At the center of it are the environmental consequences of Fracking (that's hydraulic fracturing) and the same issue which dogs oil, the difference between easily accessible reserves and those which may, someday, somehow, and at great cost be recovered. That last part first: Author Daniel Botkin, professor emeritus of UC Santa Barbara, points out that the USGS lists natural gas with four categories of reserves. 1% are 'readily available with current technologies', 5% are 'technically recoverable', 6% are 'marginal targets for accelerated technology', and the remaining 84% are 'unknown but probable'. Shale gas is in that last category.
And here's the environmental impact:
Separating the gas from the shale, a process known as hydrofracturing, involves forcing a mixture of water, chemicals, and sand at high pressure down a well bore and into rock formations, creating small fractures that release the trapped gas. The process uses a huge amount of water -- the New York State Department of Environmental Conservation estimates as much as 1 million gallons per well -- at a time when water is already a limiting and precious resource. Second, hydraulic fracturing fluid may come back to the surface, or near enough, to affect groundwater supplies. This fluid is a mixture of chemicals including friction reducers, biocides to prevent the growth of bacteria that would damage the well piping or clog the fractures, a gel to carry materials into the fractures, and various other substances. Returning to the surface, it could also bring other environmentally damaging materials, such as heavy metals.
This is something that TreeHugger and others have covered a number of times, and read the original for more info, but the the bigger principle the remember is that, albeit with different technology, this is the same story with every fossil fuel. If the environmental impact of the easily accessible sources is at one level, as reserves get depleted we can likely develop the technology to tap into harder to reach sources but the costs (both financial and environmental) just keep going up.
It's tempting to keep going down this road of familiarity, but the real solution is to take another fork. As most TreeHugger readers probably are aware, and as Prof Botkin points out, the only way the United States can really be energy independent (and do so without increasing health and environmental damage) is to develop and deploy solar and wind power. I'd add, combined with radical reductions in energy demand.
More on Natural Gas:
Does Converting Utility Vans to Natural Gas Make Sense?
Natural Gas Use to Double in US in Coming Decades: MIT Report
Because of Methane Leaks, Natural Gas Could Be As Bad As Oil & Coal