The non conventional hydrocarbon family includes compounds that differ greatly from one another, however they are all characterized by a high density and viscosity. The “heavy raw materials” are those oils whose density, according to the API (American Petroleum Institute) scale, is less than 25°, while the definition of viscous oils is a viscosity >50 cP (centiPoise; 10 Poise = 1 Pascal/s). Hydrocarbons with viscosity >10,000 cP and density <10° API (and therefore denser than water) are defined “extra heavy”. This latter category also includes tar extracted from sand and clay or oil shale.
Heavy hydrocarbons are also characterized by a significant content of foreign elements, such as sulphur (present in percentages up to 6-8%), nitrogen and heavy metals, in particular nickel and vanadium : all these components can create problems in the refining and manufacturing processes and can cause environmental pollution.
Non conventional hydrocarbons are generally found at modest depths (<1,000 m), and rarely below 3,000 m, because high temperatures decrease the viscosity; often the reservoirs are found in very porous sandstone. Heavy hydrocarbons are always on the bottom of the reservoirs, and they account for an important part of the reserves, however they can also be found in concentrations when the hydrocarbons migrate from the mother rock where they were produced (in the so called “oil window” at depths from 3,500 to 4,500 m), and undergo degradation and alteration processes (for example due to bacteria) or evaporation and dissolving processes of the lighter more precious fractions. Very often these can be found in large quantities in the basins of rivers that flow on the Earth’s surface (as for example in the Orinoco river basin in Venezuela), and it is in these areas that research is now concentrated.
Bituminous sand
The terms bituminous sand, tar sand and oil sand refer to sand deposits that are not cemented together, and are very porous, and contain non mobile viscous oils. The largest known accumulation is in the region of Alberta (Canada), with an accumulation of oil that is over 60 m thick, at depths ranging from 0 to 600 m, in porous sand. The oil that is produced has a high content of sulphur and a very high viscosity level (2 x106 cP).
Oil shale
Clays that are rich in organic substance are the most common mother rocks and many clays (oil shale) can contain large amounts of organic substance that has still not been completely transformed into hydrocarbons (kerogen), dispersed in small particles or concentrated in thin lenses or laminas: kerogen is typical in mother rocks that were never buried deep enough to generate hydrocarbons.
Where in the world
Exploiting non conventional hydrocarbons on a large scale began in the Eighties. These new fossil fuels initially contributed only small percentage amounts, but today they account for approximately 10-12% of the world production.
Research began (actually even before the Eighties) in California, Venezuela and Canada, which are considered the pioneer countries for this kind of research.
Non conventional reserves
It is not easy to estimate what lies underground, however it is believed that in the sedimentary rocks worldwide, there are probably 1.8 x 1012 cubic metres (approximately 12 x 1012 barrels) of liquid oil. Liquid hydrocarbons, even though they all belong to the same family, differ from one another. They are made up of compounds with different chemical and physical characteristics: oils, heavy oils, tar and very heavy oils.
Some history
Asphalts, tar and heavy oils are not a recent discovery, on the contrary, it may be said that these were the first hydrocarbons to be used by man. Since the dawn of human civilization, in fact, these were used for the most varied purposes: as a sealing and waterproofing material for boats and the roofs of houses, as a glue, as fuel for oil lamps and lights, and as a medication for wounds
