school energy&environment

Non-conventional characteristics

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.