Introduction to the Marcellus Shale

M A R C E L L U S
S H A L E
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I S S U E
N U M B E R
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Introduction to the Marcellus Shale
An introduction to the geological characteristics and considerations of the Marcellus
Shale, as well as its cultural history and major topics of scientific interest.
What is the Marcellus Shale?
Shale is a sedimentary rock
formed from fine, clay-like particles
deposited in low energy water environments and compressed into rock.
Fig. 1. The Marcellus Shale is exposed at
Earth’s surface north of the Finger Lakes
region, New York. Note the dark, charcoal
black color of the shale.
The Marcellus Shale is a dark shale,
sedimentary rock, and permeability
commonly called a black shale, that
is the ability of anything trapped
can be found in parts of Ohio, West
between grains in a sedimentary rock
Virginia, Pennto flow between
sylvania, and
pores. When natImportant properties
New York. It
ural gas is trapped
of
all
sedimentary
was deposited in
in a sedimentary
what was a shalrock with high
rocks are their porosity
low sea around
porosity and perand
permeability.
390 million
meability, like a
years ago dursandstone, it has
ing the Devonian period. Marcellus
the ability to flow through the rock
Shale is mostly located deep beneath to pockets of relatively low pressure.
Earth’s surface, but because the layers When natural gas is trapped in a
of rock are tilted toward the south,
sedimentary rock with low porosity
the Marcellus is deeper in the south
and permeability, like the Marcellus
and is exposed at the surface near
the north end of the Finger Lakes
region.
Shale is only one type of sedimenMUSEUM OF THE EARTH
tary rock in the Hamilton Group.
Important properties of all sedimentary rocks are their porosity and
1259 Trumansburg Road
permeability. Porosity is the amount
Ithaca, New York 14850
of space available between grains in a
www.museumoftheearth.org/marcellusshale
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DID YOU KNOW?
• Geological features are usually
named after a nearby town,
river, or other topographical
feature. The Marcellus Shale
was named after Marcellus,
NY, where it can be seen in
hillside rock exposures.
The
• Marcellus is the lowest layer of a group of shales
called the Hamilton Group,
known more commonly in
New York for its abundant
fossils, including trilobites,
clams, and coral.
• The first natural gas well was
shallow, and powered lights in
the town of Fredonia, NY in
1825.
Shale, the gas is effectively trapped
and cannot flow, which is why some
call these “tight shales.”
basins, and create shallow seas. New
York, as well as Pennsylvania, Ohio,
and West Virginia, were all covered
by a shallow sea around 390 million years ago, and this sea deposited
Marcellus Shale and many other
rock units. Rivers and streams fed
into this basin, and brought with
them small quantities of clay-like
sediments. Algae and other planktonic organisms inhabited the surface
waters of this sea, and, as they died,
sank to the bottom and mixed with
the sediment. The Marcellus Shale’s
characteristic dark color and natural
gas abundance is due to the high concentration of organic matter trapped
with the sediment that eventually
became rock.1
The deepest part of this sea was
located in the eastern part of the
basin, so more sediment and organic
matter was able to accumulate eastward. As a result, the Marcellus Shale
AC A
DIA
N
MO
UN
TA
I
NS
Marcellus Shale Origins
Sea levels have risen and fallen
throughout geologic history. When
they rise they encroach on the lowlying areas of continents, called
SHALLOW
SEA
Fig. 2. During the Devonian, parts
of the eastern U.S. were covered by a
shallow sea. The Marcellus Shale is
the result of deposition on the floor of
this sea.
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Low Permeability
& Porosity
High Permeability
& Porosity
Fig. 3. Porosity and permeability are important characteristics of sedimentary rocks. In
shale, sediments are platy and stack like cards,
effectively closing pathways between pores. In
sandstone, sediments are more rounded, which
allows connection between pores and results in
higher permeability.
today is thickest in the east and thins
westward. Because of the quantity
of organics in the shale, where the
Marcellus Shale is thicker it is likely
to contain a large amount of natural
gas and be of the most interest for
economical extraction.
Natural Gas in a Tight Shale
The natural gas in the Marcellus
Shale is a type of fossil fuel, like coal
and oil. While coal is formed from
the concentration of fossilized land
plant material, oil and gas are formed
by the concentration of vast numbers
of tiny, ocean-dwelling organisms
like zooplankton, phytoplankton
and algae. In all cases, organic tissues
become fossil fuels because they were
buried by sediment before they decomposed. Over long periods of time,
the trapped carbon compounds from
the organic material were subjected to
heat and pressure, creating coal, oil,
or natural gas.
Natural gas from Devonian shales
is usually composed primarily of
methane (80-95%), with a small
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mix of ethane and propane (3-15%)
which require processing before
commercial sale. When natural gas
and other fossil fuels are burned to
produce energy, the amount of energy produced is measured in BTUs
(British thermal units) per standard
cubic foot (scf ), with higher BTUs
indicating greater energy production.
One BTU is the amount of energy
it takes to heat 1 pound of water by
1˚ F. Because of the composition of
the natural gas varies, the potential
energy production from Devonian
natural gas ranges from 900-1300
BTUs per scf.2
What is an Unconventional
Natural Gas Resource?
The Marcellus Shale is referred to
as an unconventional source of natural gas because of the way natural gas
is trapped within the rock. Conventional sources of natural gas are often
found in permeable, porous rocks
(like sandstones), where natural gas or
oil flows toward an area of lower pressure and eventually can consolidate
the resource in ‘pools’ or ‘pockets.’
Extracting conventional resources requires locating a pocket and removing
the oil or gas.
In unconventional resources like
the Marcellus Shale, the natural gas
is stored within the pores of the shale
and unable to flow because of the
very low permeability of the shale.
Therefore, extracting unconventional
resources requires both horizontal
drilling and hydraulic fracturing to
create pathways that increase the porosity and permeability of the shale,
and allow the natural gas to travel
to the wellbore. Because natural gas
trapped in the Marcellus Shale has
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not migrated outside of the shale, gas
companies drilling into the Marcellus
are guaranteed to drill into commercial quantities of natural gas, however
the extraction methods are more expensive and labor intensive.
Gas drilling activity in the Marcellus has emerged rapidly in our region
due to three separate, coincident developments: rising natural gas prices
and increased commercial demand,
revised estimates of the amount of
natural gas stored in the Marcellus
The Reason for the Boom
Shale basin, and advances in drilling
Scientists have been aware of the
technology. Around 2000, natural
natural gas in sedimentary rocks of
gas prices began to rise dramatically,
the Appalachian Basin for over 150
and have remained relatively high
years. Fredonia, NY began to run
to date. Considering that national
gas-powered streetlights and to power predictions expect the demand for
local establishments
natural gas in the
in town as early as
U.S. to rise by 20%
National predictions
1825. Geographiby 2035, finding an
expect that natural
cally, the Marcellus
economical way to
gas consumption in
Shale gas basin is
extract natural gas
the largest in the
contained in unconthe U.S. will increase
U.S. However, beventional resources
20%
by
2035.
cause of the lower
became more imporpermeability and
tant to oil and gas
porosity of the Marcellus, the natural companies.
gas has been impossible to extract in
In 1980, the National Petroleum
commercial quantities with convenCouncil estimated that, on average,
tional technology. For this reason, it
gas content in the Marcellus Shale
was not considered a potential source was about 0.5 trillion scf (standard
for fossil fuel extraction until recentcubic feet).3 In 1988, this estimate
ly, and is called an “unconventional”
was dramatically revised to 26.5 trilresource.
lion scf 4, and in 2008 the estimate
Commercial prices for Natural Gas ($) per MMBtu
14
12
10
8
6
4
2
0
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
Fig. 4. Commercial natural gas prices have dramatically increased in the last ten years from
around $4-$5 per MMBtu to around $10 per MMBtu. (EIA citation)
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increasingly important to understand
the scientific issues associated with
development. This is the first issue in
a series of papers addressing Marcellus
Shale natural gas origins, distribution,
exploration and removal, and the associated environmental impacts.
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References
Forecast for Future Natural Gas Consumption (in tcf)
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1. Arthur, J.D., B. Bohm, and M. Layne,
2008, Hydraulic fracturing considerations for natural gas wells of the MarFig. 5. Forecast of Future Natural Gas Consumption. National energy plans predict that natucellus Shale, ALL Consulting.
ral gas consumption in the U.S. will increase 20% by 2035.7
2. Moore, B.J., and S. Sigler, 1987, Analyses of natural gases, 1917-1985, U.S.
Bureau of Mines Information Circular,
9129.
fracturing is a method of cracking
rose again to about 50 trillion scf.5
3. National Petroleum Council, 1980,
the rock with high volumes of water
Most recently, based on actual proUnconventional gas sources, volume
along the well bore to release the
duction data in the Marcellus Shale
III: Devonian Shale: Report prepared
for the U.S. Secretary of Energy, June,
natural gas from the shale, a process
gas play, the amount of natural gas
1980, National Petroleum Council,
sometimes called “stimulation.” Water
estimated to be extractable in the
Washington, D.C., 252 pp.
Marcellus increased again to 363 tril- used in hydraulic fracturing contains
4. Soeder, D.J., 1988, Porosity and permechemicals that play an important role
lion scf.6
ability of eastern Devonian gas shale,
in the extraction of the natural gas,
Concurrently with the increasing
Society of Petroleum Engineers Formation Evaluation, Society of Petroleum
price of natural gas and the exponen- and a large quantity of water (3 to 5
Engineers, 3:2, p. 116-124.
million gallons) is used per well durtial growth of estimated gas extrac5. Engelder, T., and G. Lash, 2008, Maring the process. Together, the process
tion potential in the Marcellus, two
cellus shale play’s vast resource potential
separate existing drilling technologies is called high-volume, slickwater hycreating stir in Appalachia, American
– hydraulic fracturing and horizontal draulic fracturing.
Oil and Gas Reporter, 51:6, p. 76-87.
6. Esch, M., 2008, Estimated gas yield
drilling – began to be successfully
from Marcellus shale goes up, InterSummary
combined for extracting natural gas
national Business Times, November 4,
Considering the rapid pace of Marfrom low permeability, ‘tight’ shales
2008.
like the Marcellus. Horizontal drilling cellus Shale development in Pennsyl- 7. United States Energy Information Asallows a well to be drilled along nearly vania, and of unconventional resourcsociation, 2010, accessed www.eia.doe.
gov, June, 2010.
es throughout the U.S., it is becoming
horizontal layers of rock. Hydraulic
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Partnering Organizations include
Funded by NSF GEO No. 1016359.
Cornell Cooperative Extension (naturalgas.cce.cornell edu),
New York State Water Resources Institute
(wri.cornell.edu), Cornell University Department of
Earth and Atmospheric Sciences, and
Cornell University Agricultural Experiment Station.
Any opinions, findings, and conclusions or
recommendations expressed in this material
are those of the author(s) and do not necessarily reflect the views of the National
Science Foundation.
Authored by Trisha A. Smrecak and the PRI Marcellus Shale Team
Illustrations by J. Houghton unless otherwise attributed.
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