This July 25 article from the Calgary Herald explains in a simple manner how the technology of fracing has revolutionized the oil  and gas industry in North America, and really around the world.

Fracing (pronounced “fracking”) happens after drilling a well.  Companies send fluids down oil and gas wells at very high pressures, and that fluid goes out into the rock formation that holds the hydrocarbons, cracking it up so that the oil or gas can flow to the well bore.

Most oil and gas are actually held in underground sand formations, but fracing has allowed the much better retrieval of gas held in actual rock. 

http://www.calgaryherald.com/Packers+Plus+leads+drilling+revolution/1828440/story.html