Hydraulic fracturing 1

Hydraulic fracturing

Hydraulic fracturingProcess type Mechanical

Industrial sector(s) Mining

Main technologies or sub-processes Fluid pressure

Product(s) Natural gasPetroleum

Inventor Floyd Farris; J.B. Clark (Stanolind Oil and Gas Corporation)

Year of invention 1947

Schematic depiction of hydraulic fracturing forshale gas.

Hydraulic fracturing is the propagation of fractures in a rock layer bya pressurized fluid. Some hydraulic fractures form naturally—certainveins or dikes are examples—and can create conduits along which gasand petroleum from source rocks may migrate to reservoir rocks.Induced hydraulic fracturing or hydrofracturing, commonly knownas fracing, fraccing, or fracking, is a technique used to releasepetroleum, natural gas (including shale gas, tight gas, and coal seamgas), or other substances for extraction.[1] This type of fracturingcreates fractures from a wellbore drilled into reservoir rock formations.

The first use of hydraulic fracturing was in 1947 but the modern fracturing technique, called horizontal slickwaterfracturing, that made the extraction of shale gas economical was first used in 1998 in the Barnett Shale inTexas.[1][2][3] The energy from the injection of a highly pressurized hydraulic fracturing fluid creates new channelsin the rock, which can increase the extraction rates and ultimate recovery of hydrocarbons.Proponents of hydraulic fracturing point to the economic benefits from vast amounts of formerly inaccessiblehydrocarbons the process can extract.[4] Opponents point to potential environmental impacts, includingcontamination of ground water, risks to air quality, the migration of gases and hydraulic fracturing chemicals to thesurface, surface contamination from spills and flowback and the health effects of these.[5] For these reasons hydraulicfracturing has come under scrutiny internationally, with some countries suspending or banning it.[6][7]

Geology

MechanicsFracturing in rocks at depth tends to be suppressed by the confining pressure, due to the load caused by the overlyingrock strata. This is particularly so in the case of "tensile" (Mode 1) fractures, which require the walls of the fractureto move apart, working against this confining pressure. Hydraulic fracturing occurs when the effective stress isreduced sufficiently by an increase in the pressure of fluids within the rock, such that the minimum principal stressbecomes tensile and exceeds the tensile strength of the material.[8][9] Fractures formed in this way will in the main beoriented in the plane perpendicular to the minimum principal stress and for this reason induced hydraulic fractures inwellbores are sometimes used to determine the orientation of stresses.[10] In natural examples, such as dikes orvein-filled fractures, the orientations can be used to infer past states of stress.[11]

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VeinsMost 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 beenadded in a series of discrete fracturing events, with extra vein material deposited on each occasion.[12] Onemechanism to demonstrate such examples of long-lasting repeated fracturing is the effects of seismic activity, inwhich the stress levels rise and fall episodically and large volumes of fluid may be expelled from fluid-filledfractures during earthquakes. This process is referred to as "seismic pumping".[13]

DikesHigh-level minor intrusions such as dikes propagate through the crust in the form of fluid-filled cracks, although inthis case the fluid is magma. In sedimentary rocks with a significant water content the fluid at the propagatingfracture tip will be steam.[14]

HistoryFracturing as a method to stimulate shallow, hard rock oil wells dates back to the 1860s. It was applied by oilproducers in the US states of Pennsylvania, New York, Kentucky, and West Virginia by using liquid and later alsosolidified nitroglycerin. Later, the same method was applied to water and gas wells. The idea to use acid as anonexplosive fluid for well stimulation was introduced in the 1930s. Due to acid etching, fractures would not closecompletely and therefore productivity was enhanced. The same phenomenon was discovered with water injectionand squeeze cementing operations.[15]

The relationship between well performance and treatment pressures was studied by Floyd Farris of Stanolind Oil andGas Corporation. This study became a basis of the first hydraulic fracturing experiment, which was conducted in1947 at the Hugoton gas field in Grant County of southwestern Kansas by Stanolind.[1][15] For the well treatment1,000 US gallons (3,800 l; 830 imp gal) of gelled gasoline and sand from the Arkansas River was injected into thegas-producing limestone formation at 2,400 feet (730 m). The experiment was not very successful as deliverabilityof the well did not change appreciably. The process was further described by J.B. Clark of Stanolind in his paperpublished in 1948. A patent on this process was issued in 1949 and an exclusive license was granted to theHalliburton Oil Well Cementing Company. On March 17, 1949, Halliburton performed the first two commercialhydraulic fracturing treatments in Stephens County, Oklahoma, and Archer County, Texas.[15] Since then, hydraulicfracturing has been used to stimulate approximately a million oil and gas wells.[16]

In the Soviet Union, the first hydraulic proppant fracturing was carried out in 1952. In Western Europe in1977–1985, hydraulic fracturing was conducted at Rotliegend and Carboniferous gas-bearing sandstones inGermany, Netherlands onshore and offshore gas fields, and the United Kingdoms sector of the North Sea. Othercountries in Europe and Northern Africa included Norway, the Soviet Union, Poland, Czechoslovakia, Yugoslavia,Hungary, Austria, France, Italy, Bulgaria, Romania, Turkey, Tunisia, and Algeria.[17]

Due to shale's high porosity and low permeability, technology research, development and demonstration werenecessary before hydraulic fracturing could be commercially applied to shale gas deposits. In the 1970s the UnitedStates government initiated the Eastern Gas Shales Project, a set of dozens of public-private hydraulic fracturingpilot demonstration projects. 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.[18] In 1977, theDepartment of Energy pioneered massive hydraulic fracturing in tight sandstone formations. In 1997, based onearlier 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" whichinvolves adding chemicals to water to increase the fluid flow, that made the shale gas extraction economical.[2][3][19]

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Induced hydraulic fracturingAccording to the United States Environmental Protection Agency (EPA) hydraulic fracturing is a process tostimulate a natural gas, oil, or geothermal energy well to maximize the extraction. The whole process is defined asincluding the acquisition of source water, well construction, well stimulation, and waste disposal.[20]

UsesThe 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. Hydraulicfracturing enables the production of natural gas and oil from rock formations deep below the earth's surface(generally 5000–20000 feet (1,500–6,100 m)). At such depth, there may not be sufficient permeability or reservoirpressure to allow natural gas and oil to flow from the rock into the wellbore at economic rates. Thus, creatingconductive fractures in the rock is pivotal to extract gas from shale reservoirs because of the extremely low naturalpermeability of shale, which is measured in the microdarcy to nanodarcy range.[21] Fractures provide a conductivepath connecting a larger volume of the reservoir to the well. So-called "super fracing", which creates cracks deeperin the rock formation to release more oil and gas, will increase efficiency of hydraulic fracturing.[22] The yield for atypical shale gas well generally falls off sharply after the first year or two.[23]

While the main industrial use of hydraulic fracturing is in arousing production from oil and gas wells,[24][25][26]

hydraulic fracturing is also applied:• To stimulate groundwater wells[27]

• To precondition or induce rock to cave in mining[28]

• As a means of enhancing waste remediation processes, usually hydrocarbon waste or spills[]

• 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]

MethodA hydraulic fracture is formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increasepressure downhole to exceed that of the fracture gradient (pressure gradient) of the rock.[33] The fracture gradient isdefined as the pressure increase per unit of the depth due to its density and it is usually measured in pounds persquare 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, orother particulates, that prevent the fractures from closing when the injection is stopped and the pressure of the fluidis reduced. Consideration of proppant strengths and prevention of proppant failure becomes more important atgreater depths where pressure and stresses on fractures are higher. The propped fracture is permeable enough toallow the flow of formation fluids to the well. Formation fluids include gas, oil, salt water, fresh water and fluidsintroduced 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 surroundingpermeable rock occurs. If not controlled properly, it can exceed 70% of the injected volume. This may result information matrix damage, adverse formation fluid interactions, or altered fracture geometry and thereby decreasedproduction 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

Hydraulic fracturing 4

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 morehigh-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-pressureflexible hoses, and many gauges and meters for flow rate, fluid density, and treating pressure.[36] Fracturingequipment 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 typesA distinction can be made between conventional or low-volume hydraulic fracturing used to stimulatehigh-permeability reservoirs to frac a single well, and unconventional or high-volume hydraulic fracturing, used inthe completion of tight gas and shale gas wells as unconventional wells are deeper and require higher pressures thanconventional vertical wells.[38] In addition to hydraulic fracturing of vertical wells, it is also performed in horizontalwells. When done in already highly permeable reservoirs such as sandstone-based wells, the technique is known as"well stimulation".[26]

Horizontal drilling involves wellbores where the terminal drillhole is completed as a "lateral" that extends parallelwith the rock layer containing the substance to be extracted. For example, laterals extend 1500 to 5000 feet (460 to1,500 m) in the Barnett Shale basin in Texas, and up to 10,000 feet (3,000 m) in the Bakken formation in NorthDakota. 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 reservoirrock. Drilling usually induces damage to the pore space at the wellbore wall, reducing the permeability at and nearthe wellbore. This reduces flow into the borehole from the surrounding rock formation, and partially seals off theborehole from the surrounding rock. Hydraulic fracturing can be used to restore permeability.[39]

Fracturing fluidsHigh-pressure fracture fluid is injected into the wellbore, with the pressure above the fracture gradient of the rock.The two main purposes of fracturing fluid is to extend fractures and to carry proppant into the formation, the purposeof which is to stay there without damaging the formation or production of the well. Two methods of transporting theproppant in the fluid are used – high-rate and high-viscosity. High-viscosity fracturing tends to cause large dominantfractures, while with high-rate (slickwater) fracturing causes small spread-out micro-fractures.This fracture fluid contains water-soluble gelling agents (such as guar gum) which increase viscosity and efficientlydeliver the proppant into the formation.[40]

The fluid injected into the rock is typically a slurry of water, proppants, and chemical additives.[41] Additionally,gels, foams, and compressed gases, including nitrogen, carbon dioxide and air can be injected. Typically, of thefracturing fluid 90% is water and 9.5% is sand with the chemicals accounting to about 0.5%.[33][42][43]

A proppant is a material that will keep an induced hydraulic fracture open, during or following a fracturingtreatment, and can be gel, foam, or slickwater-based. Fluids make tradeoffs in such material properties as viscosity,where more viscous fluids can carry more concentrated proppant; the energy or pressure demands to maintain acertain flux pump rate (flow velocity) that will conduct the proppant appropriately; pH, various rheological factors,among others. Types of proppant include silica sand, resin-coated sand, and man-made ceramics. These varydepending 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 ahigher porosity within the fracture, a greater amount of oil and natural gas is liberated.[44]

The fracturing fluid varies in composition depending on the type of fracturing used, the conditions of the specific well being fractured, and the water characteristics. A typical fracture treatment uses between 3 and 12 additive

Hydraulic fracturing 5

chemicals.[33] Although there may be unconventional fracturing fluids, the typical used chemical additives are:• Acids—hydrochloric acid (usually 28%-5%), or acetic acid is used in the pre-fracturing stage for cleaning the

perforations and initiating fissure in the near-wellbore rock.[43]

• Sodium chloride (salt)—delays breakdown of the gel polymer chains.[43]

• Polyacrylamide and other friction reducers—minimizes the friction between fluid and pipe, thus allowing thepumps to pump at a higher rate without having greater pressure on the surface.[43] Polyacrylamide are goodsuspension agents ensuring the proppant does not fall out.

• Ethylene glycol—prevents formation of the scale deposits in the pipe.[43]

• Borate salts—used for maintaining fluid viscosity during the temperature increase.[43]

• Sodium and potassium carbonates—used for maintaining effectiveness of crosslinkers.[43]

• Glutaraldehyde—used as disinfectant of the water (bacteria elimination).[43]

• Guar gum and other water-soluble gelling agents—increases viscosity of the fracturing fluid to deliver moreefficiently the proppant into the formation.[40][43]

• Citric acid—used for corrosion prevention.• Isopropanol—increases the viscosity of the fracture fluid.[43]

The most common chemical used for hydraulic fracturing in the United States in 2005–2009 was methanol, whilesome other most widely used chemicals were isopropyl alcohol, 2-butoxyethanol, and ethylene glycol.[45]

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 itsderivatives (hydroxypropyl guar, carboxymethyl hydroxypropyl guar) based, with other chemicals providing thenecessary chemistry for the desired results.

• Borate-crosslinked fluids. These are guar-based fluids cross-linked with boron ions (from aqueous borax/boricacid solution). These gels have higher viscosity at pH 9 onwards and are used to carry proppants. After thefracturing job the pH is reduced to 3–4 so that the cross-links are broken and the gel is less viscous and can bepumped out.

• Organometallic-crosslinked fluids zirconium, chromium, antimony, titanium salts are known to crosslink the guarbased gels. The crosslinking mechanism is not reversible. So once the proppant is pumped down along with thecross-linked gel, the fracturing part is done. The gels are broken down with appropriate breakers.[40]

• 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.

For slickwater it is common to include sweeps or a reduction in the proppant concentration temporarily to ensure thewell is not overwhelmed with proppant causing a screen-off.[46] As the fracturing process proceeds, viscosityreducing agents such as oxidizers and enzyme breakers are sometimes then added to the fracturing fluid to deactivatethe gelling agents and encourage flowback.[40] The oxidizer reacts with the gel to break it down, reducing the fluid'sviscosity and ensuring that no proppant is pulled from the formation. An enzyme acts as a catalyst for the breakingdown of the gel. Sometimes pH modifiers are used to break down the crosslink at the end of a hydraulic fracturingjob, since many require a pH buffer system to stay viscous.[46] At the end of the job the well is commonly flushedwith water (sometimes blended with a friction reducing chemical) under pressure. Injected fluid is to some degreerecovered 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 andimproved to better handle waste water and improve re-usability.[33]

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Fracture monitoringMeasurements of the pressure and rate during the growth of a hydraulic fracture, as well as knowing the properties ofthe fluid and proppant being injected into the well provides the most common and simplest method of monitoring ahydraulic fracture treatment. This data, along with knowledge of the underground geology can be used to modelinformation 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 todetermine the injection profile and location of fractures created by hydraulic fracturing.[47] The radiotracer is chosento have the readily detectable radiation, appropriate chemical properties, and a half life and toxicity level that willminimize initial and residual contamination.[48] Radioactive isotopes chemically bonded to glass (sand) and/or resinbeads may also be injected to track fractures.[49] For example, plastic pellets coated with 10 GBq of Ag-110mm maybe added to the proppant or sand may be labelled with Ir-192 so that the proppant's progress can be monitored.[48]

Radiotracers such as Tc-99m and I-131 are also used to measure flow rates.[48] The Nuclear Regulatory Commissionpublishes guidelines which list a wide range of radioactive materials in solid, liquid and gaseous forms that may beused as tracers and limit the amount that may be used per injection and per well of each radionuclide.[49]

For more advanced applications, microseismic monitoring is sometimes used to estimate the size and orientation ofhydraulically induced fractures. Microseismic activity is measured by placing an array of geophones in a nearbywellbore. By mapping the location of any small seismic events associated with the growing hydraulic fracture, theapproximate geometry of the fracture is inferred. Tiltmeter arrays, deployed on the surface or down a well, provideanother technology for monitoring the strains produced by hydraulic fracturing.[50]

Horizontal completionsSince the early 2000s, advances in drilling and completion technology have made drilling horizontal wellbores muchmore economical. Horizontal wellbores allow for far greater exposure to a formation than a conventional verticalwellbore. This is particularly useful in shale formations which do not have sufficient permeability to produceeconomically with a vertical well. Such wells when drilled onshore are now usually hydraulically fractured in anumber of stages, especially in North America. The type of wellbore completion used will affect how many timesthe formation is fractured, and at what locations along the horizontal section of the wellbore.[51]

In North America, shale reservoirs such as the Bakken, Barnett, Montney, Haynesville, Marcellus, and most recentlythe Eagle Ford, Niobrara and Utica shales are drilled, completed and fractured using this method. The method bywhich the fractures are placed along the wellbore is most commonly achieved by one of two methods, known as"plug and perf" and "sliding sleeve".[52]

The wellbore for a plug and perf job is generally composed of standard joints of steel casing, either cemented oruncemented, which is set in place at the conclusion of the drilling process. Once the drilling rig has been removed, awireline truck is used to perforate near the end of the well, following which a fracturing job is pumped (commonlycalled a stage). Once the stage is finished, the wireline truck will set a plug in the well to temporarily seal off thatsection, and then perforate the next section of the wellbore. Another stage is then pumped, and the process isrepeated as necessary along the entire length of the horizontal part of the wellbore.[53]

The wellbore for the sliding sleeve technique is different in that the sliding sleeves are included at set spacings in thesteel casing at the time it is set in place. The sliding sleeves are usually all closed at this time. When the well is readyto be fractured, using one of several activation techniques, the bottom sliding sleeve is opened and the first stage getspumped. 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.These completion techniques may allow for more than 30 stages to be pumped into the horizontal section of a singlewell if required, which is far more than would typically be pumped into a vertical well.[54]

Hydraulic fracturing 7

Benefits

Increased recoveryHydraulic 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 areestimated to amount to 208 trillion cubic metres (7.3 quadrillion cubic feet), tight gas to 76 trillion cubic metres (2.7quadrillion 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. Therefore, depending onthe 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 fracturingtechnique has facilitated shale gas and light tight oil production development in the United States and is believed todo so in the other countries with unconventional hydrocarbon resources. Significance of the extraction ofunconventional hydrocarbons lies also in the fact that these resources are less concentrated than conventional oil andgas resources.[4]

Economic ImpactsHydraulic fracturing will account for nearly 70 percent of natural gas development in the future.[55] Hydraulicfracturing and horizontal drilling apply the latest technologies and make it commercially viable to recover shale gasand oil. Without it, we would lose 45 percent of domestic natural gas production and 17 percent of our oil productionwithin 5 years.[56]

Development of shale resources supported 600,000 jobs in 2010.[57] Affordable, domestic natural gas is essential torejuvenating the chemical, manufacturing, and steel industries. The American Chemistry Council determined that a25 percent increase in the supply of ethane (a liquid derived from shale gas) could add over 400,000 jobs across theeconomy, provide over $4.4 billion annually in federal, state, and local tax revenue, and spur $16.2 billion in capitalinvestment by the chemical industry.[58]

They also note that the relatively low price of ethane would give U.S. manufacturers an essential advantage overmany global competitors. Similarly, the National Association of Manufacturers estimated that high recovery of shalegas and lower natural gas prices will help U.S. manufacturers employ 1,000,000 workers by 2025 while lowerfeedstock and energy costs could help them reduce natural gas expenditures by as much as 11.6 billion by 2025.[59]

America’s Natural Gas Association (ANGA) estimates that lower gas prices will add an additional $926 ofdisposable household income annually between 2012 and 2015, and that the amount could increase to $2,000 by2035.[60]

Environmental impactHydraulic fracturing has raised environmental concerns and is challenging the adequacy of existing regulatoryregimes.[61] These concerns have included ground water contamination, risks to air quality, migration of gases andhydraulic fracturing chemicals to the surface, mishandling of waste, and the health effects of all these, as well as itscontribution to raised atmospheric CO2 levels by enabling the extraction of previously-sequesteredhydrocarbons.[5][33][45] Because hydraulic fracturing originated in the United States,[62] its history is more extensivethere than in other regions. Most environmental impact studies have therefore taken place there.

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Research issuesSeveral organizations, researchers, and media outlets have reported difficulty in conducting and reporting the resultsof studies on hydraulic fracturing due to industry[63][64][65] and governmental pressure, and expressed concern overpossible censoring of environmental reports.[63][66][67] Researchers have recommended requiring disclosure of allhydraulic fracturing fluids, testing animals raised near fracturing sites, and closer monitoring of environmentalsamples.[68] After court cases concerning contamination from hydraulic fracturing are settled, the documents aresealed. The American Petroleum Institute deny that this practice has hidden problems with gas drilling, while othersbelieve it has and could lead to unnecessary risks to public safety and health.[69]

AirThe air emissions from hydraulic fracturing are related to methane leaks originating from wells, and emissions fromthe diesel or natural gas powered equipment such as compressors, drilling rigs, pumps etc.[33] Also transportation ofnecessary water volume for hydraulic fracturing, if done by trucks, can cause high volumes of air emissions,especially particulate matter emissions.[70]

Shale gas produced by hydraulic fracturing causes higher well-to-burner emissions than conventional gas. This ismainly due to the gas released during completing wells as some gas returns to the surface, together with thefracturing fluids. Depending on their treatment, the well-to-burner emissions are 3.5%–12% higher than forconventional gas.[61] 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 thelifetime of a well." The study claims that this represents a 30–100% increase over conventional gas production.[71]

Methane gradually breaks down in the atmosphere, forming carbon dioxide, which contributes to greenhouse gassesmore than coal or oil for timescales of less than fifty years.[71][72] Howarth's colleagues at Cornell and others havecriticized the study's design,[73][74] however several other studies have also found higher emissions from shale-gasproduction than from conventional gas production.[75][76][77][78] Howarth et al. have responded, "The latest EPAestimate for methane emissions from shale gas falls within the range of our estimates but not those of Cathles et al,which are substantially lower."[79]

In some areas, elevated air levels of harmful substances have coincided with elevated reports of health problemsamong the local populations. In DISH, Texas, elevated substance levels were detected and traced to hydraulicfracturing compressor stations,[80] and people living near shale gas drilling sites complained of health problems;[81]

though a causal relationship to hydraulic fracturing was not established.[81]

Water

Consumption

The large volumes of water required have raised concerns about hydraulic fracturing in arid areas, such as Karoo inSouth Africa.[62] During periods of low stream flow it may affect water supplies for municipalities and industriessuch as power generation, as well as recreation and aquatic life. It may also require water overland piping fromdistant sources.[82]

Hydraulic fracturing uses between 1.2 and 3.5 million US gallons (4.5 and 13 Ml) of water per well, with large projects using up to 5 million US gallons (19 Ml). Additional water is used when wells are refractured; this may be done several times.[40][83] An average well requires 3 to 8 million US gallons (11,000 to 30,000 m3) of water over its lifetime.[33][82][83][84] Using the case of the Marcellus Shale as an example, as of 2008 hydraulic fracturing 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.[82][85] The annual number of well permits, however, increased by a factor of five[86]

and the number of well starts increased by a factor of over 17 from 2008 to 2011.[87] According to the Oxford Institute for Energy Studies, greater volumes of fracturing fluids are required in Europe, where the shale depths

Hydraulic fracturing 9

average 1.5 times greater than in the U.S.[88] To minimize water consumption, recycling is one possible option.[61]

Injected fluid

There are concerns about possible contamination by hydraulic fracturing fluid both as it is injected under highpressure into the ground and as it returns to the surface.[89] To mitigate the impact of hydraulic fracturing togroundwater, the well and ideally the shale formation itself should remain hydraulically isolated from othergeological formations, especially freshwater aquifers.[61] In the United States hydraulic fracturing areas at least 36cases of groundwater contamination due to hydraulic fracturing have been suspected and in several cases EPA hasdetermined that hydraulic fracturing was likely the source of the contamination.[69][90][91][92][93][94]

While some of the chemicals used in hydraulic fracturing are common and generally harmless, some are knowncarcinogens or toxic.[45] The 2011 US House of Representatives investigative report on the chemicals used inhydraulic fracturing states that out of 2,500 hydraulic fracturing products, "more than 650 of these productscontained chemicals that are known or possible human carcinogens, regulated under the Safe Drinking Water Act, orlisted as hazardous air pollutants".[45] The report also shows that between 2005 and 2009, 279 products had at leastone 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 ofchemical 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 theinvestigation were unable to do so, leading the committee to surmise these "companies are injecting fluids containingunknown chemicals about which they may have limited understanding of the potential risks posed to human healthand the environment".[45] Without knowing the identity of the proprietary components, regulators cannot test fortheir presence. This prevents government regulators from establishing baseline levels of the substances prior tohydraulic fracturing and documenting changes in these levels, thereby making it more difficult to prove thathydraulic fracturing is contaminating the environment with these substances.[95]

Another 2011 study identified 632 chemicals used in natural gas operations. Only 353 of these are well-described inthe scientific literature. The study indicated possible long-term health effects that might not appear immediately. Thestudy recommended full disclosure of all products used, along with extensive air and water monitoring near naturalgas operations; it also recommended that hydraulic fracturing's exemption from regulation under the US SafeDrinking Water Act be rescinded.[96]

Flowback

As the fracturing fluid flows back through the well, it consists of spent fluids and may contain dissolved constituentssuch as minerals and brine waters. It may account for about 30–70% of the original fracture fluid volume. Inaddition, natural formation waters may flow to the well and need treatment. These fluids, commonly known asflowback, produced water, or wastewater, are managed by underground injection, wastewater treatment anddischarge, or recycling to fracture future wells.[97] Treatment of produced waters may be feasible through eitherself-contained systems at well sites or fields or through municipal waste water treatment plants or commercialtreatment facilities.[97] However, the quantity of waste water needing treatment and the improper configuration ofsewage plants have become an issue in some regions of the United States. Much of the wastewater from hydraulicfracturing operations is processed by public sewage treatment plants, which are not equipped to remove radioactivematerial and are not required to test for it.[98] More problematic may be the high levels of Bromide released into therivers. The Bromide in the water combines with chlorine, which is used to disinfect drinking water at water treatmentplants, and forms trihalomethanes (THMs).[99]

Hydraulic fracturing 10

Methane

Groundwater methane contamination is also a concern as it has adverse impact on water quality and in extreme casesmay lead to potential explosion.[100][101] In 2006, over 7 million cubic feet (200,000 m3) of methane were releasedfrom a blown gas well in Clark, Wyoming and shallow groundwater was found to be contaminated.[102] However,methane contamination is not always caused by hydraulic fracturing. Drilling for ordinary drinking water wells canalso cause methane release. Some studies make use of tests that can distinguish between the deep thermogenicmethane released during gas/oil drilling, and the shallower biogenic methane that can be released during water-welldrilling. While both forms of methane result from decomposition, thermogenic methane results from geothermalassistance deeper underground.[103][104]

According to the 2011 study of the MIT Energy Initiative, "there is evidence of natural gas (methane) migration intofreshwater zones in some areas, most likely as a result of substandard well completion practices i.e. poor qualitycementing job or bad casing, by a few operators."[105] 2011 studies by the Colorado School of Public Health andDuke University also pointed to methane contamination stemming from hydraulic fracturing or its surroundingprocess.[100][104] A study by Cabot Oil and Gas examined the Duke study using a larger sample size, found thatmethane concentrations were related to topography, with the highest readings found in low-lying areas, rather thanrelated to distance from gas production areas. Using a more precise isotopic analysis, they showed that the methanefound in the water wells came from both the Marcellus Shale (Middle Devonian) where hydraulic fracturingoccurred, and from the shallower Upper Devonian formations.[103]

Radioactivity

A study examining a number of fracking sites in Pennsylvania and Virginia by Pennsylvania State University, foundthat water that flows back from gas wells after hydraulic fracturing has high contents of various elements, includingradium.[106] Recycling the wastewater has been proposed as a solution but has its limitations.[107] The New YorkTimes has reported radium in wastewater from natural gas wells,[108] which releases into Pennsylvania rivers,[101]

and has compiled a map of these wells and their wastewater contamination levels,[108] and stated that some EPAreports were never made public. They did not measure beta or gamma radiation. The Times' reporting on the issuehas come under some criticism.[109][110]

SeismicityHydraulic fracturing causes induced seismicity called microseismic events or microearthquakes. The magnitude ofthese events is usually too small to be detected at the surface, although the biggest micro-earthquakes may have themagnitude of about -1.6 (Mw). The injection of waste water from gas operations, including from hydraulicfracturing, into saltwater disposal wells may cause bigger low-magnitude tremors, being registered up to3.3 (Mw).[111]

The United States Geological Survey (USGS) has reported earthquakes induced by human measures, includinghydraulic fracturing and hydraulic fracturing waste disposal wells, in several locations. According to the USGS onlya small fraction of roughly 40,000 waste fluid disposal wells for oil and gas operations have induced earthquakes thatare large enough to be of concern to the public.[112] Although the magnitudes of these quakes has been small, theUSGS says that there is no guarantee that larger quakes will not occur.[113] In addition, the frequency of the quakeshas been increasing. In 2009, there were 50 earthquakes greater than magnitude-3.0 in the area spanning Alabamaand Montana, and there were 87 quakes in 2010. In 2011 there were 134 earthquakes in the same area, a sixfoldincrease over 20th century levels.[114] There are also concerns that quakes may damage underground gas, oil, andwater lines and wells that were not designed to withstand earthquakes.[113][115]

A British Columbia Oil and Gas Commission investigation concluded that a series of 38 earthquakes (magnitudes ranging from 2.2 to 3.8 on the Richter scale) occurring in the Horn River Basin area between 2009 and 2011 were caused by fluid injection during hydraulic fracturing in proximity to pre-existing faults.[116] A report in the UK also

Hydraulic fracturing 11

concluded that hydraulic fracturing was the likely cause of some small tremors that occurred during shale gasdrilling.[117][118][119]

Several earthquakes occurring throughout 2011, including a 4.0 magnitude quake on New Year's Eve that hitYoungstown, Ohio, are likely linked to a disposal of hydraulic fracturing wastewater, according to seismologists atColumbia University.[120] A similar series of small earthquakes occurred in 2012 in Texas. Earthquakes are notcommon occurrences in either area. Disposal and injection wells are regulated under the Safe Drinking Water Actand UIC laws.[121]

Health impactConcern has been expressed over the possible long and short term health effects of air and water contamination bygas production.[122][123] A study on the effect of gas drilling, including hydraulic fracturing, published by the CornellUniversity College of Veterinary Medicine, concluded that exposure to gas drilling operations was stronglyimplicated in serious health effects on humans and animals.[124] As of May 2012, the United States Institute ofMedicine and United States National Research Council were preparing to review the potential human andenvironmental risks of hydraulic fracturing.[125][126]

In the United States the Occupational Safety and Health Administration (OSHA) and the National Institute forOccupational Safety and Health (NIOSH) have released a hazard alert based on data collected by NIOSH thatworkers may be exposed to dust with high levels of respirable crystalline silica (silica dioxide) during hydraulicfracturing.[127] NIOSH notified company representatives of these findings and provided reports withrecommendations to control exposure to crystalline silica and recommend that all hydraulic fracturing sites evaluatetheir operations to determine the potential for worker exposure to crystalline silica and implement controls asnecessary to protect workers.[128]

Public debate

Politics and public policyTo control the hydraulic fracturing industry, some governments are developing legislation and some municipalitiesare developing local zoning limitations.[129] In 2011, France became the first nation to ban hydraulic fracturing.[6][7]

Some other countries have placed a temporary moratorium on the practice. The US has the longest history withhydraulic fracturing, so its approaches to hydraulic fracturing may be modeled by other countries.[62]

The considerable opposition against hydraulic fracturing activities in local townships has led companies to adopt avariety 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, asenior executive at Anadarko Petroleum was recorded on tape saying, "Download the US Army / Marine CorpsCounterinsurgency Manual, because we are dealing with an insurgency", while referring to hydraulic fracturingopponents. Matt Pitzarella, spokesman for Range Resources also told other conference attendees that Rangeemployed psychological warfare operations veterans. According to Pitzarella, the experience learned in the MiddleEast has been valuable to Range Resources in Pennsylvania, when dealing with emotionally charged townshipmeetings and advising townships on zoning and local ordinances dealing with hydraulic fracturing.[130][131]

Hydraulic fracturing 12

Media coverageJosh Fox's 2010 film Gasland became a center of opposition to hydraulic fracturing of shale. The movie presentedproblems with ground water contamination near well sites in Pennsylvania, Wyoming, and Colorado.[132] Energy inDepth, an oil and gas industry lobbying group, called the film's facts into question.[133] In response, a rebuttal ofEnergy in Depth's claims of inaccuracy was posted on Gasland's website.[134] The Director of the Colorado Oil andGas Conservation Commission (COGCC) offered to be interviewed as part of the film if he could review what wasincluded from the interview in the final film but Fox declined the offer. The COGCC took issue with what it called"several errors" in the film after its production.[135] The Independent Petroleum Association of America laterproduced its own documentary, Truthland.[136] Exxon Mobil, Chevron Corporation and ConocoPhillips also airedadvertisements during 2011 and 2012 that describe the economic and environmental benefits of natural gas andargue hydraulic fracturing is safe.[136] The film Promised Land, starring Matt Damon, takes on hydraulicfracturing.[137] The gas industry has made plans to counter the film's criticisms of hydraulic fracturing withinformational flyers, and Twitter and Facebook posts.[136]

One New York Times report claimed that an early draft of a 2004 EPA study discussed "possible evidence" of aquifercontamination but the final report omitted that mention.[63] Some have criticized the narrowing of EPA studies,including the EPA study on hydraulic fracturing's impact on drinking water to be released in late 2014,[138] such thathydrocarbon extraction processes not unique to hydraulic fracturing, such as drilling, casing, and above groundimpacts, are considered beyond scope.[64][66][139][140][141]

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[77] Hultman, Nathan; Rebois, Dylan; Scholten, Michael; Ramig, Christopher (2011). "The greenhouse impact of unconventional gas forelectricity generation" (http:/ / iopscience. iop. org/ 1748-9326/ 6/ 4/ 044008/ pdf/ 1748-9326_6_4_044008. pdf) (PDF). EnvironmentalResearch Letters (IOP Publishing) 6 (4): 044008. Bibcode 2011ERL.....6d4008H. doi:10.1088/1748-9326/6/4/044008. . Retrieved 4 February2012.

[78] Lashof, Dan (12 April 2011). "Natural Gas Needs Tighter Production Practices to Reduce Global Warming Pollution" (http:/ / switchboard.nrdc. org/ blogs/ dlashof/ natural_gas_needs_tighter_prod. html). Natural Resources Defense Council. . Retrieved 4 February 2012.

[79] Howarth, Robert W.; Santoro, Renee; Ingraffea, Anthony (1 February 2012). "Venting and leaking of methane from shale gas development:Response to Cathles et al" (http:/ / www. springerlink. com/ content/ c338g7j559580172/ fulltext. pdf) (PDF). Climatic Change (Springer) 113(2): 537. doi:10.1007/s10584-012-0401-0. . Retrieved 4 February 2012.

[80] 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 whatcost to the environment and human health?" (http:/ / www. scientificamerican. com/ article. cfm?id=shale-gas-and-hydraulic-fracturing).Scientific American. . Retrieved 23 March 2012.

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[82] Arthur, J. Daniel; Uretsky, Mike; Wilson, Preston (May 5–6, 2010). "Water Resources and Use for Hydraulic Fracturing in the MarcellusShale Region" (http:/ / fracfocus. org/ sites/ default/ files/ publications/water_resources_and_use_for_hydraulic_fracturing_in_the_marcellus_shale_region. pdf) (PDF). Meeting of the American Institute ofProfessional Geologists. Pittsburgh: ALL Consulting. p. 3. . Retrieved 2012-05-09.

[83] Abdalla, Charles W.; Drohan, Joy R. (2010) (PDF). Water Withdrawals for Development of Marcellus Shale Gas in Pennsylvania.Introduction to Pennsylvania’s Water Resources (http:/ / pubs. cas. psu. edu/ FreePubs/ pdfs/ ua460. pdf) (Report). The Pennsylvania StateUniversity. . Retrieved 16 September 2012. "Hydrofracturing a horizontal Marcellus well may use 4 to 8 million gallons of water, typicallywithin about 1 week. However, based on experiences in other major U.S. shale gas fields, some Marcellus wells may need to behydrofractured several times over their productive life (typically five to twenty years or more)"

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Hydraulic fracturing 16

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External links• Natural Gas Extraction—Hydraulic Fracturing (http:/ / www. epa. gov/ hydraulicfracturing) (EPA website)• EPA's Draft Hydraulic Fracturing Study Plan (http:/ / www. epa. gov/ hfstudy/ )• FracFocus (http:/ / fracfocus. org/ ) Site indicating chemical composition of fracking fluid of individual wells• FracTracker.org: Maps, data, and articles from news, government, industry, and academic sources. (http:/ / www.

fractracker. org/ )• Fracking (http:/ / www. propublica. org/ series/ fracking) collected news and commentary at ProPublica• Hydraulic Fracturing (http:/ / www. earthworksaction. org/ issues/ detail/ hydraulic_fracturing_101) at

Earthworks• Hydraulic fracturing illustration (http:/ / www. propublica. org/ special/ hydraulic-fracturing-national) on

ProPublica• 60 Minutes (http:/ / www. cbsnews. com/ video/ watch/ ?id=7054210n) Report on Hydraulic Fracturing]• Shale gas and fracking (http:/ / www. guardian. co. uk/ environment/ shale-gas) collected news and commentary

at The Guardian

Article Sources and Contributors 19

Article Sources and ContributorsHydraulic fracturing  Source: http://en.wikipedia.org/w/index.php?oldid=536656604  Contributors: 17mansure, 2620:0:1052:1:BAAC:6FFF:FE89:9346, 28bytes, A13ean, AJKeown, Abandonall arr now, AdamRBrooks, Adamuwt2011, Alan Liefting, Aldenallen1, Amp71, Antillarum, Aondotri, Arjayay, Arms & Hearts, Arthur Rubin, Arzel, Bdell555, Beagel, Bearcat, Ben Ben,Bibliophile227, Biscuittin, Blackash, Blue Tie, BoogaLouie, Braculus, Brandiwessel, Brentonchina, BrianWo, BullRangifer, Bulwersator, Cameron6426a, CanberraBulldog, Candleabracadabra,Captainbeefart, Carbon13neutral, Cartoonmaster, Casey56, Causa sui, Chase.alton3, Chenopodiaceous, Chris the speller, ChrisGualtieri, Christian75, Christine1223, Coastwise,CommonsDelinker, Compdude123, Conor Strong, Cooljeanius, Crywalt, DMahalko, Darqcyde, Dawnseeker2000, Daytona2, DeRanged Resources, Deli nk, Denisarona, Dhollm, Download,Druzhnik, EagerToddler39, Easshale, EdwardLane, Elekhh, Elstree-230, Emerituseditor, EnergeticsAnalyst, EnvPolKAL, EnviroE, Epbr123, Equazcion, Eric Kvaalen, Esnascosta, Exenola,FertileCatfish, FghIJklm, Fracksand, Fuzzypeg, Gabby Merger, Gandydancer, Gautier lebon, GeoGreg, Geperdo, Gilderien, Gimmetoo, GoingBatty, GrizBizzy, Ground Zero, Guanxi, Harel,Headbomb, Hike395, Hoppenhe, IGeMiNix, Ian peters, Ihcoyc, Illia Connell, Iloveandrea, Ire2500, IrrtNie, J36miles, JTSchreiber, Jabx2, Jarble, Jdkag, Jeffthajamaican, Jfsparks, Jim1138,Joefromrandb, John of Reading, JohnEdit21, Joseph.ruggiero, Jpmsd, Jschnur, Jweiss11, Kckid, Kdammers, Keithonearth, KelseyBrook, Ketone16, Kgrr, Kitsunegami, Kleptopigstar,Klilidiplomus, Kriplozoik, Kyle assassinz, La goutte de pluie, Lamro, Laurabauer, Law of Entropy, Lbriggs, Lexein, LilHelpa, MC10, Mabuzi, Martin Hogbin, MartinGugino, Maxellus, Mdicato,Mean as custard, Men404, Mike Rosoft, Mikenorton, Mis-misanthrope, MissLoveIsMyWeapon, Mneuner, Moreau1, Morphh, MrOllie, Mrfebruary, Msiner, Mwtoews, NYCJosh,NewsAndEventsGuy, Nfaraguna, Niceguyedc, NickCT, Noegenesis, Nogginquest, NorthernThunder, OChemie, Odewey, Ohnoitsjamie, OpenMind, Owen, Oxfordwang, Palpbert, Peter Chastain,Peter Greenwell, Peterlewis, PetroleumAge, Philip Trueman, Pinethicket, PlanetEditor, Prawlings, Prestonmcconkie, Proper Stranger, R'n'B, RA0808, RTG, Racklever, Raiderredjd,Rcsprinter123, Reelrt, Rexpilger, Rich Farmbrough, Richardb43, Ricmcc1766, Rjwilmsi, Roche398, RockMagnetist, Rostz, Rreagan007, Runtzz, Rushbugled13, S1id3r0, Scgtcheck,SchreiberBike, Scott Teresi, Sgartner, Sharmeka-winnsboro, Sindinero, Sjschen, Smm201`0, Solarix, SoledadKabocha, Sophk, Soporyc, Srich32977, StephanieF79, Stephenwanjau, Sun Creator,Sustainableyes, Swliv, T.Dooshswag, T.hetton, T0pher17, Terrance.cunningham, Tgeairn, The Illusive Man, The Mark of the Beast, The wub, Timeshifter, Toddst1, Tothesungod, Tourbillon,Trovatore, Uriel8, Vegaswikian, Velella, VetPsychWars, Victorgrigas, Viriditas, Vranak, Vrenator, Vsmith, Wavelength, WebMaven2000, Whitepanthera, WikHead, Wikid77, Wikipelli, WilliamD. Walker, Wknight94, Writer1502, Yukonpeegs, 364 anonymous edits

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