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History of the shale

Wednesday, September 29th, 2010



(Photo: The vertical line through the center of this shale outcrop near Bald Eagle State Park in Pennsylvania is a natural fracture caused by a build up of pressure.)

Marcellus Shale formation. Click to enlarge. (Source: USGS)

Marcellus Shale formation. Click to enlarge. (Source: USGS)

Though there were a few hesitant stabs before 2008, the gas industry didn’t start seriously extracting natural gas from Pennsylvania’s rich Marcellus Shale until two years ago. Since then companies have sunk hundreds of wells into Pennsylvania’s gas play — and they’ve sunk hundreds of millions of dollars into swooping up leaseholds to control access to the fuel. In a short span, a world of controversy, environmental concern and economic windfall has developed. In Terry Engelder’s meticulous memory, January 17, 2008 is a sign post in the course of gas extraction that changed everything.

But more on what happened on that date later. First, let’s go back. Way back. Back before the first drill bored it’s way a mile down through the rock to reach the trapped gas. Back before drills even existed. Before Pennsylvania existed. Back hundreds of millions of years to when the continents were still forming.

As Engelder, a geology professor at Penn State University, explains it, algae in the sea died and drifted down upon the ocean floor, forming thick sediments. “Oceanic road kill,” he calls them, “green slime.” As the slime degraded, it became buried and preserved among other debris, eventually forming rock. “Typical shale is clay minerals, quartz, silt, a little bit of detrital feldspar and a sprinkling of pretty much everything else,” says Juergen Schieber, a professor at Indiana University. As this hodgepodge rock warmed and the organic material from the algae broke down, little pores formed, filled with hydrocarbons — including the methane that makes up natural gas.

Engelder stands at the foot of a vertical face of shale outcrop in central Pennsylvania. “I find it extraordinarily fascinating to think of Devonian oceans – 389 million years ago – teeming with these algae…And the atoms from that green slime, the carbon and hydrogen atoms from that green slime then come out of the rock 389 million years later as methane.”


Terry Engelder uses a chalk rubbing on a piece of shale to illustrate how a natural fracture fans out through the rock.

Terry Engelder uses a chalk rubbing on a piece of shale to illustrate how a natural fracture fans out through the rock.

Three years ago Engelder was on a conference call about natural gas, when someone asked him how much gas the Marcellus Shale contained. For all his years of working on shale, he didn’t know the extent of its most valuable resource.

“So that night I sat down and did the calculation, and ended up saying, jeepers creepers, that’s a lot of gas in there!” Engelder checked the estimate from the US Geological Survey. It was wildly different from his own number. Engelder didn’t believe his own math: 50 trillion cubic feet of recoverable gas, 500 trillion cubic feet of total gas in the rock. Engelder’s colleague fact checked the work and it held up.

On January 17, 2008 Penn State put out a press release of the estimated gas volume. “The reporters have not stopped calling since then,” Engelder says. “Including you.”

Engelder considers his estimate a magnet that drew the drills to Pennsylvania. Matt Pitzarella, a spokesman for the gas exploration and production company Range Resources, says the industry was already on its way. “People had always known there was natural gas in shale formations. In fact, people had been drilling through the Marcellus since the 1950s,” Pitzarella says. Drillers just didn’t know how to extract the gas in any efficient way.

Terry Engelder holds a piece of black shale.

Terry Engelder holds a piece of black shale.

Range had been drilling for gas in the Barnett Shale near Fort Worth, Texas for years. Pitzarella says the Barnett and Marcellus are similar, and the company exported its drilling technology to Pennsylvania in 2004 with a well dug in Washington County. It was “the first modern Marcellus shale well and really the well that unlocked this resource for the country and the Commonwealth,” Pitzarella says.

In 2005 the company began horizontal drilling, a technique that crosses the shale laterally, providing access to more gas reserves. Pitzarella says one horizontal well produces the same amount of gas as nine vertical wells in the Marcellus. Dozens of horizontal wells now worm through the Marcellus shale, with numerous permits granted for more. The US Department of Energy estimates now that there are 262 trillion cubic feet of “technically recoverable gas” (gas available for extraction), the largest gas play in the United States.


In his office at Penn State, Engelder looks through a copy of Playboy magazine. The feature that month is about natural gas in the Marcellus shale, an example of just how widespread interest in this gas play has become. It’s not just the volume of gas, Engelder says, but the structure of the rock that has made the Marcellus the target of so much industry interest.


Penn State professor Terry Engelder demonstrates what natural
fractures look like in the shale. Through hydraulic fracturing
(“fracking”) gas companies prop open fractures like these to extract
natural gas from the Marcellus shale.
(Video by Kerry Grens. Edited by Kimberly Paynter)

While drilling through the shale, companies crack the rock to prop open crevices where deposits of natural gas are trapped (the process is called fracking or hydraulic fracturing). The fractures allow the gas to seep into the well bore for collection. Engelder studies naturally occurring fractures; those that have been there for eons. When the gas is produced in the shale and becomes pressurized, the pressure splits the rock. The Marcellus shale is chock full of natural fractures, making it easier for gas companies to extract gas. “Fractures are good for business, ” says Schieber at Indiana University. “If you have enough natural fractures, it’s much cheaper to drill a production well than if you do not have them.”

At the shale outcrop in central Pennsylvania near Bald Eagle State Park (see the accompanying video on this page), Engelder points out natural fractures. They are perfectly parallel, razor-thin lines coursing vertically through the rock. Each vertical fracture is about six to 24 inches apart from one another. “The planarity of these things is as perfect a plane as any made in nature,” Engelder says with reverence.

Marcellus wells are expensive to construct, but that has not deterred companies from building them. There is estimated to be a trillion dollars’ worth of resource trapped beneath the hills of Pennsylvania, New York and West Virginia. Schieber and Engelder both support industry taking advantage of it, because of gas’s lower-carbon emissions than oil or coal. “To build a complete full-fledged alternative energy economy — wind and solar and so forth — it will take decades,” Shieber says. “In the mean time we need something to bridge that gap and gas is sort of natural for that.”


One Comment

  • Joe LaPann says:

    My primary concern with respect to water quality with Marcellus Shale drilling and completion methods is potential impact to overlying drinking water aquifers. Potable water resources have been severely compromised in areas of historic coal production in the state and we don’t want to repeat that mistake. I wonder how private wells may be contaminated by methane and frac fluids as reported at Dimock and elsewhere in the shale play. Is it always a result of poor cement bonding between casing and the vertical borehole thus allowing gas/fluids to migrate up the borehole and out into water bearing zones, or is it possible that vertical migration occurs out in the formation during the fracing process by following naturally occuring vertical fractures as demonstrated by Dr. Engelder in the photo? PADEP should be adequately staffed to review cement bond logs and any specialized geophysical logs portraying results of hydraulic fracturing in the formation for every well drilled. In areas of the play such as in State Forests where there are no private wells to monitor the effects of drilling there should be a requirement to install ground water monitoring wells.

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