complete the first successful air-drilled multi-fracture horizontal well in shale in 1986. The federal government further incentivized drilling in shale via the Section 29 tax credit for unconventional gas from 1980–2000. Microseismic imaging, a crucial input to both hydraulic fracturing in shale and offshore oil drilling, originated from coalbeds research at Sandia National Laboratories. The DOE program also applied two technologies that had been developed previously by industry, massive hydraulic fracturing and horizontal drilling, to shale gas formations, which led to microseismic imaging. Although the Eastern Gas Shales Project had increased gas production in the Appalachian and Michigan basins, shale gas was still widely seen as marginal to uneconomic without tax credits, and shale gas provided only 1.6% of US gas production in 2000, when the federal tax credits expired. George P. Mitchell is regarded as the father of the shale gas industry, since he made it commercially viable in the Barnett Shale by getting costs down to $4 per . Mitchell Energy achieved the first economical shale fracture in 1998 using slick-water fracturing. Since then, natural gas from shale has been the fastest growing contributor to total primary energy in the United States, and has led many other countries to pursue shale deposits. According to the IEA, shale gas could increase technically recoverable natural gas resources by almost 50%. In 2000 shale gas provided only 1% of U.S. natural gas production; by 2010 it was over 20% and the U.S. Energy Information Administration predicted that by 2035, 46% of the United States' natural gas supply will come from shale gas. The Obama administration believed that increased shale gas development would help reduce greenhouse gas emissions.<ref>{{cite web |date=2009-11-17 |title=Statement on U.S.-China shale gas resource initiative |url=http://www.america.gov/st/texttrans-english/2009/November/20091117145333xjsnommis0.4233515.html&distid=ucs |access-date=2013-08-06 |publisher=America.gov}}</ref> Geology Because shales ordinarily have insufficient permeability to allow significant fluid flow to a wellbore, most shales are not commercial sources of natural gas. Shale gas is one of a number of unconventional sources of natural gas; others include coalbed methane, tight sandstones, and methane hydrates. Shale gas areas are often known as resource plays (as opposed to exploration plays). The geological risk of not finding gas is low in resource plays, but the potential profits per successful well are usually also lower. Shale has low matrix permeability, and so gas production in commercial quantities requires fractures to provide permeability. Shale gas has been produced for years from shales with natural fractures;