Oil Shales are usually fine-grained sedimentary rocks containing relatively large amounts of organic matter from which significant quantities of shale oil and combustible gas can be extracted by destructive distillation. The product thus generated is known as synthetic crude or more simply, syncrude. Included in most definitions of oil shale, either stated or implied, is the potential for the profitable extraction of shale oil and combustible gas or for burning as a fuel. An oil shale, which has a very high proportion of organic matter in relation to mineral matter, is categorized as a coal.

Oil shales range in age from Cambrian to Tertiary and occur in many parts of the world. Deposits range in size from small occurrences of little or no economic value to those of enormous size that occupy thousands of square miles and contain many billion barrels of potentially extractable shale oil. Total world resources of oil shale are conservatively estimated at 2.6 trillion barrels. However, petroleum-based crude oil is cheaper to produce than shale oil because of the additional costs of mining and extracting the energy from oil shale. Because of these higher costs, only a few deposits of oil shale are currently being exploited in China, Brazil, and Estonia. However, with the continuing decline of petroleum supplies, accompanied by increasing costs of petroleum, oil shale presents opportunities for supplying some of the fossil energy needs of the world in the years ahead.

The Indian Scenario

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.

The favourable 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. Commonly, the assessment of the yield of hydrocarbons from coal or oil shale is based on pyrolysis or heating under controlled conditions. The standard method has been the Fischer Assay, a scaled down retorting process in which the residue and generated by-products viz.

hydrocarbons are collected, measured and chemically analyzed. Evaluation of the yield potential can also be determined quantitatively by another pyrolysis technique called Rock-Eval pyrolysis. In this equipment, small quantities of the sample are pyrolyzed under controlled conditions. The amount of hydrocarbons generated and expelled can be volumetrically determined by this method.

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. The Rock-Eval yields for the coal and carbonaceous shale indicate prolific hydrocarbon potential for Barail Coals, of the order of 280 kgs of hydrocarbons per ton of rock. The Barail Series oil shale gave a maximum yield of about 80 kg hydrocarbons per ton of rock. This compares favourably with some of the yield values obtained from other oil shale deposits in the world.

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..

It is learnt that OIL is considering on adoption of a more suitable technology available from China for further studies on coal liquefaction.

With respect to oil shale, the current position is that the resources are not known with any measure of confidence. Much more ground work needs to be undertaken before the reserves can be established. Once this is done, selection of the appropriate technology can be taken up.

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 Prdesh. The proposed study by DGH is expected to provide valuable information on this fossil fuel source. Considering the energy security of our country, the project is of national importance.

The exploration for oil shale deposits would involve field work, mapping, and collection of rock samples from surface exposures, drilling of few core holes, preparation of maps and feasibility studies.

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. The project is planned to be completed in about 2 years time. Geological mapping and sampling program is in progress. Analytical studies in respect of 43 samples have been completed. The first well has been drilled and the second well is currently in progress. The contractor has submitted a report in respect of the activities carried out till April, 2008.