It's well known that the Marcellus black shale in northern Appalachia, which covers hundreds of square miles in five states (New York, Pennsylvania, Ohio, Maryland and West Virginia), contains natural gas. But now, two U.S. researchers have discovered that the reserves are much bigger than previously thought. They estimate that this gas field contains at least 168 trillion cubic feet of natural gas in place. And they suggest that the reservoir could deliver up to 516 trillion cubic feet. By comparison, the yearly consumption of natural gas worldwide is slightly above 100 trillion cubic feet. The U.S. currently produces roughly 30 trillion cubic feet of gas a year. Horizontal drilling techniques could help to recover about 50 trillion cubic feet of gas from the Marcellus. But read more...
You can see above fracture joints "in the Marcellus black shale within overturned beds just north of the Allegheny Front at Antis Fort, Pennsylvania. The view is looking north at the underside of bedding." (Credit: Terry Engelder and Gary Lash)
But what are these J1 and J2 joints? "The recent application of horizontal drilling as a means of extracting natural gas from black shales of the Appalachian Basin necessitates an enhanced understanding of the origin, orientation, distribution, and permeability of fractures in these source rocks. Black shales carry two regional joint sets (J1 and J2) that formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter. ENE-trending (J1) joints parallel the maximum compressive normal stress of the contemporary tectonic stress field (SH) and are crosscut by NW-trending (J2) joints. Horizontal drilling should target J1 by drilling to the NNW to take advantage of a permeability anisotropy arising from the more densely developed J1 set that is subject to a lower normal stress." (Credit: Terry Engelder and Gary Lash)
It took 30 years to Terry Engelder, professor of geosciences at Penn State, and to Gary Lash, professor of geosciences at SUNY Fredonia, to complete this analysis. Engelder and Lash are also principals in Appalachian Fracture Systems Inc., a consulting firm.
Now, let's look at the Penn State University news release to learn how about 50 trillion cubic feet of gas could be recovered from the Marcellus field -- if the reservoir contains 516 trillion cubic feet as expected by Engelder and Lash. "Conservatively, we generally only consider 10 percent of gas in place as a potential resource," says Engelder. "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."
But horizontal drilling is not as common as vertical drilling. Why? Because the costs are higher. "It takes $800,000 to drill a vertical well in the Marcellus, but it takes $3 million to drill a horizontal well," says Engelder.
In an article titled "Massive gas field detected," the Centre Daily Times, Pennsylvania, gave additional details. "A deep reservoir of long-hidden natural gas, stretching from New York through Pennsylvania and into West Virginia, could pump more than $400 billion into the Mid-Atlantic economy and push the U.S. toward energy independence, a Penn State researcher has found."
Adam Smeltz, the author of the article, wrote that it could give the U.S. some additional time to solve the problem of energy dependence. "Engelder said the gas, lodged 6,000 to 7,000 feet underground, promises the U.S. 'a certain amount of energy security down the line.' 'This is America's resource,' he said, likening the find to the oil discoveries near Oil City in the early 1900s. 'The impact that this has on America is immeasurable.'"
For more information, you should read a paper written by Engelder and Lash, "Systematic joints in Devonian black shale: A target for horizontal drilling in the Appalachian Basin" (PDF format, 19 pages, 489 KB, courtesy of the Pittsburgh Association of Petroleum Geologists (PAPG)). The two researchers will present some of their recent work at the 2008 American Association of Petroleum Geologists Annual Convention and Exhibition this spring.
Finally, you should read the latest official energy statistics about natural gas published by the U.S. governmentin its International Energy Outlook (May 2007). It's a very instructive document with lots of charts.
Sources: Penn State University news release, January 17, 2008; Adam Smeltz, Centre Daily Times, Pennsylvania, January 18, 2008; and various websites
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