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Researchers Say Horizontal Drilling Key to Tapping Unconventional Natural Gas Reservoirs in Pennsylvania; Could Boost Proven US Reserves by Trillions of Cubic Feet

Natural gas distributed throughout the Marcellus black shale in northern Appalachia could conservatively boost proven US reserves by trillions of cubic feet if gas production companies employ horizontal drilling techniques to exploit natural fracture patterns, according to a Penn State and State University of New York, Fredonia, team.

Terry Engelder, Penn State professor of geosciences, working with Gary Lash, professor of geoscience, SUNY Fredonia, has estimated that the Marcellus shale contains 168 trillion cubic feet of natural gas in place and optimistically suggests that the amount could be as high as 516 trillion cubic feet.

The US currently produces roughly 30 trillion cubic feet of gas a year, and these numbers are dropping. According to Engelder, the technology exists to recover 50 trillion cubic feet of gas from the Marcellus.

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.

—Terry Engelder

Engelder began looking into fractures under a National Science Foundation grant 25 years ago and has identified and mapped natural fractures in the Marcellus shale.

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 Virginia. In Pennsylvania, the formation extends from the Appalachian plateau into the western valley and ridge. 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.

The natural fractures in the Marcellus shale are the key to recovering larger amounts of gas. As heavily organic sediments were laid down 365 million years ago, the black shale of the Marcellus formed. 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 area.

The patterns of fractures in the shale determine which are important for gas production. Fractures that correlate with the folding of the ridge and valley system—as in the Marcellus—are less common in black shale. 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 together. 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.

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 be reused.

It takes $800,000 to drill a vertical well in the Marcellus, but it takes $3 million to drill a horizontal well. We can go back to wells that are already drilled and played out, and then drill horizontal from there. Reusing old wells has both economic and environmental value.

—Terry Engelder

Engelder and Lash will present some of their recent work at the 2008 American Association of Petroleum Geologists Annual Convention and Exhibition this spring. Engelder and Lash are principals in Appalachian Fracture Systems Inc., a consulting firm.



There were these 2 guys.................................

What a story of multi layers of research & accomplishment!

There were these 2 guys.................................

Rafael Seidl

According to EIA, total proven natural gas reserves in the US currently stand at around 211 trillion cu. ft. If these scientists are right, horizontal drilling in this one vast field would double or triple those reserves.

While tapping into yet more fossil fuel reserves isn't good news for global warming, the location near the densely populated East Coast is. The gas could be used to avoid building additional coal-fired power stations, preferably with district heating to gradually reduce the consumption of heating oil aka diesel which is more valuable as a transportation fuel now that T2B5 can be met. Of course, the NG can also be used directly as a transportation fuel.


I hope the fractures will be refilled with CO2 once they're empty.
since the pipes are already in place, it should relatively easy.


It would be good to develop more NG in the U.S. I would prefer that to LNG and I would like to see more duel fueled cars to use it as well.


Given the Northeast's reliance on natural gas for electricity generation, this is a very good thing, and there's probably a lot more out there that will be accessible with this drilling technique. I wonder how it compared with the Microdrilling technology from about a year ago.

Mad Max

Compressed natural gas can be used as a car fuel in place of gasoline. Engines need a very small adaptation and run smooth and clean


Europe has dual fueled vehicles that run on both CNG and gasoline. If you run out of CNG, it switches over automatically. Some service trucks in the U.S. do this. With adsorption methods we can get more stored CNG in a smaller space at lower pressure.


usuall high standard of comments,
I wished phhooph that new cleaner energy sources meant less dirtier, fossils and a sensible approach, then I woke up.

Harvey D


If NG becomes much more plentiful, new power plants and many existing coal fired power plants could be modified to use NG instead of coal? That would reduce the CO2 & GHG foot print very quickly.

However, doubling (+) the NG reserves would not last that long and other clean electricity production sources such as wind-sun-nuclear etc would have to be seriously considered to feed 200 (+) million PHEVs/BEVs, electrified trains, industries, commercial activities and domestic HVACs.

Harvey D

USA's NG consumption has been rather steady @ about 20 to 22 Tcf/year since 1970. Local production is around 19 Tcf/year. The difference is made up with imports from Canada.

Boosting reserves from about 222 Tcf (about 10 years) to over 550 Tcf (about 25 years) could be a whorthwhile advantage for the energy mix. Consumption could be increased with more NG power plants and/or imports could be curtailed.

Either way, many existing NG pipelines + empthy NG wells will become available to store unwanted captured CO2.


Thanks for the comments. I am looking for information on horizontal deep well there any information that will cover this topic?

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