Oil shale is one of the unconventional alternate resources of energy that has emerged as a possible means to supplement declining conventional hydrocarbon production. These are fine grained sedimentary rocks containing relatively large amount of organic matter from which significant quantities of shale oil and combustible gas can be extracted. Based on preliminary explorations, India seems to have potential oil shale reserves; however, no commercial activity has taken place so far in this segment and there have been no indications of any significant explorations for the near future.
Oil Shale Mining and Process[ii]
Oil shale can be mined using one of two methods: underground mining using the room-and-pillar method or surface mining. After mining, the oil shale is transported to a facility for retorting, a heating process that separates the oil fractions of oil shale from the mineral fraction. The vessel in which retorting takes place is known as a retort. After retorting, the oil must be upgraded by further processing before it can be sent to a refinery, and the spent shale must be disposed of. Spent shale may be disposed of in surface impoundments, or as fill in graded areas; it may also be disposed of in previously mined areas. Eventually, the mined land is reclaimed.
Potential in India
Oil Shale reserves in India are Greater than 15 Billion Tons.[iii]
North-East India is endowed with rich deposits of coal. The coal is found in the Barail Formation of Tertiary age. Carbonaceous shale occurs interbedded with the coal. The presence of coal and shale has been recorded in wells drilled for hydrocarbons by ONGC and OIL. These formations outcrop on the surface towards the south of the oil fields in a region called the Belt of Schuppen. Studies have indicated that these coals and carbonaceous shale constitute the principal source rocks that have generated the hydrocarbons produced from the region.[iv]
- Assam shelf
- Naga Schuppen Belt
- Assam-Arakkan Fold Belt
- The favorable characteristics of Assam coal for conversion to liquid fuels have been known for a long time. CFRI (Dhanbad) had carried out a feasibility study on this subject and submitted a report as far back as in 1968.
- In the late 1980s, Oil India Limited and Robertson Research Inc. (UK) had analyzed a large number of rock samples obtained from oil wells, outcrops and coal mines in connection with hydrocarbon exploration in the region.
- In order to assess the viability of syncrude generation from the Assam coal, OIL established a pilot plant for the extraction of oil from the coals of Assam with technology from the USA.
- The Directorate General of Hydrocarbons (DGH), under the Ministry of Petroleum and Natural Gas, has embarked on a project for the evaluation of oil shale resources and their syncrude potential in parts of Upper Assam and neighboring area in Arunachal Pradesh
- The contract for the implementation of the oil shale project was signed in September, 2007 between DGH and a consortium comprising BRGM, France and MECL, India.
- First, most of it needs to be dug out in strip mining rather that drilled a process that has high environmental problems.
- Once dug out, it then needs to be heated to 450-500°C, enriched with hydrogen via steam before the resulting oil is separated. The residue is a sludge that needs to be disposed of.
- The downsides of all this are that oil shale production create more than four times as much greenhouse gases as conventional oil production.
- It uses vast quantities of water (which are not always available where the shale is).
- The energy required to extract oil from toil shale is considerable, and this could result in a low EROEI (energy returned on energy invested) Wastes something like 40% of its initial energy in production.
- Oil shale production is also considered to be quite harmful to the environment.
- Only when crude prices are high does oil shale production make economic sense feasible. In theory, it has the potential to make a minor contribution to the Indian oil requirements, but it is not expected to be a panacea to our oil-dependency.
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