Fraccing - Wikipedia

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Hydraulic fracturing is the propagation of fractures in a rock layer caused by the presence of a pressurized

fluid. Hydraulic fractures form naturally, as in the case ofveinsordikes, and is one means by which gas and

petroleum fromsource rocksmay migrate toreservoir rocks.

Energy companiesmay attempt to accelerate this process in order to releasepetroleum,natural gas,coal

seam gas, or other substances for extraction, via a technique called induced hydraulic

fracturing(illustration), often shortened tofracking[a]orhydrofracking.

[1]This type of fracturing, known

colloquially as a 'frac job',[2]

creates fractures from awellboredrilled into reservoir rock formations. A distinction

can be made between low-volume hydraulic fracturing used to stimulate high-permeability reservoirs, which

may consume typically 20,000 to 80,000 gallons of fluid per well, with high-volume hydraulic fracturing, used

in thecompletionoftight gasandshale gaswells; high-volume hydraulic fracturing can use as much as two to

three million gallons of fluid per well.[3]

This latter practice has come under scrutiny internationally, with some

countries suspending it, or even banning it completely. The first frac job was performed in 1947,[4]though the

current fracking technique was first used in the late 1990s in theBarnett Shalein Texas.[5]

The energy from

the injection of a highly-pressurizedfracking fluidcreates new channels in the rock which can increase the

extraction rates and ultimate recovery offossil fuels.

Globally, the expectation that gas use will rise by more than 50% compared to 2010 levels, and account for

over 25% of world energy demand in 2035 has led theInternational Energy Agencyin 2011 to herald a

"golden age of gas".[6]

Proponents of fracking point to the vast amounts of formerly

inaccessiblehydrocarbonsthe process can extract. However, there remain large uncertainties in the amount

of gas reserves that can be accessed in this way.[7]

Some have said that hydraulic fracturing would give the

United Statesenergy independence.[8]

However, as prices in the United States dropped, companies have

sought and received permission from theUS Department of Energy(DOE)[9]to export gas to Europe and Asia

(e.g., China and Korea), potentially threatening US national security.[10]

Companies have asked for permission

to build a new pipeline through Pennsylvania and Maryland[11][12][13][14]

to transport liquid natural gas (LNG) tonew export terminals inMarylandto facilitate the export of natural gas and oil.[10]Possible terminal locations

includeSparrow's Point,(Baltimore)[15]

andLusby,[9]

Maryland.[10]

Higher prices abroad have also lead to

acquisition of US natural gas companies by companies outside of the US[16]

and shares of companies and

their shale plays, leading to greater international control of US gas resources.[17][18]

There areenvironmentalconcerns regarding the contamination ofground water, risks to air quality, the

migration of gases and hydraulic fracturing chemicals to the surface, and the health effects of

these.[19][20][21][22][23][24]

Lower gas prices have also reduced the incentive to investigate renewable sources of

energy, perpetuating dependence on gas and oil.[25]

Contents

[hide]

1 Mechanics

2 Natural examples

o 2.1 Veins

o 2.2 Dikes

3 Induced hydraulic fracturing

o 3.1 Method
http://en.wikipedia.org/wiki/Vein_(geology)http://en.wikipedia.org/wiki/Vein_(geology)http://en.wikipedia.org/wiki/Vein_(geology)http://en.wikipedia.org/wiki/Dikehttp://en.wikipedia.org/wiki/Dikehttp://en.wikipedia.org/wiki/Dikehttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Energy_industryhttp://en.wikipedia.org/wiki/Energy_industryhttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Coal_seam_gashttp://en.wikipedia.org/wiki/Coal_seam_gashttp://en.wikipedia.org/wiki/Coal_seam_gashttp://en.wikipedia.org/wiki/Coal_seam_gashttp://www.propublica.org/special/hydraulic-fracturing-nationalhttp://www.propublica.org/special/hydraulic-fracturing-nationalhttp://www.propublica.org/special/hydraulic-fracturing-nationalhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#endnote_anonehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#endnote_anonehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Charlez-0http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Charlez-0http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Charlez-0http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-1http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-1http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-1http://en.wikipedia.org/wiki/Wellborehttp://en.wikipedia.org/wiki/Wellborehttp://en.wikipedia.org/wiki/Wellborehttp://en.wikipedia.org/wiki/Well_completionhttp://en.wikipedia.org/wiki/Well_completionhttp://en.wikipedia.org/wiki/Well_completionhttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-3http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-3http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-3http://en.wikipedia.org/wiki/Barnett_Shalehttp://en.wikipedia.org/wiki/Barnett_Shalehttp://en.wikipedia.org/wiki/Barnett_Shalehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-NYRB_08.03.2012-4http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-NYRB_08.03.2012-4http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-NYRB_08.03.2012-4http://en.wikipedia.org/wiki/Fracking_fluidhttp://en.wikipedia.org/wiki/Fracking_fluidhttp://en.wikipedia.org/wiki/Fracking_fluidhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-WEO_2011-5http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-WEO_2011-5http://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_28Jan2012-6http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_28Jan2012-6http://en.wikipedia.org/wiki/United_States_energy_independencehttp://en.wikipedia.org/wiki/United_States_energy_independencehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_07.02.2012-7http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_07.02.2012-7http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_07.02.2012-7http://en.wikipedia.org/wiki/US_Department_of_Energyhttp://en.wikipedia.org/wiki/US_Department_of_Energyhttp://en.wikipedia.org/wiki/US_Department_of_Energyhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-10http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Pipeline2006-12http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Pipeline2006-12http://en.wikipedia.org/wiki/Marylandhttp://en.wikipedia.org/wiki/Marylandhttp://en.wikipedia.org/wiki/Marylandhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Sparrows_Point,_Marylandhttp://en.wikipedia.org/wiki/Sparrows_Point,_Marylandhttp://en.wikipedia.org/wiki/Sparrows_Point,_Marylandhttp://en.wikipedia.org/wiki/Baltimorehttp://en.wikipedia.org/wiki/Baltimorehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-ToSparrowsPt-14http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-ToSparrowsPt-14http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-ToSparrowsPt-14http://en.wikipedia.org/wiki/Lusbyhttp://en.wikipedia.org/wiki/Lusbyhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Statoil_buys-15http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Statoil_buys-15http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Chinese_buy-16http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Chinese_buy-16http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Chinese_buy-16http://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Ground_waterhttp://en.wikipedia.org/wiki/Ground_waterhttp://en.wikipedia.org/wiki/Ground_waterhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-SciAm_30.03.2010-18http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-SciAm_30.03.2010-18http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-20http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_03Mar2011-22http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_03Mar2011-22http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_16.02.2012-24http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_16.02.2012-24http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_16.02.2012-24http://en.wikipedia.org/wiki/Hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Mechanicshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Mechanicshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Natural_exampleshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Natural_exampleshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Veinshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Veinshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Dikeshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Dikeshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Induced_hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Induced_hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Methodhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Methodhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Methodhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Induced_hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Dikeshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Veinshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Natural_exampleshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#Mechanicshttp://en.wikipedia.org/wiki/Hydraulic_fracturinghttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_16.02.2012-24http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_03Mar2011-22http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_03Mar2011-22http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-20http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-20http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-SciAm_30.03.2010-18http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-SciAm_30.03.2010-18http://en.wikipedia.org/wiki/Ground_waterhttp://en.wikipedia.org/wiki/Environment_(biophysical)http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Chinese_buy-16http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Chinese_buy-16http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Statoil_buys-15http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/Lusbyhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-ToSparrowsPt-14http://en.wikipedia.org/wiki/Baltimorehttp://en.wikipedia.org/wiki/Sparrows_Point,_Marylandhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Marylandhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Pipeline2006-12http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Pipeline2006-12http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-10http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-10http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-USSecurity-9http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CovePtLusbyMD-8http://en.wikipedia.org/wiki/US_Department_of_Energyhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Bloomberg_07.02.2012-7http://en.wikipedia.org/wiki/United_States_energy_independencehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Urbina_28Jan2012-6http://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-WEO_2011-5http://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fracking_fluidhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-NYRB_08.03.2012-4http://en.wikipedia.org/wiki/Barnett_Shalehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-3http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Well_completionhttp://en.wikipedia.org/wiki/Wellborehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-1http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Charlez-0http://en.wikipedia.org/wiki/Hydraulic_fracturing#endnote_anonehttp://www.propublica.org/special/hydraulic-fracturing-nationalhttp://en.wikipedia.org/wiki/Coal_seam_gashttp://en.wikipedia.org/wiki/Coal_seam_gashttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Energy_industryhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Dikehttp://en.wikipedia.org/wiki/Vein_(geology)


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3.1.1 Well types

3.1.2 Fracturing

3.1.3 Fracture monitoring

3.1.4 Horizontal completions

4 Chemicals

o 4.1 Terminology

5 Environmental concerns

o 5.1 Air emissions and pollution

o 5.2 Groundwater contamination

5.2.1 Radioactive contamination

o 5.3 Earthquakes

o 5.4 Greenhouse gas emissions

6 Public relations

7 Hydraulic fracturing by country

8 See also

9 Notes

10 References

11 External links

[edit]MechanicsFracturing in rocks at depth is suppressed by theconfining pressure, due to the load caused by the overlying

rock strata. This is particularly so in the case of 'tensile' (Mode 1) fractures, which require the walls of the

fracture to move apart, working against this confining pressure. Hydraulic fracturing occurs when theeffective

stressis reduced sufficiently by an increase in the pressure of fluids within the rock, such that the

minimumprincipal stressbecomes tensile and exceeds thetensile strengthof the material.[26][27]

Fractures

formed in this way will typically be oriented perpendicularly to the minimum principal stress and for this

reason, induced hydraulic fractures in wellbores are sometimes used to determine stress orientations.[28]

In

natural examples, such as dikes or vein-filled fractures, their orientations can be used to infer past stress

states.[29]

[edit]Natural examples

Rocks often contain evidence of past hydraulic fracturing events.

[edit]Veins

Most vein systems are a result of repeated hydraulic fracturing during periods of relatively high pore fluid

pressure. This is particularly clear in the case of 'crack-seal' veins, where the vein material can be seen to

have been added in a series of discrete fracturing events, with extra vein material deposited on each

occasion.[30]

One mechanism to explain such examples of long-lasting repeated fracturing, is the effects of

seismic activity, in which the stress levels rise and fall episodically and large volumes of fluid may be expelled

from fluid-filled fractures during earthquakes, a process referred to as 'seismic pumping'.[31]
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[edit]Dikes

High-level minor intrusions such as dikes propagate through the crust in the form of fluid-filled cracks,

although in this case the fluid ismagma. In sedimentary rocks with a significant water content the fluid at the

propagating fracture tip will be steam.[32]

[edit]Induced hydraulic fracturing

The technique of hydraulic fracturing is used to increase or restore the rate at which fluids, such asoil,water,

ornatural gascan be produced from subterranean natural reservoirs. Reservoirs are typically porous

sandstones, limestones ordolomiterocks, but also include 'unconventional reservoirs' such asshalerock

orcoalbeds. Hydraulic fracturing enables the production of natural gas and oil from rock formations deep

below the earth's surface (generally 5,00020,000 feet or 1,5006,100 m). At such depth, there may not be

sufficientporosity,permeabilityor reservoir pressure to allow natural gas and oil to flow from the rock into the

wellbore at economic rates. Thus, creating conductive fractures in the rock is essential to extractgas from

shale reservoirsbecause of the extremely low natural permeability of shale, which is measured in the

microdarcyto nanodarcy range.[33]Fractures provide a conductive path connecting a larger area of the

reservoir to the well, thereby increasing the area from which natural gas and liquids can be recovered from the

targeted formation. So-called 'super fracking', which creates deeper cracks to release more oil and gas, will

allow companies to frack more efficiently.[34]

The yield for a typical shale gas well generally falls off sharply

after the first year or two.[35]

While the main industrial use of hydraulic fracturing is in stimulating production fromoil and gas

wells,[36][37][38]hydraulic fracturing is also applied to:

Stimulatinggroundwaterwells[39]

Preconditioning rock for caving or inducing rock to cave inmining

[40]

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

[41]

Dispose of waste by injection into deep rock formations

As a method to measure the stress in the earth

For heat extraction to produce electricity in anenhanced geothermal systems[42]

[edit]Method

A hydraulic fracture is formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increase

pressure downhole to exceed that of the fracture gradient of the rock. [citation needed] The rock cracks and the

fracture fluid continues farther into the rock, extending the crack still farther, and so on. Operators typically try

to maintain "fracture width", or slow its decline, following treatment by introducing aproppantinto the injected

fluid, a material, such as grains of sand, ceramic, or other particulates, that prevent the fractures from closing

when the injection is stopped. Consideration of proppant strengths and prevention of proppant failure

becomes more important at deeper depths where pressure and stresses on fractures are higher. The propped

fracture is permeable enough to allow the flow of formation fluids to the well. Formation fluids include gas, oil,

salt water, fresh water and fluids introduced to the formation during completion of the well during

fracturing.[citation needed]

The location of one or more fractures along the length of the borehole is strictly controlled by various different

methods which create or seal-off holes in the side of the wellbore. Typically, hydraulic fracturing is performed

incasedwellbores and the zones to be fractured are accessed byperforatingthe casing at those

locations.[citation needed

]
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[edit]Well types

While hydraulic fracturing is many times performed in vertical wells, today it is also performed in horizontal

wells. When done in already highly-permeable reservoirs such assandstone-based wells, the technique is

known as "well stimulation".

Horizontal drillinginvolves wellbores where the terminal drillhole is completed as a 'lateral' that extends

parallel with the rock layer containing the substance to be extracted. For example, laterals extend 1,500 to

5,000 feet in the Barnett Shale basin in Texas, and up to 10,000 feet in theBakken formationin North Dakota.

In contrast, a vertical well only accesses the thickness of the rock layer, typically 50300 feet. Horizontal

drilling also reduces surface disruptions as fewer wells are required. Drilling usually induces damage to the

pore space at the wellbore wall, reducing the permeability at and near the wellbore. This reduces flow into the

borehole from the surrounding rock formation, and partially seals off the borehole from the surrounding rock.

Hydraulic fracturing can be used to restore permeability.[citation needed]

Hydraulic fracturing is commonly applied to wells drilled in low permeability reservoir rock.

[edit]Fracturing

The fluid injected into the rock is typically a slurry of water, proppants, and chemical additives. Additionally,

gels, foams, and compressed gases, includingnitrogen,carbon dioxideand air can be injected. Various types

of proppant include silica sand, resin-coated sand, and man-made ceramics. These vary depending on the

type of permeability or grain strength needed. Sand containing naturally radioactive minerals is sometimes

used so that the fracture trace along the wellbore can be measured. Chemical additives are applied to tailor

the injected material to the specific geological situation, protect the well, and improve its operation, though the

injected fluid is approximately 98-99.5% percent water,[43]varying slightly based on the type of well. The

composition of injected fluid is sometimes changed as the fracturing job proceeds. Often, acid is initially used

to scour the perforations and clean up the near-wellbore area. Afterward, high pressure fracture fluid is

injected into the wellbore, with the pressure above the fracture gradient of the rock. This fracture fluid contains

water-soluble gelling agents (such as guar gum) which increase viscosity and efficiently deliver the proppant

into the formation.[3]

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.[3]

The proppant's purpose is primarily to provide a permeable and permanent filler to fill

the void created during the fracturing process. At the end of the job the well is commonly flushed with water

(sometimes blended with a friction reducing chemical) under pressure. Injected fluid is to some degree

recovered and is managed by several methods, such as underground injection control, treatment and

discharge, recycling, or temporary storage in pits or containers while new technology is being developed to

better handle wastewater and improve reusability.[43]Although the concentrations of the chemical additives are

very low, the recovered fluid may be harmful due in part to hydrocarbons picked up from the formation.

Hydraulic fracturing equipment used in oil and natural gas fields usually consists of a slurry blender, one or

more high pressure, high volume fracturing pumps (typically powerful triplex, or quintiplex pumps) and a

monitoring unit. Associated equipment includes fracturing tanks, one or more units for storage and handling of

proppant, high pressure treating iron, a chemical additive unit (used to accurately monitor chemical addition),

low pressure flexible hoses, and many gauges and meters for flow rate, fluid density, and treating pressure.

Fracturing equipment operates over a range of pressures and injection rates, and can reach up to

100MPa(15,000psi) and 265 L/s (100 barrels per minute).[citation needed]

[edit]Fracture monitoring
http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=7http://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Horizontal_drillinghttp://en.wikipedia.org/wiki/Horizontal_drillinghttp://en.wikipedia.org/wiki/Bakken_formationhttp://en.wikipedia.org/wiki/Bakken_formationhttp://en.wikipedia.org/wiki/Bakken_formationhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=8http://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Pascalshttp://en.wikipedia.org/wiki/Pascalshttp://en.wikipedia.org/wiki/Pascalshttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=9http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Pounds_per_square_inchhttp://en.wikipedia.org/wiki/Pascalshttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-CRO_2009-2http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-DOE_primer-42http://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=8http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Bakken_formationhttp://en.wikipedia.org/wiki/Horizontal_drillinghttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=7


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Injection of radioactive tracers along with the other substances in hydraulic fracturing fluid is used to

determine the injection profile and location of fractures created by hydraulic fracturing.[44]

US Patent No.

5635712 (George L. Scott III, Halliburton Company, 03-June-1997) describes this process. The patent lists a

large number of gamma-emitting tracer isotopes that can be used as radioactive tracer material,

includingGold-198,Xenon-133,Iodine-131,Rubidium-86,Chromium-51,Iron-59,Antimony-124,Strontium-

85,Cobalt-58,Iridium-192,Scandium-46,Zinc-65,Silver-110,Cobalt-57,Cobalt-60, andKrypton-85.[45]

A 1983

patent, by Walter H. Fertl, for Dresser Industries (Dallas, Texas) also listsIodine-131as a potential tracer,

along withScandium-46,Zirconium-95, andIridium-192.[46]

A 1995 patent by George L. Scott III, this time for

The Energex Company (patent no. US5441110), also listsIodine-131as a suitable gamma-emitting tracer

isotope, along withPotassium-39(activated toPotassium-40),Potassium-41(activated toPotassium-

42),Potassium-43,Scandium-45(activated toScandium-46),Scandium-47,Scandium-48,Iodine-127,Iodine-

128,Iodine-129,Iodine-130,Antimony-121,Antimony-122,Antimony-123,Antimony-124,Antimony-

125,Antimony-126, andAntimony-127.[47]

Measurements of the pressure and rate during the growth of a hydraulic fracture, as well as knowing the

properties of the fluid and proppant being injected into the well provides the most common and simplestmethod 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. [citation

needed]

For more advanced applications,Microseismicmonitoring is sometimes used to estimate the size and

orientation of hydraulically induced fractures. Microseismic activity is measured by placing an array

ofgeophonesin a nearby wellbore. By mapping the location of any small seismic events associated with the

growing hydraulic fracture, the approximate geometry of the fracture is inferred.Tiltmeterarrays, deployed on

the surface or down a well, provide another technology for monitoring the strains produced by hydraulic

fracturing.[citation needed]

Emission of gases displaced by hydraulic fracturing into the atmosphere may be detected via atmospheric gas

monitoring, and can be quantified directly via theeddy covarianceflux measurements.[citation needed]

[edit]Horizontal completions

Since the early 2000s, advances indrillingandcompletiontechnology has made drilling horizontal wellbores

much more economical. Horizontal wellbores allow for far greater exposure to a formation than a conventional

vertical wellbore. This is particularly useful in shaleoilandgasformations which do not have sufficient

permeability to produce economically with a vertical well. Such wells when drilled onshore are now usually

hydraulically fractured many times, especially in North America. The type of wellbore completion used will

affect how many times the formation is fractured, and at what locations along the horizontal section of thewellbore.

[48]

In North America, tight reservoirs such as theBakken, Barnett Shale,Montney,Haynesville Shaleand most

recently Marcellus Shale are drilled, completed and fractured using this method. The method by which the

fractures are placed along the wellbore is most commonly achieved by one of two methods, known as 'plug

and perf' and 'sliding sleeve'.[citation needed]

The wellbore for a plug and perf job is generally composed of standard joints of steel casing, either cemented

or uncemented, which is set in place at the conclusion of the drilling process. Once the drilling rig has been

removed, awireline truckis used toperforatenear the end of the well, following which a fracturing job is

pumped (commonly called a stage). Once the stage is finished, the wireline truck will set a plug in the well to

temporarily seal off that section, and then perforate the next section of the wellbore. Another stage is then
http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Reis_iodine-43http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Reis_iodine-43http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Reis_iodine-43http://en.wikipedia.org/wiki/Gold-198http://en.wikipedia.org/wiki/Gold-198http://en.wikipedia.org/wiki/Gold-198http://en.wikipedia.org/wiki/Xenon-133http://en.wikipedia.org/wiki/Xenon-133http://en.wikipedia.org/wiki/Xenon-133http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Rubidium-86http://en.wikipedia.org/wiki/Rubidium-86http://en.wikipedia.org/wiki/Rubidium-86http://en.wikipedia.org/wiki/Chromium-51http://en.wikipedia.org/wiki/Chromium-51http://en.wikipedia.org/wiki/Chromium-51http://en.wikipedia.org/wiki/Iron-59http://en.wikipedia.org/wiki/Iron-59http://en.wikipedia.org/wiki/Iron-59http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Cobalt-58http://en.wikipedia.org/wiki/Cobalt-58http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Zinc-65http://en.wikipedia.org/wiki/Zinc-65http://en.wikipedia.org/wiki/Zinc-65http://en.wikipedia.org/wiki/Silver-110http://en.wikipedia.org/wiki/Silver-110http://en.wikipedia.org/wiki/Silver-110http://en.wikipedia.org/wiki/Cobalt-57http://en.wikipedia.org/wiki/Cobalt-57http://en.wikipedia.org/wiki/Cobalt-57http://en.wikipedia.org/wiki/Cobalt-60http://en.wikipedia.org/wiki/Cobalt-60http://en.wikipedia.org/wiki/Cobalt-60http://en.wikipedia.org/wiki/Krypton-85http://en.wikipedia.org/wiki/Krypton-85http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-No5635712-44http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-No5635712-44http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-No5635712-44http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Zirconium-95http://en.wikipedia.org/wiki/Zirconium-95http://en.wikipedia.org/wiki/Zirconium-95http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US4415805-45http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US4415805-45http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US4415805-45http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Potassium-39http://en.wikipedia.org/wiki/Potassium-39http://en.wikipedia.org/wiki/Potassium-39http://en.wikipedia.org/wiki/Potassium-40http://en.wikipedia.org/wiki/Potassium-40http://en.wikipedia.org/wiki/Potassium-40http://en.wikipedia.org/wiki/Potassium-41http://en.wikipedia.org/wiki/Potassium-41http://en.wikipedia.org/wiki/Potassium-41http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-43http://en.wikipedia.org/wiki/Potassium-43http://en.wikipedia.org/wiki/Potassium-43http://en.wikipedia.org/wiki/Scandium-45http://en.wikipedia.org/wiki/Scandium-45http://en.wikipedia.org/wiki/Scandium-45http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-47http://en.wikipedia.org/wiki/Scandium-47http://en.wikipedia.org/wiki/Scandium-47http://en.wikipedia.org/wiki/Scandium-48http://en.wikipedia.org/wiki/Scandium-48http://en.wikipedia.org/wiki/Scandium-48http://en.wikipedia.org/wiki/Iodine-127http://en.wikipedia.org/wiki/Iodine-127http://en.wikipedia.org/wiki/Iodine-127http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-129http://en.wikipedia.org/wiki/Iodine-129http://en.wikipedia.org/wiki/Iodine-129http://en.wikipedia.org/wiki/Iodine-130http://en.wikipedia.org/wiki/Iodine-130http://en.wikipedia.org/wiki/Iodine-130http://en.wikipedia.org/wiki/Antimony-121http://en.wikipedia.org/wiki/Antimony-121http://en.wikipedia.org/wiki/Antimony-121http://en.wikipedia.org/wiki/Antimony-122http://en.wikipedia.org/wiki/Antimony-122http://en.wikipedia.org/wiki/Antimony-122http://en.wikipedia.org/wiki/Antimony-123http://en.wikipedia.org/wiki/Antimony-123http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-126http://en.wikipedia.org/wiki/Antimony-126http://en.wikipedia.org/wiki/Antimony-126http://en.wikipedia.org/wiki/Antimony-127http://en.wikipedia.org/wiki/Antimony-127http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US5441110-46http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US5441110-46http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US5441110-46http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Microseismichttp://en.wikipedia.org/wiki/Microseismichttp://en.wikipedia.org/wiki/Microseismichttp://en.wikipedia.org/wiki/Geophonehttp://en.wikipedia.org/wiki/Geophonehttp://en.wikipedia.org/wiki/Geophonehttp://en.wikipedia.org/wiki/Tiltmeterhttp://en.wikipedia.org/wiki/Tiltmeterhttp://en.wikipedia.org/wiki/Tiltmeterhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Eddy_covariancehttp://en.wikipedia.org/wiki/Eddy_covariancehttp://en.wikipedia.org/wiki/Eddy_covariancehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=10http://en.wikipedia.org/wiki/Oil_well#Drillinghttp://en.wikipedia.org/wiki/Oil_well#Drillinghttp://en.wikipedia.org/wiki/Oil_well#Drillinghttp://en.wikipedia.org/wiki/Completion_(oil_and_gas_wells)http://en.wikipedia.org/wiki/Completion_(oil_and_gas_wells)http://en.wikipedia.org/wiki/Completion_(oil_and_gas_wells)http://en.wikipedia.org/wiki/Tight_oilhttp://en.wikipedia.org/wiki/Tight_oilhttp://en.wikipedia.org/wiki/Tight_oilhttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-47http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-47http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-47http://en.wikipedia.org/wiki/Bakken_Formationhttp://en.wikipedia.org/wiki/Bakken_Formationhttp://en.wikipedia.org/wiki/Bakken_Formationhttp://en.wikipedia.org/wiki/Montney_Formationhttp://en.wikipedia.org/wiki/Montney_Formationhttp://en.wikipedia.org/wiki/Montney_Formationhttp://en.wikipedia.org/wiki/Haynesville_Shalehttp://en.wikipedia.org/wiki/Haynesville_Shalehttp://en.wikipedia.org/wiki/Haynesville_Shalehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wireline_(cabling)http://en.wikipedia.org/wiki/Wireline_(cabling)http://en.wikipedia.org/wiki/Wireline_(cabling)http://en.wikipedia.org/wiki/Perforation_(oil_well)http://en.wikipedia.org/wiki/Perforation_(oil_well)http://en.wikipedia.org/wiki/Perforation_(oil_well)http://en.wikipedia.org/wiki/Perforation_(oil_well)http://en.wikipedia.org/wiki/Wireline_(cabling)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Haynesville_Shalehttp://en.wikipedia.org/wiki/Montney_Formationhttp://en.wikipedia.org/wiki/Bakken_Formationhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-47http://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_oilhttp://en.wikipedia.org/wiki/Completion_(oil_and_gas_wells)http://en.wikipedia.org/wiki/Oil_well#Drillinghttp://en.wikipedia.org/w/index.php?title=Hydraulic_fracturing&action=edit&section=10http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Eddy_covariancehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Tiltmeterhttp://en.wikipedia.org/wiki/Geophonehttp://en.wikipedia.org/wiki/Microseismichttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US5441110-46http://en.wikipedia.org/wiki/Antimony-127http://en.wikipedia.org/wiki/Antimony-126http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-125http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Antimony-123http://en.wikipedia.org/wiki/Antimony-122http://en.wikipedia.org/wiki/Antimony-121http://en.wikipedia.org/wiki/Iodine-130http://en.wikipedia.org/wiki/Iodine-129http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-128http://en.wikipedia.org/wiki/Iodine-127http://en.wikipedia.org/wiki/Scandium-48http://en.wikipedia.org/wiki/Scandium-47http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Scandium-45http://en.wikipedia.org/wiki/Potassium-43http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-42http://en.wikipedia.org/wiki/Potassium-41http://en.wikipedia.org/wiki/Potassium-40http://en.wikipedia.org/wiki/Potassium-39http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-US4415805-45http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Zirconium-95http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-No5635712-44http://en.wikipedia.org/wiki/Krypton-85http://en.wikipedia.org/wiki/Cobalt-60http://en.wikipedia.org/wiki/Cobalt-57http://en.wikipedia.org/wiki/Silver-110http://en.wikipedia.org/wiki/Zinc-65http://en.wikipedia.org/wiki/Scandium-46http://en.wikipedia.org/wiki/Iridium-192http://en.wikipedia.org/wiki/Cobalt-58http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Strontium-85http://en.wikipedia.org/wiki/Antimony-124http://en.wikipedia.org/wiki/Iron-59http://en.wikipedia.org/wiki/Chromium-51http://en.wikipedia.org/wiki/Rubidium-86http://en.wikipedia.org/wiki/Iodine-131http://en.wikipedia.org/wiki/Xenon-133http://en.wikipedia.org/wiki/Gold-198http://en.wikipedia.org/wiki/Hydraulic_fracturing#cite_note-Reis_iodine-43


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pumped, and the process is repeated as necessary along the entire length of the horizontal part of the

wellbore.[citation needed]

The wellbore for the sliding sleeve technique is different in that the sliding sleeves are included at set spacings

in the steel casing at the time it is set in place. The sliding sleeves are usually all closed at this time. When the

well is ready to be fractured, using one of several activation techniques, the bottom sliding sleeve is openedand 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.[citation needed]

[edit]Chemicals

Water is by far the largest component of fracking fluids. The initial drilling operation itself may consume from

65,000 gallons to 600,000 gallons of fracking fluids. Over its lifetime an average well will require up to an

additional 5 million gallons of water for the initial fracking operation and possible restimulation frac jobs.[49]The

large volumes of water required have raised concerns about fracking in arid areas, such as Karoo in South

Africa.[50]

Chemical additives used in fracturing fluids typically make up less than 2% by weight of the total fluid.[51]

Over

the life of a typical well, this may amount to 100,000 gallons of chemical additives. These additives (listed in a

U.S. House of Representatives Report[52]

) includebiocides,surfactants, viscosity-modifiers, and emulsifiers.

They vary widely in toxicity: Many are used in household products such as cosmetics, lotions, soaps,

detergents, furniture polishes, floor waxes, and paints,[53]and some are used in food products. Some,

however, are knowncarcinogens, some are toxic, and some areneurotoxins. For

example:benzene(causescancer, bone marrow failure),lead(damages the nervous system and causes

brain disorders),ethylene glycol(antifreeze, causes death),methanol(highly toxic),boric acid(kidney

damage, death),2-butoxyethanol(causeshemolysis). Gamma-emittingisotopes(radioactive; can cause

cancer) are also included in the fluid as tracers. Some of the isotopes used areAntimony-121,Antimony-

122,Antimony-123,Antimony-124,Antimony-125,Antimony-126,Antimony-127,Chromium-51,Cobalt-

57,Cobalt-58,Cobalt-60,Gold-198,Iodine-127,Iodine-128,Iodine-129,Iodine-130,Iodine-131,Iridium-

192,Iron-59,Krypton-85,Lanthanum-140,Potassium-39(activated toPotassium-40),Potassium-

41(activated toPotassium-42),Potassium-43,Rubidium-86,Scandium-45,Scandium-46,Scandium-

47,Scandium-48,Silver-110,Strontium-85,Xenon-133,Zinc-65, andZirconium-95. Several are typically

combined and injected together.[45][46][47]Their half lifes range from 40.2 hours (Lanthanum-140) to 5.27 years

(Cobalt-60).[54]

Despite concerns about the generally elevated radiation levels found near hydraulic fracturing sites and high

levels ofiodine-131(a radioactive tracer used in hydraulic fracturing) found in drinking water and

milk,[55][56][57]iodine-131 is not listed among the chemicals to be monitored in theUnited States Environmental

Protection AgencyHydraulic Fracturing Draft Study Plan. Other known radioactive tracers used in hydraulic

fracturing[45][46][47]

but not listed as chemicals to be studied includeradioactive

isotopesofgold,xenon,rubidium,iridium,scandium, andkrypton.[5]. Recently the EPA has not been very

forthcoming regarding public disclosure of environmental contamination by the oil and gas industry.[23][58]

The 2011 US House of Representatives investigative report on the chemicals used in hydraulic fracturing

shows that of the 750 compounds in hydraulic fracturing products [m]ore than 650 of these products

contained chemicals that are known or possible humancarcinogens, regulated under the Safe Drinking WaterAct, or listed as hazardous air pollutants (12). The report also shows that between 2005 and 2009 279
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products (93.6 million gallons-not including water) had at least one component listed as proprietary or trade

secret on their Occupational Safety and Health Administration (OSHA) required Material Safety Data Sheet

(MSDS). The MSDS is a list of chemical components in the products of chemical manufacturers, and

according to OSHA, a manufacturer may withhold information designated as proprietary from this sheet.

When asked to reveal the proprietary components, most companies participating in the investigation were

unable to do so, leading the committee to surmise these companies are injecting fluids containing unknown

chemicals about which they may have limited understanding of the potential risks posed to human health and

the environment (12).[59]

Without knowing the identity of the proprietary components, regulators cannot test

for their presence. This prevents government regulators from establishing baseline levels of the substances

prior to hydraulic fracturing and documenting changes in these levels, thereby making it impossible to prove

that hydraulic fracturing is contaminating the environment with these substances.[60]

Third-party laboratories

are performing analyses on soil, air, and water near the fracturing sites to measure the level of contamination

by some of the known chemicals, but not the proprietary substances, involved in hydraulic fracturing. Each

state has a contact person in charge of such regulation.[61]

A map of these contact people can be found at

FracFocus.org as well.[62]

Another 2011 study identified 632 chemicals used in natural gas operations. Only 353 of these are well-

described in the scientific literature; and of these, more than 75% could affect skin, eyes, respiratory and

gastrointestinal systems; roughly 40-50% could affect the brain and nervous, immune and cardiovascular

systems and the kidneys; 37% could affect the endocrine system; and 25% were carcinogens and mutagens.

The study indicated possible long-term health effects that might not appear immediately. The study

recommended full disclosure of all products used, along with extensive air and water monitoring near natural

gas operations; it also recommended that fracking's exemption from regulation under the US Safe Drinking

Water Act be rescinded.[63]

Some states have started requiring natural gas companies to "disclose the names of all chemicals to be

stored and used a drilling site," keeping a record on file at the states environmental agency, such as the case

in Pennsylvania with the Department of Environmental Protection and in New York with the Department of

Environmental Conservation.[64]However, the continuing concern of some activists who oppose hydraulic

fracturing is the lack of information really provided. According to Weston Wilson inAffirming Gasland, "about

50% or so of these MSDS sheets lack a specific chemical name, and some MSDS sheets simply claim

'proprietary' status and list none of the chemicals in that container."[65]As a result, some activists are calling

for specific disclosure of chemicals used, such as the Chemical Abstract Service (CAS) number and specific

chemical formulas, and increased access to such information. In hisState of the Union addressfor 2012,

Barack Obama stated his intention to force fracking companies to disclose the chemicals they use,[66]

though

the subsequent, proposed guidelines were criticised for failing to specify how drillers will disclose the

chemicals they use.[67]

[edit]Terminology

Fracture Gradient

The pressure to fracture the formation at a particular depth divided by the depth. A fracture gradient of 18

kPa/m (0.8 psi/foot) implies that at a depth of 3 km (10,000 feet) a pressure of 54 MPa (8,000 psi) will extend

a hydraulic fracture.

ISIP Initial Shut In Pressure

The pressure measured immediately after injection stops. The ISIP provides a measure of the pressure in the

fracture at the wellbore by removing contributions from fluid friction.
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Leakoff

Loss of fracturing fluid from the fracture channel into the surrounding permeable rock.

Fracturing fluid

The fluid used during a hydraulic fracture treatment of oil, gas, or water wells. The fracturing fluid has three

major functions:

1. Open and extend the fracture.

2. Transport the proppant along the fracture length.

3. Transport radioactive tracers through the fractures to determine the injection profile and track the

locations of fractures.[45][44][46][47]

Proppant

Suspended particles in the fracturing fluid that are used to hold fractures open after a hydraulic fracturing

treatment, thus producing a conductive pathway that fluids can easily flow along. Naturally occurring sand

grains or artificial ceramic material are common proppants used.

[edit]Environmental concerns

Environmental concerns with hydraulic fracturing include the potential contamination ofground water, risks

toair quality, the potential migration of gases and hydraulic fracturing chemicals to the surface, the potential

mishandling of waste, and the health effects of these, like cancer.[52][68]Many cases of suspected groundwater

contamination have been documented.[69]

With the explosive growth of natural gas wells in the US, researcher

Valerie Brown predicted in 2007 that "public exposure to the many chemicals involved in energy development

is expected to increase over the next few years, with uncertain consequences."[68]

New York State Assembly members Robert Castelli and Steve Katz call for a moratorium on hydraulic fracturing in the Croton

Watershed in October 2010.

In the US, interviews withEnvironmental Protection Agency(EPA) scientists and leaked documents have

shown that, since the 1980s, EPA investigations into the oil and gas industry's environmental impact

including the ongoing one into fracking's potential impact on drinking waterand associated reports had been

narrowed in scope and/or had negative findings removed due to industry and government

pressure.[23][70][71]The most recent example of this concerns the 2012 EPA Hydraulic Fracturing Draft Plan.

Despite concerns about the elevated levels ofiodine-131(a radioactive tracer frequently used in hydraulic
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Documents

Fraccing - Wikipedia