Many countries around the world have shown technically recoverable shale gas potential but as of now the commercially viable production is being done only few countries? Explain the reasons. How the twin techniques of horizontal drilling and hydro-fracking have revolutionized shale gas industry?

Technically recoverable shale gas potential has been shown by many countries including India but as of now, the commercial production is being done only in US, Canada and China. The reason for the same is geology of the shales which makes it difficult to be done in a commercially viable way. The insufficient permeability of shales makes it very difficult to allow significant fluid flow to a wellbore to extract the gas. Further, risk of not finding the gas is also very high with respect to shale gas. The less permeability of shales needs fractures to provide permeability and it is very costly with current technologies available.
Impact of twin techniques of horizontal drilling and hydro-fracking
Before these technologies were developed, shale gas was extracted through natural fractures. Whatever boom this industry has seen in recent years is mainly because of the development of these technologies. The reason is that the Horizontal allows to create maximum borehole surface area in contact with the shale while hydraulic fracturing allows to create extensive artificial fractures around well bores. Since shales are sufficiently brittle and rigid to maintain open fractures, these two technologies have revolutionized the shale gas industry and that is why shale gas is called bane for middle east / OPEC. Due to these two technologies, US has become number one shale gas producer around the world.