Extracting natural gas from the Marcellus Shale requires different extraction methods than the kinds
needed to extract gas from pockets underground. The Marcellus Shale is classified as a tight shale, which
means that there are few connections between pore spaces through which the gas can travel to collect in
large pockets. It is possible to crack such rocks to release the gas trapped within them. The Marcellus Shale
is also a relatively thin layer of rock (usually about 100 feet thick or less).1 As a thin, tight shale, conventional natural gas recovery methods are impractical for economic recovery of natural gas. To address these
challenges, two processes – horizontal drilling and hydraulic fracturing – are being combined to recover
natural gas from the Marcellus Shale and other tight shales