Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich sources of petroleum and natural gas.
Two major drilling techniques are used to produce shale gas. Horizontal drilling is used to provide greater access to the gas trapped deep in the producing formation. First, a vertical well is drilled to the targeted rock formation. At the desired depth, the drill bit is turned to bore a well that stretches through the reservoir horizontally, exposing the well to more of the producing shale.
Hydraulic fracturing (commonly called “fracking” or “hydrofracking”) is a technique in which water, chemicals, and sand are pumped into the well to unlock the hydrocarbons trapped in shale formations by opening cracks (fractures) in the rock and allowing natural gas to flow from the shale into the well. When used in conjunction with horizontal drilling, hydraulic fracturing enables gas producers to extract shale gas at reasonable cost. Without these techniques, natural gas does not flow to the well rapidly, and commercial quantities cannot be produced from shale.
In order to exploit shale gas & Oil in the country, Government of India on 14th October, 2013 announced the Policy Guidelines for Exploration and Exploitation of Shale Gas and Oil by National Oil Companies (ONGC and Oil India Limited (OIL)) in their onland Petroleum Exploration License (PEL) / Petroleum Mining Lease (PML) areas awarded under the nomination regimes.
In pursuance of this Policy, under the first phase of assessment ONGC has identified and initiated shale gas and oil exploration activities in 50 PEL/PML areas; and OIL has identified and initiated shale gas exploration activities in 6 PEL/PML areas. The State-wise details of the identified shale gas blocks are given below:
| S.No. | State/UT | Number of Blocks |
| 1 | Andhra Pradesh | 10 |
| 2 | Arunachal Pradesh | 2 |
| 3 | Assam | 6 |
| 4 | Gujarat | 28 |
| 5 | Tamil Nadu | 9 |
| 6 | Rajasthan | 1 |
| Total | 56 |
So far, ONGC has drilled 20 assessment wells for Shale gas and oil. OIL has completed G&G studies and Geochemical analysis in its identified areas.
Further, OIL has completed Conventional Core in one well in Rajasthan.
In order to promote exploration and exploitation of unconventional hydrocarbon resources such as CBM, shale oil & gas, Government has recently approved a Hydrocarbon Exploration and Licensing Policy (HELP) wherein companies can explore and produce all kind of hydrocarbons including shale oil/gas, CBM & gas hydrate, etc. under single license.
Shale Gas vs. Conventional Gas
Conventional gas reservoirs are created when natural gas migrates toward the Earth’s surface from an organic-rich source formation into highly permeable reservoir rock, where it is trapped by an overlying layer of impermeable rock.
In contrast, shale gas resources form within the organic-rich shale source rock. The low permeability of the shale greatly inhibits the gas from migrating to more permeable reservoir rocks.
Without horizontal drilling and hydraulic fracturing, shale gas production would not be economically feasible because the natural gas would not flow from the formation at high enough rates to justify the cost of drilling.
Environmental Concerns
However, there are some potential environmental issues that are also associated with the production of shale gas. Shale gas drilling has significant water supply issues. The drilling and fracturing of wells requires large amounts of water. In some areas of the country, significant use of water for shale gas production may affect the availability of water for other uses, and can affect aquatic habitats.
Drilling and fracturing also produce large amounts of wastewater, which may contain dissolved chemicals and other contaminants that require treatment before disposal or reuse. Because of the quantities of water used, and the complexities inherent in treating some of the chemicals used, wastewater treatment and disposal is an important and challenging issue.
If mismanaged, the hydraulic fracturing fluid can be released by spills, leaks, or various other exposure pathways. The use of potentially hazardous chemicals in the fracturing fluid means that any release of this fluid can result in the contamination of surrounding areas, including sources of drinking water, and can negatively impact natural habitats.