https://phys.org/news/2019-01-physics-big-gains-shale-oil.html

"Unconventional reservoirs are enormous and offer significant hydrocarbon reserves," said Hamid Emami-Meybodi, assistant professor of petroleum and natural gas engineering at Penn State. "The scale of these reserves means that even a 1 percent change in recovery translates into a staggering quantity of oil. This untapped oil has motivated research on improved oil recovery from unconventional reservoirs using some conventional techniques."

More than half of the daily oil produced in the United States comes from unconventional formations. And that number is growing as companies tap into the nation's more than 35 billion barrels of oil in unconventional reserves, according to the U.S. Energy Information Administration.