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Shale gas, like other petroleum products such as oil and coal, is formed from the remains of plants, animals and micro-organisms that lived millions of years ago. However, this natural gas is made up of shale formations, a common name for rock that was once layers of clay or mud. Since these rocks aren't very permeable, gas is trapped in it due to its inability to travel. This is the reason that producing shale gas is more complex than other petroleum products.
India has witnessed unprecedented growth on many fronts over the last decade including the enormous demand for energy. Unfortunately, demand still outstrips supply furthering the search for alternatives to fuel our energy appetite. Shale gas could be it but how shale-rich are we?
In India, the potentially recoverable volume of shale gas that can be produced with the current technology regardless of price & production costs and with a certain amount of risk, is estimated at 96 trillion cubic feet (Tcf) [1]. This will not only help cover the projected gap in the energy supply-demand scenario but also reduce our dependence on oil/ gas imports as it has done in the United States.
The four priority shale gas-bearing basins identified are Cambay, Krishna-Godavari, Cauvery and Damodar Valley. Other potential areas are Upper Assam, Vindhyan, Pranhita-Godavari, Rajasthan and South Rewa [1].
Hydraulic fracturing or ’ ‘fracking’, is a technique used for shale gas production. In this, water is mixed with sand and chemicals and injected at a high pressure into a well dug into the earth’s surface to create small fractures lesser than 1mm. The gas then migrates through the well and is collected at the surface to be used as an energy resource.
A major concern of ‘fracking’ in the Indian context is its impact on water. The issues of water scarcity, drought and depleting groundwater table are already a grim reality in our country. The water distress caused could be a combination of any of the following:
Each well requires 11,000 – 15,000 cubic metres (cum) of water per fracking, depending upon the well type and shale characteristics [5]. This volume is multiplied by the number of times fracking is done, which can even go up to 18 times per well. This demand will be fulfilled by tapping the nearby surface water, mining groundwater or transporting it from an adequate distant water source. Whatever the choice, this extraction can further lower the existing water table in the region.
Chemicals and proppants are added to the water for better lubrication during fracturing. The volumes of these proppants is of the order of 1000 to 4000 tonnes per well per fracking [2]. A direct spill of these additives during transport or mixing can contaminate nearby water bodies and the ecological habitat around it.
Wastewater returned to the surface as flow back is about 20% to 50% of the input. This is mixed with the chemicals used in the fracking process, along with metals, minerals and hydrocarbons leached from the reservoir rock. A surface spill of this wastewater can contaminate rivers and other water bodies. Occasionally, the leached minerals can be weakly radioactive and require specific precautions at the surface.
Taking a conservative estimate each well will dispense about 3000- 6000 cum of water that needs proper treatment before disposal or recycling. Improper disposal will raise further health and environmental issues. An answer to this problem lies in limiting the natural gas production to the available capacity of wastewater treatment plants.
The earth’s surface is drilled upto depths of more than 1.5 km. Any wastewater leak through the walls on its way to the surface is another source of worry. The lateral movement of chemicals through fissures may leach out and contaminate shallow aquifers/ groundwater.
Water consumption and availability are both a local and contextual issue. In water-abundant regions the siphoning of freshwater may not be as much of a problem as in the case of arid areas. Is the water to be mined from underground reservoirs, skimmed off the rivers, harnessed from the rain or transported from other water rich areas?
Besides a high demand for freshwater and subsequent production of large amounts of wastewater, there is the question of induced seismicity due to the small fractures in the earth. Precise knowledge of the prevailing underground stress field and mechanical properties of the rocks present is always limited, so reducing risk will be a challenging task.
Greenhouse gas footprint of shale gas is significantly larger than that of conventional gas, due to methane emissions with flow-back fluids and from the drill out of wells during well completion.
Shale gas wells are spaced more densely and extend across a much larger geographic areas. Also, shale gas reservoirs have lesser porosity so the gas is stored in less than 10% of the total volume. Their recovery rate is low as the gas can be trapped in disconnected spaces within the rock or stuck to its surface. Thus the volume of recoverable hydrocarbons per square kilometre of area is usually smaller than that for conventional gas. As larger areas are required for fracking, land acquisition will play a major role in this exercise.
The Government has approved exploration of shale gas by 2 national oil companies - Oil and Natural Gas Corporation (ONGC) and Oil India Ltd. Private players have been kept out for now.
These will be permitted three assessment phases, each with a maximum period of 3 years and the royalties and taxes would be the same as for conventional production. ONGC has plans to drill 10 wells this year and aims at commercial production of shale gas by 2014 [3].
India is the fourth largest consumer of energy in the world. So a new, cheaper energy option is certainly exciting. However, before diving into it, the limitations and constraints of shale gas production need a more serious look. An in-depth analysis on why countries like France have banned fracking, while Netherlands and Bulgaria are rethinking their choices must be done [4] [6].
In the light of growing fossil-fuel needs, the exponential growth in energy consumption and the increasing cost of imports, developing this gas to the maximum-possible is justified to a certain extent. However, a detailed, remediation and stricter enforcement policy at the forefront of this initiative will go a long way in making this ‘energetic’ jump sustainable.
Steps like disclosure of the composition of the chemical components of fracturing fluids will help in terms of public acceptance. Until recently, the chemical composition of fracturing fluids was considered a trade secret and was not made public, even though the composition of fracking fluids differs from one well to another. It is only since 2010, that voluntary disclosure has become the norm in most of the United States wells. Counter measure plans for spills & leaks, adequate control and regulation can aid development of shale gas resources.
The economics of the energy gain need to be balanced with the ecological risks, taking into account the possible regional water scarcity, water treatment & recycling capability and societal pressures. Can the wastewater be recycled economically for future use or treated at local industrial waste facilities before being discharged into local rivers or used in agriculture? What about the rising anxiety and concerns of the people whose land and water are being affected, possibly even contaminated? All these valid questions are vital to public confidence, so that the purported economical benefits to the local communities are not squashed by larger, volatile and irreversible environmental issues.
A promise of surplus energy is appealing, but not at the expense of an essential variable- water.
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