Oil shale geology Totally Explained

Everything about Oil Shale Geology totally explained

Oil shale geology is the field of the geologic sciences to study formation and composition of oil shales—fine-grained sedimentary rocks containing significant amounts of kerogen, and belonging to the group of sapropel fuels. Oil shales are formed in a number of depositional settings and have considerable compositional variation. Oil shales can be classified by their composition (carbonate minerals such as calcite or detrital minerals such as quartz and clays) or by their depositional environment (large lakes, shallow marine, and lagoon/small lake settings). Their organic content also varies widely and contains remnant matter that can include freshwater and marine algae, spores, resin, and corky material from roots. Oil shales have also been mined for metals such as uranium.

Classification and varieties

Oil shales vary considerably in mineral content, type of kerogen, age, depositional history, and organisms from which they were derived. Oil shale deposits range in age from Cambrian to Tertiary. Lithologies range from shales to marl and carbonate rocks, all of which form a mixture of tightly bound organic and inorganic materials.
Oil shales have been divided into three categories based on mineral composition: carbonate-rich shale, siliceous shale and cannel shale. Carbonate-rich shales derive their name from the large amount of carbonate minerals such as calcite and dolomite. As many as twenty carbonate minerals have been found in oil shale, the majority of which are considered authigenic or diagentic. One type of carbonate-rich shale that's valued highly is lacustrine-sourced deposits, because of the frequent occurrence of organic-rich shale layers sandwiched between carbonate-rich layers of oil shale. These deposits are hard formations that could be difficult to process using ex-situ methods. Siliceous shales are not rich in carbonates but rather in siliceous minerals such as quartz, feldspar, clay, chert and opal. Siliceous shales are not as hard or as weather-resistant as carbonate-rich shales, and may be better suited for extraction via ex-situ methods. |- !Terrestrial!!Lacustrine!!Marine |- |align="left"|cannel coal |align="left"|lamosite; torbanite |align="left"|kukersite; tasmanite; marinite |}

Cannel coal (also called candle coal) is a hydrogen-rich brown to black coal, sometimes with shaly texture, composed of resins, spores, waxes, cutinaceous and corky materials derived from terrestrial vascular plants as well as varied amounts of vitrinite and inertinite.
Lamosite is pale-brown and grayish-brown to dark-gray to black oil shale in which the chief organic constituent is lamalginite derived from lacustrine planktonic algae.
Torbanite, named after Torbane Hill in Scotland, is a black oil shale whose organic matter is telalginite derived from lipid-rich Botryococcus and related algal forms.
Kukersite, named after Kukruse in Estonia, is a light-brown marine oil shale whose principal organic component is telalginite derived from the green alga, Gloeocapsomorpha prisca.
Tasmanite, named after Tasmania, is a brown to black oil shale whose organic matter consists of telalginite derived chiefly from unicellular tasmanitid algae of marine origin.
Marinite is a gray to dark-gray to black oil shale of marine origin in which the chief organic components are lamalginite and bituminite derived from marine phytoplankton with varied admixtures of bitumen, telalginite, and vitrinite.

Composition

As a sapropel fuel, oil shale differs from humus fuels in its lower content of organic matter. The organic matter has an atomic ratio of hydrogen to carbon of about 1.5 — approximately the same as for crude oil and four to five times higher than for coals. The organic matter in oil shales forms a complex macromolecular structure that's insoluble in common organic solvents. It is mixed with varied amounts of mineral matter. For commercial grades of oil shale the ratio of organic matter to mineral matter is about 0.75:5 to 1.5:5.
The organic portion of oil shale consists largely of prebitumen bituminous groundmass, such as remains of algae, spores, pollen, plant cuticles and corky fragments of herbaceous and woody plants, and cellular debris from other lacustrine, marine, and land plants. Organic matter in oil shale also contains organic sulfur (about 1.8 % on average) and a low proportion of nitrogen.
For masses of undecayed organic matter to be preserved and to form oil shale the environment must remain uniform for prolonged periods of time to build up sufficiently thick sequences of algal matter. Eventually the algal swamp or other restricted environment is disrupted and oil shale accumulation ceases. Burial by sedimentary loading on top of the algal swamp deposits converts the organic matter to kerogen by the following normal diagenetic processes:

Compaction due to loading of the sediments on the coal which compresses the organic matter

Removal of the water in the peat

With ongoing compaction, removal of water from the intracellular structure of fossilized plants

With heat and compaction, removal of molecular water

Methanogenesis; similar to treating wood in a pressure cooker, methane is produced, removing hydrogen, some carbon, and some further oxygen (as water)

Dehydration, which removes hydroxyl groups from the cellulose and other plant molecules, resulting in the production of hydrogen-reduced coals or oil shales. The largest deposits are found in the remains of large lakes such as the deposits of the Green River Formation of Wyoming and Utah, USA. Large lake oil shale basins are typically found in areas of block faulting or crustal warping due to mountain building. Deposits such as the Green River can be as much as and yield up to 40 gallons of oil for each ton (166 l/t) of shale.
Oil-shale deposits formed in the shallow seas of continental shelves generally are much thinner than large lake basin deposits. They are typically on the order of a few metres thick. They are, however, spread over very large areas, extending up to thousands of square kilometers. Of the three lithologic types of oil shales, siliceous oil shales are most commonly found in this environment. These oil shales are not as organic rich as lake-deposited oil shales, and generally don't contain more than 30 gallons per ton of oil shale. Oil shales deposited in lagoonal or small lake environments are rarely extensive and are often associated with coal-bearing rocks. These oil shales can have high yields, as much as 40 gallons per ton (170 l/t) of oil shale. However, due to their small areal extent, they're considered unlikely candidates for commercial exploitation.

Further Information

Get more info on 'Oil Shale Geology'.

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://oil_shale_geology.totallyexplained.com">Oil shale geology Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.