Shale gas is a natural gas produced from shale, a type of sedimentary rock. Due to constant announcements of shale gas recoverable reserves, as well as drilling in Central Asia, South America and Africa, deepwater drilling, estimates are undergoing frequent updates, mostly increasing. Since 2000, some countries, notably the US and Canada, have seen large increases in proved gas reserves due to development of shale gas, but shale gas deposits in most countries are yet to be added to reserve calculations. Some analysts expect that shale gas will greatly expand worldwide energy supply. Figure  shows the major shale gas fields of the word. China is estimated to have the world's largest shale gas reserves followed by USA, Argentina, Mexico, South Africa,
Australia, and Canada

 World Shale Gas

The United States and Canada are the major producers of commercially viable natural gas from shale formations in the world, even though about a dozen other countries have conducted exploratory test wells. China is the only nation outside of North America that has registered commercially viable production of shale gas, although the volumes contribute less than 1% of the total natural gas production in that country. In comparison, shale gas as a share of total natural gas production in 2012 was 39% in the United States and 15% in Canada.

SHALE GAS IN INDIA

Shale gas has reduced America’s dependence on oil imports, leading other countries to look for such reserves. India, too, has potential to reduce its dependence on imports by tapping the potential of shale gas. Six onshore basins — Cambay, Krishna-Godavari, Cauvery, Assam-Arakan, Ganga and Gondwana/Damodar—have been identified for shale exploration. The Indian Government entered into a MoU with the United States Geological Survey (USGS) to conduct an assessment of the shale gas resources. According to the US Energy Information Administration, India could be sitting on as much as 96 TCF of recoverable shale gas reserves, equivalent to about 26 years of its gas demand, compared with its 43.8 TCF of natural gas reserves at the end of 2012. Another estimate, by Schlumberger Company, has indicated a shale gas resource base of between 600 Tcf and 2,000 Tcf.

Krishna Godavari basin, located in eastern India, is considered to hold the largest shale gas reserves in the country. The basin is estimated to have around 27 Tcf of technically recoverable gas. The Cauvery basin in Tamil Nadu state is estimated to have recoverable shale gas reserves of 7 Tcf. The Cambay basin in Gujarat is the largest basin in the country, spread across 51,800 sq km. As per the initial studies, around 20 Tcf of gas is estimated as technically recoverable reserves in the Cambay basin. ONGC had drilled the country’s first shale gas well in Jambusar in the October in 2013 to exploit the natural gas trapped within the shale formations located in Cambay basin.