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 use of oil shale for extraction of shale oil is more than 200 years old. An oil shale deposit at Autun, France ,was exploited commercially as early as 1839. The Scottish oil shale industry began about 1859, the year that Colonel Drake drilled his pioneer well at Titusville. As many as 20 beds of oil shale were mined at different times. Mining continued during the 1800s and by 1881 oil shale production had reached one million metric tons per year. With the exception of the World War II years, between 1 and 4 million metric tons of oil shale were mined yearly in Scotland from 1881 to 1955 when production began to decline, then ceased in 1962. Canada produced some shale oil from deposits in New Brunswick and Ontario in the mid-1800s. In Sweden, the alum shale was retorted for hydrocarbons on a small scale in the late 1800s. Production continued through World War II but ceased in 1966 because of the availability of cheaper supplies of petroleum crude oil.
With the introduction of the mass production of automobiles and trucks in the early 1900s, the supposed shortage of gasoline encouraged the exploitation of oil shale deposits for transportation fuels in the United States of America. Many companies were formed to develop oil shale deposits of the Green River Formation in western United States, especially in Colorado. The US has an estimated 1.8 trillion barrels of oil trapped in shale, most of it concentrated in the Green River Formation, which covers northwest Colorado and parts of Utah and Wyoming. This estimate is more than all the proven reserves of crude oil in the world today.
In the US, many licenses were issued in the 1970s for exploitation of shale oil. However, after several large-scale mine facilities were developed in the 1970s, the work gradually ceased and the last large-scale mining and retorting facility in western US which was operated by Unocal from 1980, closed down in the year 1991. Unocal produced 4.5 million barrels of oil from oil shale averaging 34 gallons of shale oil per ton of rock over the life of the project.
Various technologies for production of syncrude from coal/oil shale are currently known throughout the world. Most of the commercial processes are based on pyrolysis and/or distillation coal/oil shale in a retort to which heat can be supplied either directly through combustion within the retort or indirectly by performing the combustion outside of the retort and contacting hot gases or solids with coal/oil shale feed. Most modern oil shale technology involves variations of directly heated retorting. Some of the well known indirect processes are Lurgi-Ruhrgas, TOSCOII, Union Oil ‘A’ ad ‘B’, Petrosix, Paraho shale oil etc. All processes use the oil shale itself or its by products as the source of heat.
Retort structures may also be formed underground by a combination of explosive fracturing and mining. This is termed In-Situ Processing. The necessary heat is provided by injecting air or hot gases and steam to sustain movement of the fire front in oil shale formation in either a horizontal or vertically downward mode, causing the shale oil to collect at the bottom of the In-Situ retort, from where it can be pumped to the surface. Geo Kinetics In-Situ and Occidental Modified In-Situ processes are two well-known examples.
The processes of syncrude production results in vast quantities of spent shale. These are absolutely barren and cannot support any vegetation and may also retain toxic ingredients. The disposal of spent shale thus poses a serious environmental challenge. However, the In-Situ process has certain advantages in this aspect. For instance, the disposal of solid wastes is taken care of, the environmental degradation such as deforestation is minimized, the hazardous gases emissions into the atmosphere is contained and problems related to waste water disposal containing toxic elements is substantially reduced.
The in-situ conversion process has been adopted by Shell in their Mahogany Project in Colorado for the past several years. This technology employs heating elements to raise rock temperatures to required levels for syncrude production.
During the 3rd meeting of the oil and gas working group in Washington in July, 2006, discussions were held, inter alia, on oil shale with Ms.Brenda Pierce of United States Geological Survey (USGS) and Mr.Ted Murphy, Division Chief, Solid Minerals, Bureau of Land Management (BLM). Both these organizations are under the Dept. of the Interior, United States Government. The discussions centered on the work carried out by USGS and BLM on oil shale and status of oil shale development in USA and regulations regarding leasing of federal lands for oil shale exploitation. BLM informed that eight (8) leases have been awarded for oil shale RD & D projects to four companies in the states of Colorado, Utah and Wyoming.
DGH has also initiated a dialogue with the Colorado Energy Research Institute (CERI) for interaction on oil shale. CERI, under the Colorado School of Mines is one of the premier institutes engaged in active oil shale research and development. They organize an exclusive oil shale symposium every year that draws specialists from various countries. DGH has also participated and presented technical paper in this symposium.
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 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. 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 kg 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.
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 study, which is being carried out by a consortium comprising BRGM, France and MECL, India 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 evaluation of oil shale resources involves field work, mapping, and collection of rock samples from surface exposures, drilling of few core holes, preparation of maps and feasibility studies. The study is expected to be completed by October/November, 2009.
Phase-I (Sept.2007 to October 2009)
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 envisages assessment of oil shale resources in three discrete adjacent blocks, covering a total area of about 250 sq.km. in the states of Assam and Arunachal Pradesh. The principal work components of the project include geological mapping, sampling and geochemical analysis of oil shale, shallow geophysical survey, shallow drilling for characterizing the oil shales, development of 3-D model and preliminary environmental studies. The project is expected to be completed in the third quarter of the FY 2009-10. Geological mapping and sampling program is in progress. Analytical studies in respect of 150 samples have been completed. Out of the total 3000m of planned drilling activity, about 2500m have been completed.
Phase-II (November 2009 to October 2011)
Once the resources of oil shale in the three blocks is determined with a reasonable degree of confidence, the following steps would be required to be taken:
- Techno-economic feasibility study for extraction of shale oil from these deposits. For the techno-economic analysis, a competent consultant will have to be hired who will carry out the study for DGH.
- Environmental impact assessment study by a reputed agency from India or abroad
- Framing of legislation for simultaneous extraction of coal and oil shale deposits. Since the oil shale occurs inter-bedded with the coal deposits, it follows that the oil shale industry will be supplementary and complementary to the coal mining industry. While the coal can be mined in the same way as it is being done now, the shale which is being discarded as waste would have to be processed for extraction of shale oil using a suitable retorting technology.
- Preparation of Model Production Sharing Contract. This study would have to be outsourced.
- Delineation of blocks for offer under first round of bidding for Oil Shale.
- Preparation of NIO, BEC etc.
- Obtaining necessary clearances from MoEF, MoHA and MoD for the blocks offered.
Phase-III (November 2011 to June 2012)
- Announcement of first round of bidding for oil shale
- Organizing Road shows in selected places
- Sale of data package
- Opening of data rooms
- Receipt of Bids
- Evaluation of Bids
- Award of Blocks