The Science of Shale Gas

Lighting a New Path
Photograph by Scott Goldsmith, National Geographic
Flares from newly completed natural gas wells paint an arresting image in the Pennsylvania sky.
But the fiery scene above ground—a controlled test burn-off of initial gas that takes place at some wells for several days—is not as dramatic as what is happening a mile beneath the surface. Producers are using high-volume hydraulic fracturing and horizontal drilling to unlock a natural gas resource that geologists have known about for 75 years.
Read article: "Forcing Gas Out of Rock With Water"
Published October 22, 2010
Energy Surge
Photograph by Scott Goldsmith, National Geographic
Generators line the drilling pad at a Range Resources natural gas well site in southwestern Pennsylvania.
The rigs for this "unconventional" gas production are larger and require more space than the traditional oil and gas equipment. Surface disturbance is likely to encompass four to six acres (1.6 to 2.4 hectares), compared to one-and-a-half to three acres (.6 to 1.6 hectares) at the conventional drilling sites that were typical in Pennsylvania before the shale rush, according to a National Park Service assessment. By Pennsylvania law, the sites are to be reclaimed within nine months of drilling, leaving only a small unit of pipes and valves at the wellhead commonly called a “Christmas tree," in place to capture gas that producers expect will be flowing for the next 30 years.
Published October 22, 2010
Water Challenge
Photograph by Scott Goldsmith, National Geographic
Some of the biggest challenges the shale gas industry faces are around water, since some 4 million gallons (15 million liters) of water are required for each drilling attempt, far more than the 100,000 gallons (379,000 liters) conventional wells in Pennsylvania typically required.
Man-made ponds like this one are now commonplace where shale drilling takes place. Lined with high-density polyethylene, the impoundments hold either fresh water needed for drilling, or the drilling wastewater that flows to the surface after the well is completed. Some companies are now reusing that wastewater for drilling new wells.
Published October 22, 2010
Preparing the Pipe
Photograph by Scott Goldsmith, National Geographic
Plenty of drilling pipe is needed to tap a well into the Marcellus shale, which is found at a depth of 4,000 to 8,500 feet (1,220 to 2,590 meters).
Just above the target, the driller begins to "land the curve," and continues to drill horizontally into the shale—typically a distance of 3,500 feet (1,070 meters) or more. By reaching more surface area, the producers are able to capture more fuel. Using the measure "Mcf," which translates to "thousand cubic feet," energy companies say horizontal wells in the Marcellus shale yield from 1 million Mcf to as high as 10 million Mcf or 15 million Mcf per day, compared to just 100 Mcf to 500 Mcf of natural gas per day for conventional Pennsylvania wells.
Published October 22, 2010
Drilling Down
Photograph by Scott Goldsmith, National Geographic
Cable is used to lower and move drilling pipe extensions at a natural gas well site in southwestern Pennsylvania.
Companies from around the world have been drawn to the Marcellus shale, the largest of the shale formations in the continental United States. The populous mid-Atlantic market pays a premium price for energy, at the same time that exploration and finding costs are dramatically lower in the Marcellus than in other shales around the United States. “It’s very repeatable,” says Matt Pitzarella, spokesman for Range Resources. Referring to the mostly rural region southwest of Pittsburgh where Range Resources drilled the first Marcellus well, company spokesman Matt Pitzarella says, “Every well in Washington County is either good or great."
Published October 22, 2010
Nothing But Blue Skies
Photograph by Scott Goldsmith, National Geographic
A flag waves high above the controller's booth on a drill rig in southwestern Pennsylvania.
The shale gas companies frame their role as a pivotal one in the big U.S. energy picture, and indeed, the prospect of abundant, cheap natural gas easily delivered by pipeline to East Coast markets profoundly shakes up the energy equation in the United States. Natural gas generates electricity more efficiently than coal, with half the greenhouse gas emissions, and it's free of many other troubling pollutants like mercury, particulates and acid rain precursors. Natural gas can also power vehicles; billionaire T. Boone Pickens and others argue the new domestic source could lessen the nation's foreign oil dependence.
Published October 22, 2010
The Drama Below
Photograph by Scott Goldsmith, National Geographic
Out of what looked like a failed gas well, Range Resources in 2004 was able to produce success.
The company's Great Lakes Energy division had drilled an unsuccessful well into a formation known as the Oriskany sandstone, the bread-and-butter target for the small oil and gas firms that still operated in Pennsylvania, plumbing for finds too trivial for major energy companies. After the well came up dry, Range geologist Bill Zagorski urged his bosses to forget the sandstone, and try for the Marcellus shale about 2,000 feet (610 meters) closer to the surface, using the method that had been recently perfected in Texas for coaxing gas out of the Barnett shale near Dallas-Fort Worth.
Published October 22, 2010
Water Ways
Photograph by Scott Goldsmith, National Geographic
Temporary pipelines wind through the farmland of southwestern Pennsylvania, where they are set up to carry fresh water from impoundments to drilling sites, and to transfer wastewater from drilling back to impoundments.
No public water system could provide shale gas drillers the volume of water at the rate needed—some 4,200 gallons (16,000 liters) per minute. To haul it would require 1,500 truck trips per well. So producers set up tanks or water impoundments and transfer systems around their operations. Range Resources says it has had water piped to drill sites from as far as seven miles (11.3 kilometers) away.
Published October 22, 2010
New Neighbors
Photograph by Scott Goldsmith, National Geographic
Natural gas condensation tanks are a new feature on the landscape where shale drilling is taking place.
In southwestern Pennsylvania, the shale gas is "wet," mixed with ethanes and other compounds that must be removed and sold separately. It makes the gas here more valuable, but means that processing facilities have to be built. Compressor stations also are needed to move the natural gas through the pipeline system. In Chartiers Township, one of the most active drilling locations in Pennsylvania, probably most of the complaints about the gas industry have been around the noise of compressor stations, says Harlan Shober, president of the township board of supervisors. But he believes that the community mostly has welcomed the gas industry, even holding public meetings to learn about the technology.
Published October 22, 2010
Rock of Promise
Photograph by Scott Goldsmith, National Geographic
Break open a piece of shale and it smells like natural gas.
Drillers have known of “shows” of gas from the shale, brief blasts that would blow their tools out of the well hole or tangle their equipment as they tried to find what they thought were more promising targets deeper underground. They assumed that the gas locked in the shale rock could never be recovered economically. But when it became clear that gas companies were successfully tapping the largest such rock formation in North America, the Marcellus shale, in December 2007, Pennsylvania State University geologist Terry Engelder calculated the potential reserves. “I remember thinking, ‘Merry Christmas, America, you don’t know what’s out there,’” he says. “It’s going to be a real treat.”
Published October 22, 2010
Waiting for Water
Photograph by Scott Goldsmith, National Geographic
It typically takes 90 days to fill a plastic-lined freshwater impoundment like this one with the millions of gallons of water needed for shale gas production.
And it takes just a couple of days to pump the water to a well to break up the shale and begin gas production. About 25 percent of the water flows back to the surface immediately, more is produced slowly over the life of the well. This drilling wastewater is more salty than seawater, and can develop a stench if it sits stagnant, because it is prone to bacterial growth. How to handle the water can be a challenge in Pennsylvania, which does not have many deep underground injection wells-—the standard disposal method in Texas. Some companies are now reusing wastewater to drill new wells, but others are looking at new methods that use distillation and crystallization to solve the problem.
Published October 22, 2010

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