What is shale gas?

Last week, the government released its draft policy on auction of blocks of shale gas and oil. We explain this energy source that is increasingly becoming popular worldwide.

WHAT IS INDIA'S SHALE GAS POTENTIAL?

The government says India has several shale formations that could hold gas. The draft policy says shale gas could be present extensively in oil, gas and coal sedimentary basins such as Cambay, Gondwana, Krisha-Godawari andCauvery. The EIA study pegs India's volume of technically recoverable gas at 63 trillion cubic feet for four out of 26 sedimentary basins.

WHAT IS SHALE GAS?

Shale gas refers to natural gas trapped in shale formations, which are fine grained sedimentary rocks. The gas in the shale rocks comes from the trapped organic matter that breaks down into gas or oil because of the earth's heat. It has become an important source of energy in the United States, triggering a worldwide interest. An April 2011 study by the US Energy Information Administration estimates that 48 shale gas basins in 32 countries (including India) hold 5,760 trillion cubic feet of gas.

ANY ENVIRONMENTAL CONCERN?

Shale gas extraction could require 3-4 million gallons of water per well. The water that flows out of the well to the surface could have high content of total dissolved solids and other contaminants that could pollute both surface and groundwater.

HOW IS SHALE GAS EXTRACTED?

The gas deposits are usually found in rocks that have low permeability, ruling out the possibility of regular drilling. But technological advances have now made commercial exploitation of these reserves possible. The most commonly used method is called fracking, It is a process by which the shale rock is fractured using a high-pressure mixture of water, sand and chemicals. As opposed to vertical drilling for traditional gas, in this case horizontal drilling is carried out.