Shale gas refers to natural gas that is trapped within shale formations due to their low permeability and cannot escape to the surface as easily as Conventional Natural Gas. Shales are fine-grained sedimentary rocks that can be rich resources of petroleum and natural gas.
Sedimentary rocks are rocks formed by the accumulation of sediments at the Earth's surface and within bodies of water. Common sedimentary rocks include sandstone, limestone, and shale.
The extraction process of shale gas involves two methods
• Horizontal drilling:
Under this technique a vertical well is drilled to the targeted rock formation and then at the desired depth, the drill bit is turned horizontally, exposing the well to more of the producing shale.
• Hydraulic Fracturing:
In this technique, water along with chemicals and sand are pumped into the well and a fracture or crack is developed in the shale rock to release the hydrocarbons trapped in shale formations to flow from the shale into the well. Hydraulic fracturing when used in conjunction with horizontal drilling, it enables gas producers to extract shale gas at reasonable cost and rapidly as it enhances the flow of gas quickly to the desired well.
Problems in Extraction:
The importance of shale gas can be gauged from the fact that an estimated 35% of world surface rock is made of shale formations. However, extraction of shale gas is difficult and tardy process. The difficulty is mainly because of less permeability of the shale rocks, which does not allow significant fluid flow.
Due to low permeability, commercially viable production of shale gas needs fracturing of the rocks for, the fracturing provides permeability. For many years, this gas was produced from natural fractures, but as there was development of modern technologies such as horizontal drilling / hydraulic fracturing (aka fracking); more and more artificial fractures around the well bores were created.
This skyrocketed the production of shale gas and led to the so called Shale Gas Boom in United States. This shale gas boom has also contributed partially in the recent fall of global oil prices. The hydraulic farming aided shale gas production has rejuvenated the natural gas industry in the United States.
Shale Gas in India Various estimates, including those by leading firms, put Indian reserves of shale oil and gas at large numbers describing Shale oil and gas are more widespread than natural oil and gas. Major regions of availability are Gujarat, Rajasthan-Cambay, Central India-Gondwana, Krishna and Godavari Basin and offshore areas in Bay of Bengal, Indo-gangetic plains, Cauvery onshore and Assam-Arakan.
The assessment of shale formations has started in India at various sites. Also, a MoU have been signed between USA and India for sharing technical knowledge in shale-gas exploration. According to the Energy Information Administration report, India's shale gas reserves equals 96 trillion cubic feet which can supply for 26 years of the country's Gas demand. As per the National Geophysical Research Institute (NGRI) Hyderabad, claimed to identify 28 sedimentary basins of shale gas (natural gas found trapped in shale formations under the ground), including ten potential producing basins, across India. These have been classified according to their hydrocarbon potential, and hold an estimated 527 trillion cubic feet (TCF) of reserves.
located near Vadodara in Gujarat is India's first shale gas exploratory successfully drilled by ONGC in Cambay region which is estimated to have a shale gas potential of 20 TCF (trillion cubic feet).
Challenges and Environmental concerns:
• A potential problem in India could be that shale is mostly found about 2,000 meters deep on shore, in areas of human habitation; unlike oil drilling that takes place offshore. Specially designed water bore-wells may be needed in such areas to tackle escaping methane gas. Use of high-power compressors and other equipment could also unsettle local populations, while shale drilling could affect groundwater reserves.
• Also the Land acquisition will be a big problem in India.
• The gas produced from such reservoir rocks is known as 'tight gas' and it requires massive hydraulic fracturing technique. So the potential impacts of hydraulic fracturing locally and downstream of drilling areas is also a big concern. Hydraulic fracturing involves drilling through the water table into deep underground shale gas reserves. Millions of gallons of water are then used to break the shale and release the gas. In theory, all wells should be completely incased until past the water table level. This is also a big challenge in India due to it's lax and corrupt system. Because even after having highly strict rules and regulations in countries like US and UK, there have been numerous instances of cases breaking or being improperly formed and hazardous water being released into the groundwater. This contaminated groundwater then allows for gas to enter homes and soil, creating potentially dangerous situations, including exploding homes
• Of the 344 chemicals used for drilling, many of which have little to no safety information associated with them, over 75% are known to cause skin, eye, and sensory organ irritation. 20 to 30% cause reproductive, mutagenic, or cancerous complications. These chemicals are commonly transmitted through the air and water. Benzene, a known carcinogen, is commonly found at levels far exceeding standards in the air around fracking sites.
Shale gas is definitely going to be a useful additional energy resource for India. But the challenge lies in making it sustainable and safe.