. {{cite document}}: Check date values in: |date= (help); Unknown parameter |accessdate= ignored (help); Unknown parameter |authors= ignored (help); Unknown parameter |format= ignored (help); Unknown parameter |url= ignored (help)

[EPA_nuclides-113] "Radionuclides in public drinking water". EPA. 8 March 2012. Retrieved 4 May 2012.

[Carbon_County-114] Bauers, Sandy (21 July 2011). "Cancer patients' urine suspected in Wissahickon iodine-131 levels". Philadelphia inquirer, Carbon County Groundwater Guardians. Retrieved 25 February 2012.

[worldwatch-115] Zoback, Mark; Kitasei, Saya; Copithorne, Brad (2010). Addressing the Environmental Risks from Shale Gas Development (PDF) (Report). Worldwatch Institute. p. 9. Retrieved 2012-05-24. {{cite report}}: Unknown parameter |month= ignored (help)

[BBC_08.06.2012-116] "Shale gas fracking: MPs call for safety inquiry after tremors". BBC News. 8 June 2011. Retrieved 22 February 2012.

[AutoZV-34-117] "Fracking tests near Blackpool 'likely cause' of tremors". BBC News. 2 November 2011. Retrieved 22 February 2012.

[AutoZV-35-118] Pater, C.J.; Baisch, S. (2 November 2011). Geomechanical Study of Bowland Shale Seismicity (PDF) (Report). Cuadrilla Resources. Retrieved 22 February 2012.

[AutoZV-36-119] "FAQs – Earthquakes, Faults, Plate Tectonics, Earth Structure: Can we cause earthquakes? Is there any way to prevent earthquakes?". USGS. 27 October 2009. Retrieved 22 February 2012.

[Underground_Injection-120] "EPA Underground Injection Control Program". Retrieved 2012-04-13.

[AutoZV-37-121] "Ohio Quakes Probably Triggered by Waste Disposal Well, Say Seismologists" (Press release). Lamont–Doherty Earth Observatory. 6 January 2012. Retrieved 22 February 2012.

[Fountain03102012-122] Niquette, Mark (22 March 2012). "Fracking Fluid Soaks Ohio". Bloomberg Businessweek. Retrieved 2 April 2012.

[PA_zoning_bill-123] "Local zoning provisions in Pa.'s gas drilling law". USA Today. Associated Press. 3 March 2012. Retrieved 23 February 2012. {{cite news}}: Text "Frontpage" ignored (help); Text "newswell" ignored (help); Text "s" ignored (help); Text "text" ignored (help)^{[dead link]}

[Ohio2004bill-124] Suddes, Thomasn (14 Jan 2012). "'Fracking' debate exposes weaknesses in Ohio Statehouse – term limits and the death of home rule". The Plain Dealer. Retrieved 26 March 2012.

[natlawreview-125] "Recent Court Decisions May Affect Hydraulic Fracturing in New York and Ohio". The National Law Review. McDermott Will & Emery. 2012-04-01. Retrieved 2012-07-03.

[Tavernise12142011-126] Tavernise, Sabrina (14 Dec 2011). "As Gas Drilling Spreads, Towns Stand Ground Over Control Applied". The New York Times. Retrieved 26 March 2012.

[PA_Dr_access_bill-127] Sheppard, Kate (23 March 2012). "For Pennsylvania's Doctors, a Gag Order on Fracking Chemicals. A new provision could forbid the state's doctors from sharing information with patients exposed to toxic fracking solutions". Mother Jones. Retrieved 23 March 2012.

[psyops-128] Javers, Eamon (8 Nov 2011). "Oil Executive: Military-Style 'Psy Ops' Experience Applied". CNBC.

[AutoZV-38-129] Phillips, Susan (9 Nov 2011). "'We're Dealing with an Insurgency,' says Energy Company Exec of Fracking Foes". National Public Radio.

[AutoZV-39-130] "Chemicals that may be used in Australian CSG fraccing fluid" (PDF). Australian Petroleum Ptoduction & Exploration Association Limited. Retrieved 22 February 2012.

[AutoZV-40-131] Stephen D. Simpson (12 July 2010). "Will The EPA Crack Down On 'Fracking'?". Investopedia. Retrieved 22 February 2012. ^{[unreliable source?]}

[AutoZV-41-132] "HydraulicFracturing.com". Chesapeake Energy. Retrieved 2011-07-13.

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@@ Line 20: / Line 20: @@
 }}
-'''Hydraulic fracturing''' is the propagation of fractures in a [[Stratum|rock layer]], as a result of the action of a pressurized fluid. Some hydraulic fractures form naturally—certain [[Vein (geology)|vein]]s or [[dike (geology)|dike]]s are examples—and can create conduits along which gas and [[petroleum]] from [[source rock]]s may migrate to [[reservoir rock]]s. '''Induced hydraulic fracturing''' or '''hydrofracking''', commonly known as '''fraccing''' or '''fracking''', is a technique used to release petroleum, [[natural gas]] (including [[shale gas]], [[tight gas]] and [[coal seam gas]]), or other substances for extraction.{{ref label|a|a|none}}<ref name="Charlez"/>  This type of fracturing creates fractures from a [[wellbore]] drilled into reservoir rock formations.
+'''Hydraulic fracturing''' is the propagation of fractures in a [[Stratum|rock layer]], as a result of the action of a pressurized fluid. Some hydraulic fractures form naturally—certain [[Vein (geology)|vein]]s or [[dike (geology)|dike]]s are examples—and can create conduits along which gas and [[petroleum]] from [[source rock]]s may migrate to [[reservoir rock]]s. '''Induced hydraulic fracturing''' or '''hydrofracking''', commonly known as '''fraccing''' or '''fracking''', is a technique used to release petroleum, [[natural gas]] (including [[shale gas]], [[tight gas]] and [[coal seam gas]]), or other substances for extraction.{{ref label|a|a|none}}<ref name="Charlez"/>
-The first use of hydraulic fracturing was in 1947 but the modern fracking technique that made the extraction of shale gas economical was first used in 1997 in the [[Barnett Shale]] in Texas.<ref name="Charlez"/><ref name="AutoZV-10"/><ref name="SPE-20"/> The energy from the injection of a highly pressurized [[fracking fluid]] creates new channels in the rock, which can increase the extraction rates and ultimate recovery of [[hydrocarbon]]s.
+The first use of hydraulic fracturing was in 1947 but the modern fraccing technique that made the extraction of shale gas economical was first used in 1997 in the [[Barnett Shale]] in Texas.<ref name="Charlez"/><ref name="AutoZV-10"/><ref name="SPE-20"/> The energy from the injection of a highly pressurized [[fracking fluid]] creates new channels in the rock which can increase the extraction rates and ultimate recovery of [[hydrocarbon]]s.
-Proponents of fracking point to the vast amounts of formerly inaccessible [[hydrocarbons]] the process can extract.<ref name="WEO2012 Special"/>  Opponents point to potential [[Environment (biophysical)|environment]]al impacts, including contamination of [[ground water]], risks to [[air quality]], the migration of gases and hydraulic fracturing chemicals to the surface, surface contamination from spills and flowback and the [[health effect]]s of these.<ref name="HeatOnGas"/> For these reasons hydraulic fracturing has come under scrutiny internationally, with some countries suspending or even banning it.
+Proponents of fraccing point to the vast amounts of formerly inaccessible [[hydrocarbons]] the process can extract.<ref name="WEO2012 Special"/>  Opponents point to potential [[Environment (biophysical)|environment]]al impacts, including contamination of [[ground water]], risks to [[air quality]], the migration of gases and hydraulic fracturing chemicals to the surface, surface contamination from spills and flowback and the [[health effect]]s of these.<ref name="HeatOnGas"/>
 [[File:HydroFrac.png|thumb|400px|Schematic depiction of hydraulic fracturing for shale gas, showing potential [[environmental effect]]s.]]
@@ Line 54: / Line 54: @@
 ==Induced hydraulic fracturing==
 ===Uses===
-The technique of hydraulic fracturing is used to increase or restore the rate at which fluids, such as petroleum, water, or natural gas can be produced from subterranean natural reservoirs. Reservoirs are typically porous [[sandstone]]s, [[limestone]]s 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 {{convert|5000|–|20000|ft}}).  At such depth, there may not be sufficient [[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 pivotal to extract gas from shale reservoirs because of the extremely low natural permeability of shale, which is measured in the micro[[darcy]] to nanodarcy range.<ref name="AutoZV-2"/> Fractures provide a conductive path connecting a larger volume of the reservoir to the well. So-called "super fracking", which creates cracks deeper in the rock formation to release more oil and gas, will allow companies to frack more efficiently.<ref name="BW 19.01.2012"/>  The yield for a typical shale gas well generally falls off sharply after the first year or two.<ref name="Geosoc yield"/>
+The technique of hydraulic fracturing is used to increase or restore the rate at which fluids, such as petroleum, water or natural gas can be produced from subterranean natural reservoirs. Reservoirs are typically porous [[sandstone]]s, [[limestone]]s 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 {{convert|5000|–|20000|ft}}).  At such depth, there may not be sufficient [[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 pivotal to extract gas from shale reservoirs because of the extremely low natural permeability of shale, which is measured in the micro[[darcy]] to nanodarcy range.<ref name="AutoZV-2"/> Fractures provide a conductive path connecting a larger volume of the reservoir to the well. So-called "super fracking", which creates cracks deeper in the rock formation to release more oil and gas, will allow companies to frack more efficiently.<ref name="BW 19.01.2012"/>  The yield for a typical shale gas well generally falls off sharply after the first year or two.<ref name="Geosoc yield"/>
 While the main industrial use of hydraulic fracturing is in arousing production from [[Oil well|oil and gas wells]],<ref name="AutoZV-3"/><ref name="AutoZV-4"/><ref name="Economides"/> hydraulic fracturing is also applied:
@@ Line 72: / Line 72: @@
 The location of one or more fractures along the length of the borehole is strictly controlled by various methods that 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.<ref name="Arthur"/>
-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 quintuplex 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.<ref name="Chilingar"/> Fracturing equipment operates over a range of pressures and injection rates, and can reach up to {{convert|100|MPa|psi}} and {{convert|265|L/s}} (100 barrels per minute).<ref name="Love"/>
+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 quintuplex 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.<ref name="Chilingar"/> Fracturing equipment operates over a range of pressures and injection rates and can reach up to {{convert|100|MPa|psi}} and {{convert|265|L/s}} (100 barrels per minute).<ref name="Love"/>
 ===Well types===
@@ Line 87: / Line 87: @@
 The fluid injected into the rock is typically a [[slurry]] of water, proppants, and [[List of additives for hydraulic fracturing|chemical additives]]. Additionally, gels, foams, and compressed gases, including [[nitrogen]], [[carbon dioxide]] and air can be injected. Typically, of the fracturing fluid over 98–99.5% is water and sand with the chemicals accounting to about 0.5%.<ref name="DOE primer"/><ref name="Hartnett"/>
-Hydraulic fracturing may use between {{convert|1.2|and|3.5|e6USgal}} of fluid per well, with large projects using up to {{convert|5|e6USgal}}. Additional fluid is used when wells are refractured; this may be done several times.<ref name="CRO 2009"/>{{rp|7, 33}} Water is by far the largest component of fracking fluids. The initial drilling operation itself may consume from {{convert|6000|to|600000|USgal}} of fracking fluids.
+Hydraulic fracturing may use between {{convert|1.2|and|3.5|e6USgal}} of fluid per well, with large projects using up to {{convert|5|e6USgal}}. Additional fluid is used when wells are refractured; this may be done several times.<ref name="CRO 2009"/>{{rp|7, 33}}
-====Preparation====
-Initially it is common to pump some amount (normally 6000 gallons or less) of [[HCl]] (usually 28%-5%), or [[acetic acid]] (usually 45%-5%), to clean the perforations or break down the near well bore and ultimately reduce pressure seen on the surface. Then the proppant is started and stepped up in concentration.
 ====Proppants====
@@ Line 112: / Line 108: @@
 ====Other chemical additives====
 {{See also|List of additives for hydraulic fracturing}}
 [[List of additives for hydraulic fracturing|Chemical additives]] are applied to tailor the injected material to the specific geological situation, protect the well, and improve its operation, 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 name="CRO 2009"/>  As the fracturing process proceeds, viscosity reducing agents such as [[oxidizer]]s and [[enzyme]] breakers are sometimes then added to the fracturing fluid to deactivate the gelling agents and encourage flowback.<ref name="CRO 2009"/>  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 continually being developed and improved to better handle wastewater and improve reusability.<ref name="DOE primer"/>  Although the concentrations of the chemical additives are very low, the recovered fluid may be harmful due in part to minerals picked up from the formation.{{citation needed|date=May 2012}} Over the life of a typical gas well, up to {{convert|100000|USgal}} of chemical additives may be used.<ref name="house1"/>
 ===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.<ref name="DOE primer"/>
@@ Line 127: / Line 125: @@
 ===Horizontal completions===
 Since the early 2000s, advances in [[Oil well#Drilling|drilling]] and [[Completion (oil and gas wells)|completion]] technology have 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 formations which do not have sufficient permeability to produce economically with a vertical well.  Such wells when drilled onshore are now usually hydraulically fractured in a number of stages, 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 name="AutoZV-13"/>
-In North America, shale reservoirs such as the Bakken, Barnett, [[Montney Formation|Montney]], [[Haynesville]], [[Marcellus Formation|Marcellus]], and most recently the [[Eagle Ford Formation|Eagle Ford]], [[Niobrara Formation|Niobrara]] and [[Utica Shale|Utica]] shales 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". {{Citation needed|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.<ref name="AutoZV-14"/>
-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.{{Citation needed|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.<ref name="mooney" />
 ==Increased recovery==
 {{see also|Shale gas}}
 Hydraulic fracturing has been seen as one key methods of extracting unconventional oil and gas resources. According to the [[International Energy Agency]], the remaining technically recoverable resources of shale gas are estimated to amount to {{convert|208|e12m3|abbr=off}}, tight gas to {{convert|76|e12m3|abbr=off}}, and coalbed methane to {{convert|47|e12m3|abbr=off}}. As a rule, formations of these resources have lower permeability than conventional gas formations and therefore, depending on the geological characteristics of the formation, specific technologies, such as hydraulic fracturing, are required. Although there are also other methods to extract these resources, such as conventional drilling or horizontal drilling, hydraulic fracturing is one of the key methods making their extraction technically viable. The multi-stage fracturing technique has facilitated shale gas and light tight oil production development in the United States and is believed to do so in the other countries with unconventional hydrocarbon resources. Significance of the extraction of unconventional hydrocarbons lies also in the fact that these resources are less concentrated than of conventional oil and gas resources.<ref name="WEO2012 Special"/>
 == Environmental impact ==
 {{Main|Environmental impact of hydraulic fracturing}}
 {{See also|Environmental impact of hydraulic fracturing in the United States}}
@@ Line 160: / Line 157: @@
 === Research issues ===
 Several organizations, researchers, and media outlets have reported difficulty in conducting and reporting the results of studies on hydraulic fracturing due to industry<ref name="Urbina 03Mar2011" /><ref name="EPA re study" /><ref name="Chesapeake" /> and governmental pressure, and expressed concern over possible censoring of environmental reports.<ref name="Urbina 03Mar2011" /><ref name="NYT lobbying docs" /><ref name="NYT Docs" /> Researchers have recommended requiring disclosure of all hydraulic fracturing fluids, testing animals raised near fracturing sites, and closer monitoring of environmental samples.<ref name="Cornellvet03092012" /> After court cases concerning contamination from hydraulic fracturing are settled, the documents are sealed. The [[American Petroleum Institute]] deny that this practice has hidden problems with gas drilling, while others believe it has and could lead to unnecessary risks to public safety and health.<ref name="Urbina 03Aug2011" />
@@ Line 167: / Line 165: @@
 === Air ===
 {{see also|Environmental impact of hydraulic fracturing in the United States#Air emissions}}
 The air emissions from hydraulic fracking are related to [[methane]] leaks originating from wells, and emissions from the diesel or natural gas powered equipment such as compressors, drilling rigs, pumps etc.<ref name="DOE primer"/>
@@ Line 179: / Line 178: @@
 === Water ===
 {{main|Environmental impact of hydraulic fracturing in the United States#Groundwater contamination}}
 ==== Consumption ====
-The large volumes of water required have raised concerns about fracking in arid areas, such as Karoo in South Africa.<ref name="NYTUrbina30Dec2011"/>  During periods of low stream flow it may affect [[Water supply network|water supplies]] for municipalities and industries such as [[power generation]], as well as recreation and [[aquatic life]]. It may also require water overland piping from distant sources.<ref name="ALL-Marcellus"/> Over its lifetime an average well requires {{convert|3|to|5|e6USgal|m3}} of water for the initial hydraulic fracturing operation and possible restimulation frac jobs.<ref name="DOE primer"/><ref name="ALL-Marcellus"/> Using the case of the Marcellus Shale as an example, fracking accounted for {{convert|650|e6USgal/a|m3/a}} or less than 0.8% of annual water use in the area overlying the Marcellus Shale as of 2010.<ref name="ALL-Marcellus"/> To minimize water consumption, recycling is one possible option.<ref name="WEO2011full"/>
+The large volumes of water required have raised concerns about fraccing in arid areas, such as Karoo in South Africa.<ref name="NYTUrbina30Dec2011"/>  During periods of low stream flow it may affect [[Water supply network|water supplies]] for municipalities and industries such as [[power generation]], as well as recreation and [[aquatic life]]. It may also require water overland piping from distant sources.<ref name="ALL-Marcellus"/> Over its lifetime an average well requires {{convert|3|to|5|e6USgal|m3}} of water for the initial hydraulic fracturing operation and possible restimulation frac jobs.<ref name="DOE primer"/><ref name="ALL-Marcellus"/> Using the case of the Marcellus Shale as an example, fracking accounted for {{convert|650|e6USgal/a|m3/a}} or less than 0.8% of annual water use in the area overlying the Marcellus Shale as of 2010.<ref name="ALL-Marcellus"/> To minimize water consumption, recycling is one possible option.<ref name="WEO2011full"/>
 ====Waste water====
 As the fracturing fluid flows back through the well, it consists of spent fluids and may contain dissolved constituents such as minerals and [[brine water]]s. It may account for about 30–70% of the original fracture fluid volume. In addition, natural [[formation water]]s may flow to the well and need treatment. These fluids, commonly known as [[produced water]], should be managed by [[underground injection]], [[wastewater treatment]] and discharge, or recycling to fracture future wells.<ref name=Arthur2/> Treatment of produced waters may be feasible through either self‐contained systems at well sites or fields or through municipal waste water treatment plants or commercial treatment facilities.<ref name=Arthur2/> However, the quantity of waste water needing treatment and the improper configuration of sewage plants have become an issue in some regions of the United States. Much of the wastewater from hydraulic fracturing operations is processed by public sewage treatment plants, which are not equipped to remove radioactive material and are not required to test for it.<ref name="Neshaminy 2009"/><ref name="Urbina 26Feb2011"/>
@@ Line 192: / Line 194: @@
 ==== Methane ====
 Groundwater methane contamination is also a concern as it has adverse impact on water quality and in extreme cases may lead to potential explosion.<ref name="Duke study 2010"/>  However, methane contamination is not always caused by fracking. Drilling for ordinary drinking water wells can also cause methane release. Some studies make use of tests that can distinguish between the deep [[thermogenic]] methane released during gas/oil drilling, and the shallower [[biogenic]] methane that can be released during water-well drilling. While both forms of methane result from decomposition, thermogenic methane results from [[geothermal]] assistance deeper underground.<ref name=molofsky/><ref name="AutoZV-32"/>
@@ Line 197: / Line 200: @@
 ====Chemicals====
 {{Main|List of additives for hydraulic fracturing}}
 While some of the [[List of additives for hydraulic fracturing|chemicals used in hydraulic fracturing]] are common and generally harmless, some are known [[carcinogens]] or toxic.<ref name="house1"/> The most common chemical used for hydraulic fracturing in the United States in 2005–2009 was [[methanol]], while some other most widely used chemicals were [[isopropyl alcohol]], [[2-butoxyethanol]], and [[ethylene glycol]].<ref name="house1"/>
@@ Line 209: / Line 213: @@
 ==== Radioactivity ====
 {{main|Environmental impact of hydraulic fracturing in the United States#Radioactive contamination}}
 [[Radioactive tracer]]s are injected with the other substances in hydraulic-fracturing fluid. <ref name="Reis_iodine" /> In addition, hydraulic fracturing fluid might release heavy metals and radioactive materials from the deposit which may reflow to the surface by the flowback.<ref name=stevens/><ref name="NYT Waste Docs 26Feb2011" /><ref name="Urbina 07Apr2011" /><ref name="Bucks Co Water" />  ''[[The New York Times]]'' has reported radium and gross alpha radiation in wastewater from natural gas wells, which releases into [[Pennsylvania]] rivers,<ref name="Urbina 26Feb2011" /> compiled a map of these wells and their wastewater contamination levels,<ref name="TimesMap" /> and stated that some EPA reports were never made public. They did not measure beta or gamma radiation. The ''Times''' reporting on the issue has come under some criticism.<ref name="NYT letters 05Mar2011" /><ref name="Petit 02Mar2011" /> Recycling the wastewater has been proposed as a solution but has its limitations.<ref name="Urbina 01Mar2011" />
@@ Line 215: / Line 220: @@
 === Seismic ===
 Hydraulic fracturing causes [[induced seismicity]] called microseismic events or [[microearthquake]]s.  The magnitude of these events is usually too small to be detected at the surface, although the biggest micro-earthquakes may have the magnitude of about -1.6&nbsp;[[Moment magnitude scale|(M<sub>w</sub>)]].  The injection of waste water from gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude [[earthquake|tremor]]s, being registered up to 3.3&nbsp;(M<sub>w</sub>).<ref name=worldwatch/>
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 ==Public policy, information, and relations==
 Governments are developing legislation related to hydraulic fracturing. The US has the longest history with hydraulic fracturing, so its approaches to hydraulic fracturing may be modeled by other countries.<ref name="NYTUrbina30Dec2011" /> In the US, some states have introduced legislation that limits the ability of municipalities to use zoning to protect citizens from  exposure to pollutants from hydraulic fracturing by protecting residential areas. For instance, in Pennsylvania, the new Marcellus Shale Law (House Bill 1950)<ref name="PA zoning bill"/> requires all municipalities to allow Marcellus Shale well drilling in all zoning districts, including residential, and allow water and wastewater pits in all zoning district, including residential. Compressor stations must be allowed in industrial and agricultural zoning districts, and gas processing plants allowed in industrial zoning districts. Municipalities are no longer permitted to limit the hours of operation of gas related activities. Gas pipelines must be allowed in all zoning districts.<ref name="PA zoning bill" /> Similar laws have been created in Ohio,<ref name="Ohio2004bill"/> and New York,<ref name=natlawreview/> Colorado, and Texas are battling over related legislation.<ref name="Tavernise12142011"/> Pennsylvania's Marcellus Shale Law (House Bill 1950) also contains a provision that allows doctors in Pennsylvania access to the list of chemicals in hydraulic fracturing fluid in emergency situations only, and forbids them from ever discussing this information with their patients.<ref name="PA Dr access bill"/>
-A number of public information resources have been developed by governments and news sources (see external links section below). The US Environmental Protection Agency has a site labelled ''Natural Gas Extraction - Hydraulic Fracturing''. Other sites include ''FracFocus'', a site indicating the chemical composition of fracking fluid of individual wells and [[ProPublica]]'s sites containing collected news, commentary and illustration. ''The Guardian'' has posted Shale gas and fracking site. ''The New York Times'' also has a page dedicated to hydraulic fracturing.
+A number of public information resources have been developed by governments and news sources (see external links section below). The US Environmental Protection Agency has a site labelled ''Natural Gas Extraction - Hydraulic Fracturing''. Other sites include ''FracFocus'', a site indicating the chemical composition of fraccing fluid of individual wells and [[ProPublica]]'s sites containing collected news, commentary and illustration. ''The Guardian'' has posted Shale gas and fracking site. ''The New York Times'' also has a page dedicated to hydraulic fracturing.
-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 learned 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"/><ref name="AutoZV-38"/>
+The considerable opposition against fraccing activities in local townships has led companies to adopt a variety of public relations measures to assuage fears about fraccing, 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 fraccing opponents. Matt Pitzarella, spokesman for the most important fraccing company in Pennsylvania, [[Range Resources]], also told other conference attendees that Range employed [[psychological warfare]] operations veterans. According to Pitzarella, the experience learned 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 fraccing.<ref name="psyops"/><ref name="AutoZV-38"/>
 ==See also==

v t e Shale gas
Geological formations	Antrim Barnett Conasauga Duvernay Eagle Ford Fayetteville Haynesville Horn River Marcellus Montney Muskwa New Albany Utica
Technology	Geosteering Directional drilling Hydraulic fracturing Logging while drilling Measurement while drilling
By country	Canada China Romania United Kingdom United States List of countries by recoverable shale gas
Protests	Frack Off Balcombe drilling protest 2012–14 Romanian protests against shale gas