ENERGY IN CONTEXT: A FOSSIL FUEL PRIMER - Hydrofracking: What Everyone Needs to Know - page 11

over 20 percent, and by 2035 the EIA estimates that 46 percent of US natural gas
will come from shale gas. 45
Today, “Technically recoverable unconventional gas”—which refers to shale
gas, tight sands, and coal bed methane—account for 60 percent of America's on-
shore reserves. According to the EIA, these resources could supply the nation for
the next 90 years. (Other estimates predict the supply could last even longer.) 46
What Is Tight Gas?
Tight gas is natural gas that is trapped in areas of low-porosity silt and sand. Tight
gas has less than 10 percent porosity and less than 0.1 millidarcy of permeability.
Porosity is the proportion of void space to the total volume of rock. While beach
sand has a porosity of about 50 percent, tight gas is trapped in pores up to 20,000
times narrower than a human hair.
Permeability is the ability of fluid to move through pores. A person can blow
air through rock with 1,000 millidarcies permeability. 47
What Is Sour Gas?
In certain regions, like the Rocky Mountains, natural gas is mixed with elevated
levels of sulfur, which creates the corrosive gas H 2 S, or hydrogen sulfide. Known
as sour gas, H 2 S requires extra processing to purify it.
What Is Shale Oil?
These are heavy, viscous crude deposits that cannot be produced and refined by
conventional methods. Heavy crude oils usually contain high concentrations of sul-
fur and a number of metals, particularly nickel and vanadium. These properties
make them difficult to pump out of the ground or through a pipeline and interfere
with refining. These properties also create serious environmental challenges. 48 The
best-known reserve of shale oils is Venezuela's Orinoco heavy oil belt, which con-
tains an estimated 1.2 trillion barrels.