COMMONWEALTH OF PENNSYLVANIA
Dept. of Environmental Protection
Commonwealth News Bureau
Room 308, Main Capitol Building
Harrisburg PA., 17120
Unconventional Natural Gas Reservoir in Pa. Poised to Dramatically
Increase U.S. Production
18 January 2008
UNIVERSITY PARK -- Natural gas distributed throughout the
Marcellus black shale in northern Appalachia could conservatively
boost proven U.S. reserves by trillions of cubic feet if gas
production companies employ horizontal drilling techniques,
according to a Penn State and State University of New York,
"The value of this science
could increment the net worth of U.S. energy resources by a trillion
dollars, plus or minus billions," says Terry Engelder, professor of
geosciences, at Penn State.
The Marcellus shale runs from
the southern tier of New York, through the western portion of
Pennsylvania into the eastern half of Ohio and through West
In Pennsylvania, the formation
extends from the Appalachian plateau into the western valley and
This area has produced natural
gas for years, but the Marcellus shale, a deep layer of rock, is
officially identified as holding a relatively small amount of proven
or potential reserves.
However, many gas production
companies are now interested in the Marcellus.
Engelder, working with Gary
Lash, professor of geoscience, SUNY Fredonia, has conservatively
estimated that the Marcellus shale contains 168 trillion cubic feet
of natural gas in place and optimistically suggests that the amounts
could be as high as 516 trillion cubic feet.
"Conservatively, we generally
only consider 10 percent of gas in place as a potential resource,"
"The key, of course, is that
the Marcellus is more easily produced by horizontal drilling across
fractures, and until recently, gas production companies seemed
unaware of the presence of the natural fractures necessary for
magnifying the success of horizontal drilling in the Marcellus."
The U.S. currently produces
roughly 30 trillion cubic feet of gas a year, and these numbers are
According to Engelder, the
technology exists to recover 50 trillion cubic feet of gas from the
Marcellus, thus keeping the U.S. production up. If this recovery is
realized, the Marcellus reservoir would be considered a Super Giant
Engelder, who has studied this
area of the U.S. for most of his career and began looking into
fractures under a National Science Foundation grant 25 years ago,
has identified and mapped natural fractures in the Marcellus shale.
He and Lash will present some
of their recent work at the 2008 American Association of Petroleum
Geologists Annual Convention and Exhibition this spring.
The researchers look at the
patterns of fractures in the shale and determine which are important
for gas production.
Fractures that correlate with
the folding of the ridge and valley system are less common in black
However, because of their
orientation, the fractures that formed prior to the folding will
release gas if the wells cross the fracture zones.
These fractures, referred to as
J1 fractures by Engelder and Lash, run as slices from the northeast
to the southwest in the Marcellus shale and are fairly close
While a vertical well may cross
one of these fractures and other less productive fractures, a
horizontally drilled well aimed to the north northwest will cross a
series of very productive J1 fractures.
"It takes $800,000 to drill a
vertical well in the Marcellus, but it takes $3 million to drill a
horizontal well," says Engelder.
Companies that drill gas wells
need to be certain that horizontal drilling will produce the gas
they expect and the work by Engelder and Lash suggests that it will.
"We know that the Marcellus
shale appears as an outcrop near Batavia, N.Y., east of Buffalo,"
"And we can see the fractures
in the Marcellus in the exposed sections of the ridge and valley
areas to the southeast.
Because we see them going
through the folded areas, we know they were there before the
If it happened earlier, then we
know they have to be in the intervening basin as well."
The natural fractures in the
Marcellus shale are the key to recovering large amounts of gas.
As heavily organic sediments
were laid down 365 million years ago, the black shale of the
As the organic material decayed
and degraded, methane and other components of natural gas formed and
dispersed through the pores in the rock.
About 300 million years ago,
the pressure of the gas caused fractures to form in the shale.
It was not until 280 million
years ago that the eastern portion of Pennsylvania was pushed into
the folding of the ridge and valley province that makes up that
Gas that occurs in pockets
underground is considered a conventional reservoir; gas that is
distributed throughout the rock, like the Marcellus, is called an
The Penn State-Fredonia
approach is not restricted to production of the Marcellus shale, but
can be applied to any gas-bearing shale with this type of fracture.
Because the approach begins
with a vertical well and then drills horizontally in the direction
that will crosscut the productive fractures, old vertical wells can
"We can go back to wells that
are already drilled and played out, and then drill horizontal from
there," says Engelder.
"Reusing old wells has both
economic and environmental value."
Engelder and Lash are
principals in Appalachian Fracture Systems Inc., a consulting firm.
For more information,
website, keyword: Oil and Gas.
COMMONWEALTH OF PENNSYLVANIA