ABSTRACT:

The hunt for alternative energy sources to petroleum has increased these days because of increasing need and depletion of petroleum reserves. Due to this, the importance of oil shale as an economically viable substitute has enhanced many folds in last 20 years. Oil shale is a compact laminated rock of sedimentary origin containing organic matter known as kerogen which yields oil when distilled. Therefore, it is very important to understand the physico-mechanical behavior of such anisotropic rocks. The favorable characteristics of Assam coal for conversion to liquid fuels have been known for a long time. Studies have indicated that these coals and carbonaceous shale constitute the principal source rocks that have generated the hydrocarbons produced from the region. In the present work an attempt is made to understand the engineering behavior of Indian oil shales experimentally. The in situ coring is performed to get the samples for testing purposes, as coring in laboratory is very difficult due to its highly anisotropic nature. Different tests are performed to understand the petrology of these samples, further the chemical analyses are also done to exactly quantify the organic and inorganic contents in these rocks. The physical and mechanical properties of these rocks are investigated by considering different anisotropic angles. These properties and correlations will further help in increasing the yield of these rocks.

1 INTRODUCTION

The search for alternative energy sources to petroleum has increased these days because of increase in need and depletion of petroleum reserves. Due to this the importance of oil shales as an economically viable substitute has increased many folds in last 20 years. Oil shale are defined as a compact laminated rock of sedimentary origin and contains organic matter that yields oil when distilled (Yen & Chilingarian 1976, Shanks et al. 1976, Robinson 1976). Oil shales are formed from the contemporaneous deposition of fine grained mineral debris and organic degradation products derived from the breakdown of biota. Conditions required for the formation of oil shales include abundant organic productivity, early development of anaerobic conditions, and a lack of destructive organisms.

These oil shales come under unconventional oil in unconventional rocks. Depth of these rocks varies from few meters to few thousand meters. Oil extraction from these rocks can be done by retorting process, which involves drastically breaking the bond between the organic and inorganic matter. The two approaches for retorting are surface retorting and in-situ processing. In surface retorting, the mined and crushed oil shales are subjected to temperature ranging from 400–600°C. Due to high temperature conditions the chemical bonds between the organic and inorganic compound are broken. In the case of In-situ process, mining of shale is not required. This process involves, fracturing, injection to achieve communication, and fluid migration at the underground location. Upon heating (retorting) oil shale at temperatures in the range of 300 to 400°C, the kerogen decomposes into oil, gas and residual carbon (Nowacki 1981).

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