Hydraulic fracturing

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Induced hydraulic fracturing
Schematic depiction of hydraulic fracturing for shale gas.
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

Hydraulic fracturing (also hydrofracturing, fracking, or fraccing) is a well-stimulation technique in which rock is fractured by a hydraulically pressurized liquid. A high-pressure fluid (usually chemicals and sand suspended in water) is injected into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (either sand or aluminium oxide) hold the fractures open once the deep rock achieves geologic equilibrium.

The hydraulic fracturing technique is commonly applied to wells for shale gas, tight gas, tight oil, and coal seam gas.[1][2] Such well-stimulation is common throughout the exploitation of the field to greatly increase the flow rate. Stimulation is intensified to extend the period before production declines.[citation needed]

Hydraulic fracturing began as an experiment in 1947, and the first commercially successful application followed in 1949. As of 2012, 2.5 million hydraulic fracturing operations had been performed worldwide on oil and gas wells; over one million of those within the U.S.[3][4]

Hydraulic fracturing is highly controversial, proponents advocating economic benefits of readily accessible hydrocarbons,[5][6] and opponents concerned for the environmental impact of hydraulic fracturing including contamination of ground water, depletion of fresh water, degradation of the air quality, the triggering of earthquakes, noise pollution, surface pollution, and the consequential risks to health and the environment.[7]

Increases in seismic activity following hydraulic fracturing are usually caused by the deep-injection disposal of flowback and brine (which is produced from hydraulically fractured wells).[8] For these reasons, hydraulic fracturing is under international scrutiny, restricted in some countries, and banned altogether in others.[9][10][11] Some of those countries, notably the U.K., have repealed bans on hydraulic fracturing in favour of regulation. The European Union is drafting regulations that would permit controlled application of hydraulic fracturing.[12]


Halliburton fracturing operation in the Bakken Formation, North Dakota, United States
A fracturing operation in progress
Main article: Fracture (geology)


Fracturing in rocks at depth tends to be suppressed by the pressure of the overlying rock stratas weight, and the cementation of the formation. This is particularly significant in "tensile" (Mode 1) fractures which require the walls of the fracture to move against this pressure. Fracturing occurs when effective stress is overcome by the pressure of fluids within the rock. The minimum principal stress becomes tensile and exceeds the tensile strength of the material.[13][14] Fractures formed in this way are generally oriented in a plane perpendicular to the minimum principal stress, and for this reason, hydraulic fractures in well bores can be used to determine the orientation of stresses.[15] In natural examples, such as dikes or vein-filled fractures, the orientations can be used to infer past states of stress.[16]


Most mineral vein systems are a result of repeated natural fracturing during periods of relatively high pore fluid pressure. This is particularly evident in "crack-seal" veins, where the vein material is part of a series of discrete fracturing events, and extra vein material is deposited on each occasion.[17] One example of long-term repeated natural fracturing is in the effects of seismic activity. Stress levels rise and fall episodically, and earthquakes can cause large volumes of connate water to be expelled from fluid-filled fractures. This process is referred to as "seismic pumping".[18]


Low-level[clarification needed] minor intrusions, such as dikes, propagate through the crust in the form of fluid-filled cracks. In such case, the fluid is magma. In sedimentary rocks with a significant water content, fluid at fracture tip will be steam.[19]



Fracturing as a method to stimulate shallow, hard rock oil wells dates back to the 1860s. Soon after the first commercial U.S. oil well in 1859, dynamite or nitroglycerin detonations were used to increase oil and natural gas production from petroleum bearing formations. On April 25, 1865, Civil War veteran Col. Edward A. L. Roberts received the first of his many patents for an “exploding torpedo.”[20] It was employed by oil producers in the US states of Pennsylvania, New York, Kentucky, and West Virginia using liquid and also, later, solidified nitroglycerin. Later still the same method was applied to water and gas wells. Stimulation of wells with acid, in stead of explosive fluids, was introduced in the 1930s. Due to acid etching, fractures would not close completely resulting in further productivity increase.[21]

Oil and gas wells[edit]

The relationship between well performance and treatment pressures was studied by Floyd Farris of Stanolind Oil and Gas Corporation. This study was the basis of the first hydraulic fracturing experiment, conducted in 1947 at the Hugoton gas field in Grant County of southwestern Kansas by Stanolind.[1][22] For the well treatment, 1,000 US gallons (3,800 l; 830 imp gal) of gelled gasoline (essentially napalm) 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 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.[22] Since then, hydraulic fracturing has been used to stimulate approximately one million oil and gas wells[23] in various geologic regimes with good success.

In contrast with large-scale hydraulic fracturing used in low-permeability formations, small hydraulic fracturing treatments are commonly used in high-permeability formations to remedy skin[clarification needed] damage at the rock-borehole interface. In such cases the fracturing may extend only a few feet from the borehole.[24]

In the Soviet Union, the first hydraulic proppant fracturing was carried out in 1952. Other countries in Europe and Northern Africa subsequently employed hydraulic fracturing techniques including Norway, Poland, Czechoslovakia, Yugoslavia, Hungary, Austria, France, Italy, Bulgaria, Romania, Turkey, Tunisia, and Algeria.[25]

Massive fracturing[edit]

Well Head where fluids are injected into the ground
Well head after all the hydraulic fracturing equipment has been taken off location

Massive hydraulic fracturing (also known as high-volume hydraulic fracturing) is a technique first applied by Pan American Petroleum in Stephens County, Oklahoma, USA in 1968. The definition of massive hydraulic fracturing varies somewhat, but is generally reference to treatments injecting greater than about 150 short tons, or approximately 300,000 pounds (136 metric tonnes), of proppant.[26]

American geologists became increasingly aware that there were huge volumes of gas-saturated sandstones with permeability too low (generally less than 0.1 millidarcy) to recover the gas economically.[26] Starting in 1973, massive hydraulic fracturing was used in thousands of gas wells in the San Juan Basin, Denver Basin,[27] the Piceance Basin,[28] and the Green River Basin, and in other hard rock formations of the western US. Other tight sandstone wells in the US made economically viable by massive hydraulic fracturing were in the Clinton-Medina Sandstone, and Cotton Valley Sandstone.[26]

Massive hydraulic fracturing quickly spread in the late 1970s to western Canada, Rotliegend and Carboniferous gas-bearing sandstones in Germany, Netherlands (onshore and offshore gas fields), and the United Kingdom in the North Sea.[25]

Horizontal oil or gas wells were unusual until the late 1980s. Then, operators in Texas began completing thousands of oil wells by drilling horizontally in the Austin Chalk, and giving massive slickwater hydraulic fracturing treatments to the wellbores. Horizontal wells proved much more effective than vertical wells in producing oil from tight chalk;[29] shale runs horizontally, so a horizontal well reaches much more of the resource.[30] The first horizontal well was drilled in the Barnett Shale in 1991[30] and slickwater fluids were introduced in 1996.[30]


Due to shale's high porosity and low permeability, technological research, development and demonstration were necessary before hydraulic fracturing accepted for commercial application to shale gas deposits. In 1976, the United States government started the Eastern Gas Shales Project, a set of dozens of public-private hydraulic fracturing demonstration projects.[31] During the same period, the Gas Research Institute, a gas industry research consortium, received approval for research and funding from the Federal Energy Regulatory Commission.[32]

In 1997, taking the slickwater fracturing technique used in East Texas by Union Pacific Resources (now part of Anadarko Petroleum Corporation), Mitchell Energy (now part of Devon Energy), learned how to use the technique in the Barnett Shale of north Texas. This made shale gas extraction widely economical.[33][34][35] George P. Mitchell has been called the "father of fracking" because of his role in applying it in shales.[36]

As of 2013, massive hydraulic fracturing is being applied on a commercial scale to shales in the United States, Canada, and China. Several countries are planning to use hydraulic fracturing.[37][38][39]


According to the United States Environmental Protection Agency (EPA) hydraulic fracturing is a process to stimulate a natural gas, oil, or geothermal energy well to maximize extraction. EPA defines the broader process as including the acquisition of source water, well construction, well stimulation, and waste disposal.[40]


A hydraulic fracture is formed by pumping fracturing fluid into a wellbore at a rate sufficient to increase pressure at the target depth (determined by the location of the well casing perforations), to exceed that of the fracture gradient (pressure gradient) of the rock.[41] The fracture gradient is defined as pressure increase per unit of depth relative to density, and is usually measured in pounds per square inch, per foot, or bars per metre. The rock cracks, and the fracture fluid permeates the rock extending the crack further, and further, and so on. Fractures are localized as pressure drops off with the rate of frictional loss, which is relevant to the distance from the well. Operators typically try to maintain "fracture width", or slow its decline following treatment, by introducing a proppant into the injected fluid – a material such as grains of sand, ceramic, or other particulate, thus preventing the fractures from closing when injection is stopped and pressure removed. Consideration of proppant strength 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 and hydraulic fracturing fluids.[41]

During the process, fracturing fluid leakoff (loss of fracturing fluid from the fracture channel into the surrounding permeable rock) occurs. If not controlled, it can exceed 70% of the injected volume. This may result in formation matrix damage, adverse formation fluid interaction, and altered fracture geometry, thereby decreasing efficiency.[42]

The location of one or more fractures along the length of the borehole is strictly controlled by various methods that create or seal holes in the side of the wellbore. Hydraulic fracturing is performed in cased wellbores, and the zones to be fractured are accessed by perforating the casing at those locations.[43]

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[clarification needed], 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.[44] Chemical additives are typically 0.5% percent of the total fluid volume. 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).[45]

Well types[edit]

A distinction can be made between conventional, low-volume hydraulic fracturing, used to stimulate high-permeability reservoirs for a single well, and unconventional, high-volume hydraulic fracturing, used in the completion of tight gas and shale gas wells. Unconventional wells are deeper and require higher pressures than conventional vertical wells.[46]

Horizontal drilling involves wellbores with a terminal drillhole 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 reduces surface disruptions as fewer wells are required to access the same volume of rock. Drilling usually induces damage to the pore space at the wellbore wall, reducing 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,[47] but is not typically administered in this way.

Fracturing fluids in the United States[edit]

Water tanks preparing for hydraulic fracturing

The main purposes of fracturing fluid are to extend fractures, add lubrication, change gel strength, and to carry proppant into the formation. There are two methods of transporting proppant in the fluid – high-rate and high-viscosity. High-viscosity fracturing tends to cause large dominant fractures, while high-rate (slickwater) fracturing causes small spread-out micro-fractures.[citation needed]

Water-soluble gelling agents (such as guar gum) increase viscosity and efficiently deliver proppant into the formation.[48]

Process of mixing water with hydraulic fracturing fluids to be injected into the ground

Fluid is typically a slurry of water, proppant, and chemical additives.[49] Additionally, gels, foams, and compressed gases, including nitrogen, carbon dioxide and air can be injected. Typically, 90% of the fluid is water and 9.5% is sand with chemical additives accounting to about 0.5%.[41][50][51] However, fracturing fluids have been developed using liquefied petroleum gas (LPG) and propane in which water is unnecessary.[52]

A proppant is a material that will keep an induced hydraulic fracture open during or following a fracturing treatment, and can be gel, foam, or slickwater-based. Fluid choices are tradeoffs material properties such as viscosity, where more viscous fluids can carry more concentrated proppant, energy or pressure demands to maintain a flux pump rate (flow velocity) that will conduct the proppant appropriately, pH, various rheological factors, and others. 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.[53]

The fracturing fluid varies dependant on fracturing type, conditions of specific wells being fractured, and water characteristics. A typical fracture treatment uses between 3 and 12 additive chemicals.[41] Although there may be unconventional fracturing fluids, typical chemical additives can include one or more of the following:

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.[54]

Typical fluid types are:

For slickwater it is common to include sweeps[clarification needed] or a temporary reduction in the proppant concentration to ensure the well is not overwhelmed with proppant causing a screen-off[clarification needed].[55] 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.[48] 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 breaking down the gel. Sometimes pH modifiers are used to break down the crosslink at the end of a hydraulic fracturing job since many require a pH buffer system to stay viscous.[55] 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 recovered to some degree and managed by several methods such as underground injection control, treatment and discharge, recycling, or temporary storage in pits or containers. New technology is continually being developed to better handle waste water and improve re-usability.[41]

Fracture monitoring[edit]

Measurements of the pressure and rate during the growth of a hydraulic fracture, with knowledge of fluid properties 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.[41]

Injection of radioactive tracers along with the fracturing fluid is sometimes used to determine the injection profile and location of created fractures.[56] Radiotracers are selected to have the readily detectable radiation, appropriate chemical properties, and a half life and toxicity level that will minimize initial and residual contamination.[57] Radioactive isotopes chemically bonded to glass (sand) and/or resin beads may also be injected to track fractures.[58] For example, plastic pellets coated with 10 GBq of Ag-110mm may be added to the proppant, or sand may be labelled with Ir-192, so that the proppant's progress can be monitored.[57] Radiotracers such as Tc-99m and I-131 are also used to measure flow rates.[57] 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.[58]

Microseismic monitoring[edit]

For more advanced applications, microseismic monitoring is sometimes used to estimate the size and orientation of 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 fracture, the approximate geometry of the fracture is inferred. Tiltmeter arrays deployed on the surface or down a well provide another technology for monitoring strain[59]

Microseismic mapping is very similar geophysically to seismology. In earthquake seismology, seismometers scattered on or near the surface of the earth record S-waves and P-waves that are released during an earthquake event. This allows for motion[clarification needed] along the fault plane to be estimated and its location in the earth’s subsurface mapped. Hydraulic fracturing, an increase in formation stress proportional to the net fracturing pressure, as well as an increase in pore pressure due to leakoff.[60] Tensile stresses are generated ahead of the fractures tip generating large amounts of shear stress. The increase in pore water pressure and formation stress combine and affect weaknesses (natural fractures, joints, and bedding planes) near the hydraulic fracture.[61]

Different methods have different location errors[clarification needed] and advantages. Accuracy of microseismic event mapping is dependent on the signal-to-noise ratio and the distribution of sensors. Accuracy of events located by seismic inversion is improved by sensors placed in multiple azimuths from the monitored borehole. In a downhole array location, accuracy of events is improved by being close to the monitored borehole (high signal-to-noise ratio).

Monitoring of microseismic events induced by reservoir[clarification needed] stimulation has become a key aspect in evaluation of hydraulic fractures, and their optimization. The main goal of hydraulic fracture monitoring is to completely characterize the induced fracture structure, and distribution of conductivity within a formation. Geomechanical analysis, such as understanding a formations material properties, in-situ conditions, and geometries, helps monitoring by providing a better definition of the environment in which the fracture network propagates.[62] The next task is to know the location of proppant within the fracture and the distribution of fracture conductivity. This can be monitored using multiple types of techniques to finally develop a reservoir model than accurately predicts well performance.

Horizontal completions[edit]

Since the early 2000s, advances in drilling and completion technology have made horizontal wellbores much[clarification needed] more economical. Horizontal wellbores allow far greater exposure to a formation than conventional vertical wellbores. 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 is used to determine how many times a formation is fractured, and at what locations along the horizontal section.[63]

In North America, shale reservoirs such as the Bakken, Barnett, Montney, Haynesville, Marcellus, and most recently the Eagle Ford, Niobrara and Utica shales are drilled, completed and fractured horizontally.[citation needed] 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".[64]

The wellbore for a plug and perf

job is generally composed of standard joints of steel casing, cemented or uncemented, set in the drilled hole. Once the drilling rig has been removed, a wireline truck is used to perforate near the end of the well, and then fracturing fluid is pumped. This process is repeated in what are known as stages. Then the wireline truck sets 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 along the horizontal length of the wellbore.[65]

The wellbore for the sliding sleeve[clarification needed] 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 due 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]


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.[66]


Hydraulic fracturing is used to increase the rate at which fluids, such as petroleum, water, or natural gas can be recovered 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 extraction of natural gas and oil from rock formations deep below the earth's surface (generally 2,000–6,000 m (5,000–20,000 ft)), which is greatly below typical groundwater reservoir levels. At such depth, there may be insufficient permeability or reservoir pressure to allow natural gas and oil to flow from the rock into the wellbore at high economic return. Thus, creating conductive fractures in the rock is instrumental in extraction from naturally impermeable shale reservoirs. Permeability is measured in the microdarcy to nanodarcy range.[67] Fractures are a conductive path connecting a larger volume of reservoir to the well. So-called "super fracking," creates cracks deeper in the rock formation to release more oil and gas, and increases efficiency.[68] The yield for typical shale bores generally falls off after the first year or two, but the peak producing life of a well can be extended to several decades.[69]

While the main industrial use of hydraulic fracturing is in stimulating production from oil and gas wells,[70][71][72] hydraulic fracturing is also applied:

Since the late 1970s, hydraulic fracturing has been used, in some cases, to increase the yield of drinking water from wells in a number of countries, including the US, Australia, and South Africa.[80][81][82]

Economic effects[edit]

See also: Shale gas and Tight oil

Hydraulic fracturing has been seen as one of the 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 (208,000 km3), tight gas to 76 trillion cubic metres (76,000 km3), and coalbed methane to 47 trillion cubic metres (47,000 km3). As a rule, formations of these resources have lower permeability than conventional gas formations. 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 economically viable. The multi-stage fracturing technique has facilitated the development of shale gas and light tight oil production in the United States and is believed to do so in the other countries with unconventional hydrocarbon resources.[5]

The National Petroleum Council estimates that hydraulic fracturing will eventually account for nearly 70% of natural gas development in North America.[83] Hydraulic fracturing and horizontal drilling apply the latest technologies and make it commercially viable to recover shale gas and oil. In the United States, 45% of domestic natural gas production and 17% of oil production would be lost within 5 years without usage of hydraulic fracturing.[84]

U.S.-based refineries have gained a competitive edge with their access to relatively inexpensive shale oil and Canadian crude. The U.S. is exporting more refined petroleum products, and also more liquified petroleum gas (LP gas). LP gas is produced from hydrocarbons called natural gas liquids, released by the hydraulic fracturing of petroliferous shale, in a variety of shale gas that's relatively easy to export. Propane, for example, costs around $620 a ton in the U.S. compared with more than $1,000 a ton in China, as of early 2014. Japan, for instance, is importing extra LP gas to fuel power plants, replacing idled nuclear plants. Trafigura Beheer BV, the third-largest independent trader of crude oil and refined products, said last month that "growth in U.S. shale production has turned the distillates market on its head."[85]

Some studies call into question the claim that what has been called the "shale gas revolution" has a significant macro-economic impact. A study released in the beginning of 2014 by the IDDRI shows the contrary. It demonstrates that, on the long-term as well as on the short-run, the "shale gas revolution" due to hydraulic fracturing in the United States has had very little impact on economic growth and competitiveness. It is also very unlikely to make some substantial contribution to GDP growth in the future. It would most likely be the same in Europe according to the study, despite of dramatically increased levels of production of unconventional oil and unconventional gas. Providing an optimistic hypothesis, in other words an upper estimation of shale gas effects on the level of US GDP, the study estimates the impact of hydraulic fracturing on the level of US GDP at 0.84% between 2012 and 2035, also estimating it as 0.88% of GDP growth during the period 2007-2012. Although the study found that on the very short-term, it has had a positive impact on GDP, estimated at 0.4%, due to a fall in gas prices, these effects are located and non-replicable over time ("one-off burst"). Overall, the study reads that "the US trade balance shows no sign of a large shift in competitiveness in non-petroleum and gas sectors."[86]

In Europe, using hydraulic fracturing would have very little advantage in terms of competitiveness and energy security. Indeed, for the period 2030-2035, shale gas is estimated to cover 3 to 10% of EU projected energy demand, which is not enough to have a significant impact on energetic independence and competitiveness .[86]

Hydraulic fracturing operations can damage transportation infrastructure, creating costs for local taxpayers. An article in Bloomberg BusinessWeek brought attention to the damage to rural roads caused by the heavy trucks used in hydraulic fracturing operations. Drilling companies can be contractually obligated to cover the costs of road repair. Measures to ensure that roads are repaired don’t always include the full cost of damage, adding another burden to the taxpayers.[87]

In addition to these issues, there have been recent concerns with the accuracy of predictions about the economic potential of shale formations that would employ hydraulic fracturing as a method of extraction. A joint report by the INTEK Inc. and U.S. Energy Information Agency in 2011 stated that there are 15.4 billion barrels of recoverable oil in the Monterey Shale formation,[88] information used by a University of Southern California economic analysis that concluded that this amount of recoverable oil would add $24.6 billion a year and 2.8 million jobs to the California economy by 2020.[89] However, according to a joint report by the Post Carbon Institute (PCI) and the Physicians, Scientists, and Engineers for Healthy Energy (PSE), comprehensive technical and scientific analyses show that the recoverable sources of the Monterey Shale site are considerably less than 15.4 billion barrels. Moreover, the 2.8 million jobs the EIA/INTEK and USC report stated are unlikely due to the local landscape, geology, and historical characteristics of the site (thicker, tighter, and more complex structures, and in decline since its peak in 1980).[90] The potential implications of such reports are of great consequence: many proponents of hydraulic fracturing at the state and federal level look to economic reports and analyses by trusted organizations and associations to make big decisions about their communities.

The economic effect of energy extraction in rural towns was classified by one study as the Boomtown Impact Model. In this model, the emergence of a boomtown in a rural area that is rich in energy resources brings short and long term economic consequences, both positive and negative. Historical energy boomtowns (for example from the days of coal and uranium plants) show rapid increases and decreases of a local population and economy where drilling sites create jobs for the present, inevitably decline, and leave numbers of citizens jobless, with lack of goods, services, and housing, and leave local businesses downtrodden when demand falls short of supply.[91] A case study in Sublette County, Wyoming found that the boomtown produced by the natural gas drilling in the area had mixed effects. There was a significant growth of jobs however the town experienced inflation and the cost of living increased.[92] The boomtown model presented in this study almost inevitably ends with an economic bust.

It has also been pointed out that economic growth for some is not guaranteed to spread to the entire community and individuals can be negatively affected if they are not able to participate in the rapid growth.[93] Reports that fail to include the uneven distribution of impacts (both positive and negative) in its estimates leave out important issues that should be addressed for optimal assessment of the values of the entire system. Studies, and in many cases personal experience, have revealed that certain workers, businesses, and communities will have more benefit more than others, sometimes at their expense.[94] For example, landowners, drilling companies, and tourist businesses (hotels, restaurants, and shopping arenas) will be more likely to benefit than those who are subject to the noise of drilling sites, increased traffic, and "possible degradation of waterways, forests, and open space, and strains of local labor supply."[94] The accuracy and veracity of public reports responding to these complex issues are crucial to the future of the hydraulic fracturing and cannot be overstated.

A few academic studies from universities have emerged recently.[95][96] The core insights from these studies is that unconventional shale oil and gas may have the potential to dramatically alter the geography of energy production in the US. In the short run, there are significant employment effects and spillovers in counties where resource extraction is happening. One paper finds that employment in the oil and gas sector has more than doubled in counties located above shale deposits in the last 10 years, with significant spill-overs in local transport-, construction but also manufacturing sectors.[95] The latter benefits from significantly lower energy prices, giving the US manufacturing sector a competitive edge compared to the rest of the world. On average, natural gas prices have gone down by more than 30% in counties above shale deposits compared to the rest of the US. However, some research has also highlighted that there are negative effects on house prices for properties that lie in the direct vicinity of unconventional wells.[97] This study finds that local house prices in Pennsylvania go down if the property is close to an unconventional gas well and is not connected to utility water, suggesting that the fears of ground water pollution are priced by markets.

Environmental impact[edit]

Hydraulic fracturing has raised environmental concerns and is challenging the adequacy of existing regulatory regimes.[98] 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.[7][41][54] An additional concern is that oil obtained through hydraulic fracturing contains chemicals used in hydraulic fracturing, which may increase the rate at which rail tank cars and pipelines corrode, potentially releasing their load and its gases.[99][100] Also, the use of large machinery in hydraulic fracturing causes concern for destruction of landscape.[101]


Air emissions from hydraulic fracturing are related to methane leaks originating from wells, and emissions from diesel or natural gas powered equipment such as compressors, drilling rigs, and pumps.[41] Transportation of water and sand by trucks can involve high volumes of particulate air pollution.[102] There are reports of health problems associated with compressor stations and drilling sites,[103][104] but a causal relationship was not established for the wells studied.[dubious ][104] A Texas government one-time sampling study of volatile organic compounds (VOC's) in 28 people's urine and blood found VOC's but "could not identify with any degree of certainty a source for all of the exposures".[105]

Whether natural gas produced by hydraulic fracturing causes higher well-to-burner emissions than gas produced from conventional wells is a matter of contention. Some studies have found that hydraulic fracturing has higher emissions due to 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, but less than half the emissions of burning coal.[98][106][107] Methane leakage has been calculated at the rate of 1–7% with the United States Environmental Protection Agency's estimated leakage rate to be about 2.4%.[108][109]


Water usage[edit]

Massive hydraulic fracturing uses traditionally between 1.2 and 3.5 million US gallons (4.5 and 13.2 Ml) of water per well, with large projects using up to 5 million US gallons (19 Ml). Additional water is used when wells are re-fractured.[48][110] An average well requires 3 to 8 million US gallons (11,000 to 30,000 m3) of water over its lifetime.[41][110][111][112] According to the Oxford Institute for Energy Studies, greater volumes of fracturing fluids are required in Europe, where the shale depths average 1.5 times greater than in the U.S.[113]

Use of water for hydraulic fracturing can divert water from stream flow, water supplies for municipalities and industries such as power generation, as well as recreation and aquatic life.[114] The large volumes of water required for most common hydraulic fracturing methods have raised concerns for arid regions such as Karoo in South Africa,[115] in Pennsylvania,[116][117] and in drought-prone Texas and Colorado in North America.[118] To provide a perspective, Texas has used 110 of the (at least) 250 billion of gallons of water the United States has used for hydraulic fracturing from 2005 to 2013.[107] According to Environment America, there are concerns for farmers competing with oil and gas for water.[107]

Some producers have developed hydraulic fracturing techniques that could reduce the need for water by re-using recycled flowback water, or using carbon dioxide, liquid propane or other gases instead of water.[98][119][120] According to researchers water used in hydraulic fractring is permanently lost to the water cycle, as it either remains in the well, is recycled (used in the hydraulic fracturing of new wells), or is disposed of in deep injection wells, where it is unavailable to recharge aquifers.[107] As hydraulic fracturing helps develop shale gas reserves which contributes to replacing coal usage with natural gas, by some data water saved by using natural gas combined cycle plants instead of coal steam turbine plants makes the overall water usage balance more positive.[121]

Injected fluid[edit]

While some of the chemicals used in hydraulic fracturing are common and generally harmless, some additives used in the United States are known carcinogens.[54] Out of 2,500 hydraulic fracturing additives, more than 650 contained known or possible human carcinogens regulated under the Safe Drinking Water Act or listed as hazardous air pollutants".[54] Another 2011 study identified 632 chemicals used in United States natural gas operations, of which only 353 are well-described in the scientific literature.[122]

Well casing or cement bond failure in injection wells, have the potential to leak methane into groundwater aquifers. Wellbores used in fracturing operations also have the potential to cause oil and gas to rise and mix into freshwater aquifers, causing most immediate harm to those communities that rely on nearby local water sources.[123]

A comprehensive study in the US about the impact of hydraulic fracturing on groundwater is to be released in 2014 by the EPA. It will be the first study of this scale to address whether or not there is an impact of hydraulic fracturing on groundwater contamination,[124] previous having only shown evidence for very localized areas like in West Virginia as reported in 1987.[125]


Estimates of the fluid that returns to the surface with the gas range from 15-20%[126] to 30–70%. Additional fluid may return to the surface through abandoned wells or other pathways.[127] After the flowback is recovered, formation water, usually brine, may continue to flow to the surface, requiring treatment or disposal. Approaches to managing these fluids, commonly known as flowback, produced water, or wastewater, include underground injection, municipal waste water treatment plants, industrial wastewater treatment, self-contained systems at well sites or fields, and recycling to fracture future wells.[106][128][129][130] When flowback fluid is not accepted in the local state or waste water treatment facilities they can be shipped for disposal in injection wells.[107] According to Frontier Group about 100 million gallons of water was shipped from Pennsylvania to Ohio in 2011 for disposal into underground injection wells.[107]

Flowback water can be recycled, but is an expensive time- and chemical-consuming process, and can only be recycled up until it reaches a certain total dissolved solids (TDS) concentration level. Some facilities that treat produced water cannot remove large amounts of dissolved solids, and the contents of hydraulic fracturing fluids (salt, organic compounds, and metal concentrations) can have adverse affects on the treatment.[123]

Water sources from flowback or reinjection fluid can be treated (in varying degrees of standards) and reused in oil development, for water/stream flooding, or, it has been reported, for human/animal consumption.[123] While reinjection and treatment of hydraulic fracturing fluids and flowback may be safely regulated and reused, this requires strong policy frameworks and enforcement, transparency, and oversight at the state, local, and regional level.


A study by MIT in 2011 found that there was evidence of natural gas (methane) migration into freshwater zones in some areas, most likely as a result of substandard well completion practices, such as poor quality cementing jobs or bad casings, by a few operators.[131] 2011 studies by the Colorado School of Public Health and Duke University also pointed to methane contamination stemming from the drilling process.[132][133] Groundwater methane contamination has adverse effect on water quality and in extreme cases may lead to potential explosion.[132][134] The correlation between drilling activity and methane pollution of the drinking water has been noted; however, studies to date have not established that methane contamination is caused by hydraulic fracturing itself, rather than by other well drilling or completion practices.[135] Most recent 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.[133][136]


In some cases hydraulic fracturing may dislodge uranium, radium, radon and thorium from formation and these substances may consist in flowback fluid.[137] Therefore there are concerns about the levels of radioactivity in wastewater from hydraulic fracturing and its potential impact on public health. Recycling the wastewater has been proposed as a partial solution, but this approach has limitations.[138]


Hydraulic fracturing routinely produces microseismic events too small to be detected except by sensitive instruments, but it sometimes produces bigger events that can be felt by local populations. These microseismic events are often used to map the horizontal and vertical extent of the fracturing.[59] As of late 2012, there have been four known instances of hydraulic fracturing, through induced seismicity, triggering quakes large enough to be felt by people: one each in the United States and Canada, and two in England.[8][139][140] The injection of waste water from oil and gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude tremors, being registered up to 3.3 (Mw).[141]

Several earthquakes in 2011, including a 4.0 magnitude quake on New Year's Eve that hit Youngstown, Ohio, are likely linked to a disposal of hydraulic fracturing wastewater,[8] according to seismologists at Columbia University.[142] Although the magnitudes of these quakes has been small, the United States Geological Survey has said that there is no guarantee that larger quakes will not occur.[143] A report in the United Kingdom concluded that hydraulic fracturing was the likely cause of two small tremors (magnitudes 2.3 and 1.4 on the Richter scale) that occurred during hydraulic fracturing of shale in April and May 2011.[144][145][146] These tremors were felt by local populations. Because of these two events, seismicity is the impact mostly related to hydraulic fracturing in the UK's public opinion.[147]

In addition, the frequency of the quakes has been increasing. In 2009, there were 50 earthquakes greater than magnitude 3.0 in the area spanning Alabama and Montana, and there were 87 quakes in 2010. In 2011 there were 134 earthquakes in the same area, a sixfold increase over 20th century levels.[148] According to a study at the U.S. Geological Survey in Menlo Park, California, the increase in hydraulic fracturing over the years is related to the increase in quakes.[149]

Health effects[edit]

Concern has been expressed over the possible long and short term health effects of air and water contamination and radiation exposure by gas production.[137][150][151] Health consequences of concern include infertility, birth defects and cancer.[152][153][154]

A 2012 study concluded that risk prevention efforts should be directed towards reducing air emission exposures for persons living and working near wells during well completions.[155]

A study conducted in Garfield County, Colorado and published in Endocrinology suggested that natural gas drilling operations may result in elevated endocrine-disrupting chemical activity in surface and ground water.[153]

A 2014 study of households using groundwater near active natural gas drilling in Washington County, Pennsylvania found that upper respiratory illnesses and skin diseases were much more prevalent closer to fracking activity. Respiratory problems were found in 18% of the population 1.2 miles or more from drilling, compared to 39% of those within 0.6 miles of new natural gas wells. People with clinically significant skin problems increased from 3% to 13% over the same distances.[156]


Countries using or considering to use hydraulic fracturing have implemented different regulations, including developing federal and regional legislation, and local zoning limitations.[157][158] In 2011, after public pressure France became the first nation to ban hydraulic fracturing, based on the precautionary principle as well as the principal of preventive and corrective action of environmental hazards.[10][11][159][160] The ban was upheld by an October 2013 ruling of the Constitutional Council.[161] Some other countries have placed a temporary moratorium on the practice.[162] Countries like the United Kingdom and South Africa, have lifted their bans, choosing to focus on regulation instead of outright prohibition.[163][164] Germany has announced draft regulations that would allow using hydraulic fracturing for the exploitation of shale gas deposits with the exception of wetland areas.[165]

The European Union has adopted a recommendation for minimum principles for using high-volume hydraulic fracturing.[12] Its regulatory regime requires full disclosure of all additives.[166] In the United States, the Ground Water Protection Council launched FracFocus.org, an online voluntary disclosure database for hydraulic fracturing fluids funded by oil and gas trade groups and the U.S. Department of Energy.[167][168] Hydraulic fracturing is excluded from the Safe Drinking Water Act's underground injection control's regulation, except when diesel fuel is used. The EPA assures surveillance of the issuance of drilling permits when diesel fuel is employed.[169]

Public debate[edit]

Poster against hydraulic fracturing in Vitoria-Gasteiz, Spain, October 2012

Politics and public policy[edit]

The considerable opposition against hydraulic fracturing activities in local townships has led companies to adopt a variety of public relations measures to assuage fears about hydraulic fracturing, 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 hydraulic fracturing opponents. Matt Pitzarella, spokesman for 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 hydraulic fracturing.[170][171]

Police officers have at the same time recently been forced to deal with intentionally disruptive and even potentially violent opposition to oil and gas development. In March 2013, ten people were arrested[172] during an "anti-fracking protest" near New Matamoras, Ohio, after they illegally entered a development zone and latched themselves to drilling equipment. In northwest Pennsylvania, there was a drive-by shooting at a well site, in which an individual shot two rounds of a small-caliber rifle in the direction of a drilling rig, just before shouting profanities at the site and fleeing the scene.[173] And in Washington County, Pennsylvania, a contractor working on a gas pipeline found a pipe bomb that had been placed where a pipeline was to be constructed, which local authorities said would have caused a “catastrophe” had they not discovered and detonated it.[174]

Media coverage[edit]

Josh Fox's 2010 Academy Award nominated film Gasland [175] became a center of opposition to hydraulic fracturing of shale. The movie presented problems with ground water contamination near well sites in Pennsylvania, Wyoming, and Colorado.[176] Energy in Depth, an oil and gas industry lobbying group, called the film's facts into question.[177] In response, a rebuttal of Energy in Depth's claims of inaccuracy was refuted on Gasland's website.[178]

The Director of the Colorado Oil and Gas Conservation Commission (COGCC) offered to be interviewed as part of the film if he could review what was included from the interview in the final film but Fox declined the offer.[179] Exxon Mobil, Chevron Corporation and ConocoPhillips aired advertisements during 2011 and 2012 that claimed to describe the economic and environmental benefits of natural gas and argue that hydraulic fracturing was safe.[180]

The film Promised Land, starring Matt Damon, takes on hydraulic fracturing.[181] The gas industry is making plans to try to counter the film's criticisms of hydraulic fracturing with informational flyers, and Twitter and Facebook posts.[180]

On January 22, 2013 Northern Irish journalist and filmmaker Phelim McAleer released a crowdfunded[182] documentary called FrackNation as a response to the claims made by Fox in Gasland. FrackNation premiered on Mark Cuban's AXS TV. The premiere corresponded with the release of Promised Land.[183]

On April 21, 2013, Josh Fox released Gasland 2, a documentary that declares the gas industry's portrayal of natural gas as a clean and safe alternative to oil is a myth, and that hydraulically fractured wells inevitably leak over time, contaminating water and air, hurting families, and endangering the earth's climate with the potent greenhouse gas methane.

Research issues[edit]

Typically the funding source of the research studies is a focal point of controversy. Concerns have been raised about research funded by foundations and corporations, or by environmental groups, which can at times lead to at least the appearance of unreliable studies.[184][185] Several organizations, researchers, and media outlets have reported difficulty in conducting and reporting the results of studies on hydraulic fracturing due to industry[186] and governmental pressure,[9] and expressed concern over possible censoring of environmental reports.[186][187][188] Researchers have recommended requiring disclosure of all hydraulic fracturing fluids, testing animals raised near fracturing sites, and closer monitoring of environmental samples.[189] Many believe there is a need for more research into the environmental and health effects of the technique.[190][191]

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