8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 1/18

 What Is Tight Gas, and How Is It Produced?

•

•

•

•

While conventional natural gas streams from the earth relatively easily, unconventional gas

finds are more difficult to develop and more costly to produce. As technologies and skillsimprove, unconventional gas is a variable concept because some finds may become moreeasily or economically produced over time, no longer making them unconventional. Right now,there are six main types of unconventional gas, including deep gas, gas-containing shales,coalbed methane, geopressurized zones, Arctic and subsea hydrates, and tight gas.

Major Tight Gas Reserves in the US Source : EIA, www.eia.doe.gov 

Unconventional natural gas deposits are likely to account for much of the world's remainingreserves. According to the EIA, there is more than 309 Tcf of recoverable tight natural gasdeposits in the US, which represents some 17% of the total natural gas reserves in the country.

Helping to boost interest in developing technologies that can overcome the challenges of producing unconventional gas resources in the United States, the Natural Gas Policy Act offersincentives to companies exploring for and producing unconventional gas plays.

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 2/18

 What Is Tight Gas?

Tight gas refers to natural gas reservoirs locked in extraordinarily impermeable, hard rock,making the underground formation extremely "tight." Tight gas can also be trapped in sandstoneor limestone formations that are atypically impermeable or nonporous, also known as tight sand.

Impermeable Pores in Tight Gas FormationSource : USGS, www.energy.usgs.gov 

While a conventional gas formation can be relatively easily drilled and extracted from the groundunassisted, tight gas requires more effort to pull it from the ground because of the extremelytight formation in which it is located. In other words, the pores in the rock formation in which thegas is trapped are either irregularly distributed or badly connected with overly narrow capillaries,lessening permeability -- or the ability of the gas to travel through the rock. Without secondaryproduction methods, gas from a tight formation would flow at very slow rates, making productionuneconomical.

While conventional gas formations tend to be found in the younger Tertiary basins, tight gasformations are much older. Deposited some 248 million years ago, tight gas formations aretypically found in Palaeozoic formations. Over time, the rock formations have been compactedand have undergone cementation and recrystallisation, which all reduce the level of permeabilityin the rock.

Typical conventional natural gas deposits boast a permeability level of .01 to .5 darcy, but theformations trapping tight gas reserves portray permeability levels of merely a fraction of that,measuring in the millidarcy or microdarcy range.

In order to overcome the challenges that the tight formation presents, there are a number of additional procedures that can be enacted to help produce tight gas. Deviating drilling practicesand more specific seismic data can help in tapping tight gas, as well as artificial stimulation,such as fracturing and acidizing.

Developing Tight Gas

One of the most important aspects of drilling for any petroleum is predetermining the successrate of the operation. Operators do not just drill anywhere. Extensive seismic data is gatheredand analyzed to determine where to drill and just what might be located below the earth'ssurface.

These seismic surveys can help to pinpoint the best areas to tap tight gas reserves. A surveymight be able to locate an area that portrays an improved porosity or permeability in the rock in

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 3/18

which the gas is located. Should wells directly hit the best area to develop the reserve, costs of development can be minimized.

Most tight gas formations are found onshore, and land seismic techniques are undergoingtransformations to better map out where drilling and development of these unconventionalplays. Typical land seismic techniques include exploding dynamite and vibroseis, or measuringvibrations produced by purpose-built trucks. While these techniques can produce informationalsurveys, advancements inmarine seismic technologies are now being applied to land seismicsurveys, enhancing the information available about the world below.

Not only providing operators with the best locations for drilling wells into tight gas formations,extensive seismic surveys can help drilling engineers determine where and to what extentdrilling directions should be deviated.

Directional Drilling Source : MacKenzie Gas Project, www.mackenziegasproject.com

While vertical wells may be easier and less expensive to drill, they are not the most conducive

to developing tight gas. In a tight gas formation, it is important to expose as much of thereservoir as possible, making horizontal and directional drilling a must. Here, the well can runalong the formation, opening up more opportunities for the natural gas to enter the wellbore.

A common technique for developing tight gas reserves includes drilling more wells. The morethe formation is tapped, the more the gas will be able to escape the formation. This can beachieved through drilling myriad directional wells from one location, lessening the operator'sfootprint and lowering costs.

Production Stimulation

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 4/18

After seismic data has illuminated the best well locations, and the wells have been drilled,production stimulation is employed on tight gas reservoirs to promote a greater rate of flow.Production stimulation can be achieved on tight gas reservoirs through both fracturing andacidizing the wells.

Fracturing, also known as "fracing," a well involves breaking the rocks in the formation apart.Performed after the well has been drilled andcompleted, hydraulic fracturing is achieved bypumping the well full of frac fluids under high pressure to break the rocks in the reservoir apartand improve permeability, or the ability of the gas to flow through the formation.Additionally, acidizing the well is employed to improve permeability and production rates of tightgas formations. Acidation involves pumping the well with acids that dissolve the limestone,dolomite and calcite cement between the sediment grains of the reservoir rocks. This form of production stimulation helps to reinvigorate permeability by reestablishing the natural fissuresthat were present in the formation before compaction and cementation.Furthermore, deliquification of the tight gas wells can help to overcome some productionchallenges. In many tight gas formations, the reservoirs also contain small amounts of water.This water can collect and undermine production processes. Deliquification is achieved in thisinstance through artificial lift techniques, such as using a beam pumping system to remove thewater from the reservoir, although this has not proven the most effective way to overcome this

challenge.Engineers continue to develop new techniques and technologies to better produce tight gas.Through their efforts, maybe one day, tight gas will no longer be considered an unconventionalplay.

How Does LNG Work?

•

•

•

•

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 5/18

Because of its physical state, natural gas is inherently a domestic product. As a gas, thehydrocarbon must be transported by pipeline, which restricts the number of end users. LiquefiedNatural Gas (LNG) was developed in 1964 as a solution to this problem.

With LNG, gas is liquefied and transported internationally via tankers and then regasified into its

original state for distribution and sale. Additionally, the hydrocarbon takes up significantly lessspace as a liquid than a gas; LNG is approximately 1/600th the volume of the same amount of natural gas.

LNG Liquefaction PlantSource : Center for Liquefied Natural Gas

LNG has transformed the natural gas market, making previously unrecoverable natural gasfinds an economic reality. In other words, stranded gas reservoirs, for which pipelines were toocostly to construct, can now be produced, transformed into LNG and transported via tanker.

Liquefaction

When in the reservoir, natural gas is found in three states: non-associated, where there is no oilcontact; gas cap, where it is overlying an oil reserve; and associated gas, which is dissolved inthe oil. The composition of the natural gas defines how it will be processed for transport.Whether staying in its gaseous state or being transformed into a liquid, natural gas from the wellmust undergo separation processes to remove water, acid gases and heavy hydrocarbons fromthe recovered natural gas.

The next step in processing is determined by what type of transport the gas will undergo, andspecifications are met according to the transportation system. For LNG, additional processing isrequired before the condensation of the gas to remove the threat of crystallization in the heatexchangers in the liquefaction plant. When chemical conversion is used to liquefy natural gas,the conversion process determines which preliminary process must be used. Additionally,fractionation between methane and heavier hydrocarbons is performed during liquefaction. Thisway, after regasification the fuel can be loaded directing into the distribution network of pipelines.

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 6/18

LNG Liquefaction PlantSource : Center for Liquefied Natural Gas

Natural gas is liquefied by lowering the temperature of the hydrocarbon to approximately -260degrees Fahrenheit (-160 degrees Celsius). This temperature drop liquefies the methanepresent in the natural gas, making transportation at atmospheric pressure in the form of LNGpossible. LNG is mainly constituted of methane and generally contains ethane, as well.Liquefied Petroleum Gas (LPG) may also be present in the LNG.

Transportation

LNG is then introduced into specially insulated tankers and transported around the world. LNGis kept in its liquid form via autorefrigeration. This is a process in which the fuel is kept at itsboiling point. Through autorefrigeration any additions of heat are offset by the energy lost from

the LNG vapor, vented out of the storage and used to power the tanker.

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 7/18

LNG Being Loaded Onto a Tanker Source : Center for Liquefied Natural Gas

LNG Tanker at SeaSource : Center for Liquefied Natural Gas

LNG has little to no chance of igniting or exploding should a spill occur. When LNG is vaporized

into its gaseous form, the fuel will only burn when mixed with air in concentrations of 5 and 15%.Additionally, LNG and the vapors associated with it do not explode in an open environment.

Regasification

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 8/18

LNG Regasification PlantSource : Center for Liquefied Natural Gas

Once it has reached its destination, the LNG is offloaded from the tanker and either stored or regasified. The LNG is dehydrated into a gaseous state again through a process that involvespassing the LNG through a series of vaporizers that reheat the fuel above the -260 degreeFahrenheit (-160 degrees Celsius) temperature mark. The fuel is then sent via establishedtransportation methods, such as pipelines, to the end users.

 ApplicationsAlthough limited because of the number of liquefaction and regasification facilities locatedworldwide, LNG is gaining momentum. Major ongoing LNG projects include the multi-billion-dollar GorgonLNG project in Australia, as well as the Olokola LNG project in Nigeria andthe LionGas LNG project in the Netherlands.

According to the EIA, countries in Asia Pacific are the largest exporters of LNG, and the MiddleEast is also a leading LNG exporting region. Historically some of the largest importers of LNG,Japan and South Korea depend almost solely on internationally produced LNG for their naturalgas needs. European countries also import a large percentage of the LNG produced globally.Emerging markets for the fuel are China and India, although those countries are currentlypursuing major pipeline deals in an effort to increase their natural gas imports.

Currently, LNG represents only about 1% of the natural gas consumed in the United States.Right now, the country imports LNG from Trinidad and Tobago, Qatar, Algeria, Nigeria, Oman,Australia, Indonesia and the UAE.

According to the US Federal Energy Regulatory Commission (FERC), there are currently eightLNG processing facilities in operation in the country; seven are regasification plants, and one is

a liquefaction facility. Presently, there are 40 additional LNG projects under consideration in theUS. LNG imports are expected to increase to an average of 15.8% or 4.8 Tcf of the natural gasused in the US by 2025.

Shale gasFrom Wikipedia, the free encyclopedia

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 9/18

For gas generated by oil shale pyrolysis, see Oil shale gas.

48 Shale basins in 38 nations, per the EIA

Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of 

natural gas in the United States over the past decade, and interest has spread to potential gas shales in the

rest of the world. One analyst expects shale gas to supply as much as half the natural gas production in North

America by 2020.[1][dead link ]

Some analysts expect that shale gas will greatly expand worldwide energy supply.[2] A study by the Baker 

Institute of Public Policy at Rice University concluded that increased shale gas production in the US and

Canada could help prevent Russia and Persian Gulf countries from dictating higher prices for the gas it exports

to European countries.[3] The Obama administration believes that increased shale gas development will help

reduce greenhouse gas emissions.[4]However, there is growing evidence that the extraction and use of shale

gas results in the release of more greenhouse gases than conventional natural gas, and may lead to emissions

greater than those of oil or coal.[5]

Contents

  [hide]

• 1 Geolog

y

• 2 Enviro

nment

• 3 Econo

mics

• 4 See

also

• 5 Refere

nces

• 6 Extern

al links

[edit]Geology

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 10/18

Illustration of shale gas compared to other types of gas deposits.

Because shales ordinarily have insufficient permeability to allow significant fluid flow to a well bore, most shales

are not commercial sources of natural gas. Shale gas is one of a number of unconventional sources of natural

gas; other unconventional sources of natural gas includecoalbed methane, tight sandstones, and methane

hydrates. Shale gas areas are often known asresource plays[6] (as opposed to exploration plays). The

geological risk of not finding gas is low in resource plays, but the potential profits per successful well are

usually also lower.[citation needed ]

Shale has low matrix permeability, so gas production in commercial quantities requires fractures to provide

permeability. Shale gas has been produced for years from shales with natural fractures; the shale gas boom in

recent years has been due to modern technology in hydraulic fracturing(fracking) to create extensive artificial

fractures around well bores.[citation needed ]

Horizontal drilling is often used with shale gas wells, with lateral lengths up to 10,000 feet (3,000 m) within the

shale, to create maximum borehole surface area in contact with the shale.[citation needed ]

Shales that host economic quantities of gas have a number of common properties. They are rich in organic

material (0.5% to 25%),[7] and are usually mature petroleum source rocks in the thermogenic gas window,

where high heat and pressure have converted petroleum to natural gas. They are sufficiently brittle and rigid

enough to maintain open fractures. In some areas, shale intervals with high natural gamma radiationare themost productive, as high gamma radiation is often correlated with high organic carbon content.[citation needed ]

Some of the gas produced is held in natural fractures, some in pore spaces, and some is adsorbed onto the

organic material. The gas in the fractures is produced immediately; the gas adsorbed onto organic material is

released as the formation pressure is drawn down by the well.[citation needed ]

[edit]Environment

See also: Environmental and health effects of hydraulic fracturing 

As noted above, US President Obama's administration has sometimes promoted shale gas, in part because of 

their belief that it releases fewer greenhouse gas (GHG) emissions than other fossil fuels. However, there is

evidence that shale gas emits more greenhouse gases than does conventional natural gas, and may emit as

much or more than oil or coal. In a May 2010 letter to US President Obama, the Council of Scientific Society

Presidents[8] urged great caution against a national policy of developing shale gas without a better scientific

basis for the policy. This umbrella organization that represents 1.4 million scientists noted that shale gas might

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 11/18

actually aggravate global warming, rather than help mitigate it. In late 2010, the U. S. Environmental Protection

Agency[9] issued a new report, the first update on emission factors for greenhouse gas emissions by the oil and

gas industry by the EPA since 1996. In this new report, EPA concluded that shale gas emits much larger 

amounts of methane, a potent greenhouse gas, than does conventional gas. Methane is a very powerful

greenhouse gas, although it stays in the atmosphere for only one tenth as long a period as carbon dioxide.

Recent evidence indicates that methane has a global warming potential that is 105-fold greater than carbon

dioxide when viewed over a 20-year period and 33-fold greater when viewed over a 100-year period, compared

mass-to-mass.[10] A recent 2011 study in Climatic Change Letters provides the first comprehensive analysis of 

the greenhouse gas footprint of shale gas.[11] In that peer-reviewed paper, Cornell University professor Robert

W. Howarth and colleagues find that once methane leak and venting impacts are included, the life-cycle

greenhouse gas footprint of shale gas is far worse than those of coal and fuel oil when viewed for the

integrated 20-year period after emission. On the 100-year integrated time frame, this analysis finds shale gas

comparable to coal and worse than fuel oil.

Chemicals are added to the water to facilitate the underground fracturing process that releases natural gas.

Only about 50% to 70% of the resulting volume of contaminated water is recovered and stored in above-ground

ponds to await removal by tanker. The remaining "produced water" is left in the earth where it can lead to

contamination of groundwater aquifers, though the industry deems this "highly unlikely". However the

wastewater from such operations often lead to foul-smelling odors and heavy metals contaminating the local

water supply above-ground. [12]

The 2010 U.S. documentary film Gasland  by Josh Fox, which focuses on the impact of hydraulic fracturing, is

critical of the industry's assertions of its safety and its exemption from the Safe Drinking Water Act in

the Energy Policy Act of 2005.

A study published in May 2011 concluded that fracking has seriously contaminated shallow groundwater 

supplies in northeast Pennsylvania with flammable methane. However the study does not discuss how

pervasive such contamination might be in other areas where drilling for shale gas has taken place.[13]

The United States Environmental Protection Agency (EPA) announced June 23, 2011 that it will examine

claims of water pollution related to hydraulic fracturing in Texas, North Dakota, Pennsylvania, Colorado and

Louisiana. [14] On December 8, 2011, the EPA issued a draft finding which stated that groundwater 

contamination in Pavillion, Wyoming may be the result of fracking in the area. The EPA stated that the finding

was specific to the Pavillion area, where the fracking techniques differ from those used in other parts of the

U.S. Doug Hock, a spokesman for the company which owns the Pavillion gas field, said that it is unclear 

whether the contamination came from the fracking process.[15]

A 2011 study by the Massachusetts Institute of Technology concluded that "The environmental impacts of 

shale development are challenging but manageable." The study addressed groundwater contamination, noting

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 12/18

"There has been concern that these fractures can also penetrate shallow freshwater zones and contaminate

them with fracturing fluid, but there is no evidence that this is occurring". This study blames known instances of 

methane contamination on a small number of sub-standard operations, and encourages the use of industry

best practices to prevent such events from recurring. [16]

[edit]Economics

Although shale gas has been produced for more than 100 years in the Appalachian Basin and the Illinois

Basin of the United States, the wells were often marginally economical. Higher natural-gas prices in recent

years[when? ] and advances in hydraulic fracturing and horizontal completions have made shale-gas wells more

profitable.[17] As of June 2011, the validity of the claims of economic viability of these wells has begun to be

publicly questioned.[18] Shale gas tends to cost more to produce than gas from conventional wells, because of 

the expense of the massive hydraulic fracturing treatments required to produce shale gas, and of horizontal

drilling. However, this is often offset by the low risk of shale-gas wells.[citation needed ]

As of 2011 all successful shale-gas wells have exploited Paleozoic and Mesozoic rocks.[citation needed ]

North America has been the leader in developing and producing shale gas. The great economic success of 

the Barnett Shale play in Texas in particular has spurred the search for other sources of shale gas across

the United States and Canada.[citation needed ]

Research has calculated the 2011 worth of the global shale-gas market as $26.66bn.[19]

However, a June, 2011 New York Times investigation of industrial emails and internal documents found that

the financial benefits of unconventional shale gas extraction may be less than previously thought, due to

companies intentionally overstating the productivity of their wells and the size of their reserves.[20]

[edit]See also

Shale gas by country

Hydraulic fracturing

[edit]References

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 13/18

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay

minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz andcalcite. The ratio

of clay to other minerals is variable.[1] Shale is characterized by breaks along thin laminae or parallel

layering or bedding less than one centimeter in thickness, calledfissility.[1] Mudstones, on the other hand,

are similar in composition but do not show the fissility.

Contents

  [hide]

• 1 Texture

• 2 Composition and

color 

• 3 Formation

• 4 See also

• 5 References

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 14/18

 [edit]Texture

Shale typically exhibits varying degrees of  fissility breaking into thin layers, often splintery and usually

parallel to the otherwise indistinguishable bedding plane because of parallel orientation of clay mineral

flakes.[1] Non-fissile rocks of similar composition but made of particles smaller than 0.06 mm are

described as mudstones (1/3 to 2/3 silt particles) or claystone (less than 1/3 silt). Rocks with similar 

particle sizes but with less clay (greater than 2/3 silt) and therefore grittier are siltstones.[1] Shale is the

most common sedimentary rock.[2]

Sample of  drill cuttings of shale while drilling an oil well in Louisiana. Sand grain = 2 mm. in dia.

[edit]Composition and color 

Shales are typically composed of variable amounts of clay minerals and quartz grains and the typical

color is gray. Addition of variable amounts of minor constituents alters the color of the rock. Black shale

results from the presence of greater than one percent carbonaceous material and indicates

a reducing environment.[1] Black shale can also be referred to as black metal.[3] Red, brown and green

colors are indicative of ferric oxide (hematite - reds), iron hydroxide (goethite - browns and limonite -yellow), or micaceous minerals (chlorite, biotite and illite - greens).[1]

Clays are the major constituent of shales and other mudrocks. The clay minerals represented are

largely kaolinite, montmorillonite and illite. Clay minerals of Late Tertiary mudstones are

expandable smectites whereas in older rocks especially in mid to early Paleozoic shales illites

predominate. The transformation of smectite to illite produces silica, sodium, calcium, magnesium, iron

and water. These released elements

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 15/18

form authigenic quartz, chert, calcite,dolomite, ankerite, hematite and albite, all trace to minor (except

quartz) minerals found in shales and other mudrocks.[1]

Shales and mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks. However,

this amounts to less than one percent by mass in an average shale. Black shales which form in anoxic

conditions contain reduced free carbon along with ferrous iron (Fe2+) and sulfur (S2-). Pyrite and

amorphous iron sulfide along with carbon produce the black and purple coloration .[1]

[edit]Formation

Limey shale overlaid by limestone,Cumberland Plateau, Tennessee

The process in the rock cycle which forms shale is compaction. The fine particles that compose shale can

remain suspended in water long after the larger and denser particles of sand have deposited. Shales are

typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river 

deltas, on floodplains and offshore from beach sands. They can also be deposited on the continental

shelf , in relatively deep, quiet water. This process could have taken millions of years to complete.

'Black shales' are dark, as a result of being especially rich in unoxidized carbon. Common in

somePaleozoic and Mesozoic strata, black shales were deposited in anoxic, reducing environments, such

as in stagnant water columns. Some black shales contain abundant heavy metals such as molybdenum,

uranium, vanadium, and zinc.[4][5][6] The enriched values are of controversial origin, having been

alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow

accumulation from sea water over long periods of sedimentation.[5][7][8]

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 16/18

Splitting shale with a large knife to reveal fossils

Fossils, animal tracks/burrows and even raindrop impact craters are sometimes preserved on shale

bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite, or various carbonateminerals.

Shales that are subject to heat and pressure of metamorphism alter into a hard, fissile,metamorphic

rock known as slate. With continued increase in metamorphic grade the sequence isphyllite,

then schist and finally to gneiss.

Weathering shale at a road cut in southeastern Kentucky

Horizontal Drilling and Hydraulic Fracturing 

Over the past decade, the combination of  horizontal drilling andhydraulic f racturing has allowed access to large

volumes of shale gas that were previously uneconomical to produce. The production of natural gas from shale

formations has rejuvenated the natural gas industry in the United States.

What is a Shale "Play"?

Shale gas is found in shale "plays," which are shale formations containing significant accumulations of natural gas

and which share similar geologic and geographic properties. A decade of production has come from theBarnett

Shale play in Texas. Experience and information gained from developing the Barnett Shale have improved the

efficiency of shale gas development around the country.

Horizontal Drilling

Two major drilling techniques are used to produce shale gas.Horizontal drilling is used to provide greater access to

the gas trapped deep in the producing formation. First, a vertical well is drilled to the targeted rock formation. At the

desired depth, the drill bit is turned to bore a well that stretches through the reservoir horizontally, exposing the well to

more of the producing shale.

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 17/18

Hydraulic Fracturing 

Hydraulic fracturing (commonly called "fracking" or "hydrofracking") is a technique in which water, chemicals, and

sand are pumped into the well to unlock the hydrocarbons trapped in shale formations by opening cracks (fractures)

in the rock and allowing natural gas to flow from the shale into the well. When used in conjunction with horizontal

drilling, hydraulic fracturing enables gas producers to extract shale gas at reasonable cost. Without these techniques,

natural gas does not flow to the well rapidly, and commercial quantities cannot be produced from shale.

Did You Know? Shale gas in 2009 made up 14% of total U.S. natural gas supply. Production of shale gas is

expected to continue to increase, and constitute 45% of U.S. total natural gas supply in 2035, as projected in the

EIA Annual Energy Outlook 2011.

Shale Gas vs. Conventional Gas

Conventional gas reservoirs are created when natural gas migrates toward the Earth's surface from an organic-rich

source formation into highly permeable reservoir rock, where it is trapped by an overlying layer of impermeable rock.

In contrast, shale gas resources form within the organic-rich shale source rock. The low permeability of the shale

greatly inhibits the gas from migrating to more permeable reservoir rocks. Without horizontal drilling and hydraulic

fracturing, shale gas production would not be economically feasible because the natural gas would not flow from the

formation at high enough rates to justify the cost of drilling.

Shale Gas Forcast

8/3/2019 Tight Gas, Shale Gas and Hydrates

http://slidepdf.com/reader/full/tight-gas-shale-gas-and-hydrates 18/18

Chart showing the shale gas forcast from the EIA, Annual Energy Outlook 2011. Image by EIA.