Pastoral scene: Drilling for natural gas in the Marcellus shale is under way in rural areas of southwestern Pennsylvania and other parts of the state. Advocates argue that the process has only a marginal environmental impact and, once the drilling is completed and the well is producing, leaves a small footprint on the landscape. Critics worry that the chemicals and huge amounts of water required to stimulate the wells will damage the surrounding areas.
Range and other gas producers rely on drilling techniques that have been used for the past decade in the shale-gas fields of northeast Texas. Inside the trailer that serves as a field office, the complexity of the task is evident. On a wall is a chart mapping the drilling plans. The drill bit will head down more than a thousand meters through various types of sediments. Then, over the course of roughly 275 meters, it will gradually turn 90°, so that when it enters the layer of Marcellus shale at around 2,000 meters, it will be traveling horizontally through the gas-rich rock. Drillers can control the location of the bit to within several centimeters. Staying within a six-meter window, the bit will follow the Marcellus layer for up to 1,600 meters. The horizontal approach is crucial, allowing the well to tap into a large area of the shale layer. Eventually, the several wells at the site will spread out underneath the countryside, draining gas from hundreds of acres of shale.
The trickiest part of the operation comes after the drilling is done and the large rig is removed. A small armada of specialized equipment, including dozens of tanker trucks filled with water, will move in to perform a procedure called hydraulic fracture stimulation, or hydrofracturing, which is designed to get the gas flowing efficiently into the well. Although the Marcellus shale is soaked with gas, the rock holds the hydrocarbon tightly trapped. To allow it to escape, engineers will force millions of gallons of water down the well and into the shale formation at high pressure. If all goes well, the natural gas will rush out of the shale and into the pipe after the water is pumped back out.
That the process works is a tribute to the wonders of geology and the ingenuity of the drilling engineers. Like the black shale on the shores of Lake Erie, the Marcellus shale is riddled with tiny natural fractures created million of years ago as the newly formed hydrocarbon gases expanded. The high-pressure water, which is mixed with fine sand and chemical additives, works to enlarge those cracks. The results: gas-permeable zones of damaged rock a hundred or more meters across, radiating out from the well pipe.
Geologists like Gary Lash and Terry Engelder have long known that the black shale in the Appalachian basin contains large amounts of natural gas. In fact, the nation’s first natural-gas well was drilled in Fredonia, NY, in 1825, a few miles from Lake Erie; wooden pipes were built to transport the fuel so that it could light houses in the town. But the geologists have been surprised to discover that so much gas can be recovered economically. After Range released its initial drilling results in 2007, Engelder recalls, he was asked during a conference call with investors in New York just how much natural gas the Marcellus shale contained. It wasn’t a calculation he had ever bothered to do. Engelder remembers pausing and then answering, “I’m not sure, but by the end of the day I will be dead certain.” He did some calculations based on the size of the formation and the likely gas content of the rock; then he called Lash and asked him to do his own. The next day, Lash called back with his numbers. They had come to the same conclusion, says Engelder: “Holy cow, there’s a lot of gas.”