Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shale basins in Canada, Europe, Asia and Australia, as per Reportlinker. Although shale gas has been produced for more than 100 years in the Appalachian Basin and the Illinois Basin of the United States, the wells were often marginally economical. Higher natural gas prices in recent years and advances in hydraulic fracturing and horizontal completions type of technology have made shale gas wells more profitable. Shale gas tends to cost more to produce than gas from conventional wells, because of the expense of massive hydraulic fracturing treatments required to produce shale gas. However, this is often offset by the low risk of shale gas wells. Shale gas contributed to nearly 17% of the total gas production in USA as of 2010. As per MarketsandMarkets, shale gas is an unconventional natural gas obtained from shale formations that act as both reservoir and source for natural gas. Geologic studies, seismic imaging and magnetometer tests, and geological surveys are undertaken to explore shale gas resources. The gas exists in shale in different forms as free gas in rock pores, natural fractures and absorbed gas on organic matter and mineral surfaces. The production wells are drilled either horizontally or vertically; most of which are hydraulically fractured to stimulate production. Global shale gas production is expected to grow from 4,130 billion cubic feet in 2011 to 6,991 billion cubic feet in 2021 at CAGR of 5.4%. Shale gas production is expected to become online from EMEA, Asia Pacific, and ROW by the year 2016 based on current exploration activities undertaken by major oil and gas companies. Global shale gas production is expected to grow from 5,563 billion cubic feet in 2016 to 6,991 billion cubic feet in 2021 at CAGR of 4.7% for the same period. The markets representing high growth rate from 2016 to 2021 are China (6.2%), Poland (6%), France (5.4%), South Africa (5.1%), and U.S. (5%). North America is expected to remain largest shale gas producer globally by the year 2021 with share of 78% followed by EMEA (13%), Asia Pacific (7%), and ROW (2%) due to technological expertise and availability of resources. The major drivers for shale gas market are identified as proved abundance of shale gas resources across the globe, improving supply and distribution infrastructure, decline in natural gas prices, and improvements in drilling technology. The capital intensive nature of shale gas projects and water contamination and usage issues for fracturing requirements hinder shale gas development. The opportunities are cited in probable increase in ethylene volumes through shale gas and new basins discovered in countries like Poland, China, and Australia. The increasing shale gas production is likely to boost ethylene production by 6.6% by 2021. The another challenge of reducing fracturing water requirement from average well consumption of 3.15 mln gallons/well can be overcome by water recycling and increasing well productivity. According to research, if well productivity is over 9 BCF/well, water requirement can be reduced by 35% than that required with average well productivity of 5.4 BCF/well. The largest shale gas repository in North America is the Marcellus formation that is primarily located in New York, Pennsylvania, West Virginia and Ohio. Others include Haynesville in the Southeast, Eagle Ford in Texas, and Horn River and Montney in Canada, as per Jonathan Katz in Industry week. The shale boom should contribute to an expected record for natural gas production in United States this year. Higher oil prices triggered demand for more natural gas supplies. This coupled with improvements in production technologies called hydraulic fracturing and horizontal drilling, were key drivers of the current natural gas boom. Long-term benefits from shale gas exploration include lower raw materials costs for chemical makers enabling them to double their exports as a share of total production over the past four years. Advances in new, and sometimes controversial, technologies have allowed oil and gas developers to extract natural gas from shale formations across North America more easily. Increasing proximity to feedstocks has created new opportunities for chemicals producers. Dow Chemical Co. announced a plan to build a new ethylene production plant in the Gulf Coast to take advantage of shale gas supplies in the Eagle Ford and Marcellus shale regions. Bayer Corp. has an industrial park in Institute, W.Va., with about 460 acres, that is located in the center of the Marcellus gas field, and is in discussions with chemicals companies that may be interested in building an ethane cracker at the industrial park. Like any advancing technology, the promise of shale gas does not come without its share of controversy or challenges. The primary one concerns hydraulic fracturing, or "fracking," a method used to extract gas from shale rock. As described in the IHS report, fracking involves injecting high-pressure fluids into a well to create fractures in the reservoir rock. The fractures allow the natural gas trapped in the rock to eventually flow toward the surface. The fluid typically comprises water and sand or another solid to keep the fractures open. Chemicals used in the process make up less than 1% of fracking fluid. Combining hydraulic fracturing with another technology called horizontal drilling was considered a major breakthrough in shale gas exploration around 2002-2003. Environmentalists are concerned that fracking fluids could contaminate groundwater.