The Bent of Tau Beta Pi did a nice piece titled

“There’s Gas in Them Thar Shales!  Shale Gas Recovery 101”

 Revolutionary engineering developments that have made shale gas economically feasible in the last  decade are horizontal drilling and multistage hydraulic fracturing.

To learn more about shale, read on here:

http://www.tbp.org/pubs/Features/Su13Bell.pdf