Shale gas and other hydrocarbons, trapped within massive shale formations, has become an important source of natural gas and oil in the United States since the start of the 21st century and interest has spread to potential gas shales across the rest of the world. Europe now stands at having an estimated 21 trillion cubic feet, as indicated in the latest environmental impact studies by the US Energy Information Administration (EIA). In 2000 shale gas resources provided less than 1% of total US natural gas production, but by 2010 shale gas accounted for over 20% and the EIA predicts that by 2035, 46% of the United States' natural gas supply will come from shale reservoirs. Some analysts expect that shale gas will come to play an expanding role in world energy supply with potential shale gas and shale oil reservoirs in India, Romania, France, Austria, Poland, Ukraine, Saudi Arabia, Russia and China are but a few countries having large estimated unconventional resources. Today, low permeability source rock (including shale gas, tight-sand gas, and coalseam gas) is made economically productive in wells drilled and hydraulically fractured (propagating fractures in the hydrocarbontrapped rock layers). This fracturing is done by pumping fluids carrying proppant including sand, sintered bauxite and similar materials and pressurising the formation until it fractures. The fractures will continue to propagate, typically horizontally, away from the wellbore until the pumping pressure decreases below the fracturing pressure of the formation. The proppant serves to hold the fractured pathways open, creating what is termed 'conductivity' for the release of liquid hydrocarbons or natural gas. The combination of two existing technologies, horizontal drilling and hydraulic fracturing, has made it possible to tap into this hydrocarbon-resource, leading to a shale gas and oil revolution that is seeing thousands of horizontal wells drilled and completed annually.
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