Still awaiting a patent in the U.S., the technique has been used about 1,000 times since 2008, mainly in gas wells in the Canadian provinces of Alberta, British Columbia and New Brunswick and a smaller handful of test wells in states that include Texas, Pennsylvania, Colorado, Oklahoma and New Mexico, said GasFrac Chief Technology Officer Robert Lestz.Like water, propane gel is pumped into deep shale formations a mile or more underground, creating immense pressure that cracks rocks to free trapped natural gas bubbles. Like water, the gel also carries small particles of sand or man-made material—known as proppant—that are forced into cracks to hold them open so the gas can flow out.Unlike water, the gel does a kind of disappearing act underground. It reverts to vapor due to pressure and heat, then returns to the surface—along with the natural gas—for collection, possible reuse and ultimate resale.And also unlike water, propane does not carry back to the surface drilling chemicals, ancient seabed salts and underground radioactivity.“We leave the nasties in the ground, where they belong,” said Lestz.