Natural gas

Fracking by David W. Coffin (not for reuse)

N atural gas is a blend of hydrocarbon gases, primarily methane. Like oil and coal, it is a fossil fuel that can be refined to produce energy. Scientists believe fossil fuels are formed when the remains of plants, animals, and microorganisms are compressed under high pressure beneath the earth’s surface for a long period. Unlike oil and coal, natural gas is considered clean burning; it produces lower levels of potentially harmful emissions.

• Oil is created at lower temperatures than natural gas. Natural gas tends to be more abundant than oil as you go deeper into the earth, where the temperature increases. In the 1820s, scientists knew that large deposits of natural gas were embedded in shale, and commercial drilling was first attempted, with limited success.
• Beginning in 1947, a process called hydraulic fracturing, or “fracking,” was applied to limestone and sandstone deposits to extract natural gas. Fracking is also used to extract natural gas from shale; this is more difficult than extraction from limestone and sandstone. The method involves injecting a combination of sand, water, and chemicals into a well bore at high pressure, which fractures the rock and opens millions of cracks. Gas seeps through these cracks into a pipeline. Improvements to a technique called massive hydraulic fracturing, which was developed in the late 1970s, started the modern gas boom. In 1998, slick-water fracking (adding friction-reducing chemicals to water to increase the fluid flow) was introduced. Today, a new drilling method – high-volume horizontal hydraulic fracturing, or “hydrofracking” – is in use.
• Shales now yield more than 25 percent of American natural gas resources, up from 2 percent in 2001. The U.S. Energy Information Administration estimates that the world has 6,622 trillion cubic feet of recoverable shale gas resources. China has the largest supply; the United States is second. Mexico and Canada also have large supplies, making North America the continent with the greatest shale gas resources. The largest shale gas formation in North America is the Marcellus Shale, the bulk of which is in Pennsylvania, Ohio, New York, and West Virginia.
• Environmental concerns about fracking relate to its possible impact on the water supply. Wastewater associated with shale gas extraction can contain fracturing-fluid additives and chemicals including the carcinogen benzene and naturally occurring radioactive materials.
• By 2009, the United States had 493,000 active natural gas wells across 31 states. About 90 percent used fracking to get more gas flowing. Although the Environmental Protection Agency supervises regulations for underground drinking water, states set regulations for fracking. Vermont is the only state that has banned fracking. In 2010, the EPA announced a $1.9 million peer review study on the effect of fracking on water quality and public health, which may inform future policy decisions.